net/http: speed up ServeMux matching

Scanning through all path patterns is not necessary, since the
paths do not change frequently.  Instead, maintain a sorted list
of path prefixes and return the first match.

name            old time/op  new time/op  delta
ServerMatch-12   134ns ± 3%    17ns ± 4%  -86.95%  (p=0.000 n=19+20)

Change-Id: I15b4483dc30db413321435ee6815fc9bf2bcc546
Reviewed-on: https://go-review.googlesource.com/c/144937
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/http/server.go

@@ -22,6 +22,7 @@ import (
 	"os"
 	"path"
 	"runtime"
+	"sort"
 	"strconv"
 	"strings"
 	"sync"
@@ -2179,7 +2180,8 @@ func RedirectHandler(url string, code int) Handler {
 type ServeMux struct {
 	mu    sync.RWMutex
 	m     map[string]muxEntry
-	hosts bool // whether any patterns contain hostnames
+	es    []muxEntry // slice of entries sorted from longest to shortest.
+	hosts bool       // whether any patterns contain hostnames
 }
 
 type muxEntry struct {
@@ -2195,19 +2197,6 @@ var DefaultServeMux = &defaultServeMux
 
 var defaultServeMux ServeMux
 
-// Does path match pattern?
-func pathMatch(pattern, path string) bool {
-	if len(pattern) == 0 {
-		// should not happen
-		return false
-	}
-	n := len(pattern)
-	if pattern[n-1] != '/' {
-		return pattern == path
-	}
-	return len(path) >= n && path[0:n] == pattern
-}
-
 // cleanPath returns the canonical path for p, eliminating . and .. elements.
 func cleanPath(p string) string {
 	if p == "" {
@@ -2252,19 +2241,14 @@ func (mux *ServeMux) match(path string) (h Handler, pattern string) {
 		return v.h, v.pattern
 	}
 
-	// Check for longest valid match.
-	var n = 0
-	for k, v := range mux.m {
-		if !pathMatch(k, path) {
-			continue
-		}
-		if h == nil || len(k) > n {
-			n = len(k)
-			h = v.h
-			pattern = v.pattern
+	// Check for longest valid match.  mux.es contains all patterns
+	// that end in / sorted from longest to shortest.
+	for _, e := range mux.es {
+		if strings.HasPrefix(path, e.pattern) {
+			return e.h, e.pattern
 		}
 	}
-	return
+	return nil, ""
 }
 
 // redirectToPathSlash determines if the given path needs appending "/" to it.
@@ -2410,13 +2394,32 @@ func (mux *ServeMux) Handle(pattern string, handler Handler) {
 	if mux.m == nil {
 		mux.m = make(map[string]muxEntry)
 	}
-	mux.m[pattern] = muxEntry{h: handler, pattern: pattern}
+	e := muxEntry{h: handler, pattern: pattern}
+	mux.m[pattern] = e
+	if pattern[len(pattern)-1] == '/' {
+		mux.es = appendSorted(mux.es, e)
+	}
 
 	if pattern[0] != '/' {
 		mux.hosts = true
 	}
 }
 
+func appendSorted(es []muxEntry, e muxEntry) []muxEntry {
+	n := len(es)
+	i := sort.Search(n, func(i int) bool {
+		return len(es[i].pattern) < len(e.pattern)
+	})
+	if i == n {
+		return append(es, e)
+	}
+	// we now know that i points at where we want to insert
+	es = append(es, muxEntry{}) // try to grow the slice in place, any entry works.
+	copy(es[i+1:], es[i:])      // Move shorter entries down
+	es[i] = e
+	return es
+}
+
 // HandleFunc registers the handler function for the given pattern.
 func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
 	if handler == nil {

src/net/http/server_test.go

@@ -0,0 +1,45 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Server unit tests
+
+package http
+
+import (
+	"fmt"
+	"testing"
+)
+
+func BenchmarkServerMatch(b *testing.B) {
+	fn := func(w ResponseWriter, r *Request) {
+		fmt.Fprintf(w, "OK")
+	}
+	mux := NewServeMux()
+	mux.HandleFunc("/", fn)
+	mux.HandleFunc("/index", fn)
+	mux.HandleFunc("/home", fn)
+	mux.HandleFunc("/about", fn)
+	mux.HandleFunc("/contact", fn)
+	mux.HandleFunc("/robots.txt", fn)
+	mux.HandleFunc("/products/", fn)
+	mux.HandleFunc("/products/1", fn)
+	mux.HandleFunc("/products/2", fn)
+	mux.HandleFunc("/products/3", fn)
+	mux.HandleFunc("/products/3/image.jpg", fn)
+	mux.HandleFunc("/admin", fn)
+	mux.HandleFunc("/admin/products/", fn)
+	mux.HandleFunc("/admin/products/create", fn)
+	mux.HandleFunc("/admin/products/update", fn)
+	mux.HandleFunc("/admin/products/delete", fn)
+
+	paths := []string{"/", "/notfound", "/admin/", "/admin/foo", "/contact", "/products",
+		"/products/", "/products/3/image.jpg"}
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		if h, p := mux.match(paths[i%len(paths)]); h != nil && p == "" {
+			b.Error("impossible")
+		}
+	}
+	b.StopTimer()
+}