reverse_proxy: WIP refactor and support for FastCGI

17 files changed, 2741 insertions, 888 deletions

diff --git a/cmd/caddy/main.go b/cmd/caddy/main.go
index 5f6b8bb..14b8865 100644
--- a/cmd/caddy/main.go
+++ b/cmd/caddy/main.go
@@ -29,6 +29,7 @@ import (
 	_ "github.com/caddyserver/caddy/v2/modules/caddyhttp/markdown"
 	_ "github.com/caddyserver/caddy/v2/modules/caddyhttp/requestbody"
 	_ "github.com/caddyserver/caddy/v2/modules/caddyhttp/reverseproxy"
+	_ "github.com/caddyserver/caddy/v2/modules/caddyhttp/reverseproxy/fastcgi"
 	_ "github.com/caddyserver/caddy/v2/modules/caddyhttp/rewrite"
 	_ "github.com/caddyserver/caddy/v2/modules/caddyhttp/templates"
 	_ "github.com/caddyserver/caddy/v2/modules/caddytls"
diff --git a/go.mod b/go.mod
index d63097a..315dcfd 100644
--- a/go.mod
+++ b/go.mod
@@ -8,7 +8,6 @@ require (
 	github.com/Masterminds/semver v1.4.2 // indirect
 	github.com/Masterminds/sprig v2.20.0+incompatible
 	github.com/andybalholm/brotli v0.0.0-20190704151324-71eb68cc467c
-	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/dustin/go-humanize v1.0.0
 	github.com/go-acme/lego v2.6.0+incompatible
 	github.com/google/go-cmp v0.3.1 // indirect
@@ -17,7 +16,6 @@ require (
 	github.com/imdario/mergo v0.3.7 // indirect
 	github.com/klauspost/compress v1.7.1-0.20190613161414-0b31f265a57b
 	github.com/klauspost/cpuid v1.2.1
-	github.com/kr/pretty v0.1.0 // indirect
 	github.com/mholt/certmagic v0.6.2
 	github.com/mitchellh/go-ps v0.0.0-20170309133038-4fdf99ab2936
 	github.com/rs/cors v1.6.0
@@ -26,8 +24,7 @@ require (
 	github.com/starlight-go/starlight v0.0.0-20181207205707-b06f321544f3
 	go.starlark.net v0.0.0-20190604130855-6ddc71c0ba77
 	golang.org/x/net v0.0.0-20190603091049-60506f45cf65
-	golang.org/x/sys v0.0.0-20190422165155-953cdadca894 // indirect
+	golang.org/x/sys v0.0.0-20190228124157-a34e9553db1e // indirect
 	golang.org/x/time v0.0.0-20190308202827-9d24e82272b4
-	gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 // indirect
 	gopkg.in/yaml.v2 v2.2.2 // indirect
 )
diff --git a/go.sum b/go.sum
index 4180648..8771eb1 100644
--- a/go.sum
+++ b/go.sum
@@ -12,8 +12,6 @@ github.com/cenkalti/backoff v2.1.1+incompatible h1:tKJnvO2kl0zmb/jA5UKAt4VoEVw1q
 github.com/cenkalti/backoff v2.1.1+incompatible/go.mod h1:90ReRw6GdpyfrHakVjL/QHaoyV4aDUVVkXQJJJ3NXXM=
 github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
-github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
-github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/dustin/go-humanize v1.0.0 h1:VSnTsYCnlFHaM2/igO1h6X3HA71jcobQuxemgkq4zYo=
 github.com/dustin/go-humanize v1.0.0/go.mod h1:HtrtbFcZ19U5GC7JDqmcUSB87Iq5E25KnS6fMYU6eOk=
 github.com/go-acme/lego v2.5.0+incompatible/go.mod h1:yzMNe9CasVUhkquNvti5nAtPmG94USbYxYrZfTkIn0M=
@@ -34,11 +32,6 @@ github.com/klauspost/compress v1.7.1-0.20190613161414-0b31f265a57b/go.mod h1:RyI
 github.com/klauspost/cpuid v1.2.0/go.mod h1:Pj4uuM528wm8OyEC2QMXAi2YiTZ96dNQPGgoMS4s3ek=
 github.com/klauspost/cpuid v1.2.1 h1:vJi+O/nMdFt0vqm8NZBI6wzALWdA2X+egi0ogNyrC/w=
 github.com/klauspost/cpuid v1.2.1/go.mod h1:Pj4uuM528wm8OyEC2QMXAi2YiTZ96dNQPGgoMS4s3ek=
-github.com/kr/pretty v0.1.0 h1:L/CwN0zerZDmRFUapSPitk6f+Q3+0za1rQkzVuMiMFI=
-github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
-github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
-github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
-github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
 github.com/mholt/certmagic v0.6.2 h1:yy9cKm3rtxdh12SW4E51lzG3Eo6N59LEOfBQ0CTnMms=
 github.com/mholt/certmagic v0.6.2/go.mod h1:g4cOPxcjV0oFq3qwpjSA30LReKD8AoIfwAY9VvG35NY=
 github.com/miekg/dns v1.1.3 h1:1g0r1IvskvgL8rR+AcHzUA+oFmGcQlaIm4IqakufeMM=
@@ -71,16 +64,14 @@ golang.org/x/sync v0.0.0-20181221193216-37e7f081c4d4/go.mod h1:RxMgew5VJxzue5/jJ
 golang.org/x/sys v0.0.0-20190124100055-b90733256f2e/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a h1:1BGLXjeY4akVXGgbC9HugT3Jv3hCI0z56oJR5vAMgBU=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
-golang.org/x/sys v0.0.0-20190422165155-953cdadca894 h1:Cz4ceDQGXuKRnVBDTS23GTn/pU5OE2C0WrNTOYK1Uuc=
-golang.org/x/sys v0.0.0-20190422165155-953cdadca894/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20190228124157-a34e9553db1e h1:ZytStCyV048ZqDsWHiYDdoI2Vd4msMcrDECFxS+tL9c=
+golang.org/x/sys v0.0.0-20190228124157-a34e9553db1e/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/time v0.0.0-20190308202827-9d24e82272b4 h1:SvFZT6jyqRaOeXpc5h/JSfZenJ2O330aBsf7JfSUXmQ=
 golang.org/x/time v0.0.0-20190308202827-9d24e82272b4/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
-gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 h1:qIbj1fsPNlZgppZ+VLlY7N33q108Sa+fhmuc+sWQYwY=
-gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/square/go-jose.v2 v2.2.2 h1:orlkJ3myw8CN1nVQHBFfloD+L3egixIa4FvUP6RosSA=
 gopkg.in/square/go-jose.v2 v2.2.2/go.mod h1:M9dMgbHiYLoDGQrXy7OpJDJWiKiU//h+vD76mk0e1AI=
 gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
diff --git a/listeners.go b/listeners.go
index d97674d..3c3a704 100644
--- a/listeners.go
+++ b/listeners.go
@@ -24,6 +24,8 @@ import (
 	"time"
 )
 
+// TODO: Can we use the new UsagePool type?
+
 // Listen returns a listener suitable for use in a Caddy module.
 // Always be sure to close listeners when you are done with them.
 func Listen(network, addr string) (net.Listener, error) {
diff --git a/modules/caddyhttp/caddyhttp.go b/modules/caddyhttp/caddyhttp.go
index b4b1ec6..300b5fd 100644
--- a/modules/caddyhttp/caddyhttp.go
+++ b/modules/caddyhttp/caddyhttp.go
@@ -518,6 +518,20 @@ func (ws WeakString) String() string {
 	return string(ws)
 }
 
+// StatusCodeMatches returns true if a real HTTP status code matches
+// the configured status code, which may be either a real HTTP status
+// code or an integer representing a class of codes (e.g. 4 for all
+// 4xx statuses).
+func StatusCodeMatches(actual, configured int) bool {
+	if actual == configured {
+		return true
+	}
+	if configured < 100 && actual >= configured*100 && actual < (configured+1)*100 {
+		return true
+	}
+	return false
+}
+
 const (
 	// DefaultHTTPPort is the default port for HTTP.
 	DefaultHTTPPort = 80
diff --git a/modules/caddyhttp/matchers.go b/modules/caddyhttp/matchers.go
index 0dac151..2ddefd0 100644
--- a/modules/caddyhttp/matchers.go
+++ b/modules/caddyhttp/matchers.go
@@ -616,10 +616,7 @@ func (rm ResponseMatcher) matchStatusCode(statusCode int) bool {
 		return true
 	}
 	for _, code := range rm.StatusCode {
-		if statusCode == code {
-			return true
-		}
-		if code < 100 && statusCode >= code*100 && statusCode < (code+1)*100 {
+		if StatusCodeMatches(statusCode, code) {
 			return true
 		}
 	}
diff --git a/modules/caddyhttp/reverseproxy/fastcgi/client.go b/modules/caddyhttp/reverseproxy/fastcgi/client.go
new file mode 100644
index 0000000..ae0de00
--- /dev/null
+++ b/modules/caddyhttp/reverseproxy/fastcgi/client.go
@@ -0,0 +1,578 @@
+// Copyright 2015 Matthew Holt and The Caddy Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Forked Jan. 2015 from http://bitbucket.org/PinIdea/fcgi_client
+// (which is forked from https://code.google.com/p/go-fastcgi-client/).
+// This fork contains several fixes and improvements by Matt Holt and
+// other contributors to the Caddy project.
+
+// Copyright 2012 Junqing Tan <ivan@mysqlab.net> and The Go Authors
+// Use of this source code is governed by a BSD-style
+// Part of source code is from Go fcgi package
+
+package fastcgi
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"encoding/binary"
+	"errors"
+	"io"
+	"io/ioutil"
+	"mime/multipart"
+	"net"
+	"net/http"
+	"net/http/httputil"
+	"net/textproto"
+	"net/url"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+)
+
+// FCGIListenSockFileno describes listen socket file number.
+const FCGIListenSockFileno uint8 = 0
+
+// FCGIHeaderLen describes header length.
+const FCGIHeaderLen uint8 = 8
+
+// Version1 describes the version.
+const Version1 uint8 = 1
+
+// FCGINullRequestID describes the null request ID.
+const FCGINullRequestID uint8 = 0
+
+// FCGIKeepConn describes keep connection mode.
+const FCGIKeepConn uint8 = 1
+
+const (
+	// BeginRequest is the begin request flag.
+	BeginRequest uint8 = iota + 1
+	// AbortRequest is the abort request flag.
+	AbortRequest
+	// EndRequest is the end request flag.
+	EndRequest
+	// Params is the parameters flag.
+	Params
+	// Stdin is the standard input flag.
+	Stdin
+	// Stdout is the standard output flag.
+	Stdout
+	// Stderr is the standard error flag.
+	Stderr
+	// Data is the data flag.
+	Data
+	// GetValues is the get values flag.
+	GetValues
+	// GetValuesResult is the get values result flag.
+	GetValuesResult
+	// UnknownType is the unknown type flag.
+	UnknownType
+	// MaxType is the maximum type flag.
+	MaxType = UnknownType
+)
+
+const (
+	// Responder is the responder flag.
+	Responder uint8 = iota + 1
+	// Authorizer is the authorizer flag.
+	Authorizer
+	// Filter is the filter flag.
+	Filter
+)
+
+const (
+	// RequestComplete is the completed request flag.
+	RequestComplete uint8 = iota
+	// CantMultiplexConns is the multiplexed connections flag.
+	CantMultiplexConns
+	// Overloaded is the overloaded flag.
+	Overloaded
+	// UnknownRole is the unknown role flag.
+	UnknownRole
+)
+
+const (
+	// MaxConns is the maximum connections flag.
+	MaxConns string = "MAX_CONNS"
+	// MaxRequests is the maximum requests flag.
+	MaxRequests string = "MAX_REQS"
+	// MultiplexConns is the multiplex connections flag.
+	MultiplexConns string = "MPXS_CONNS"
+)
+
+const (
+	maxWrite = 65500 // 65530 may work, but for compatibility
+	maxPad   = 255
+)
+
+type header struct {
+	Version       uint8
+	Type          uint8
+	ID            uint16
+	ContentLength uint16
+	PaddingLength uint8
+	Reserved      uint8
+}
+
+// for padding so we don't have to allocate all the time
+// not synchronized because we don't care what the contents are
+var pad [maxPad]byte
+
+func (h *header) init(recType uint8, reqID uint16, contentLength int) {
+	h.Version = 1
+	h.Type = recType
+	h.ID = reqID
+	h.ContentLength = uint16(contentLength)
+	h.PaddingLength = uint8(-contentLength & 7)
+}
+
+type record struct {
+	h    header
+	rbuf []byte
+}
+
+func (rec *record) read(r io.Reader) (buf []byte, err error) {
+	if err = binary.Read(r, binary.BigEndian, &rec.h); err != nil {
+		return
+	}
+	if rec.h.Version != 1 {
+		err = errors.New("fcgi: invalid header version")
+		return
+	}
+	if rec.h.Type == EndRequest {
+		err = io.EOF
+		return
+	}
+	n := int(rec.h.ContentLength) + int(rec.h.PaddingLength)
+	if len(rec.rbuf) < n {
+		rec.rbuf = make([]byte, n)
+	}
+	if _, err = io.ReadFull(r, rec.rbuf[:n]); err != nil {
+		return
+	}
+	buf = rec.rbuf[:int(rec.h.ContentLength)]
+
+	return
+}
+
+// FCGIClient implements a FastCGI client, which is a standard for
+// interfacing external applications with Web servers.
+type FCGIClient struct {
+	mutex     sync.Mutex
+	rwc       io.ReadWriteCloser
+	h         header
+	buf       bytes.Buffer
+	stderr    bytes.Buffer
+	keepAlive bool
+	reqID     uint16
+}
+
+// DialWithDialerContext connects to the fcgi responder at the specified network address, using custom net.Dialer
+// and a context.
+// See func net.Dial for a description of the network and address parameters.
+func DialWithDialerContext(ctx context.Context, network, address string, dialer net.Dialer) (fcgi *FCGIClient, err error) {
+	var conn net.Conn
+	conn, err = dialer.DialContext(ctx, network, address)
+	if err != nil {
+		return
+	}
+
+	fcgi = &FCGIClient{
+		rwc:       conn,
+		keepAlive: false,
+		reqID:     1,
+	}
+
+	return
+}
+
+// DialContext is like Dial but passes ctx to dialer.Dial.
+func DialContext(ctx context.Context, network, address string) (fcgi *FCGIClient, err error) {
+	// TODO: why not set timeout here?
+	return DialWithDialerContext(ctx, network, address, net.Dialer{})
+}
+
+// Dial connects to the fcgi responder at the specified network address, using default net.Dialer.
+// See func net.Dial for a description of the network and address parameters.
+func Dial(network, address string) (fcgi *FCGIClient, err error) {
+	return DialContext(context.Background(), network, address)
+}
+
+// Close closes fcgi connection
+func (c *FCGIClient) Close() {
+	c.rwc.Close()
+}
+
+func (c *FCGIClient) writeRecord(recType uint8, content []byte) (err error) {
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+	c.buf.Reset()
+	c.h.init(recType, c.reqID, len(content))
+	if err := binary.Write(&c.buf, binary.BigEndian, c.h); err != nil {
+		return err
+	}
+	if _, err := c.buf.Write(content); err != nil {
+		return err
+	}
+	if _, err := c.buf.Write(pad[:c.h.PaddingLength]); err != nil {
+		return err
+	}
+	_, err = c.rwc.Write(c.buf.Bytes())
+	return err
+}
+
+func (c *FCGIClient) writeBeginRequest(role uint16, flags uint8) error {
+	b := [8]byte{byte(role >> 8), byte(role), flags}
+	return c.writeRecord(BeginRequest, b[:])
+}
+
+func (c *FCGIClient) writeEndRequest(appStatus int, protocolStatus uint8) error {
+	b := make([]byte, 8)
+	binary.BigEndian.PutUint32(b, uint32(appStatus))
+	b[4] = protocolStatus
+	return c.writeRecord(EndRequest, b)
+}
+
+func (c *FCGIClient) writePairs(recType uint8, pairs map[string]string) error {
+	w := newWriter(c, recType)
+	b := make([]byte, 8)
+	nn := 0
+	for k, v := range pairs {
+		m := 8 + len(k) + len(v)
+		if m > maxWrite {
+			// param data size exceed 65535 bytes"
+			vl := maxWrite - 8 - len(k)
+			v = v[:vl]
+		}
+		n := encodeSize(b, uint32(len(k)))
+		n += encodeSize(b[n:], uint32(len(v)))
+		m = n + len(k) + len(v)
+		if (nn + m) > maxWrite {
+			w.Flush()
+			nn = 0
+		}
+		nn += m
+		if _, err := w.Write(b[:n]); err != nil {
+			return err
+		}
+		if _, err := w.WriteString(k); err != nil {
+			return err
+		}
+		if _, err := w.WriteString(v); err != nil {
+			return err
+		}
+	}
+	w.Close()
+	return nil
+}
+
+func encodeSize(b []byte, size uint32) int {
+	if size > 127 {
+		size |= 1 << 31
+		binary.BigEndian.PutUint32(b, size)
+		return 4
+	}
+	b[0] = byte(size)
+	return 1
+}
+
+// bufWriter encapsulates bufio.Writer but also closes the underlying stream when
+// Closed.
+type bufWriter struct {
+	closer io.Closer
+	*bufio.Writer
+}
+
+func (w *bufWriter) Close() error {
+	if err := w.Writer.Flush(); err != nil {
+		w.closer.Close()
+		return err
+	}
+	return w.closer.Close()
+}
+
+func newWriter(c *FCGIClient, recType uint8) *bufWriter {
+	s := &streamWriter{c: c, recType: recType}
+	w := bufio.NewWriterSize(s, maxWrite)
+	return &bufWriter{s, w}
+}
+
+// streamWriter abstracts out the separation of a stream into discrete records.
+// It only writes maxWrite bytes at a time.
+type streamWriter struct {
+	c       *FCGIClient
+	recType uint8
+}
+
+func (w *streamWriter) Write(p []byte) (int, error) {
+	nn := 0
+	for len(p) > 0 {
+		n := len(p)
+		if n > maxWrite {
+			n = maxWrite
+		}
+		if err := w.c.writeRecord(w.recType, p[:n]); err != nil {
+			return nn, err
+		}
+		nn += n
+		p = p[n:]
+	}
+	return nn, nil
+}
+
+func (w *streamWriter) Close() error {
+	// send empty record to close the stream
+	return w.c.writeRecord(w.recType, nil)
+}
+
+type streamReader struct {
+	c   *FCGIClient
+	buf []byte
+}
+
+func (w *streamReader) Read(p []byte) (n int, err error) {
+
+	if len(p) > 0 {
+		if len(w.buf) == 0 {
+
+			// filter outputs for error log
+			for {
+				rec := &record{}
+				var buf []byte
+				buf, err = rec.read(w.c.rwc)
+				if err != nil {
+					return
+				}
+				// standard error output
+				if rec.h.Type == Stderr {
+					w.c.stderr.Write(buf)
+					continue
+				}
+				w.buf = buf
+				break
+			}
+		}
+
+		n = len(p)
+		if n > len(w.buf) {
+			n = len(w.buf)
+		}
+		copy(p, w.buf[:n])
+		w.buf = w.buf[n:]
+	}
+
+	return
+}
+
+// Do made the request and returns a io.Reader that translates the data read
+// from fcgi responder out of fcgi packet before returning it.
+func (c *FCGIClient) Do(p map[string]string, req io.Reader) (r io.Reader, err error) {
+	err = c.writeBeginRequest(uint16(Responder), 0)
+	if err != nil {
+		return
+	}
+
+	err = c.writePairs(Params, p)
+	if err != nil {
+		return
+	}
+
+	body := newWriter(c, Stdin)
+	if req != nil {
+		_, _ = io.Copy(body, req)
+	}
+	body.Close()
+
+	r = &streamReader{c: c}
+	return
+}
+
+// clientCloser is a io.ReadCloser. It wraps a io.Reader with a Closer
+// that closes FCGIClient connection.
+type clientCloser struct {
+	*FCGIClient
+	io.Reader
+}
+
+func (f clientCloser) Close() error { return f.rwc.Close() }
+
+// Request returns a HTTP Response with Header and Body
+// from fcgi responder
+func (c *FCGIClient) Request(p map[string]string, req io.Reader) (resp *http.Response, err error) {
+	r, err := c.Do(p, req)
+	if err != nil {
+		return
+	}
+
+	rb := bufio.NewReader(r)
+	tp := textproto.NewReader(rb)
+	resp = new(http.Response)
+
+	// Parse the response headers.
+	mimeHeader, err := tp.ReadMIMEHeader()
+	if err != nil && err != io.EOF {
+		return
+	}
+	resp.Header = http.Header(mimeHeader)
+
+	if resp.Header.Get("Status") != "" {
+		statusParts := strings.SplitN(resp.Header.Get("Status"), " ", 2)
+		resp.StatusCode, err = strconv.Atoi(statusParts[0])
+		if err != nil {
+			return
+		}
+		if len(statusParts) > 1 {
+			resp.Status = statusParts[1]
+		}
+
+	} else {
+		resp.StatusCode = http.StatusOK
+	}
+
+	// TODO: fixTransferEncoding ?
+	resp.TransferEncoding = resp.Header["Transfer-Encoding"]
+	resp.ContentLength, _ = strconv.ParseInt(resp.Header.Get("Content-Length"), 10, 64)
+
+	if chunked(resp.TransferEncoding) {
+		resp.Body = clientCloser{c, httputil.NewChunkedReader(rb)}
+	} else {
+		resp.Body = clientCloser{c, ioutil.NopCloser(rb)}
+	}
+	return
+}
+
+// Get issues a GET request to the fcgi responder.
+func (c *FCGIClient) Get(p map[string]string, body io.Reader, l int64) (resp *http.Response, err error) {
+
+	p["REQUEST_METHOD"] = "GET"
+	p["CONTENT_LENGTH"] = strconv.FormatInt(l, 10)
+
+	return c.Request(p, body)
+}
+
+// Head issues a HEAD request to the fcgi responder.
+func (c *FCGIClient) Head(p map[string]string) (resp *http.Response, err error) {
+
+	p["REQUEST_METHOD"] = "HEAD"
+	p["CONTENT_LENGTH"] = "0"
+
+	return c.Request(p, nil)
+}
+
+// Options issues an OPTIONS request to the fcgi responder.
+func (c *FCGIClient) Options(p map[string]string) (resp *http.Response, err error) {
+
+	p["REQUEST_METHOD"] = "OPTIONS"
+	p["CONTENT_LENGTH"] = "0"
+
+	return c.Request(p, nil)
+}
+
+// Post issues a POST request to the fcgi responder. with request body
+// in the format that bodyType specified
+func (c *FCGIClient) Post(p map[string]string, method string, bodyType string, body io.Reader, l int64) (resp *http.Response, err error) {
+	if p == nil {
+		p = make(map[string]string)
+	}
+
+	p["REQUEST_METHOD"] = strings.ToUpper(method)
+
+	if len(p["REQUEST_METHOD"]) == 0 || p["REQUEST_METHOD"] == "GET" {
+		p["REQUEST_METHOD"] = "POST"
+	}
+
+	p["CONTENT_LENGTH"] = strconv.FormatInt(l, 10)
+	if len(bodyType) > 0 {
+		p["CONTENT_TYPE"] = bodyType
+	} else {
+		p["CONTENT_TYPE"] = "application/x-www-form-urlencoded"
+	}
+
+	return c.Request(p, body)
+}
+
+// PostForm issues a POST to the fcgi responder, with form
+// as a string key to a list values (url.Values)
+func (c *FCGIClient) PostForm(p map[string]string, data url.Values) (resp *http.Response, err error) {
+	body := bytes.NewReader([]byte(data.Encode()))
+	return c.Post(p, "POST", "application/x-www-form-urlencoded", body, int64(body.Len()))
+}
+
+// PostFile issues a POST to the fcgi responder in multipart(RFC 2046) standard,
+// with form as a string key to a list values (url.Values),
+// and/or with file as a string key to a list file path.
+func (c *FCGIClient) PostFile(p map[string]string, data url.Values, file map[string]string) (resp *http.Response, err error) {
+	buf := &bytes.Buffer{}
+	writer := multipart.NewWriter(buf)
+	bodyType := writer.FormDataContentType()
+
+	for key, val := range data {
+		for _, v0 := range val {
+			err = writer.WriteField(key, v0)
+			if err != nil {
+				return
+			}
+		}
+	}
+
+	for key, val := range file {
+		fd, e := os.Open(val)
+		if e != nil {
+			return nil, e
+		}
+		defer fd.Close()
+
+		part, e := writer.CreateFormFile(key, filepath.Base(val))
+		if e != nil {
+			return nil, e
+		}
+		_, err = io.Copy(part, fd)
+		if err != nil {
+			return
+		}
+	}
+
+	err = writer.Close()
+	if err != nil {
+		return
+	}
+
+	return c.Post(p, "POST", bodyType, buf, int64(buf.Len()))
+}
+
+// SetReadTimeout sets the read timeout for future calls that read from the
+// fcgi responder. A zero value for t means no timeout will be set.
+func (c *FCGIClient) SetReadTimeout(t time.Duration) error {
+	if conn, ok := c.rwc.(net.Conn); ok && t != 0 {
+		return conn.SetReadDeadline(time.Now().Add(t))
+	}
+	return nil
+}
+
+// SetWriteTimeout sets the write timeout for future calls that send data to
+// the fcgi responder. A zero value for t means no timeout will be set.
+func (c *FCGIClient) SetWriteTimeout(t time.Duration) error {
+	if conn, ok := c.rwc.(net.Conn); ok && t != 0 {
+		return conn.SetWriteDeadline(time.Now().Add(t))
+	}
+	return nil
+}
+
+// Checks whether chunked is part of the encodings stack
+func chunked(te []string) bool { return len(te) > 0 && te[0] == "chunked" }
diff --git a/modules/caddyhttp/reverseproxy/fastcgi/client_test.go b/modules/caddyhttp/reverseproxy/fastcgi/client_test.go
new file mode 100644
index 0000000..c090f3c
--- /dev/null
+++ b/modules/caddyhttp/reverseproxy/fastcgi/client_test.go
@@ -0,0 +1,301 @@
+// Copyright 2015 Matthew Holt and The Caddy Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// NOTE: These tests were adapted from the original
+// repository from which this package was forked.
+// The tests are slow (~10s) and in dire need of rewriting.
+// As such, the tests have been disabled to speed up
+// automated builds until they can be properly written.
+
+package fastcgi
+
+import (
+	"bytes"
+	"crypto/md5"
+	"encoding/binary"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log"
+	"math/rand"
+	"net"
+	"net/http"
+	"net/http/fcgi"
+	"net/url"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"testing"
+	"time"
+)
+
+// test fcgi protocol includes:
+// Get, Post, Post in multipart/form-data, and Post with files
+// each key should be the md5 of the value or the file uploaded
+// specify remote fcgi responder ip:port to test with php
+// test failed if the remote fcgi(script) failed md5 verification
+// and output "FAILED" in response
+const (
+	scriptFile = "/tank/www/fcgic_test.php"
+	//ipPort = "remote-php-serv:59000"
+	ipPort = "127.0.0.1:59000"
+)
+
+var globalt *testing.T
+
+type FastCGIServer struct{}
+
+func (s FastCGIServer) ServeHTTP(resp http.ResponseWriter, req *http.Request) {
+
+	if err := req.ParseMultipartForm(100000000); err != nil {
+		log.Printf("[ERROR] failed to parse: %v", err)
+	}
+
+	stat := "PASSED"
+	fmt.Fprintln(resp, "-")
+	fileNum := 0
+	{
+		length := 0
+		for k0, v0 := range req.Form {
+			h := md5.New()
+			_, _ = io.WriteString(h, v0[0])
+			_md5 := fmt.Sprintf("%x", h.Sum(nil))
+
+			length += len(k0)
+			length += len(v0[0])
+
+			// echo error when key != _md5(val)
+			if _md5 != k0 {
+				fmt.Fprintln(resp, "server:err ", _md5, k0)
+				stat = "FAILED"
+			}
+		}
+		if req.MultipartForm != nil {
+			fileNum = len(req.MultipartForm.File)
+			for kn, fns := range req.MultipartForm.File {
+				//fmt.Fprintln(resp, "server:filekey ", kn )
+				length += len(kn)
+				for _, f := range fns {
+					fd, err := f.Open()
+					if err != nil {
+						log.Println("server:", err)
+						return
+					}
+					h := md5.New()
+					l0, err := io.Copy(h, fd)
+					if err != nil {
+						log.Println(err)
+						return
+					}
+					length += int(l0)
+					defer fd.Close()
+					md5 := fmt.Sprintf("%x", h.Sum(nil))
+					//fmt.Fprintln(resp, "server:filemd5 ", md5 )
+
+					if kn != md5 {
+						fmt.Fprintln(resp, "server:err ", md5, kn)
+						stat = "FAILED"
+					}
+					//fmt.Fprintln(resp, "server:filename ", f.Filename )
+				}
+			}
+		}
+
+		fmt.Fprintln(resp, "server:got data length", length)
+	}
+	fmt.Fprintln(resp, "-"+stat+"-POST(", len(req.Form), ")-FILE(", fileNum, ")--")
+}
+
+func sendFcgi(reqType int, fcgiParams map[string]string, data []byte, posts map[string]string, files map[string]string) (content []byte) {
+	fcgi, err := Dial("tcp", ipPort)
+	if err != nil {
+		log.Println("err:", err)
+		return
+	}
+
+	length := 0
+
+	var resp *http.Response
+	switch reqType {
+	case 0:
+		if len(data) > 0 {
+			length = len(data)
+			rd := bytes.NewReader(data)
+			resp, err = fcgi.Post(fcgiParams, "", "", rd, int64(rd.Len()))
+		} else if len(posts) > 0 {
+			values := url.Values{}
+			for k, v := range posts {
+				values.Set(k, v)
+				length += len(k) + 2 + len(v)
+			}
+			resp, err = fcgi.PostForm(fcgiParams, values)
+		} else {
+			rd := bytes.NewReader(data)
+			resp, err = fcgi.Get(fcgiParams, rd, int64(rd.Len()))
+		}
+
+	default:
+		values := url.Values{}
+		for k, v := range posts {
+			values.Set(k, v)
+			length += len(k) + 2 + len(v)
+		}
+
+		for k, v := range files {
+			fi, _ := os.Lstat(v)
+			length += len(k) + int(fi.Size())
+		}
+		resp, err = fcgi.PostFile(fcgiParams, values, files)
+	}
+
+	if err != nil {
+		log.Println("err:", err)
+		return
+	}
+
+	defer resp.Body.Close()
+	content, _ = ioutil.ReadAll(resp.Body)
+
+	log.Println("c: send data length ≈", length, string(content))
+	fcgi.Close()
+	time.Sleep(1 * time.Second)
+
+	if bytes.Contains(content, []byte("FAILED")) {
+		globalt.Error("Server return failed message")
+	}
+
+	return
+}
+
+func generateRandFile(size int) (p string, m string) {
+
+	p = filepath.Join(os.TempDir(), "fcgict"+strconv.Itoa(rand.Int()))
+
+	// open output file
+	fo, err := os.Create(p)
+	if err != nil {
+		panic(err)
+	}
+	// close fo on exit and check for its returned error
+	defer func() {
+		if err := fo.Close(); err != nil {
+			panic(err)
+		}
+	}()
+
+	h := md5.New()
+	for i := 0; i < size/16; i++ {
+		buf := make([]byte, 16)
+		binary.PutVarint(buf, rand.Int63())
+		if _, err := fo.Write(buf); err != nil {
+			log.Printf("[ERROR] failed to write buffer: %v\n", err)
+		}
+		if _, err := h.Write(buf); err != nil {
+			log.Printf("[ERROR] failed to write buffer: %v\n", err)
+		}
+	}
+	m = fmt.Sprintf("%x", h.Sum(nil))
+	return
+}
+
+func DisabledTest(t *testing.T) {
+	// TODO: test chunked reader
+	globalt = t
+
+	rand.Seed(time.Now().UTC().UnixNano())
+
+	// server
+	go func() {
+		listener, err := net.Listen("tcp", ipPort)
+		if err != nil {
+			log.Println("listener creation failed: ", err)
+		}
+
+		srv := new(FastCGIServer)
+		if err := fcgi.Serve(listener, srv); err != nil {
+			log.Print("[ERROR] failed to start server: ", err)
+		}
+	}()
+
+	time.Sleep(1 * time.Second)
+
+	// init
+	fcgiParams := make(map[string]string)
+	fcgiParams["REQUEST_METHOD"] = "GET"
+	fcgiParams["SERVER_PROTOCOL"] = "HTTP/1.1"
+	//fcgi_params["GATEWAY_INTERFACE"] = "CGI/1.1"
+	fcgiParams["SCRIPT_FILENAME"] = scriptFile
+
+	// simple GET
+	log.Println("test:", "get")
+	sendFcgi(0, fcgiParams, nil, nil, nil)
+
+	// simple post data
+	log.Println("test:", "post")
+	sendFcgi(0, fcgiParams, []byte("c4ca4238a0b923820dcc509a6f75849b=1&7b8b965ad4bca0e41ab51de7b31363a1=n"), nil, nil)
+
+	log.Println("test:", "post data (more than 60KB)")
+	data := ""
+	for i := 0x00; i < 0xff; i++ {
+		v0 := strings.Repeat(string(i), 256)
+		h := md5.New()
+		_, _ = io.WriteString(h, v0)
+		k0 := fmt.Sprintf("%x", h.Sum(nil))
+		data += k0 + "=" + url.QueryEscape(v0) + "&"
+	}
+	sendFcgi(0, fcgiParams, []byte(data), nil, nil)
+
+	log.Println("test:", "post form (use url.Values)")
+	p0 := make(map[string]string, 1)
+	p0["c4ca4238a0b923820dcc509a6f75849b"] = "1"
+	p0["7b8b965ad4bca0e41ab51de7b31363a1"] = "n"
+	sendFcgi(1, fcgiParams, nil, p0, nil)
+
+	log.Println("test:", "post forms (256 keys, more than 1MB)")
+	p1 := make(map[string]string, 1)
+	for i := 0x00; i < 0xff; i++ {
+		v0 := strings.Repeat(string(i), 4096)
+		h := md5.New()
+		_, _ = io.WriteString(h, v0)
+		k0 := fmt.Sprintf("%x", h.Sum(nil))
+		p1[k0] = v0
+	}
+	sendFcgi(1, fcgiParams, nil, p1, nil)
+
+	log.Println("test:", "post file (1 file, 500KB)) ")
+	f0 := make(map[string]string, 1)
+	path0, m0 := generateRandFile(500000)
+	f0[m0] = path0
+	sendFcgi(1, fcgiParams, nil, p1, f0)
+
+	log.Println("test:", "post multiple files (2 files, 5M each) and forms (256 keys, more than 1MB data")
+	path1, m1 := generateRandFile(5000000)
+	f0[m1] = path1
+	sendFcgi(1, fcgiParams, nil, p1, f0)
+
+	log.Println("test:", "post only files (2 files, 5M each)")
+	sendFcgi(1, fcgiParams, nil, nil, f0)
+
+	log.Println("test:", "post only 1 file")
+	delete(f0, "m0")
+	sendFcgi(1, fcgiParams, nil, nil, f0)
+
+	if err := os.Remove(path0); err != nil {
+		log.Println("[ERROR] failed to remove path: ", err)
+	}
+	if err := os.Remove(path1); err != nil {
+		log.Println("[ERROR] failed to remove path: ", err)
+	}
+}
diff --git a/modules/caddyhttp/reverseproxy/fastcgi/fastcgi.go b/modules/caddyhttp/reverseproxy/fastcgi/fastcgi.go
new file mode 100644
index 0000000..32f094b
--- /dev/null
+++ b/modules/caddyhttp/reverseproxy/fastcgi/fastcgi.go
@@ -0,0 +1,342 @@
+// Copyright 2015 Matthew Holt and The Caddy Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package fastcgi
+
+import (
+	"context"
+	"crypto/tls"
+	"fmt"
+	"net/http"
+	"path"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/caddyserver/caddy/v2/modules/caddytls"
+
+	"github.com/caddyserver/caddy/v2"
+)
+
+func init() {
+	caddy.RegisterModule(Transport{})
+}
+
+type Transport struct {
+	//////////////////////////////
+	// TODO: taken from v1 Handler type
+
+	SoftwareName    string
+	SoftwareVersion string
+	ServerName      string
+	ServerPort      string
+
+	//////////////////////////
+	// TODO: taken from v1 Rule type
+
+	// The base path to match. Required.
+	// Path string
+
+	// upstream load balancer
+	// balancer
+
+	// Always process files with this extension with fastcgi.
+	// Ext string
+
+	// Use this directory as the fastcgi root directory. Defaults to the root
+	// directory of the parent virtual host.
+	Root string
+
+	// The path in the URL will be split into two, with the first piece ending
+	// with the value of SplitPath. The first piece will be assumed as the
+	// actual resource (CGI script) name, and the second piece will be set to
+	// PATH_INFO for the CGI script to use.
+	SplitPath string
+
+	// If the URL ends with '/' (which indicates a directory), these index
+	// files will be tried instead.
+	IndexFiles []string
+
+	// Environment Variables
+	EnvVars [][2]string
+
+	// Ignored paths
+	IgnoredSubPaths []string
+
+	// The duration used to set a deadline when connecting to an upstream.
+	DialTimeout time.Duration
+
+	// The duration used to set a deadline when reading from the FastCGI server.
+	ReadTimeout time.Duration
+
+	// The duration used to set a deadline when sending to the FastCGI server.
+	WriteTimeout time.Duration
+}
+
+// CaddyModule returns the Caddy module information.
+func (Transport) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		Name: "http.handlers.reverse_proxy.transport.fastcgi",
+		New:  func() caddy.Module { return new(Transport) },
+	}
+}
+
+func (t Transport) RoundTrip(r *http.Request) (*http.Response, error) {
+	// Create environment for CGI script
+	env, err := t.buildEnv(r)
+	if err != nil {
+		return nil, fmt.Errorf("building environment: %v", err)
+	}
+
+	// TODO:
+	// Connect to FastCGI gateway
+	// address, err := f.Address()
+	// if err != nil {
+	// 	return http.StatusBadGateway, err
+	// }
+	// network, address := parseAddress(address)
+	network, address := "tcp", r.URL.Host // TODO:
+
+	ctx := context.Background()
+	if t.DialTimeout > 0 {
+		var cancel context.CancelFunc
+		ctx, cancel = context.WithTimeout(ctx, t.DialTimeout)
+		defer cancel()
+	}
+
+	fcgiBackend, err := DialContext(ctx, network, address)
+	if err != nil {
+		return nil, fmt.Errorf("dialing backend: %v", err)
+	}
+	// fcgiBackend is closed when response body is closed (see clientCloser)
+
+	// read/write timeouts
+	if err := fcgiBackend.SetReadTimeout(t.ReadTimeout); err != nil {
+		return nil, fmt.Errorf("setting read timeout: %v", err)
+	}
+	if err := fcgiBackend.SetWriteTimeout(t.WriteTimeout); err != nil {
+		return nil, fmt.Errorf("setting write timeout: %v", err)
+	}
+
+	var resp *http.Response
+
+	var contentLength int64
+	// if ContentLength is already set
+	if r.ContentLength > 0 {
+		contentLength = r.ContentLength
+	} else {
+		contentLength, _ = strconv.ParseInt(r.Header.Get("Content-Length"), 10, 64)
+	}
+	switch r.Method {
+	case "HEAD":
+		resp, err = fcgiBackend.Head(env)
+	case "GET":
+		resp, err = fcgiBackend.Get(env, r.Body, contentLength)
+	case "OPTIONS":
+		resp, err = fcgiBackend.Options(env)
+	default:
+		resp, err = fcgiBackend.Post(env, r.Method, r.Header.Get("Content-Type"), r.Body, contentLength)
+	}
+
+	// TODO:
+	return resp, err
+
+	// Stuff brought over from v1 that might not be necessary here:
+
+	// if resp != nil && resp.Body != nil {
+	// 	defer resp.Body.Close()
+	// }
+
+	// if err != nil {
+	// 	if err, ok := err.(net.Error); ok && err.Timeout() {
+	// 		return http.StatusGatewayTimeout, err
+	// 	} else if err != io.EOF {
+	// 		return http.StatusBadGateway, err
+	// 	}
+	// }
+
+	// // Write response header
+	// writeHeader(w, resp)
+
+	// // Write the response body
+	// _, err = io.Copy(w, resp.Body)
+	// if err != nil {
+	// 	return http.StatusBadGateway, err
+	// }
+
+	// // Log any stderr output from upstream
+	// if fcgiBackend.stderr.Len() != 0 {
+	// 	// Remove trailing newline, error logger already does this.
+	// 	err = LogError(strings.TrimSuffix(fcgiBackend.stderr.String(), "\n"))
+	// }
+
+	// // Normally we would return the status code if it is an error status (>= 400),
+	// // however, upstream FastCGI apps don't know about our contract and have
+	// // probably already written an error page. So we just return 0, indicating
+	// // that the response body is already written. However, we do return any
+	// // error value so it can be logged.
+	// // Note that the proxy middleware works the same way, returning status=0.
+	// return 0, err
+}
+
+// buildEnv returns a set of CGI environment variables for the request.
+func (t Transport) buildEnv(r *http.Request) (map[string]string, error) {
+	var env map[string]string
+
+	// Separate remote IP and port; more lenient than net.SplitHostPort
+	var ip, port string
+	if idx := strings.LastIndex(r.RemoteAddr, ":"); idx > -1 {
+		ip = r.RemoteAddr[:idx]
+		port = r.RemoteAddr[idx+1:]
+	} else {
+		ip = r.RemoteAddr
+	}
+
+	// Remove [] from IPv6 addresses
+	ip = strings.Replace(ip, "[", "", 1)
+	ip = strings.Replace(ip, "]", "", 1)
+
+	// TODO: respect index files? or leave that to matcher/rewrite (I prefer that)?
+	fpath := r.URL.Path
+
+	// Split path in preparation for env variables.
+	// Previous canSplit checks ensure this can never be -1.
+	// TODO: I haven't brought over canSplit; make sure this doesn't break
+	splitPos := t.splitPos(fpath)
+
+	// Request has the extension; path was split successfully
+	docURI := fpath[:splitPos+len(t.SplitPath)]
+	pathInfo := fpath[splitPos+len(t.SplitPath):]
+	scriptName := fpath
+
+	// Strip PATH_INFO from SCRIPT_NAME
+	scriptName = strings.TrimSuffix(scriptName, pathInfo)
+
+	// SCRIPT_FILENAME is the absolute path of SCRIPT_NAME
+	scriptFilename := filepath.Join(t.Root, scriptName)
+
+	// Add vhost path prefix to scriptName. Otherwise, some PHP software will
+	// have difficulty discovering its URL.
+	pathPrefix, _ := r.Context().Value(caddy.CtxKey("path_prefix")).(string)
+	scriptName = path.Join(pathPrefix, scriptName)
+
+	// TODO: Disabled for now
+	// // Get the request URI from context. The context stores the original URI in case
+	// // it was changed by a middleware such as rewrite. By default, we pass the
+	// // original URI in as the value of REQUEST_URI (the user can overwrite this
+	// // if desired). Most PHP apps seem to want the original URI. Besides, this is
+	// // how nginx defaults: http://stackoverflow.com/a/12485156/1048862
+	// reqURL, _ := r.Context().Value(httpserver.OriginalURLCtxKey).(url.URL)
+
+	// // Retrieve name of remote user that was set by some downstream middleware such as basicauth.
+	// remoteUser, _ := r.Context().Value(httpserver.RemoteUserCtxKey).(string)
+
+	requestScheme := "http"
+	if r.TLS != nil {
+		requestScheme = "https"
+	}
+
+	// Some variables are unused but cleared explicitly to prevent
+	// the parent environment from interfering.
+	env = map[string]string{
+		// Variables defined in CGI 1.1 spec
+		"AUTH_TYPE":         "", // Not used
+		"CONTENT_LENGTH":    r.Header.Get("Content-Length"),
+		"CONTENT_TYPE":      r.Header.Get("Content-Type"),
+		"GATEWAY_INTERFACE": "CGI/1.1",
+		"PATH_INFO":         pathInfo,
+		"QUERY_STRING":      r.URL.RawQuery,
+		"REMOTE_ADDR":       ip,
+		"REMOTE_HOST":       ip, // For speed, remote host lookups disabled
+		"REMOTE_PORT":       port,
+		"REMOTE_IDENT":      "", // Not used
+		// "REMOTE_USER":       remoteUser, // TODO:
+		"REQUEST_METHOD":  r.Method,
+		"REQUEST_SCHEME":  requestScheme,
+		"SERVER_NAME":     t.ServerName,
+		"SERVER_PORT":     t.ServerPort,
+		"SERVER_PROTOCOL": r.Proto,
+		"SERVER_SOFTWARE": t.SoftwareName + "/" + t.SoftwareVersion,
+
+		// Other variables
+		// "DOCUMENT_ROOT":   rule.Root,
+		"DOCUMENT_URI": docURI,
+		"HTTP_HOST":    r.Host, // added here, since not always part of headers
+		// "REQUEST_URI":     reqURL.RequestURI(), // TODO:
+		"SCRIPT_FILENAME": scriptFilename,
+		"SCRIPT_NAME":     scriptName,
+	}
+
+	// compliance with the CGI specification requires that
+	// PATH_TRANSLATED should only exist if PATH_INFO is defined.
+	// Info: https://www.ietf.org/rfc/rfc3875 Page 14
+	if env["PATH_INFO"] != "" {
+		env["PATH_TRANSLATED"] = filepath.Join(t.Root, pathInfo) // Info: http://www.oreilly.com/openbook/cgi/ch02_04.html
+	}
+
+	// Some web apps rely on knowing HTTPS or not
+	if r.TLS != nil {
+		env["HTTPS"] = "on"
+		// and pass the protocol details in a manner compatible with apache's mod_ssl
+		// (which is why these have a SSL_ prefix and not TLS_).
+		v, ok := tlsProtocolStrings[r.TLS.Version]
+		if ok {
+			env["SSL_PROTOCOL"] = v
+		}
+		// and pass the cipher suite in a manner compatible with apache's mod_ssl
+		for k, v := range caddytls.SupportedCipherSuites {
+			if v == r.TLS.CipherSuite {
+				env["SSL_CIPHER"] = k
+				break
+			}
+		}
+	}
+
+	// Add env variables from config (with support for placeholders in values)
+	repl := r.Context().Value(caddy.ReplacerCtxKey).(caddy.Replacer)
+	for _, envVar := range t.EnvVars {
+		env[envVar[0]] = repl.ReplaceAll(envVar[1], "")
+	}
+
+	// Add all HTTP headers to env variables
+	for field, val := range r.Header {
+		header := strings.ToUpper(field)
+		header = headerNameReplacer.Replace(header)
+		env["HTTP_"+header] = strings.Join(val, ", ")
+	}
+	return env, nil
+}
+
+// splitPos returns the index where path should
+// be split based on t.SplitPath.
+func (t Transport) splitPos(path string) int {
+	// TODO:
+	// if httpserver.CaseSensitivePath {
+	// 	return strings.Index(path, r.SplitPath)
+	// }
+	return strings.Index(strings.ToLower(path), strings.ToLower(t.SplitPath))
+}
+
+// TODO:
+// Map of supported protocols to Apache ssl_mod format
+// Note that these are slightly different from SupportedProtocols in caddytls/config.go
+var tlsProtocolStrings = map[uint16]string{
+	tls.VersionTLS10: "TLSv1",
+	tls.VersionTLS11: "TLSv1.1",
+	tls.VersionTLS12: "TLSv1.2",
+	tls.VersionTLS13: "TLSv1.3",
+}
+
+var headerNameReplacer = strings.NewReplacer(" ", "_", "-", "_")
diff --git a/modules/caddyhttp/reverseproxy/healthchecker.go b/modules/caddyhttp/reverseproxy/healthchecker.go
deleted file mode 100755
index c557d3f..0000000
--- a/modules/caddyhttp/reverseproxy/healthchecker.go
+++ /dev/null
@@ -1,86 +0,0 @@
-// Copyright 2015 Matthew Holt and The Caddy Authors
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package reverseproxy
-
-import (
-	"net/http"
-	"time"
-)
-
-// Upstream represents the interface that must be satisfied to use the healthchecker.
-type Upstream interface {
-	SetHealthiness(bool)
-}
-
-// HealthChecker represents a worker that periodically evaluates if proxy upstream host is healthy.
-type HealthChecker struct {
-	upstream   Upstream
-	Ticker     *time.Ticker
-	HTTPClient *http.Client
-	StopChan   chan bool
-}
-
-// ScheduleChecks periodically runs health checks against an upstream host.
-func (h *HealthChecker) ScheduleChecks(url string) {
-	// check if a host is healthy on start vs waiting for timer
-	h.upstream.SetHealthiness(h.IsHealthy(url))
-	stop := make(chan bool)
-	h.StopChan = stop
-
-	go func() {
-		for {
-			select {
-			case <-h.Ticker.C:
-				h.upstream.SetHealthiness(h.IsHealthy(url))
-			case <-stop:
-				return
-			}
-		}
-	}()
-}
-
-// Stop stops the healthchecker from makeing further requests.
-func (h *HealthChecker) Stop() {
-	h.Ticker.Stop()
-	close(h.StopChan)
-}
-
-// IsHealthy attempts to check if a upstream host is healthy.
-func (h *HealthChecker) IsHealthy(url string) bool {
-	req, err := http.NewRequest(http.MethodGet, url, nil)
-	if err != nil {
-		return false
-	}
-
-	resp, err := h.HTTPClient.Do(req)
-	if err != nil {
-		return false
-	}
-
-	if resp.StatusCode < 200 || resp.StatusCode >= 400 {
-		return false
-	}
-
-	return true
-}
-
-// NewHealthCheckWorker returns a new instance of a HealthChecker.
-func NewHealthCheckWorker(u Upstream, interval time.Duration, client *http.Client) *HealthChecker {
-	return &HealthChecker{
-		upstream:   u,
-		Ticker:     time.NewTicker(interval),
-		HTTPClient: client,
-	}
-}
diff --git a/modules/caddyhttp/reverseproxy/httptransport.go b/modules/caddyhttp/reverseproxy/httptransport.go
new file mode 100644
index 0000000..36dd776
--- /dev/null
+++ b/modules/caddyhttp/reverseproxy/httptransport.go
@@ -0,0 +1,133 @@
+// Copyright 2015 Matthew Holt and The Caddy Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package reverseproxy
+
+import (
+	"net"
+	"net/http"
+	"time"
+
+	"github.com/caddyserver/caddy/v2"
+)
+
+func init() {
+	caddy.RegisterModule(HTTPTransport{})
+}
+
+// TODO: This is the default transport, basically just http.Transport, but we define JSON struct tags...
+type HTTPTransport struct {
+	// TODO: Actually this is where the TLS config should go, technically...
+	// as well as keepalives and dial timeouts...
+	// TODO: It's possible that other transports (like fastcgi) might be
+	// able to borrow/use at least some of these config fields; if so,
+	// move them into a type called CommonTransport and embed it
+
+	TLS                   *TLSConfig     `json:"tls,omitempty"`
+	KeepAlive             *KeepAlive     `json:"keep_alive,omitempty"`
+	Compression           *bool          `json:"compression,omitempty"`
+	MaxConnsPerHost       int            `json:"max_conns_per_host,omitempty"` // TODO: NOTE: we use our health check stuff to enforce max REQUESTS per host, but this is connections
+	DialTimeout           caddy.Duration `json:"dial_timeout,omitempty"`
+	FallbackDelay         caddy.Duration `json:"dial_fallback_delay,omitempty"`
+	ResponseHeaderTimeout caddy.Duration `json:"response_header_timeout,omitempty"`
+	ExpectContinueTimeout caddy.Duration `json:"expect_continue_timeout,omitempty"`
+	MaxResponseHeaderSize int64          `json:"max_response_header_size,omitempty"`
+	WriteBufferSize       int            `json:"write_buffer_size,omitempty"`
+	ReadBufferSize        int            `json:"read_buffer_size,omitempty"`
+	// TODO: ProxyConnectHeader?
+
+	RoundTripper http.RoundTripper `json:"-"`
+}
+
+// CaddyModule returns the Caddy module information.
+func (HTTPTransport) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		Name: "http.handlers.reverse_proxy.transport.http",
+		New:  func() caddy.Module { return new(HTTPTransport) },
+	}
+}
+
+func (h *HTTPTransport) Provision(ctx caddy.Context) error {
+	dialer := &net.Dialer{
+		Timeout:       time.Duration(h.DialTimeout),
+		FallbackDelay: time.Duration(h.FallbackDelay),
+		// TODO: Resolver
+	}
+	rt := &http.Transport{
+		DialContext:            dialer.DialContext,
+		MaxConnsPerHost:        h.MaxConnsPerHost,
+		ResponseHeaderTimeout:  time.Duration(h.ResponseHeaderTimeout),
+		ExpectContinueTimeout:  time.Duration(h.ExpectContinueTimeout),
+		MaxResponseHeaderBytes: h.MaxResponseHeaderSize,
+		WriteBufferSize:        h.WriteBufferSize,
+		ReadBufferSize:         h.ReadBufferSize,
+	}
+
+	if h.TLS != nil {
+		rt.TLSHandshakeTimeout = time.Duration(h.TLS.HandshakeTimeout)
+		// TODO: rest of TLS config
+	}
+
+	if h.KeepAlive != nil {
+		dialer.KeepAlive = time.Duration(h.KeepAlive.ProbeInterval)
+
+		if enabled := h.KeepAlive.Enabled; enabled != nil {
+			rt.DisableKeepAlives = !*enabled
+		}
+		rt.MaxIdleConns = h.KeepAlive.MaxIdleConns
+		rt.MaxIdleConnsPerHost = h.KeepAlive.MaxIdleConnsPerHost
+		rt.IdleConnTimeout = time.Duration(h.KeepAlive.IdleConnTimeout)
+	}
+
+	if h.Compression != nil {
+		rt.DisableCompression = !*h.Compression
+	}
+
+	h.RoundTripper = rt
+
+	return nil
+}
+
+func (h HTTPTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	return h.RoundTripper.RoundTrip(req)
+}
+
+type TLSConfig struct {
+	CAPool             []string       `json:"ca_pool,omitempty"`
+	ClientCertificate  string         `json:"client_certificate,omitempty"`
+	InsecureSkipVerify bool           `json:"insecure_skip_verify,omitempty"`
+	HandshakeTimeout   caddy.Duration `json:"handshake_timeout,omitempty"`
+}
+
+type KeepAlive struct {
+	Enabled             *bool          `json:"enabled,omitempty"`
+	ProbeInterval       caddy.Duration `json:"probe_interval,omitempty"`
+	MaxIdleConns        int            `json:"max_idle_conns,omitempty"`
+	MaxIdleConnsPerHost int            `json:"max_idle_conns_per_host,omitempty"`
+	IdleConnTimeout     caddy.Duration `json:"idle_timeout,omitempty"` // how long should connections be kept alive when idle
+}
+
+var (
+	defaultDialer = net.Dialer{
+		Timeout:   10 * time.Second,
+		KeepAlive: 30 * time.Second,
+	}
+
+	// TODO: does this need to be configured to enable HTTP/2?
+	defaultTransport = &http.Transport{
+		DialContext:         defaultDialer.DialContext,
+		TLSHandshakeTimeout: 5 * time.Second,
+		IdleConnTimeout:     2 * time.Minute,
+	}
+)
diff --git a/modules/caddyhttp/reverseproxy/module.go b/modules/caddyhttp/reverseproxy/module.go
deleted file mode 100755
index 21aca1d..0000000
--- a/modules/caddyhttp/reverseproxy/module.go
+++ /dev/null
@@ -1,53 +0,0 @@
-// Copyright 2015 Matthew Holt and The Caddy Authors
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package reverseproxy
-
-import (
-	"github.com/caddyserver/caddy/v2"
-	"github.com/caddyserver/caddy/v2/caddyconfig/httpcaddyfile"
-	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
-)
-
-func init() {
-	caddy.RegisterModule(new(LoadBalanced))
-	httpcaddyfile.RegisterHandlerDirective("reverse_proxy", parseCaddyfile) // TODO: "proxy"?
-}
-
-// CaddyModule returns the Caddy module information.
-func (*LoadBalanced) CaddyModule() caddy.ModuleInfo {
-	return caddy.ModuleInfo{
-		Name: "http.handlers.reverse_proxy",
-		New:  func() caddy.Module { return new(LoadBalanced) },
-	}
-}
-
-// parseCaddyfile sets up the handler from Caddyfile tokens. Syntax:
-//
-//     proxy [<matcher>] <to>
-//
-// TODO: This needs to be finished. It definitely needs to be able to open a block...
-func parseCaddyfile(h httpcaddyfile.Helper) (caddyhttp.MiddlewareHandler, error) {
-	lb := new(LoadBalanced)
-	for h.Next() {
-		allTo := h.RemainingArgs()
-		if len(allTo) == 0 {
-			return nil, h.ArgErr()
-		}
-		for _, to := range allTo {
-			lb.Upstreams = append(lb.Upstreams, &UpstreamConfig{Host: to})
-		}
-	}
-	return lb, nil
-}
diff --git a/modules/caddyhttp/reverseproxy/reverseproxy.go b/modules/caddyhttp/reverseproxy/reverseproxy.go
index 68393de..e312d71 100755..100644
--- a/modules/caddyhttp/reverseproxy/reverseproxy.go
+++ b/modules/caddyhttp/reverseproxy/reverseproxy.go
@@ -15,7 +15,9 @@
 package reverseproxy
 
 import (
+	"bytes"
 	"context"
+	"encoding/json"
 	"fmt"
 	"io"
 	"log"
@@ -24,219 +26,229 @@ import (
 	"net/url"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"time"
 
+	"github.com/caddyserver/caddy/v2"
+	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
 	"golang.org/x/net/http/httpguts"
 )
 
-// ReverseProxy is an HTTP Handler that takes an incoming request and
-// sends it to another server, proxying the response back to the
-// client.
-type ReverseProxy struct {
-	// Director must be a function which modifies
-	// the request into a new request to be sent
-	// using Transport. Its response is then copied
-	// back to the original client unmodified.
-	// Director must not access the provided Request
-	// after returning.
-	Director func(*http.Request)
-
-	// The transport used to perform proxy requests.
-	// If nil, http.DefaultTransport is used.
-	Transport http.RoundTripper
-
-	// FlushInterval specifies the flush interval
-	// to flush to the client while copying the
-	// response body.
-	// If zero, no periodic flushing is done.
-	// A negative value means to flush immediately
-	// after each write to the client.
-	// The FlushInterval is ignored when ReverseProxy
-	// recognizes a response as a streaming response;
-	// for such responses, writes are flushed to the client
-	// immediately.
-	FlushInterval time.Duration
-
-	// ErrorLog specifies an optional logger for errors
-	// that occur when attempting to proxy the request.
-	// If nil, logging goes to os.Stderr via the log package's
-	// standard logger.
-	ErrorLog *log.Logger
-
-	// BufferPool optionally specifies a buffer pool to
-	// get byte slices for use by io.CopyBuffer when
-	// copying HTTP response bodies.
-	BufferPool BufferPool
-
-	// ModifyResponse is an optional function that modifies the
-	// Response from the backend. It is called if the backend
-	// returns a response at all, with any HTTP status code.
-	// If the backend is unreachable, the optional ErrorHandler is
-	// called without any call to ModifyResponse.
-	//
-	// If ModifyResponse returns an error, ErrorHandler is called
-	// with its error value. If ErrorHandler is nil, its default
-	// implementation is used.
-	ModifyResponse func(*http.Response) error
-
-	// ErrorHandler is an optional function that handles errors
-	// reaching the backend or errors from ModifyResponse.
-	//
-	// If nil, the default is to log the provided error and return
-	// a 502 Status Bad Gateway response.
-	ErrorHandler func(http.ResponseWriter, *http.Request, error)
-}
-
-// A BufferPool is an interface for getting and returning temporary
-// byte slices for use by io.CopyBuffer.
-type BufferPool interface {
-	Get() []byte
-	Put([]byte)
+func init() {
+	caddy.RegisterModule(Handler{})
 }
 
-func singleJoiningSlash(a, b string) string {
-	aslash := strings.HasSuffix(a, "/")
-	bslash := strings.HasPrefix(b, "/")
-	switch {
-	case aslash && bslash:
-		return a + b[1:]
-	case !aslash && !bslash:
-		return a + "/" + b
+type Handler struct {
+	TransportRaw  json.RawMessage `json:"transport,omitempty"`
+	LoadBalancing *LoadBalancing  `json:"load_balancing,omitempty"`
+	HealthChecks  *HealthChecks   `json:"health_checks,omitempty"`
+	// UpstreamStorageRaw json.RawMessage `json:"upstream_storage,omitempty"` // TODO:
+	Upstreams HostPool `json:"upstreams,omitempty"`
+
+	// UpstreamProvider UpstreamProvider  `json:"-"` // TODO:
+	Transport http.RoundTripper `json:"-"`
+}
+
+// CaddyModule returns the Caddy module information.
+func (Handler) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		Name: "http.handlers.reverse_proxy",
+		New:  func() caddy.Module { return new(Handler) },
 	}
-	return a + b
 }
 
-// NewSingleHostReverseProxy returns a new ReverseProxy that routes
-// URLs to the scheme, host, and base path provided in target. If the
-// target's path is "/base" and the incoming request was for "/dir",
-// the target request will be for /base/dir.
-// NewSingleHostReverseProxy does not rewrite the Host header.
-// To rewrite Host headers, use ReverseProxy directly with a custom
-// Director policy.
-func NewSingleHostReverseProxy(target *url.URL) *ReverseProxy {
-	targetQuery := target.RawQuery
-	director := func(req *http.Request) {
-		req.URL.Scheme = target.Scheme
-		req.URL.Host = target.Host
-		req.URL.Path = singleJoiningSlash(target.Path, req.URL.Path)
-		if targetQuery == "" || req.URL.RawQuery == "" {
-			req.URL.RawQuery = targetQuery + req.URL.RawQuery
-		} else {
-			req.URL.RawQuery = targetQuery + "&" + req.URL.RawQuery
+func (h *Handler) Provision(ctx caddy.Context) error {
+	if h.TransportRaw != nil {
+		val, err := ctx.LoadModuleInline("protocol", "http.handlers.reverse_proxy.transport", h.TransportRaw)
+		if err != nil {
+			return fmt.Errorf("loading transport module: %s", err)
 		}
-		if _, ok := req.Header["User-Agent"]; !ok {
-			// explicitly disable User-Agent so it's not set to default value
-			req.Header.Set("User-Agent", "")
+		h.Transport = val.(http.RoundTripper)
+		h.TransportRaw = nil // allow GC to deallocate - TODO: Does this help?
+	}
+	if h.LoadBalancing != nil && h.LoadBalancing.SelectionPolicyRaw != nil {
+		val, err := ctx.LoadModuleInline("policy",
+			"http.handlers.reverse_proxy.selection_policies",
+			h.LoadBalancing.SelectionPolicyRaw)
+		if err != nil {
+			return fmt.Errorf("loading load balancing selection module: %s", err)
 		}
+		h.LoadBalancing.SelectionPolicy = val.(Selector)
+		h.LoadBalancing.SelectionPolicyRaw = nil // allow GC to deallocate - TODO: Does this help?
 	}
-	return &ReverseProxy{Director: director}
-}
 
-func copyHeader(dst, src http.Header) {
-	for k, vv := range src {
-		for _, v := range vv {
-			dst.Add(k, v)
-		}
+	if h.Transport == nil {
+		h.Transport = defaultTransport
 	}
-}
 
-func cloneHeader(h http.Header) http.Header {
-	h2 := make(http.Header, len(h))
-	for k, vv := range h {
-		vv2 := make([]string, len(vv))
-		copy(vv2, vv)
-		h2[k] = vv2
+	if h.LoadBalancing == nil {
+		h.LoadBalancing = new(LoadBalancing)
+	}
+	if h.LoadBalancing.SelectionPolicy == nil {
+		h.LoadBalancing.SelectionPolicy = RandomSelection{}
+	}
+	if h.LoadBalancing.TryDuration > 0 && h.LoadBalancing.TryInterval == 0 {
+		// a non-zero try_duration with a zero try_interval
+		// will always spin the CPU for try_duration if the
+		// upstream is local or low-latency; default to some
+		// sane waiting period before try attempts
+		h.LoadBalancing.TryInterval = caddy.Duration(250 * time.Millisecond)
 	}
-	return h2
-}
 
-// Hop-by-hop headers. These are removed when sent to the backend.
-// As of RFC 7230, hop-by-hop headers are required to appear in the
-// Connection header field. These are the headers defined by the
-// obsoleted RFC 2616 (section 13.5.1) and are used for backward
-// compatibility.
-var hopHeaders = []string{
-	"Connection",
-	"Proxy-Connection", // non-standard but still sent by libcurl and rejected by e.g. google
-	"Keep-Alive",
-	"Proxy-Authenticate",
-	"Proxy-Authorization",
-	"Te",      // canonicalized version of "TE"
-	"Trailer", // not Trailers per URL above; https://www.rfc-editor.org/errata_search.php?eid=4522
-	"Transfer-Encoding",
-	"Upgrade",
-}
+	for _, upstream := range h.Upstreams {
+		// url parser requires a scheme
+		if !strings.Contains(upstream.Address, "://") {
+			upstream.Address = "http://" + upstream.Address
+		}
+		u, err := url.Parse(upstream.Address)
+		if err != nil {
+			return fmt.Errorf("invalid upstream address %s: %v", upstream.Address, err)
+		}
+		upstream.hostURL = u
+
+		// if host already exists from a current config,
+		// use that instead; otherwise, add it
+		// TODO: make hosts modular, so that their state can be distributed in enterprise for example
+		// TODO: If distributed, the pool should be stored in storage...
+		var host Host = new(upstreamHost)
+		activeHost, loaded := hosts.LoadOrStore(u.String(), host)
+		if loaded {
+			host = activeHost.(Host)
+		}
+		upstream.Host = host
+
+		// if the passive health checker has a non-zero "unhealthy
+		// request count" but the upstream has no MaxRequests set
+		// (they are the same thing, but one is a default value for
+		// for upstreams with a zero MaxRequests), copy the default
+		// value into this upstream, since the value in the upstream
+		// is what is used during availability checks
+		if h.HealthChecks != nil &&
+			h.HealthChecks.Passive != nil &&
+			h.HealthChecks.Passive.UnhealthyRequestCount > 0 &&
+			upstream.MaxRequests == 0 {
+			upstream.MaxRequests = h.HealthChecks.Passive.UnhealthyRequestCount
+		}
 
-func (p *ReverseProxy) defaultErrorHandler(rw http.ResponseWriter, req *http.Request, err error) {
-	p.logf("http: proxy error: %v", err)
-	rw.WriteHeader(http.StatusBadGateway)
-}
+		// TODO: active health checks
 
-func (p *ReverseProxy) getErrorHandler() func(http.ResponseWriter, *http.Request, error) {
-	if p.ErrorHandler != nil {
-		return p.ErrorHandler
+		if h.HealthChecks != nil {
+			// upstreams need independent access to the passive
+			// health check policy so they can, you know, passively
+			// do health checks
+			upstream.healthCheckPolicy = h.HealthChecks.Passive
+		}
 	}
-	return p.defaultErrorHandler
+
+	return nil
 }
 
-// modifyResponse conditionally runs the optional ModifyResponse hook
-// and reports whether the request should proceed.
-func (p *ReverseProxy) modifyResponse(rw http.ResponseWriter, res *http.Response, req *http.Request) bool {
-	if p.ModifyResponse == nil {
-		return true
-	}
-	if err := p.ModifyResponse(res); err != nil {
-		res.Body.Close()
-		p.getErrorHandler()(rw, req, err)
-		return false
+func (h *Handler) Cleanup() error {
+	// TODO: finish this up, make sure it takes care of any active health checkers or whatever
+	for _, upstream := range h.Upstreams {
+		hosts.Delete(upstream.hostURL.String())
 	}
-	return true
+	return nil
 }
 
-func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) (*http.Response, error) {
-	transport := p.Transport
-	if transport == nil {
-		transport = http.DefaultTransport
+func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyhttp.Handler) error {
+	// prepare the request for proxying; this is needed only once
+	err := h.prepareRequest(r)
+	if err != nil {
+		return caddyhttp.Error(http.StatusInternalServerError,
+			fmt.Errorf("preparing request for upstream round-trip: %v", err))
 	}
 
-	ctx := req.Context()
-	if cn, ok := rw.(http.CloseNotifier); ok {
-		var cancel context.CancelFunc
-		ctx, cancel = context.WithCancel(ctx)
-		defer cancel()
-		notifyChan := cn.CloseNotify()
-		go func() {
-			select {
-			case <-notifyChan:
-				cancel()
-			case <-ctx.Done():
+	start := time.Now()
+
+	var proxyErr error
+	for {
+		// choose an available upstream
+		upstream := h.LoadBalancing.SelectionPolicy.Select(h.Upstreams, r)
+		if upstream == nil {
+			if proxyErr == nil {
+				proxyErr = fmt.Errorf("no available upstreams")
+			}
+			if !h.tryAgain(start, proxyErr) {
+				break
 			}
-		}()
+			continue
+		}
+
+		// proxy the request to that upstream
+		proxyErr = h.reverseProxy(w, r, upstream)
+		if proxyErr == nil {
+			return nil
+		}
+
+		// remember this failure (if enabled)
+		h.countFailure(upstream)
+
+		// if we've tried long enough, break
+		if !h.tryAgain(start, proxyErr) {
+			break
+		}
 	}
 
-	outreq := req.WithContext(ctx) // includes shallow copies of maps, but okay
+	return caddyhttp.Error(http.StatusBadGateway, proxyErr)
+}
+
+// prepareRequest modifies req so that it is ready to be proxied,
+// except for directing to a specific upstream. This method mutates
+// headers and other necessary properties of the request and should
+// be done just once (before proxying) regardless of proxy retries.
+// This assumes that no mutations of the request are performed
+// by h during or after proxying.
+func (h Handler) prepareRequest(req *http.Request) error {
+	// ctx := req.Context()
+	// TODO: do we need to support CloseNotifier? It was deprecated years ago.
+	// All this does is wrap CloseNotify with context cancel, for those responsewriters
+	// which didn't support context, but all the ones we'd use should nowadays, right?
+	// if cn, ok := rw.(http.CloseNotifier); ok {
+	// 	var cancel context.CancelFunc
+	// 	ctx, cancel = context.WithCancel(ctx)
+	// 	defer cancel()
+	// 	notifyChan := cn.CloseNotify()
+	// 	go func() {
+	// 		select {
+	// 		case <-notifyChan:
+	// 			cancel()
+	// 		case <-ctx.Done():
+	// 		}
+	// 	}()
+	// }
+
+	// TODO: do we need to call WithContext, since we won't be changing req.Context() above if we remove the CloseNotifier stuff?
+	// TODO: (This is where references to req were originally "outreq", a shallow clone, which I think is unnecessary in our case)
+	// req = req.WithContext(ctx) // includes shallow copies of maps, but okay
 	if req.ContentLength == 0 {
-		outreq.Body = nil // Issue 16036: nil Body for http.Transport retries
+		req.Body = nil // Issue golang/go#16036: nil Body for http.Transport retries
 	}
 
-	outreq.Header = cloneHeader(req.Header)
+	// TODO: is this needed?
+	// req.Header = cloneHeader(req.Header)
 
-	p.Director(outreq)
-	outreq.Close = false
+	req.Close = false
 
-	reqUpType := upgradeType(outreq.Header)
-	removeConnectionHeaders(outreq.Header)
+	// if User-Agent is not set by client, then explicitly
+	// disable it so it's not set to default value by std lib
+	if _, ok := req.Header["User-Agent"]; !ok {
+		req.Header.Set("User-Agent", "")
+	}
+
+	reqUpType := upgradeType(req.Header)
+	removeConnectionHeaders(req.Header)
 
 	// Remove hop-by-hop headers to the backend. Especially
 	// important is "Connection" because we want a persistent
 	// connection, regardless of what the client sent to us.
 	for _, h := range hopHeaders {
-		hv := outreq.Header.Get(h)
+		hv := req.Header.Get(h)
 		if hv == "" {
 			continue
 		}
 		if h == "Te" && hv == "trailers" {
-			// Issue 21096: tell backend applications that
+			// Issue golang/go#21096: tell backend applications that
 			// care about trailer support that we support
 			// trailers. (We do, but we don't go out of
 			// our way to advertise that unless the
@@ -244,40 +256,65 @@ func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) (*ht
 			// worth mentioning)
 			continue
 		}
-		outreq.Header.Del(h)
+		req.Header.Del(h)
 	}
 
 	// After stripping all the hop-by-hop connection headers above, add back any
 	// necessary for protocol upgrades, such as for websockets.
 	if reqUpType != "" {
-		outreq.Header.Set("Connection", "Upgrade")
-		outreq.Header.Set("Upgrade", reqUpType)
+		req.Header.Set("Connection", "Upgrade")
+		req.Header.Set("Upgrade", reqUpType)
 	}
 
 	if clientIP, _, err := net.SplitHostPort(req.RemoteAddr); err == nil {
 		// If we aren't the first proxy retain prior
 		// X-Forwarded-For information as a comma+space
 		// separated list and fold multiple headers into one.
-		if prior, ok := outreq.Header["X-Forwarded-For"]; ok {
+		if prior, ok := req.Header["X-Forwarded-For"]; ok {
 			clientIP = strings.Join(prior, ", ") + ", " + clientIP
 		}
-		outreq.Header.Set("X-Forwarded-For", clientIP)
+		req.Header.Set("X-Forwarded-For", clientIP)
 	}
 
-	res, err := transport.RoundTrip(outreq)
+	return nil
+}
+
+// TODO:
+// this code is the entry point to what was borrowed from the net/http/httputil package in the standard library.
+func (h *Handler) reverseProxy(rw http.ResponseWriter, req *http.Request, upstream *Upstream) error {
+	// TODO: count this active request
+
+	// point the request to this upstream
+	h.directRequest(req, upstream)
+
+	// do the round-trip
+	start := time.Now()
+	res, err := h.Transport.RoundTrip(req)
+	latency := time.Since(start)
 	if err != nil {
-		p.getErrorHandler()(rw, outreq, err)
-		return nil, err
+		return err
 	}
 
-	// Deal with 101 Switching Protocols responses: (WebSocket, h2c, etc)
-	if res.StatusCode == http.StatusSwitchingProtocols {
-		if !p.modifyResponse(rw, res, outreq) {
-			return res, nil
+	// perform passive health checks (if enabled)
+	if h.HealthChecks != nil && h.HealthChecks.Passive != nil {
+		// strike if the status code matches one that is "bad"
+		for _, badStatus := range h.HealthChecks.Passive.UnhealthyStatus {
+			if caddyhttp.StatusCodeMatches(res.StatusCode, badStatus) {
+				h.countFailure(upstream)
+			}
 		}
 
-		p.handleUpgradeResponse(rw, outreq, res)
-		return res, nil
+		// strike if the roundtrip took too long
+		if h.HealthChecks.Passive.UnhealthyLatency > 0 &&
+			latency >= time.Duration(h.HealthChecks.Passive.UnhealthyLatency) {
+			h.countFailure(upstream)
+		}
+	}
+
+	// Deal with 101 Switching Protocols responses: (WebSocket, h2c, etc)
+	if res.StatusCode == http.StatusSwitchingProtocols {
+		h.handleUpgradeResponse(rw, req, res)
+		return nil
 	}
 
 	removeConnectionHeaders(res.Header)
@@ -286,10 +323,6 @@ func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) (*ht
 		res.Header.Del(h)
 	}
 
-	if !p.modifyResponse(rw, res, outreq) {
-		return res, nil
-	}
-
 	copyHeader(rw.Header(), res.Header)
 
 	// The "Trailer" header isn't included in the Transport's response,
@@ -305,15 +338,16 @@ func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) (*ht
 
 	rw.WriteHeader(res.StatusCode)
 
-	err = p.copyResponse(rw, res.Body, p.flushInterval(req, res))
+	err = h.copyResponse(rw, res.Body, h.flushInterval(req, res))
 	if err != nil {
 		defer res.Body.Close()
 		// Since we're streaming the response, if we run into an error all we can do
-		// is abort the request. Issue 23643: ReverseProxy should use ErrAbortHandler
+		// is abort the request. Issue golang/go#23643: ReverseProxy should use ErrAbortHandler
 		// on read error while copying body.
+		// TODO: Look into whether we want to panic at all in our case...
 		if !shouldPanicOnCopyError(req) {
-			p.logf("suppressing panic for copyResponse error in test; copy error: %v", err)
-			return nil, err
+			// p.logf("suppressing panic for copyResponse error in test; copy error: %v", err)
+			return err
 		}
 
 		panic(http.ErrAbortHandler)
@@ -331,7 +365,7 @@ func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) (*ht
 
 	if len(res.Trailer) == announcedTrailers {
 		copyHeader(rw.Header(), res.Trailer)
-		return res, nil
+		return nil
 	}
 
 	for k, vv := range res.Trailer {
@@ -341,46 +375,90 @@ func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) (*ht
 		}
 	}
 
-	return res, nil
+	return nil
 }
 
-var inOurTests bool // whether we're in our own tests
-
-// shouldPanicOnCopyError reports whether the reverse proxy should
-// panic with http.ErrAbortHandler. This is the right thing to do by
-// default, but Go 1.10 and earlier did not, so existing unit tests
-// weren't expecting panics. Only panic in our own tests, or when
-// running under the HTTP server.
-func shouldPanicOnCopyError(req *http.Request) bool {
-	if inOurTests {
-		// Our tests know to handle this panic.
-		return true
+// tryAgain takes the time that the handler was initially invoked
+// as well as any error currently obtained and returns true if
+// another attempt should be made at proxying the request. If
+// true is returned, it has already blocked long enough before
+// the next retry (i.e. no more sleeping is needed). If false is
+// returned, the handler should stop trying to proxy the request.
+func (h Handler) tryAgain(start time.Time, proxyErr error) bool {
+	// if downstream has canceled the request, break
+	if proxyErr == context.Canceled {
+		return false
 	}
-	if req.Context().Value(http.ServerContextKey) != nil {
-		// We seem to be running under an HTTP server, so
-		// it'll recover the panic.
-		return true
+	// if we've tried long enough, break
+	if time.Since(start) >= time.Duration(h.LoadBalancing.TryDuration) {
+		return false
 	}
-	// Otherwise act like Go 1.10 and earlier to not break
-	// existing tests.
-	return false
+	// otherwise, wait and try the next available host
+	time.Sleep(time.Duration(h.LoadBalancing.TryInterval))
+	return true
 }
 
-// removeConnectionHeaders removes hop-by-hop headers listed in the "Connection" header of h.
-// See RFC 7230, section 6.1
-func removeConnectionHeaders(h http.Header) {
-	if c := h.Get("Connection"); c != "" {
-		for _, f := range strings.Split(c, ",") {
-			if f = strings.TrimSpace(f); f != "" {
-				h.Del(f)
-			}
-		}
+// directRequest modifies only req.URL so that it points to the
+// given upstream host. It must modify ONLY the request URL.
+func (h Handler) directRequest(req *http.Request, upstream *Upstream) {
+	target := upstream.hostURL
+	req.URL.Scheme = target.Scheme
+	req.URL.Host = target.Host
+	req.URL.Path = singleJoiningSlash(target.Path, req.URL.Path) // TODO: This might be a bug (if any part of the path was augmented from a previously-tried upstream; need to start from clean original path of request, same for query string!)
+	if target.RawQuery == "" || req.URL.RawQuery == "" {
+		req.URL.RawQuery = target.RawQuery + req.URL.RawQuery
+	} else {
+		req.URL.RawQuery = target.RawQuery + "&" + req.URL.RawQuery
 	}
 }
 
+func (h Handler) handleUpgradeResponse(rw http.ResponseWriter, req *http.Request, res *http.Response) {
+	reqUpType := upgradeType(req.Header)
+	resUpType := upgradeType(res.Header)
+	if reqUpType != resUpType {
+		// p.getErrorHandler()(rw, req, fmt.Errorf("backend tried to switch protocol %q when %q was requested", resUpType, reqUpType))
+		return
+	}
+
+	copyHeader(res.Header, rw.Header())
+
+	hj, ok := rw.(http.Hijacker)
+	if !ok {
+		// p.getErrorHandler()(rw, req, fmt.Errorf("can't switch protocols using non-Hijacker ResponseWriter type %T", rw))
+		return
+	}
+	backConn, ok := res.Body.(io.ReadWriteCloser)
+	if !ok {
+		// p.getErrorHandler()(rw, req, fmt.Errorf("internal error: 101 switching protocols response with non-writable body"))
+		return
+	}
+	defer backConn.Close()
+	conn, brw, err := hj.Hijack()
+	if err != nil {
+		// p.getErrorHandler()(rw, req, fmt.Errorf("Hijack failed on protocol switch: %v", err))
+		return
+	}
+	defer conn.Close()
+	res.Body = nil // so res.Write only writes the headers; we have res.Body in backConn above
+	if err := res.Write(brw); err != nil {
+		// p.getErrorHandler()(rw, req, fmt.Errorf("response write: %v", err))
+		return
+	}
+	if err := brw.Flush(); err != nil {
+		// p.getErrorHandler()(rw, req, fmt.Errorf("response flush: %v", err))
+		return
+	}
+	errc := make(chan error, 1)
+	spc := switchProtocolCopier{user: conn, backend: backConn}
+	go spc.copyToBackend(errc)
+	go spc.copyFromBackend(errc)
+	<-errc
+	return
+}
+
 // flushInterval returns the p.FlushInterval value, conditionally
 // overriding its value for a specific request/response.
-func (p *ReverseProxy) flushInterval(req *http.Request, res *http.Response) time.Duration {
+func (h Handler) flushInterval(req *http.Request, res *http.Response) time.Duration {
 	resCT := res.Header.Get("Content-Type")
 
 	// For Server-Sent Events responses, flush immediately.
@@ -390,10 +468,11 @@ func (p *ReverseProxy) flushInterval(req *http.Request, res *http.Response) time
 	}
 
 	// TODO: more specific cases? e.g. res.ContentLength == -1?
-	return p.FlushInterval
+	// return h.FlushInterval
+	return 0
 }
 
-func (p *ReverseProxy) copyResponse(dst io.Writer, src io.Reader, flushInterval time.Duration) error {
+func (h Handler) copyResponse(dst io.Writer, src io.Reader, flushInterval time.Duration) error {
 	if flushInterval != 0 {
 		if wf, ok := dst.(writeFlusher); ok {
 			mlw := &maxLatencyWriter{
@@ -405,18 +484,25 @@ func (p *ReverseProxy) copyResponse(dst io.Writer, src io.Reader, flushInterval
 		}
 	}
 
+	// TODO: Figure out how we want to do this... using custom buffer pool type seems unnecessary
+	// or maybe it is, depending on how we want to handle errors,
+	// see: https://github.com/golang/go/issues/21814
+	// buf := bufPool.Get().(*bytes.Buffer)
+	// buf.Reset()
+	// defer bufPool.Put(buf)
+	// _, err := io.CopyBuffer(dst, src, )
 	var buf []byte
-	if p.BufferPool != nil {
-		buf = p.BufferPool.Get()
-		defer p.BufferPool.Put(buf)
-	}
-	_, err := p.copyBuffer(dst, src, buf)
+	// if h.BufferPool != nil {
+	// 	buf = h.BufferPool.Get()
+	// 	defer h.BufferPool.Put(buf)
+	// }
+	_, err := h.copyBuffer(dst, src, buf)
 	return err
 }
 
 // copyBuffer returns any write errors or non-EOF read errors, and the amount
 // of bytes written.
-func (p *ReverseProxy) copyBuffer(dst io.Writer, src io.Reader, buf []byte) (int64, error) {
+func (h Handler) copyBuffer(dst io.Writer, src io.Reader, buf []byte) (int64, error) {
 	if len(buf) == 0 {
 		buf = make([]byte, 32*1024)
 	}
@@ -424,7 +510,13 @@ func (p *ReverseProxy) copyBuffer(dst io.Writer, src io.Reader, buf []byte) (int
 	for {
 		nr, rerr := src.Read(buf)
 		if rerr != nil && rerr != io.EOF && rerr != context.Canceled {
-			p.logf("httputil: ReverseProxy read error during body copy: %v", rerr)
+			// TODO: this could be useful to know (indeed, it revealed an error in our
+			// fastcgi PoC earlier; but it's this single error report here that necessitates
+			// a function separate from io.CopyBuffer, since io.CopyBuffer does not distinguish
+			// between read or write errors; in a reverse proxy situation, write errors are not
+			// something we need to report to the client, but read errors are a problem on our
+			// end for sure. so we need to decide what we want.)
+			// p.logf("copyBuffer: ReverseProxy read error during body copy: %v", rerr)
 		}
 		if nr > 0 {
 			nw, werr := dst.Write(buf[:nr])
@@ -447,12 +539,36 @@ func (p *ReverseProxy) copyBuffer(dst io.Writer, src io.Reader, buf []byte) (int
 	}
 }
 
-func (p *ReverseProxy) logf(format string, args ...interface{}) {
-	if p.ErrorLog != nil {
-		p.ErrorLog.Printf(format, args...)
-	} else {
-		log.Printf(format, args...)
+// countFailure remembers 1 failure for upstream for the
+// configured duration. If passive health checks are
+// disabled or failure expiry is 0, this is a no-op.
+func (h Handler) countFailure(upstream *Upstream) {
+	// only count failures if passive health checking is enabled
+	// and if failures are configured have a non-zero expiry
+	if h.HealthChecks == nil || h.HealthChecks.Passive == nil {
+		return
+	}
+	failDuration := time.Duration(h.HealthChecks.Passive.FailDuration)
+	if failDuration == 0 {
+		return
+	}
+
+	// count failure immediately
+	err := upstream.Host.CountFail(1)
+	if err != nil {
+		log.Printf("[ERROR] proxy: upstream %s: counting failure: %v",
+			upstream.hostURL, err)
 	}
+
+	// forget it later
+	go func(host Host, failDuration time.Duration) {
+		time.Sleep(failDuration)
+		err := host.CountFail(-1)
+		if err != nil {
+			log.Printf("[ERROR] proxy: upstream %s: expiring failure: %v",
+				upstream.hostURL, err)
+		}
+	}(upstream.Host, failDuration)
 }
 
 type writeFlusher interface {
@@ -508,6 +624,61 @@ func (m *maxLatencyWriter) stop() {
 	}
 }
 
+// switchProtocolCopier exists so goroutines proxying data back and
+// forth have nice names in stacks.
+type switchProtocolCopier struct {
+	user, backend io.ReadWriter
+}
+
+func (c switchProtocolCopier) copyFromBackend(errc chan<- error) {
+	_, err := io.Copy(c.user, c.backend)
+	errc <- err
+}
+
+func (c switchProtocolCopier) copyToBackend(errc chan<- error) {
+	_, err := io.Copy(c.backend, c.user)
+	errc <- err
+}
+
+// shouldPanicOnCopyError reports whether the reverse proxy should
+// panic with http.ErrAbortHandler. This is the right thing to do by
+// default, but Go 1.10 and earlier did not, so existing unit tests
+// weren't expecting panics. Only panic in our own tests, or when
+// running under the HTTP server.
+// TODO: I don't know if we want this at all...
+func shouldPanicOnCopyError(req *http.Request) bool {
+	// if inOurTests {
+	// 	// Our tests know to handle this panic.
+	// 	return true
+	// }
+	if req.Context().Value(http.ServerContextKey) != nil {
+		// We seem to be running under an HTTP server, so
+		// it'll recover the panic.
+		return true
+	}
+	// Otherwise act like Go 1.10 and earlier to not break
+	// existing tests.
+	return false
+}
+
+func copyHeader(dst, src http.Header) {
+	for k, vv := range src {
+		for _, v := range vv {
+			dst.Add(k, v)
+		}
+	}
+}
+
+func cloneHeader(h http.Header) http.Header {
+	h2 := make(http.Header, len(h))
+	for k, vv := range h {
+		vv2 := make([]string, len(vv))
+		copy(vv2, vv)
+		h2[k] = vv2
+	}
+	return h2
+}
+
 func upgradeType(h http.Header) string {
 	if !httpguts.HeaderValuesContainsToken(h["Connection"], "Upgrade") {
 		return ""
@@ -515,62 +686,177 @@ func upgradeType(h http.Header) string {
 	return strings.ToLower(h.Get("Upgrade"))
 }
 
-func (p *ReverseProxy) handleUpgradeResponse(rw http.ResponseWriter, req *http.Request, res *http.Response) {
-	reqUpType := upgradeType(req.Header)
-	resUpType := upgradeType(res.Header)
-	if reqUpType != resUpType {
-		p.getErrorHandler()(rw, req, fmt.Errorf("backend tried to switch protocol %q when %q was requested", resUpType, reqUpType))
-		return
+func singleJoiningSlash(a, b string) string {
+	aslash := strings.HasSuffix(a, "/")
+	bslash := strings.HasPrefix(b, "/")
+	switch {
+	case aslash && bslash:
+		return a + b[1:]
+	case !aslash && !bslash:
+		return a + "/" + b
 	}
+	return a + b
+}
 
-	copyHeader(res.Header, rw.Header())
-
-	hj, ok := rw.(http.Hijacker)
-	if !ok {
-		p.getErrorHandler()(rw, req, fmt.Errorf("can't switch protocols using non-Hijacker ResponseWriter type %T", rw))
-		return
-	}
-	backConn, ok := res.Body.(io.ReadWriteCloser)
-	if !ok {
-		p.getErrorHandler()(rw, req, fmt.Errorf("internal error: 101 switching protocols response with non-writable body"))
-		return
+// removeConnectionHeaders removes hop-by-hop headers listed in the "Connection" header of h.
+// See RFC 7230, section 6.1
+func removeConnectionHeaders(h http.Header) {
+	if c := h.Get("Connection"); c != "" {
+		for _, f := range strings.Split(c, ",") {
+			if f = strings.TrimSpace(f); f != "" {
+				h.Del(f)
+			}
+		}
 	}
-	defer backConn.Close()
-	conn, brw, err := hj.Hijack()
-	if err != nil {
-		p.getErrorHandler()(rw, req, fmt.Errorf("Hijack failed on protocol switch: %v", err))
-		return
+}
+
+type LoadBalancing struct {
+	SelectionPolicyRaw json.RawMessage `json:"selection_policy,omitempty"`
+	TryDuration        caddy.Duration  `json:"try_duration,omitempty"`
+	TryInterval        caddy.Duration  `json:"try_interval,omitempty"`
+
+	SelectionPolicy Selector `json:"-"`
+}
+
+type Selector interface {
+	Select(HostPool, *http.Request) *Upstream
+}
+
+type HealthChecks struct {
+	Active  *ActiveHealthChecks  `json:"active,omitempty"`
+	Passive *PassiveHealthChecks `json:"passive,omitempty"`
+}
+
+type ActiveHealthChecks struct {
+	Path         string         `json:"path,omitempty"`
+	Port         int            `json:"port,omitempty"`
+	Interval     caddy.Duration `json:"interval,omitempty"`
+	Timeout      caddy.Duration `json:"timeout,omitempty"`
+	MaxSize      int            `json:"max_size,omitempty"`
+	ExpectStatus int            `json:"expect_status,omitempty"`
+	ExpectBody   string         `json:"expect_body,omitempty"`
+}
+
+type PassiveHealthChecks struct {
+	MaxFails              int            `json:"max_fails,omitempty"`
+	FailDuration          caddy.Duration `json:"fail_duration,omitempty"`
+	UnhealthyRequestCount int            `json:"unhealthy_request_count,omitempty"`
+	UnhealthyStatus       []int          `json:"unhealthy_status,omitempty"`
+	UnhealthyLatency      caddy.Duration `json:"unhealthy_latency,omitempty"`
+}
+
+// Hop-by-hop headers. These are removed when sent to the backend.
+// As of RFC 7230, hop-by-hop headers are required to appear in the
+// Connection header field. These are the headers defined by the
+// obsoleted RFC 2616 (section 13.5.1) and are used for backward
+// compatibility.
+var hopHeaders = []string{
+	"Connection",
+	"Proxy-Connection", // non-standard but still sent by libcurl and rejected by e.g. google
+	"Keep-Alive",
+	"Proxy-Authenticate",
+	"Proxy-Authorization",
+	"Te",      // canonicalized version of "TE"
+	"Trailer", // not Trailers per URL above; https://www.rfc-editor.org/errata_search.php?eid=4522
+	"Transfer-Encoding",
+	"Upgrade",
+}
+
+var bufPool = sync.Pool{
+	New: func() interface{} {
+		return new(bytes.Buffer)
+	},
+}
+
+//////////////////////////////////
+// TODO:
+
+type Host interface {
+	NumRequests() int
+	Fails() int
+	Unhealthy() bool
+
+	CountRequest(int) error
+	CountFail(int) error
+}
+
+type HostPool []*Upstream
+
+type upstreamHost struct {
+	numRequests int64 // must be first field to be 64-bit aligned on 32-bit systems (see https://golang.org/pkg/sync/atomic/#pkg-note-BUG)
+	fails       int64
+	unhealthy   int32
+}
+
+func (uh upstreamHost) NumRequests() int {
+	return int(atomic.LoadInt64(&uh.numRequests))
+}
+func (uh upstreamHost) Fails() int {
+	return int(atomic.LoadInt64(&uh.fails))
+}
+func (uh upstreamHost) Unhealthy() bool {
+	return atomic.LoadInt32(&uh.unhealthy) == 1
+}
+func (uh *upstreamHost) CountRequest(delta int) error {
+	result := atomic.AddInt64(&uh.numRequests, int64(delta))
+	if result < 0 {
+		return fmt.Errorf("count below 0: %d", result)
 	}
-	defer conn.Close()
-	res.Body = nil // so res.Write only writes the headers; we have res.Body in backConn above
-	if err := res.Write(brw); err != nil {
-		p.getErrorHandler()(rw, req, fmt.Errorf("response write: %v", err))
-		return
+	return nil
+}
+func (uh *upstreamHost) CountFail(delta int) error {
+	result := atomic.AddInt64(&uh.fails, int64(delta))
+	if result < 0 {
+		return fmt.Errorf("count below 0: %d", result)
 	}
-	if err := brw.Flush(); err != nil {
-		p.getErrorHandler()(rw, req, fmt.Errorf("response flush: %v", err))
-		return
+	return nil
+}
+
+type Upstream struct {
+	Host `json:"-"`
+
+	Address     string `json:"address,omitempty"`
+	MaxRequests int    `json:"max_requests,omitempty"`
+
+	// TODO: This could be really cool, to say that requests with
+	// certain headers or from certain IPs always go to this upstream
+	// HeaderAffinity string
+	// IPAffinity     string
+
+	healthCheckPolicy *PassiveHealthChecks
+
+	hostURL *url.URL
+}
+
+func (u Upstream) Available() bool {
+	return u.Healthy() && !u.Full()
+}
+
+func (u Upstream) Healthy() bool {
+	healthy := !u.Host.Unhealthy()
+	if healthy && u.healthCheckPolicy != nil {
+		healthy = u.Host.Fails() < u.healthCheckPolicy.MaxFails
 	}
-	errc := make(chan error, 1)
-	spc := switchProtocolCopier{user: conn, backend: backConn}
-	go spc.copyToBackend(errc)
-	go spc.copyFromBackend(errc)
-	<-errc
-	return
+	return healthy
 }
 
-// switchProtocolCopier exists so goroutines proxying data back and
-// forth have nice names in stacks.
-type switchProtocolCopier struct {
-	user, backend io.ReadWriter
+func (u Upstream) Full() bool {
+	return u.MaxRequests > 0 && u.Host.NumRequests() >= u.MaxRequests
 }
 
-func (c switchProtocolCopier) copyFromBackend(errc chan<- error) {
-	_, err := io.Copy(c.user, c.backend)
-	errc <- err
+func (u Upstream) URL() *url.URL {
+	return u.hostURL
 }
 
-func (c switchProtocolCopier) copyToBackend(errc chan<- error) {
-	_, err := io.Copy(c.backend, c.user)
-	errc <- err
+var hosts = caddy.NewUsagePool()
+
+// TODO: ...
+type UpstreamProvider interface {
 }
+
+// Interface guards
+var (
+	_ caddyhttp.MiddlewareHandler = (*Handler)(nil)
+	_ caddy.Provisioner           = (*Handler)(nil)
+	_ caddy.CleanerUpper          = (*Handler)(nil)
+)
diff --git a/modules/caddyhttp/reverseproxy/selectionpolicies.go b/modules/caddyhttp/reverseproxy/selectionpolicies.go
new file mode 100644
index 0000000..e0518c9
--- /dev/null
+++ b/modules/caddyhttp/reverseproxy/selectionpolicies.go
@@ -0,0 +1,351 @@
+// Copyright 2015 Matthew Holt and The Caddy Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package reverseproxy
+
+import (
+	"fmt"
+	"hash/fnv"
+	weakrand "math/rand"
+	"net"
+	"net/http"
+	"sync/atomic"
+	"time"
+
+	"github.com/caddyserver/caddy/v2"
+)
+
+func init() {
+	caddy.RegisterModule(RandomSelection{})
+	caddy.RegisterModule(RandomChoiceSelection{})
+	caddy.RegisterModule(LeastConnSelection{})
+	caddy.RegisterModule(RoundRobinSelection{})
+	caddy.RegisterModule(FirstSelection{})
+	caddy.RegisterModule(IPHashSelection{})
+	caddy.RegisterModule(URIHashSelection{})
+	caddy.RegisterModule(HeaderHashSelection{})
+
+	weakrand.Seed(time.Now().UTC().UnixNano())
+}
+
+// RandomSelection is a policy that selects
+// an available host at random.
+type RandomSelection struct{}
+
+// CaddyModule returns the Caddy module information.
+func (RandomSelection) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		Name: "http.handlers.reverse_proxy.selection_policies.random",
+		New:  func() caddy.Module { return new(RandomSelection) },
+	}
+}
+
+// Select returns an available host, if any.
+func (r RandomSelection) Select(pool HostPool, request *http.Request) *Upstream {
+	// use reservoir sampling because the number of available
+	// hosts isn't known: https://en.wikipedia.org/wiki/Reservoir_sampling
+	var randomHost *Upstream
+	var count int
+	for _, upstream := range pool {
+		if !upstream.Available() {
+			continue
+		}
+		// (n % 1 == 0) holds for all n, therefore a
+		// upstream will always be chosen if there is at
+		// least one available
+		count++
+		if (weakrand.Int() % count) == 0 {
+			randomHost = upstream
+		}
+	}
+	return randomHost
+}
+
+// RandomChoiceSelection is a policy that selects
+// two or more available hosts at random, then
+// chooses the one with the least load.
+type RandomChoiceSelection struct {
+	Choose int `json:"choose,omitempty"`
+}
+
+// CaddyModule returns the Caddy module information.
+func (RandomChoiceSelection) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		Name: "http.handlers.reverse_proxy.selection_policies.random_choice",
+		New:  func() caddy.Module { return new(RandomChoiceSelection) },
+	}
+}
+
+func (r *RandomChoiceSelection) Provision(ctx caddy.Context) error {
+	if r.Choose == 0 {
+		r.Choose = 2
+	}
+	return nil
+}
+
+func (r RandomChoiceSelection) Validate() error {
+	if r.Choose < 2 {
+		return fmt.Errorf("choose must be at least 2")
+	}
+	return nil
+}
+
+// Select returns an available host, if any.
+func (r RandomChoiceSelection) Select(pool HostPool, _ *http.Request) *Upstream {
+	k := r.Choose
+	if k > len(pool) {
+		k = len(pool)
+	}
+	choices := make([]*Upstream, k)
+	for i, upstream := range pool {
+		if !upstream.Available() {
+			continue
+		}
+		j := weakrand.Intn(i)
+		if j < k {
+			choices[j] = upstream
+		}
+	}
+	return leastRequests(choices)
+}
+
+// LeastConnSelection is a policy that selects the
+// host with the least active requests. If multiple
+// hosts have the same fewest number, one is chosen
+// randomly. The term "conn" or "connection" is used
+// in this policy name due to its similar meaning in
+// other software, but our load balancer actually
+// counts active requests rather than connections,
+// since these days requests are multiplexed onto
+// shared connections.
+type LeastConnSelection struct{}
+
+// CaddyModule returns the Caddy module information.
+func (LeastConnSelection) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		Name: "http.handlers.reverse_proxy.selection_policies.least_conn",
+		New:  func() caddy.Module { return new(LeastConnSelection) },
+	}
+}
+
+// Select selects the up host with the least number of connections in the
+// pool. If more than one host has the same least number of connections,
+// one of the hosts is chosen at random.
+func (LeastConnSelection) Select(pool HostPool, _ *http.Request) *Upstream {
+	var bestHost *Upstream
+	var count int
+	var leastReqs int
+
+	for _, host := range pool {
+		if !host.Available() {
+			continue
+		}
+		numReqs := host.NumRequests()
+		if numReqs < leastReqs {
+			leastReqs = numReqs
+			count = 0
+		}
+
+		// among hosts with same least connections, perform a reservoir
+		// sample: https://en.wikipedia.org/wiki/Reservoir_sampling
+		if numReqs == leastReqs {
+			count++
+			if (weakrand.Int() % count) == 0 {
+				bestHost = host
+			}
+		}
+	}
+
+	return bestHost
+}
+
+// RoundRobinSelection is a policy that selects
+// a host based on round-robin ordering.
+type RoundRobinSelection struct {
+	robin uint32
+}
+
+// CaddyModule returns the Caddy module information.
+func (RoundRobinSelection) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		Name: "http.handlers.reverse_proxy.selection_policies.round_robin",
+		New:  func() caddy.Module { return new(RoundRobinSelection) },
+	}
+}
+
+// Select returns an available host, if any.
+func (r *RoundRobinSelection) Select(pool HostPool, _ *http.Request) *Upstream {
+	n := uint32(len(pool))
+	if n == 0 {
+		return nil
+	}
+	for i := uint32(0); i < n; i++ {
+		atomic.AddUint32(&r.robin, 1)
+		host := pool[r.robin%n]
+		if host.Available() {
+			return host
+		}
+	}
+	return nil
+}
+
+// FirstSelection is a policy that selects
+// the first available host.
+type FirstSelection struct{}
+
+// CaddyModule returns the Caddy module information.
+func (FirstSelection) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		Name: "http.handlers.reverse_proxy.selection_policies.first",
+		New:  func() caddy.Module { return new(FirstSelection) },
+	}
+}
+
+// Select returns an available host, if any.
+func (FirstSelection) Select(pool HostPool, _ *http.Request) *Upstream {
+	for _, host := range pool {
+		if host.Available() {
+			return host
+		}
+	}
+	return nil
+}
+
+// IPHashSelection is a policy that selects a host
+// based on hashing the remote IP of the request.
+type IPHashSelection struct{}
+
+// CaddyModule returns the Caddy module information.
+func (IPHashSelection) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		Name: "http.handlers.reverse_proxy.selection_policies.ip_hash",
+		New:  func() caddy.Module { return new(IPHashSelection) },
+	}
+}
+
+// Select returns an available host, if any.
+func (IPHashSelection) Select(pool HostPool, req *http.Request) *Upstream {
+	clientIP, _, err := net.SplitHostPort(req.RemoteAddr)
+	if err != nil {
+		clientIP = req.RemoteAddr
+	}
+	return hostByHashing(pool, clientIP)
+}
+
+// URIHashSelection is a policy that selects a
+// host by hashing the request URI.
+type URIHashSelection struct{}
+
+// CaddyModule returns the Caddy module information.
+func (URIHashSelection) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		Name: "http.handlers.reverse_proxy.selection_policies.uri_hash",
+		New:  func() caddy.Module { return new(URIHashSelection) },
+	}
+}
+
+// Select returns an available host, if any.
+func (URIHashSelection) Select(pool HostPool, req *http.Request) *Upstream {
+	return hostByHashing(pool, req.RequestURI)
+}
+
+// HeaderHashSelection is a policy that selects
+// a host based on a given request header.
+type HeaderHashSelection struct {
+	Field string `json:"field,omitempty"`
+}
+
+// CaddyModule returns the Caddy module information.
+func (HeaderHashSelection) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		Name: "http.handlers.reverse_proxy.selection_policies.header",
+		New:  func() caddy.Module { return new(HeaderHashSelection) },
+	}
+}
+
+// Select returns an available host, if any.
+func (s HeaderHashSelection) Select(pool HostPool, req *http.Request) *Upstream {
+	if s.Field == "" {
+		return nil
+	}
+	val := req.Header.Get(s.Field)
+	if val == "" {
+		return RandomSelection{}.Select(pool, req)
+	}
+	return hostByHashing(pool, val)
+}
+
+// leastRequests returns the host with the
+// least number of active requests to it.
+// If more than one host has the same
+// least number of active requests, then
+// one of those is chosen at random.
+func leastRequests(upstreams []*Upstream) *Upstream {
+	if len(upstreams) == 0 {
+		return nil
+	}
+	var best []*Upstream
+	var bestReqs int
+	for _, upstream := range upstreams {
+		reqs := upstream.NumRequests()
+		if reqs == 0 {
+			return upstream
+		}
+		if reqs <= bestReqs {
+			bestReqs = reqs
+			best = append(best, upstream)
+		}
+	}
+	return best[weakrand.Intn(len(best))]
+}
+
+// hostByHashing returns an available host
+// from pool based on a hashable string s.
+func hostByHashing(pool []*Upstream, s string) *Upstream {
+	poolLen := uint32(len(pool))
+	if poolLen == 0 {
+		return nil
+	}
+	index := hash(s) % poolLen
+	for i := uint32(0); i < poolLen; i++ {
+		index += i
+		upstream := pool[index%poolLen]
+		if upstream.Available() {
+			return upstream
+		}
+	}
+	return nil
+}
+
+// hash calculates a fast hash based on s.
+func hash(s string) uint32 {
+	h := fnv.New32a()
+	h.Write([]byte(s))
+	return h.Sum32()
+}
+
+// Interface guards
+var (
+	_ Selector = (*RandomSelection)(nil)
+	_ Selector = (*RandomChoiceSelection)(nil)
+	_ Selector = (*LeastConnSelection)(nil)
+	_ Selector = (*RoundRobinSelection)(nil)
+	_ Selector = (*FirstSelection)(nil)
+	_ Selector = (*IPHashSelection)(nil)
+	_ Selector = (*URIHashSelection)(nil)
+	_ Selector = (*HeaderHashSelection)(nil)
+
+	_ caddy.Validator   = (*RandomChoiceSelection)(nil)
+	_ caddy.Provisioner = (*RandomChoiceSelection)(nil)
+)
diff --git a/modules/caddyhttp/reverseproxy/selectionpolicies_test.go b/modules/caddyhttp/reverseproxy/selectionpolicies_test.go
new file mode 100644
index 0000000..8006fb1
--- /dev/null
+++ b/modules/caddyhttp/reverseproxy/selectionpolicies_test.go
@@ -0,0 +1,363 @@
+// Copyright 2015 Matthew Holt and The Caddy Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package reverseproxy
+
+// TODO: finish migrating these
+
+// import (
+// 	"net/http"
+// 	"net/http/httptest"
+// 	"os"
+// 	"testing"
+// )
+
+// var workableServer *httptest.Server
+
+// func TestMain(m *testing.M) {
+// 	workableServer = httptest.NewServer(http.HandlerFunc(
+// 		func(w http.ResponseWriter, r *http.Request) {
+// 			// do nothing
+// 		}))
+// 	r := m.Run()
+// 	workableServer.Close()
+// 	os.Exit(r)
+// }
+
+// type customPolicy struct{}
+
+// func (customPolicy) Select(pool HostPool, _ *http.Request) Host {
+// 	return pool[0]
+// }
+
+// func testPool() HostPool {
+// 	pool := []*UpstreamHost{
+// 		{
+// 			Name: workableServer.URL, // this should resolve (healthcheck test)
+// 		},
+// 		{
+// 			Name: "http://localhost:99998", // this shouldn't
+// 		},
+// 		{
+// 			Name: "http://C",
+// 		},
+// 	}
+// 	return HostPool(pool)
+// }
+
+// func TestRoundRobinPolicy(t *testing.T) {
+// 	pool := testPool()
+// 	rrPolicy := &RoundRobin{}
+// 	request, _ := http.NewRequest("GET", "/", nil)
+
+// 	h := rrPolicy.Select(pool, request)
+// 	// First selected host is 1, because counter starts at 0
+// 	// and increments before host is selected
+// 	if h != pool[1] {
+// 		t.Error("Expected first round robin host to be second host in the pool.")
+// 	}
+// 	h = rrPolicy.Select(pool, request)
+// 	if h != pool[2] {
+// 		t.Error("Expected second round robin host to be third host in the pool.")
+// 	}
+// 	h = rrPolicy.Select(pool, request)
+// 	if h != pool[0] {
+// 		t.Error("Expected third round robin host to be first host in the pool.")
+// 	}
+// 	// mark host as down
+// 	pool[1].Unhealthy = 1
+// 	h = rrPolicy.Select(pool, request)
+// 	if h != pool[2] {
+// 		t.Error("Expected to skip down host.")
+// 	}
+// 	// mark host as up
+// 	pool[1].Unhealthy = 0
+
+// 	h = rrPolicy.Select(pool, request)
+// 	if h == pool[2] {
+// 		t.Error("Expected to balance evenly among healthy hosts")
+// 	}
+// 	// mark host as full
+// 	pool[1].Conns = 1
+// 	pool[1].MaxConns = 1
+// 	h = rrPolicy.Select(pool, request)
+// 	if h != pool[2] {
+// 		t.Error("Expected to skip full host.")
+// 	}
+// }
+
+// func TestLeastConnPolicy(t *testing.T) {
+// 	pool := testPool()
+// 	lcPolicy := &LeastConn{}
+// 	request, _ := http.NewRequest("GET", "/", nil)
+
+// 	pool[0].Conns = 10
+// 	pool[1].Conns = 10
+// 	h := lcPolicy.Select(pool, request)
+// 	if h != pool[2] {
+// 		t.Error("Expected least connection host to be third host.")
+// 	}
+// 	pool[2].Conns = 100
+// 	h = lcPolicy.Select(pool, request)
+// 	if h != pool[0] && h != pool[1] {
+// 		t.Error("Expected least connection host to be first or second host.")
+// 	}
+// }
+
+// func TestCustomPolicy(t *testing.T) {
+// 	pool := testPool()
+// 	customPolicy := &customPolicy{}
+// 	request, _ := http.NewRequest("GET", "/", nil)
+
+// 	h := customPolicy.Select(pool, request)
+// 	if h != pool[0] {
+// 		t.Error("Expected custom policy host to be the first host.")
+// 	}
+// }
+
+// func TestIPHashPolicy(t *testing.T) {
+// 	pool := testPool()
+// 	ipHash := &IPHash{}
+// 	request, _ := http.NewRequest("GET", "/", nil)
+// 	// We should be able to predict where every request is routed.
+// 	request.RemoteAddr = "172.0.0.1:80"
+// 	h := ipHash.Select(pool, request)
+// 	if h != pool[1] {
+// 		t.Error("Expected ip hash policy host to be the second host.")
+// 	}
+// 	request.RemoteAddr = "172.0.0.2:80"
+// 	h = ipHash.Select(pool, request)
+// 	if h != pool[1] {
+// 		t.Error("Expected ip hash policy host to be the second host.")
+// 	}
+// 	request.RemoteAddr = "172.0.0.3:80"
+// 	h = ipHash.Select(pool, request)
+// 	if h != pool[2] {
+// 		t.Error("Expected ip hash policy host to be the third host.")
+// 	}
+// 	request.RemoteAddr = "172.0.0.4:80"
+// 	h = ipHash.Select(pool, request)
+// 	if h != pool[1] {
+// 		t.Error("Expected ip hash policy host to be the second host.")
+// 	}
+
+// 	// we should get the same results without a port
+// 	request.RemoteAddr = "172.0.0.1"
+// 	h = ipHash.Select(pool, request)
+// 	if h != pool[1] {
+// 		t.Error("Expected ip hash policy host to be the second host.")
+// 	}
+// 	request.RemoteAddr = "172.0.0.2"
+// 	h = ipHash.Select(pool, request)
+// 	if h != pool[1] {
+// 		t.Error("Expected ip hash policy host to be the second host.")
+// 	}
+// 	request.RemoteAddr = "172.0.0.3"
+// 	h = ipHash.Select(pool, request)
+// 	if h != pool[2] {
+// 		t.Error("Expected ip hash policy host to be the third host.")
+// 	}
+// 	request.RemoteAddr = "172.0.0.4"
+// 	h = ipHash.Select(pool, request)
+// 	if h != pool[1] {
+// 		t.Error("Expected ip hash policy host to be the second host.")
+// 	}
+
+// 	// we should get a healthy host if the original host is unhealthy and a
+// 	// healthy host is available
+// 	request.RemoteAddr = "172.0.0.1"
+// 	pool[1].Unhealthy = 1
+// 	h = ipHash.Select(pool, request)
+// 	if h != pool[2] {
+// 		t.Error("Expected ip hash policy host to be the third host.")
+// 	}
+
+// 	request.RemoteAddr = "172.0.0.2"
+// 	h = ipHash.Select(pool, request)
+// 	if h != pool[2] {
+// 		t.Error("Expected ip hash policy host to be the third host.")
+// 	}
+// 	pool[1].Unhealthy = 0
+
+// 	request.RemoteAddr = "172.0.0.3"
+// 	pool[2].Unhealthy = 1
+// 	h = ipHash.Select(pool, request)
+// 	if h != pool[0] {
+// 		t.Error("Expected ip hash policy host to be the first host.")
+// 	}
+// 	request.RemoteAddr = "172.0.0.4"
+// 	h = ipHash.Select(pool, request)
+// 	if h != pool[1] {
+// 		t.Error("Expected ip hash policy host to be the second host.")
+// 	}
+
+// 	// We should be able to resize the host pool and still be able to predict
+// 	// where a request will be routed with the same IP's used above
+// 	pool = []*UpstreamHost{
+// 		{
+// 			Name: workableServer.URL, // this should resolve (healthcheck test)
+// 		},
+// 		{
+// 			Name: "http://localhost:99998", // this shouldn't
+// 		},
+// 	}
+// 	pool = HostPool(pool)
+// 	request.RemoteAddr = "172.0.0.1:80"
+// 	h = ipHash.Select(pool, request)
+// 	if h != pool[0] {
+// 		t.Error("Expected ip hash policy host to be the first host.")
+// 	}
+// 	request.RemoteAddr = "172.0.0.2:80"
+// 	h = ipHash.Select(pool, request)
+// 	if h != pool[1] {
+// 		t.Error("Expected ip hash policy host to be the second host.")
+// 	}
+// 	request.RemoteAddr = "172.0.0.3:80"
+// 	h = ipHash.Select(pool, request)
+// 	if h != pool[0] {
+// 		t.Error("Expected ip hash policy host to be the first host.")
+// 	}
+// 	request.RemoteAddr = "172.0.0.4:80"
+// 	h = ipHash.Select(pool, request)
+// 	if h != pool[1] {
+// 		t.Error("Expected ip hash policy host to be the second host.")
+// 	}
+
+// 	// We should get nil when there are no healthy hosts
+// 	pool[0].Unhealthy = 1
+// 	pool[1].Unhealthy = 1
+// 	h = ipHash.Select(pool, request)
+// 	if h != nil {
+// 		t.Error("Expected ip hash policy host to be nil.")
+// 	}
+// }
+
+// func TestFirstPolicy(t *testing.T) {
+// 	pool := testPool()
+// 	firstPolicy := &First{}
+// 	req := httptest.NewRequest(http.MethodGet, "/", nil)
+
+// 	h := firstPolicy.Select(pool, req)
+// 	if h != pool[0] {
+// 		t.Error("Expected first policy host to be the first host.")
+// 	}
+
+// 	pool[0].Unhealthy = 1
+// 	h = firstPolicy.Select(pool, req)
+// 	if h != pool[1] {
+// 		t.Error("Expected first policy host to be the second host.")
+// 	}
+// }
+
+// func TestUriPolicy(t *testing.T) {
+// 	pool := testPool()
+// 	uriPolicy := &URIHash{}
+
+// 	request := httptest.NewRequest(http.MethodGet, "/test", nil)
+// 	h := uriPolicy.Select(pool, request)
+// 	if h != pool[0] {
+// 		t.Error("Expected uri policy host to be the first host.")
+// 	}
+
+// 	pool[0].Unhealthy = 1
+// 	h = uriPolicy.Select(pool, request)
+// 	if h != pool[1] {
+// 		t.Error("Expected uri policy host to be the first host.")
+// 	}
+
+// 	request = httptest.NewRequest(http.MethodGet, "/test_2", nil)
+// 	h = uriPolicy.Select(pool, request)
+// 	if h != pool[1] {
+// 		t.Error("Expected uri policy host to be the second host.")
+// 	}
+
+// 	// We should be able to resize the host pool and still be able to predict
+// 	// where a request will be routed with the same URI's used above
+// 	pool = []*UpstreamHost{
+// 		{
+// 			Name: workableServer.URL, // this should resolve (healthcheck test)
+// 		},
+// 		{
+// 			Name: "http://localhost:99998", // this shouldn't
+// 		},
+// 	}
+
+// 	request = httptest.NewRequest(http.MethodGet, "/test", nil)
+// 	h = uriPolicy.Select(pool, request)
+// 	if h != pool[0] {
+// 		t.Error("Expected uri policy host to be the first host.")
+// 	}
+
+// 	pool[0].Unhealthy = 1
+// 	h = uriPolicy.Select(pool, request)
+// 	if h != pool[1] {
+// 		t.Error("Expected uri policy host to be the first host.")
+// 	}
+
+// 	request = httptest.NewRequest(http.MethodGet, "/test_2", nil)
+// 	h = uriPolicy.Select(pool, request)
+// 	if h != pool[1] {
+// 		t.Error("Expected uri policy host to be the second host.")
+// 	}
+
+// 	pool[0].Unhealthy = 1
+// 	pool[1].Unhealthy = 1
+// 	h = uriPolicy.Select(pool, request)
+// 	if h != nil {
+// 		t.Error("Expected uri policy policy host to be nil.")
+// 	}
+// }
+
+// func TestHeaderPolicy(t *testing.T) {
+// 	pool := testPool()
+// 	tests := []struct {
+// 		Name               string
+// 		Policy             *Header
+// 		RequestHeaderName  string
+// 		RequestHeaderValue string
+// 		NilHost            bool
+// 		HostIndex          int
+// 	}{
+// 		{"empty config", &Header{""}, "", "", true, 0},
+// 		{"empty config+header+value", &Header{""}, "Affinity", "somevalue", true, 0},
+// 		{"empty config+header", &Header{""}, "Affinity", "", true, 0},
+
+// 		{"no header(fallback to roundrobin)", &Header{"Affinity"}, "", "", false, 1},
+// 		{"no header(fallback to roundrobin)", &Header{"Affinity"}, "", "", false, 2},
+// 		{"no header(fallback to roundrobin)", &Header{"Affinity"}, "", "", false, 0},
+
+// 		{"hash route to host", &Header{"Affinity"}, "Affinity", "somevalue", false, 1},
+// 		{"hash route to host", &Header{"Affinity"}, "Affinity", "somevalue2", false, 0},
+// 		{"hash route to host", &Header{"Affinity"}, "Affinity", "somevalue3", false, 2},
+// 		{"hash route with empty value", &Header{"Affinity"}, "Affinity", "", false, 1},
+// 	}
+
+// 	for idx, test := range tests {
+// 		request, _ := http.NewRequest("GET", "/", nil)
+// 		if test.RequestHeaderName != "" {
+// 			request.Header.Add(test.RequestHeaderName, test.RequestHeaderValue)
+// 		}
+
+// 		host := test.Policy.Select(pool, request)
+// 		if test.NilHost && host != nil {
+// 			t.Errorf("%d: Expected host to be nil", idx)
+// 		}
+// 		if !test.NilHost && host == nil {
+// 			t.Errorf("%d: Did not expect host to be nil", idx)
+// 		}
+// 		if !test.NilHost && host != pool[test.HostIndex] {
+// 			t.Errorf("%d: Expected Header policy to be host %d", idx, test.HostIndex)
+// 		}
+// 	}
+// }
diff --git a/modules/caddyhttp/reverseproxy/upstream.go b/modules/caddyhttp/reverseproxy/upstream.go
deleted file mode 100755
index 1f0693e..0000000
--- a/modules/caddyhttp/reverseproxy/upstream.go
+++ /dev/null
@@ -1,450 +0,0 @@
-// Copyright 2015 Matthew Holt and The Caddy Authors
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-// Package reverseproxy implements a load-balanced reverse proxy.
-package reverseproxy
-
-import (
-	"context"
-	"encoding/json"
-	"fmt"
-	"math/rand"
-	"net"
-	"net/http"
-	"net/url"
-	"strings"
-	"sync"
-	"sync/atomic"
-	"time"
-
-	"github.com/caddyserver/caddy/v2"
-	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
-)
-
-// CircuitBreaker defines the functionality of a circuit breaker module.
-type CircuitBreaker interface {
-	Ok() bool
-	RecordMetric(statusCode int, latency time.Duration)
-}
-
-type noopCircuitBreaker struct{}
-
-func (ncb noopCircuitBreaker) RecordMetric(statusCode int, latency time.Duration) {}
-func (ncb noopCircuitBreaker) Ok() bool {
-	return true
-}
-
-const (
-	// TypeBalanceRoundRobin represents the value to use for configuring a load balanced reverse proxy to use round robin load balancing.
-	TypeBalanceRoundRobin = iota
-
-	// TypeBalanceRandom represents the value to use for configuring a load balanced reverse proxy to use random load balancing.
-	TypeBalanceRandom
-
-	// TODO: add random with two choices
-
-	// msgNoHealthyUpstreams is returned if there are no upstreams that are healthy to proxy a request to
-	msgNoHealthyUpstreams = "No healthy upstreams."
-
-	// by default perform health checks every 30 seconds
-	defaultHealthCheckDur = time.Second * 30
-
-	// used when an upstream is unhealthy, health checks can be configured to perform at a faster rate
-	defaultFastHealthCheckDur = time.Second * 1
-)
-
-var (
-	// defaultTransport is the default transport to use for the reverse proxy.
-	defaultTransport = &http.Transport{
-		Dial: (&net.Dialer{
-			Timeout: 5 * time.Second,
-		}).Dial,
-		TLSHandshakeTimeout: 5 * time.Second,
-	}
-
-	// defaultHTTPClient is the default http client to use for the healthchecker.
-	defaultHTTPClient = &http.Client{
-		Timeout:   time.Second * 10,
-		Transport: defaultTransport,
-	}
-
-	// typeMap maps caddy load balance configuration to the internal representation of the loadbalance algorithm type.
-	typeMap = map[string]int{
-		"round_robin": TypeBalanceRoundRobin,
-		"random":      TypeBalanceRandom,
-	}
-)
-
-// NewLoadBalancedReverseProxy returns a collection of Upstreams that are to be loadbalanced.
-func NewLoadBalancedReverseProxy(lb *LoadBalanced, ctx caddy.Context) error {
-	// set defaults
-	if lb.NoHealthyUpstreamsMessage == "" {
-		lb.NoHealthyUpstreamsMessage = msgNoHealthyUpstreams
-	}
-
-	if lb.TryInterval == "" {
-		lb.TryInterval = "20s"
-	}
-
-	// set request retry interval
-	ti, err := time.ParseDuration(lb.TryInterval)
-	if err != nil {
-		return fmt.Errorf("NewLoadBalancedReverseProxy: %v", err.Error())
-	}
-	lb.tryInterval = ti
-
-	// set load balance algorithm
-	t, ok := typeMap[lb.LoadBalanceType]
-	if !ok {
-		t = TypeBalanceRandom
-	}
-	lb.loadBalanceType = t
-
-	// setup each upstream
-	var us []*upstream
-	for _, uc := range lb.Upstreams {
-		// pass the upstream decr and incr methods to keep track of unhealthy nodes
-		nu, err := newUpstream(uc, lb.decrUnhealthy, lb.incrUnhealthy)
-		if err != nil {
-			return err
-		}
-
-		// setup any configured circuit breakers
-		var cbModule = "http.handlers.reverse_proxy.circuit_breaker"
-		var cb CircuitBreaker
-
-		if uc.CircuitBreaker != nil {
-			if _, err := caddy.GetModule(cbModule); err == nil {
-				val, err := ctx.LoadModule(cbModule, uc.CircuitBreaker)
-				if err == nil {
-					cbv, ok := val.(CircuitBreaker)
-					if ok {
-						cb = cbv
-					} else {
-						fmt.Printf("\nerr: %v; cannot load circuit_breaker, using noop", err.Error())
-						cb = noopCircuitBreaker{}
-					}
-				} else {
-					fmt.Printf("\nerr: %v; cannot load circuit_breaker, using noop", err.Error())
-					cb = noopCircuitBreaker{}
-				}
-			} else {
-				fmt.Println("circuit_breaker module not loaded, using noop")
-				cb = noopCircuitBreaker{}
-			}
-		} else {
-			cb = noopCircuitBreaker{}
-		}
-		nu.CB = cb
-
-		// start a healthcheck worker which will periodically check to see if an upstream is healthy
-		// to proxy requests to.
-		nu.healthChecker = NewHealthCheckWorker(nu, defaultHealthCheckDur, defaultHTTPClient)
-
-		// TODO :- if path is empty why does this empty the entire Target?
-		// nu.Target.Path = uc.HealthCheckPath
-
-		nu.healthChecker.ScheduleChecks(nu.Target.String())
-		lb.HealthCheckers = append(lb.HealthCheckers, nu.healthChecker)
-
-		us = append(us, nu)
-	}
-
-	lb.upstreams = us
-
-	return nil
-}
-
-// LoadBalanced represents a collection of upstream hosts that are loadbalanced. It
-// contains multiple features like health checking and circuit breaking functionality
-// for upstreams.
-type LoadBalanced struct {
-	mu              sync.Mutex
-	numUnhealthy    int32
-	selectedServer  int // used during round robin load balancing
-	loadBalanceType int
-	tryInterval     time.Duration
-	upstreams       []*upstream
-
-	// The following struct fields are set by caddy configuration.
-	// TryInterval is the max duration for which request retrys will be performed for a request.
-	TryInterval string `json:"try_interval,omitempty"`
-
-	// Upstreams are the configs for upstream hosts
-	Upstreams []*UpstreamConfig `json:"upstreams,omitempty"`
-
-	// LoadBalanceType is the string representation of what loadbalancing algorithm to use. i.e. "random" or "round_robin".
-	LoadBalanceType string `json:"load_balance_type,omitempty"`
-
-	// NoHealthyUpstreamsMessage is returned as a response when there are no healthy upstreams to loadbalance to.
-	NoHealthyUpstreamsMessage string `json:"no_healthy_upstreams_message,omitempty"`
-
-	// TODO :- store healthcheckers as package level state where each upstream gets a single healthchecker
-	// currently a healthchecker is created for each upstream defined, even if a healthchecker was previously created
-	// for that upstream
-	HealthCheckers []*HealthChecker `json:"health_checkers,omitempty"`
-}
-
-// Cleanup stops all health checkers on a loadbalanced reverse proxy.
-func (lb *LoadBalanced) Cleanup() error {
-	for _, hc := range lb.HealthCheckers {
-		hc.Stop()
-	}
-
-	return nil
-}
-
-// Provision sets up a new loadbalanced reverse proxy.
-func (lb *LoadBalanced) Provision(ctx caddy.Context) error {
-	return NewLoadBalancedReverseProxy(lb, ctx)
-}
-
-// ServeHTTP implements the caddyhttp.MiddlewareHandler interface to
-// dispatch an HTTP request to the proper server.
-func (lb *LoadBalanced) ServeHTTP(w http.ResponseWriter, r *http.Request, _ caddyhttp.Handler) error {
-	// ensure requests don't hang if an upstream does not respond or is not eventually healthy
-	var u *upstream
-	var done bool
-
-	retryTimer := time.NewTicker(lb.tryInterval)
-	defer retryTimer.Stop()
-
-	go func() {
-		select {
-		case <-retryTimer.C:
-			done = true
-		}
-	}()
-
-	// keep trying to get an available upstream to process the request
-	for {
-		switch lb.loadBalanceType {
-		case TypeBalanceRandom:
-			u = lb.random()
-		case TypeBalanceRoundRobin:
-			u = lb.roundRobin()
-		}
-
-		// if we can't get an upstream and our retry interval has ended return an error response
-		if u == nil && done {
-			w.WriteHeader(http.StatusBadGateway)
-			fmt.Fprint(w, lb.NoHealthyUpstreamsMessage)
-
-			return fmt.Errorf(msgNoHealthyUpstreams)
-		}
-
-		// attempt to get an available upstream
-		if u == nil {
-			continue
-		}
-
-		start := time.Now()
-
-		// if we get an error retry until we get a healthy upstream
-		res, err := u.ReverseProxy.ServeHTTP(w, r)
-		if err != nil {
-			if err == context.Canceled {
-				return nil
-			}
-
-			continue
-		}
-
-		// record circuit breaker metrics
-		go u.CB.RecordMetric(res.StatusCode, time.Now().Sub(start))
-
-		return nil
-	}
-}
-
-// incrUnhealthy increments the amount of unhealthy nodes in a loadbalancer.
-func (lb *LoadBalanced) incrUnhealthy() {
-	atomic.AddInt32(&lb.numUnhealthy, 1)
-}
-
-// decrUnhealthy decrements the amount of unhealthy nodes in a loadbalancer.
-func (lb *LoadBalanced) decrUnhealthy() {
-	atomic.AddInt32(&lb.numUnhealthy, -1)
-}
-
-// roundRobin implements a round robin load balancing algorithm to select
-// which server to forward requests to.
-func (lb *LoadBalanced) roundRobin() *upstream {
-	if atomic.LoadInt32(&lb.numUnhealthy) == int32(len(lb.upstreams)) {
-		return nil
-	}
-
-	selected := lb.upstreams[lb.selectedServer]
-
-	lb.mu.Lock()
-	lb.selectedServer++
-	if lb.selectedServer >= len(lb.upstreams) {
-		lb.selectedServer = 0
-	}
-	lb.mu.Unlock()
-
-	if selected.IsHealthy() && selected.CB.Ok() {
-		return selected
-	}
-
-	return nil
-}
-
-// random implements a random server selector for load balancing.
-func (lb *LoadBalanced) random() *upstream {
-	if atomic.LoadInt32(&lb.numUnhealthy) == int32(len(lb.upstreams)) {
-		return nil
-	}
-
-	n := rand.Int() % len(lb.upstreams)
-	selected := lb.upstreams[n]
-
-	if selected.IsHealthy() && selected.CB.Ok() {
-		return selected
-	}
-
-	return nil
-}
-
-// UpstreamConfig represents the config of an upstream.
-type UpstreamConfig struct {
-	// Host is the host name of the upstream server.
-	Host string `json:"host,omitempty"`
-
-	// FastHealthCheckDuration is the duration for which a health check is performed when a node is considered unhealthy.
-	FastHealthCheckDuration string `json:"fast_health_check_duration,omitempty"`
-
-	CircuitBreaker json.RawMessage `json:"circuit_breaker,omitempty"`
-
-	// // CircuitBreakerConfig is the config passed to setup a circuit breaker.
-	// CircuitBreakerConfig *circuitbreaker.Config `json:"circuit_breaker,omitempty"`
-	circuitbreaker CircuitBreaker
-
-	// HealthCheckDuration is the default duration for which a health check is performed.
-	HealthCheckDuration string `json:"health_check_duration,omitempty"`
-
-	// HealthCheckPath is the path at the upstream host to use for healthchecks.
-	HealthCheckPath string `json:"health_check_path,omitempty"`
-}
-
-// upstream represents an upstream host.
-type upstream struct {
-	Healthy            int32 // 0 = false, 1 = true
-	Target             *url.URL
-	ReverseProxy       *ReverseProxy
-	Incr               func()
-	Decr               func()
-	CB                 CircuitBreaker
-	healthChecker      *HealthChecker
-	healthCheckDur     time.Duration
-	fastHealthCheckDur time.Duration
-}
-
-// newUpstream returns a new upstream.
-func newUpstream(uc *UpstreamConfig, d func(), i func()) (*upstream, error) {
-	host := strings.TrimSpace(uc.Host)
-	protoIdx := strings.Index(host, "://")
-	if protoIdx == -1 || len(host[:protoIdx]) == 0 {
-		return nil, fmt.Errorf("protocol is required for host")
-	}
-
-	hostURL, err := url.Parse(host)
-	if err != nil {
-		return nil, err
-	}
-
-	// parse healthcheck durations
-	hcd, err := time.ParseDuration(uc.HealthCheckDuration)
-	if err != nil {
-		hcd = defaultHealthCheckDur
-	}
-
-	fhcd, err := time.ParseDuration(uc.FastHealthCheckDuration)
-	if err != nil {
-		fhcd = defaultFastHealthCheckDur
-	}
-
-	u := upstream{
-		healthCheckDur:     hcd,
-		fastHealthCheckDur: fhcd,
-		Target:             hostURL,
-		Decr:               d,
-		Incr:               i,
-		Healthy:            int32(0), // assume is unhealthy on start
-	}
-
-	u.ReverseProxy = newReverseProxy(hostURL, u.SetHealthiness)
-	return &u, nil
-}
-
-// SetHealthiness sets whether an upstream is healthy or not. The health check worker is updated to
-// perform checks faster if a node is unhealthy.
-func (u *upstream) SetHealthiness(ok bool) {
-	h := atomic.LoadInt32(&u.Healthy)
-	var wasHealthy bool
-	if h == 1 {
-		wasHealthy = true
-	} else {
-		wasHealthy = false
-	}
-
-	if ok {
-		u.healthChecker.Ticker = time.NewTicker(u.healthCheckDur)
-
-		if !wasHealthy {
-			atomic.AddInt32(&u.Healthy, 1)
-			u.Decr()
-		}
-	} else {
-		u.healthChecker.Ticker = time.NewTicker(u.fastHealthCheckDur)
-
-		if wasHealthy {
-			atomic.AddInt32(&u.Healthy, -1)
-			u.Incr()
-		}
-	}
-}
-
-// IsHealthy returns whether an Upstream is healthy or not.
-func (u *upstream) IsHealthy() bool {
-	i := atomic.LoadInt32(&u.Healthy)
-	if i == 1 {
-		return true
-	}
-
-	return false
-}
-
-// newReverseProxy returns a new reverse proxy handler.
-func newReverseProxy(target *url.URL, setHealthiness func(bool)) *ReverseProxy {
-	errorHandler := func(w http.ResponseWriter, r *http.Request, err error) {
-		// we don't need to worry about cancelled contexts since this doesn't necessarilly mean that
-		// the upstream is unhealthy.
-		if err != context.Canceled {
-			setHealthiness(false)
-		}
-	}
-
-	rp := NewSingleHostReverseProxy(target)
-	rp.ErrorHandler = errorHandler
-	rp.Transport = defaultTransport // use default transport that times out in 5 seconds
-	return rp
-}
-
-// Interface guards
-var (
-	_ caddyhttp.MiddlewareHandler = (*LoadBalanced)(nil)
-	_ caddy.Provisioner           = (*LoadBalanced)(nil)
-	_ caddy.CleanerUpper          = (*LoadBalanced)(nil)
-)
diff --git a/usagepool.go b/usagepool.go
new file mode 100644
index 0000000..3b8e975
--- /dev/null
+++ b/usagepool.go
@@ -0,0 +1,86 @@
+// Copyright 2015 Matthew Holt and The Caddy Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package caddy
+
+import (
+	"fmt"
+	"sync"
+	"sync/atomic"
+)
+
+// UsagePool is a thread-safe map that pools values
+// based on usage; a LoadOrStore operation increments
+// the usage, and a Delete decrements from the usage.
+// If the usage count reaches 0, the value will be
+// removed from the map. There is no way to overwrite
+// existing keys in the pool without first deleting
+// it as many times as it was stored. Deleting too
+// many times will panic.
+//
+// An empty UsagePool is NOT safe to use; always call
+// NewUsagePool() to make a new value.
+type UsagePool struct {
+	pool *sync.Map
+}
+
+// NewUsagePool returns a new usage pool.
+func NewUsagePool() *UsagePool {
+	return &UsagePool{pool: new(sync.Map)}
+}
+
+// Delete decrements the usage count for key and removes the
+// value from the underlying map if the usage is 0. It returns
+// true if the usage count reached 0 and the value was deleted.
+// It panics if the usage count drops below 0; always call
+// Delete precisely as many times as LoadOrStore.
+func (up *UsagePool) Delete(key interface{}) (deleted bool) {
+	usageVal, ok := up.pool.Load(key)
+	if !ok {
+		return false
+	}
+	upv := usageVal.(*usagePoolVal)
+	newUsage := atomic.AddInt32(&upv.usage, -1)
+	if newUsage == 0 {
+		up.pool.Delete(key)
+		return true
+	} else if newUsage < 0 {
+		panic(fmt.Sprintf("deleted more than stored: %#v (usage: %d)",
+			upv.value, upv.usage))
+	}
+	return false
+}
+
+// LoadOrStore puts val in the pool and returns false if key does
+// not already exist; otherwise if the key exists, it loads the
+// existing value, increments the usage for that value, and returns
+// the value along with true.
+func (up *UsagePool) LoadOrStore(key, val interface{}) (actual interface{}, loaded bool) {
+	usageVal := &usagePoolVal{
+		usage: 1,
+		value: val,
+	}
+	actual, loaded = up.pool.LoadOrStore(key, usageVal)
+	if loaded {
+		upv := actual.(*usagePoolVal)
+		actual = upv.value
+		atomic.AddInt32(&upv.usage, 1)
+	}
+	return
+}
+
+type usagePoolVal struct {
+	usage int32 // accessed atomically; must be 64-bit aligned for 32-bit systems
+	value interface{}
+}