caddyhttp: Add 'map' handler (#3199)

* inital map implementation

* resolve the value during middleware execution

* use regex instead

* pr feedback

* renamed mmap to maphandler

* refactored GetString implementation

* fixed mispelling

* additional feedback

6 files changed, 328 insertions, 0 deletions

diff --git a/caddyconfig/httpcaddyfile/directives.go b/caddyconfig/httpcaddyfile/directives.go
index c9f4ad9..ee73078 100644
--- a/caddyconfig/httpcaddyfile/directives.go
+++ b/caddyconfig/httpcaddyfile/directives.go
@@ -37,6 +37,7 @@ import (
 // The header directive goes second so that headers
 // can be manipulated before doing redirects.
 var directiveOrder = []string{
+	"map",
 	"root",
 
 	"header",
diff --git a/caddytest/integration/map_test.go b/caddytest/integration/map_test.go
new file mode 100644
index 0000000..e31b95a
--- /dev/null
+++ b/caddytest/integration/map_test.go
@@ -0,0 +1,143 @@
+package integration
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/caddyserver/caddy/v2/caddytest"
+)
+
+func TestMap(t *testing.T) {
+
+	// arrange
+	tester := caddytest.NewTester(t)
+	tester.InitServer(`{
+		http_port     9080
+		https_port    9443
+	}
+
+	localhost:9080 {
+
+		map http.request.method dest-name {
+			default unknown
+			G.T get-called
+			POST post-called
+		}
+
+		respond /version 200 {
+			body "hello from localhost {dest-name}"
+		}	
+	}
+	`, "caddyfile")
+
+	// act and assert
+	tester.AssertGetResponse("http://localhost:9080/version", 200, "hello from localhost get-called")
+	tester.AssertPostResponseBody("http://localhost:9080/version", []string{}, bytes.NewBuffer([]byte{}), 200, "hello from localhost post-called")
+}
+
+func TestMapRespondWithDefault(t *testing.T) {
+
+	// arrange
+	tester := caddytest.NewTester(t)
+	tester.InitServer(`{
+		http_port     9080
+		https_port    9443
+		}
+		
+		localhost:9080 {
+	
+			map http.request.method dest-name {
+				default unknown
+				GET get-called
+			}
+		
+			respond /version 200 {
+				body "hello from localhost {dest-name}"
+			}	
+		}
+	`, "caddyfile")
+
+	// act and assert
+	tester.AssertGetResponse("http://localhost:9080/version", 200, "hello from localhost get-called")
+	tester.AssertPostResponseBody("http://localhost:9080/version", []string{}, bytes.NewBuffer([]byte{}), 200, "hello from localhost unknown")
+}
+
+func TestMapAsJson(t *testing.T) {
+
+	// arrange
+	tester := caddytest.NewTester(t)
+	tester.InitServer(`{
+		"apps": {
+			"http": {
+			"http_port": 9080,
+			"https_port": 9443,
+			"servers": {
+				"srv0": {
+				"listen": [
+					":9080"
+				],
+				"routes": [
+					{
+					"handle": [
+						{
+						"handler": "subroute",
+						"routes": [
+							{
+							"handle": [
+								{
+								"handler": "map",
+								"source": "http.request.method",
+								"destination": "dest-name",
+								"default": "unknown",
+								"items": [
+									{
+									"expression": "GET",
+									"value": "get-called"
+									},
+									{
+									"expression": "POST",
+									"value": "post-called"
+									}
+								]
+								}
+							]
+							},
+							{
+							"handle": [
+								{
+								"body": "hello from localhost {dest-name}",
+								"handler": "static_response",
+								"status_code": 200
+								}
+							],
+							"match": [
+								{
+								"path": [
+									"/version"
+								]
+								}
+							]
+							}
+						]
+						}
+					],
+					"match": [
+						{
+						"host": [
+							"localhost"
+						]
+						}
+					],
+					"terminal": true
+					}
+				]
+				}
+			}
+			}
+		}
+		}
+		`, "json")
+
+	tester.AssertGetResponse("http://localhost:9080/version", 200, "hello from localhost get-called")
+	tester.AssertPostResponseBody("http://localhost:9080/version", []string{}, bytes.NewBuffer([]byte{}), 200, "hello from localhost post-called")
+}
diff --git a/modules/caddyhttp/map/caddyfile.go b/modules/caddyhttp/map/caddyfile.go
new file mode 100644
index 0000000..5737971
--- /dev/null
+++ b/modules/caddyhttp/map/caddyfile.go
@@ -0,0 +1,71 @@
+// 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 maphandler
+
+import (
+	"github.com/caddyserver/caddy/v2/caddyconfig/httpcaddyfile"
+	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
+)
+
+func init() {
+	httpcaddyfile.RegisterHandlerDirective("map", parseCaddyfile)
+}
+
+// parseCaddyfile sets up the handler for a map from Caddyfile tokens. Syntax:
+//
+//     map <source> <dest> {
+//         [default <default>] - used if not match is found
+//         [<regexp> <replacement>] - regular expression to match against the source find and the matching replacement value
+//         ...
+//     }
+//
+// The map takes a source variable and maps it into the dest variable. The mapping process
+// will check the source variable for the first successful match against a list of regular expressions.
+// If a successful match is found the dest variable will contain the replacement value.
+// If no successful match is found and the default is specified then the dest will contain the default value.
+//
+func parseCaddyfile(h httpcaddyfile.Helper) (caddyhttp.MiddlewareHandler, error) {
+	m := new(Handler)
+
+	for h.Next() {
+		// first see if source and dest are configured
+		if h.NextArg() {
+			m.Source = h.Val()
+			if h.NextArg() {
+				m.Destination = h.Val()
+			}
+		}
+
+		// load the rules
+		for h.NextBlock(0) {
+			expression := h.Val()
+			if expression == "default" {
+				args := h.RemainingArgs()
+				if len(args) != 1 {
+					return m, h.ArgErr()
+				}
+				m.Default = args[0]
+			} else {
+				args := h.RemainingArgs()
+				if len(args) != 1 {
+					return m, h.ArgErr()
+				}
+				m.Items = append(m.Items, Item{Expression: expression, Value: args[0]})
+			}
+		}
+	}
+
+	return m, nil
+}
diff --git a/modules/caddyhttp/map/map.go b/modules/caddyhttp/map/map.go
new file mode 100644
index 0000000..d2a0a0a
--- /dev/null
+++ b/modules/caddyhttp/map/map.go
@@ -0,0 +1,105 @@
+// 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 maphandler
+
+import (
+	"net/http"
+	"regexp"
+
+	"github.com/caddyserver/caddy/v2"
+	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
+)
+
+func init() {
+	caddy.RegisterModule(Handler{})
+}
+
+// Handler is a middleware that maps a source placeholder to a destination
+// placeholder.
+//
+// The mapping process happens early in the request handling lifecycle so that
+// the Destination placeholder is calculated and available for substitution.
+// The Items array contains pairs of regex expressions and values, the
+// Source is matched against the expression, if they match then the destination
+// placeholder is set to the value.
+//
+// The Default is optional, if no Item expression is matched then the value of
+// the Default will be used.
+//
+type Handler struct {
+	// Source is a placeholder
+	Source string `json:"source,omitempty"`
+	// Destination is a new placeholder
+	Destination string `json:"destination,omitempty"`
+	// Default is an optional value to use if no other was found
+	Default string `json:"default,omitempty"`
+	// Items is an array of regex expressions and values
+	Items []Item `json:"items,omitempty"`
+}
+
+// CaddyModule returns the Caddy module information.
+func (Handler) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		ID:  "http.handlers.map",
+		New: func() caddy.Module { return new(Handler) },
+	}
+}
+
+// Provision will compile all regular expressions
+func (h *Handler) Provision(_ caddy.Context) error {
+	for i := 0; i < len(h.Items); i++ {
+		h.Items[i].compiled = regexp.MustCompile(h.Items[i].Expression)
+	}
+	return nil
+}
+
+func (h Handler) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyhttp.Handler) error {
+	repl := r.Context().Value(caddy.ReplacerCtxKey).(*caddy.Replacer)
+
+	// get the source value, if the source value was not found do no
+	// replacement.
+	val, ok := repl.GetString(h.Source)
+	if ok {
+		found := false
+		for i := 0; i < len(h.Items); i++ {
+			if h.Items[i].compiled.MatchString(val) {
+				found = true
+				repl.Set(h.Destination, h.Items[i].Value)
+				break
+			}
+		}
+
+		if !found && h.Default != "" {
+			repl.Set(h.Destination, h.Default)
+		}
+	}
+	return next.ServeHTTP(w, r)
+}
+
+// Item defines each entry in the map
+type Item struct {
+	// Expression is the regular expression searched for
+	Expression string `json:"expression,omitempty"`
+	// Value to use once the expression has been found
+	Value string `json:"value,omitempty"`
+	// compiled expression, internal use
+	compiled *regexp.Regexp
+}
+
+// Interface guards
+var (
+	_ caddy.Provisioner           = (*Handler)(nil)
+	_ caddyhttp.MiddlewareHandler = (*Handler)(nil)
+)
diff --git a/modules/caddyhttp/standard/imports.go b/modules/caddyhttp/standard/imports.go
index a0ccf6e..dabec81 100644
--- a/modules/caddyhttp/standard/imports.go
+++ b/modules/caddyhttp/standard/imports.go
@@ -9,6 +9,7 @@ import (
 	_ "github.com/caddyserver/caddy/v2/modules/caddyhttp/encode/zstd"
 	_ "github.com/caddyserver/caddy/v2/modules/caddyhttp/fileserver"
 	_ "github.com/caddyserver/caddy/v2/modules/caddyhttp/headers"
+	_ "github.com/caddyserver/caddy/v2/modules/caddyhttp/map"
 	_ "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"
diff --git a/replacer.go b/replacer.go
index 86cd729..29d8e26 100644
--- a/replacer.go
+++ b/replacer.go
@@ -66,6 +66,13 @@ func (r *Replacer) Get(variable string) (interface{}, bool) {
 	return nil, false
 }
 
+// GetString  is the same as Get, but coerces the value to a
+// string representation.
+func (r *Replacer) GetString(variable string) (string, bool) {
+	s, found := r.Get(variable)
+	return toString(s), found
+}
+
 // Delete removes a variable with a static value
 // that was created using Set.
 func (r *Replacer) Delete(variable string) {