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// 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 httpcache
import (
"bytes"
"encoding/gob"
"fmt"
"io"
"log"
"net/http"
"sync"
"github.com/caddyserver/caddy/v2"
"github.com/caddyserver/caddy/v2/modules/caddyhttp"
"github.com/golang/groupcache"
)
func init() {
caddy.RegisterModule(Cache{})
}
// Cache implements a simple distributed cache.
type Cache struct {
Self string `json:"self,omitempty"`
Peers []string `json:"peers,omitempty"`
MaxSize int64 `json:"max_size,omitempty"`
group *groupcache.Group
}
// CaddyModule returns the Caddy module information.
func (Cache) CaddyModule() caddy.ModuleInfo {
return caddy.ModuleInfo{
ID: "http.handlers.cache",
New: func() caddy.Module { return new(Cache) },
}
}
// Provision provisions c.
func (c *Cache) Provision(ctx caddy.Context) error {
// TODO: use UsagePool so that cache survives config reloads - TODO: a single cache for whole process?
maxSize := c.MaxSize
if maxSize == 0 {
const maxMB = 512
maxSize = int64(maxMB << 20)
}
poolMu.Lock()
if pool == nil {
pool = groupcache.NewHTTPPool(c.Self)
c.group = groupcache.NewGroup(groupName, maxSize, groupcache.GetterFunc(c.getter))
} else {
c.group = groupcache.GetGroup(groupName)
}
pool.Set(append(c.Peers, c.Self)...)
poolMu.Unlock()
return nil
}
// Validate validates c.
func (c *Cache) Validate() error {
if c.Self == "" {
return fmt.Errorf("address of this instance (self) is required")
}
if c.MaxSize < 0 {
return fmt.Errorf("size must be greater than 0")
}
return nil
}
func (c *Cache) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyhttp.Handler) error {
// TODO: proper RFC implementation of cache control headers...
if r.Header.Get("Cache-Control") == "no-cache" || (r.Method != "GET" && r.Method != "HEAD") {
return next.ServeHTTP(w, r)
}
ctx := getterContext{w, r, next}
// TODO: rigorous performance testing
// TODO: pretty much everything else to handle the nuances of HTTP caching...
// TODO: groupcache has no explicit cache eviction, so we need to embed
// all information related to expiring cache entries into the key; right
// now we just use the request URI as a proof-of-concept
key := r.RequestURI
var cachedBytes []byte
err := c.group.Get(ctx, key, groupcache.AllocatingByteSliceSink(&cachedBytes))
if err == errUncacheable {
return nil
}
if err != nil {
return err
}
// the cached bytes consists of two parts: first a
// gob encoding of the status and header, immediately
// followed by the raw bytes of the response body
rdr := bytes.NewReader(cachedBytes)
// read the header and status first
var hs headerAndStatus
err = gob.NewDecoder(rdr).Decode(&hs)
if err != nil {
return err
}
// set and write the cached headers
for k, v := range hs.Header {
w.Header()[k] = v
}
w.WriteHeader(hs.Status)
// write the cached response body
io.Copy(w, rdr)
return nil
}
func (c *Cache) getter(ctx groupcache.Context, key string, dest groupcache.Sink) error {
combo := ctx.(getterContext)
// the buffer will store the gob-encoded header, then the body
buf := bufPool.Get().(*bytes.Buffer)
buf.Reset()
defer bufPool.Put(buf)
// we need to record the response if we are to cache it; only cache if
// request is successful (TODO: there's probably much more nuance needed here)
rr := caddyhttp.NewResponseRecorder(combo.rw, buf, func(status int, header http.Header) bool {
shouldBuf := status < 300
if shouldBuf {
// store the header before the body, so we can efficiently
// and conveniently use a single buffer for both; gob
// decoder will only read up to end of gob message, and
// the rest will be the body, which will be written
// implicitly for us by the recorder
err := gob.NewEncoder(buf).Encode(headerAndStatus{
Header: header,
Status: status,
})
if err != nil {
log.Printf("[ERROR] Encoding headers for cache entry: %v; not caching this request", err)
return false
}
}
return shouldBuf
})
// execute next handlers in chain
err := combo.next.ServeHTTP(rr, combo.req)
if err != nil {
return err
}
// if response body was not buffered, response was
// already written and we are unable to cache
if !rr.Buffered() {
return errUncacheable
}
// add to cache
dest.SetBytes(buf.Bytes())
return nil
}
type headerAndStatus struct {
Header http.Header
Status int
}
type getterContext struct {
rw http.ResponseWriter
req *http.Request
next caddyhttp.Handler
}
var bufPool = sync.Pool{
New: func() interface{} {
return new(bytes.Buffer)
},
}
var (
pool *groupcache.HTTPPool
poolMu sync.Mutex
)
var errUncacheable = fmt.Errorf("uncacheable")
const groupName = "http_requests"
// Interface guards
var (
_ caddy.Provisioner = (*Cache)(nil)
_ caddy.Validator = (*Cache)(nil)
_ caddyhttp.MiddlewareHandler = (*Cache)(nil)
)
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