net/http: add GODEBUG setting for old ServeMux behavior

Add the GODEBUG setting httpmuxgo121.
When set to "1", ServeMux behaves exactly like it did in Go 1.21.

Implemented by defining a new, unexported type, serveMux121, that
uses the original code.

Updates #61410.

Change-Id: I0a9d0fe2a2286e442d680393e62895ab50683cea
Reviewed-on: https://go-review.googlesource.com/c/go/+/530461
Run-TryBot: Jonathan Amsterdam <jba@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>

doc/godebug.md

@@ -138,6 +138,12 @@ Go 1.22 made it an error for a request or response read by a net/http
 client or server to have an empty Content-Length header.
 This behavior is controlled by the `httplaxcontentlength` setting.
 
+Go 1.22 changed the behavior of ServeMux to accept extended
+patterns and unescape both patterns and request paths by segment.
+This behavior can be controlled by the
+[`httpmuxgo121` setting](/pkg/net/http/#ServeMux).
+
+
 ### Go 1.21
 
 Go 1.21 made it a run-time error to call `panic` with a nil interface value,

src/internal/godebugs/table.go

@@ -33,6 +33,7 @@ var All = []Info{
 	{Name: "http2debug", Package: "net/http", Opaque: true},
 	{Name: "http2server", Package: "net/http"},
 	{Name: "httplaxcontentlength", Package: "net/http", Changed: 22, Old: "1"},
+	{Name: "httpmuxgo121", Package: "net/http", Changed: 22, Old: "1"},
 	{Name: "installgoroot", Package: "go/build"},
 	{Name: "jstmpllitinterp", Package: "html/template"},
 	//{Name: "multipartfiles", Package: "mime/multipart"},

src/net/http/request_test.go

@@ -1554,54 +1554,3 @@ func TestStatus(t *testing.T) {
 		}
 	}
 }
-
-func TestEscapedPathsAndPatterns(t *testing.T) {
-	matches := []struct {
-		pattern string
-		paths   []string
-	}{
-		{
-			"/a", // this pattern matches a path that unescapes to "/a"
-			[]string{"/a", "/%61"},
-		},
-		{
-			"/%62", // patterns are unescaped by segment; matches paths that unescape to "/b"
-			[]string{"/b", "/%62"},
-		},
-		{
-			"/%7B/%7D", // the only way to write a pattern that matches '{' or '}'
-			[]string{"/{/}", "/%7b/}", "/{/%7d", "/%7B/%7D"},
-		},
-		{
-			"/%x", // patterns that do not unescape are left unchanged
-			[]string{"/%25x"},
-		},
-	}
-
-	mux := NewServeMux()
-	var gotPattern string
-	for _, m := range matches {
-		mux.HandleFunc(m.pattern, func(w ResponseWriter, r *Request) {
-			gotPattern = m.pattern
-		})
-	}
-
-	server := httptest.NewServer(mux)
-	defer server.Close()
-
-	for _, m := range matches {
-		for _, p := range m.paths {
-			res, err := Get(server.URL + p)
-			if err != nil {
-				t.Fatal(err)
-			}
-			if res.StatusCode != 200 {
-				t.Errorf("%s: got code %d, want 200", p, res.StatusCode)
-				continue
-			}
-			if g, w := gotPattern, m.pattern; g != w {
-				t.Errorf("%s: pattern: got %q, want %q", p, g, w)
-			}
-		}
-	}
-}

src/net/http/servemux121.go

@@ -0,0 +1,211 @@
+// Copyright 2009 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.
+
+package http
+
+// This file implements ServeMux behavior as in Go 1.21.
+// The behavior is controlled by a GODEBUG setting.
+// Most of this code is derived from commit 08e35cc334.
+// Changes are minimal: aside from the different receiver type,
+// they mostly involve renaming functions, usually by unexporting them.
+
+import (
+	"internal/godebug"
+	"net/url"
+	"sort"
+	"strings"
+	"sync"
+)
+
+var httpmuxgo121 = godebug.New("httpmuxgo121")
+
+var use121 bool
+
+// Read httpmuxgo121 once at startup, since dealing with changes to it during
+// program execution is too complex and error-prone.
+func init() {
+	if httpmuxgo121.Value() == "1" {
+		use121 = true
+		httpmuxgo121.IncNonDefault()
+	}
+}
+
+// serveMux121 holds the state of a ServeMux needed for Go 1.21 behavior.
+type serveMux121 struct {
+	mu    sync.RWMutex
+	m     map[string]muxEntry
+	es    []muxEntry // slice of entries sorted from longest to shortest.
+	hosts bool       // whether any patterns contain hostnames
+}
+
+type muxEntry struct {
+	h       Handler
+	pattern string
+}
+
+// Formerly ServeMux.Handle.
+func (mux *serveMux121) handle(pattern string, handler Handler) {
+	mux.mu.Lock()
+	defer mux.mu.Unlock()
+
+	if pattern == "" {
+		panic("http: invalid pattern")
+	}
+	if handler == nil {
+		panic("http: nil handler")
+	}
+	if _, exist := mux.m[pattern]; exist {
+		panic("http: multiple registrations for " + pattern)
+	}
+
+	if mux.m == nil {
+		mux.m = make(map[string]muxEntry)
+	}
+	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
+}
+
+// Formerly ServeMux.HandleFunc.
+func (mux *serveMux121) handleFunc(pattern string, handler func(ResponseWriter, *Request)) {
+	if handler == nil {
+		panic("http: nil handler")
+	}
+	mux.handle(pattern, HandlerFunc(handler))
+}
+
+// Formerly ServeMux.Handler.
+func (mux *serveMux121) findHandler(r *Request) (h Handler, pattern string) {
+
+	// CONNECT requests are not canonicalized.
+	if r.Method == "CONNECT" {
+		// If r.URL.Path is /tree and its handler is not registered,
+		// the /tree -> /tree/ redirect applies to CONNECT requests
+		// but the path canonicalization does not.
+		if u, ok := mux.redirectToPathSlash(r.URL.Host, r.URL.Path, r.URL); ok {
+			return RedirectHandler(u.String(), StatusMovedPermanently), u.Path
+		}
+
+		return mux.handler(r.Host, r.URL.Path)
+	}
+
+	// All other requests have any port stripped and path cleaned
+	// before passing to mux.handler.
+	host := stripHostPort(r.Host)
+	path := cleanPath(r.URL.Path)
+
+	// If the given path is /tree and its handler is not registered,
+	// redirect for /tree/.
+	if u, ok := mux.redirectToPathSlash(host, path, r.URL); ok {
+		return RedirectHandler(u.String(), StatusMovedPermanently), u.Path
+	}
+
+	if path != r.URL.Path {
+		_, pattern = mux.handler(host, path)
+		u := &url.URL{Path: path, RawQuery: r.URL.RawQuery}
+		return RedirectHandler(u.String(), StatusMovedPermanently), pattern
+	}
+
+	return mux.handler(host, r.URL.Path)
+}
+
+// handler is the main implementation of findHandler.
+// The path is known to be in canonical form, except for CONNECT methods.
+func (mux *serveMux121) handler(host, path string) (h Handler, pattern string) {
+	mux.mu.RLock()
+	defer mux.mu.RUnlock()
+
+	// Host-specific pattern takes precedence over generic ones
+	if mux.hosts {
+		h, pattern = mux.match(host + path)
+	}
+	if h == nil {
+		h, pattern = mux.match(path)
+	}
+	if h == nil {
+		h, pattern = NotFoundHandler(), ""
+	}
+	return
+}
+
+// Find a handler on a handler map given a path string.
+// Most-specific (longest) pattern wins.
+func (mux *serveMux121) match(path string) (h Handler, pattern string) {
+	// Check for exact match first.
+	v, ok := mux.m[path]
+	if ok {
+		return v.h, 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 nil, ""
+}
+
+// redirectToPathSlash determines if the given path needs appending "/" to it.
+// This occurs when a handler for path + "/" was already registered, but
+// not for path itself. If the path needs appending to, it creates a new
+// URL, setting the path to u.Path + "/" and returning true to indicate so.
+func (mux *serveMux121) redirectToPathSlash(host, path string, u *url.URL) (*url.URL, bool) {
+	mux.mu.RLock()
+	shouldRedirect := mux.shouldRedirectRLocked(host, path)
+	mux.mu.RUnlock()
+	if !shouldRedirect {
+		return u, false
+	}
+	path = path + "/"
+	u = &url.URL{Path: path, RawQuery: u.RawQuery}
+	return u, true
+}
+
+// shouldRedirectRLocked reports whether the given path and host should be redirected to
+// path+"/". This should happen if a handler is registered for path+"/" but
+// not path -- see comments at ServeMux.
+func (mux *serveMux121) shouldRedirectRLocked(host, path string) bool {
+	p := []string{path, host + path}
+
+	for _, c := range p {
+		if _, exist := mux.m[c]; exist {
+			return false
+		}
+	}
+
+	n := len(path)
+	if n == 0 {
+		return false
+	}
+	for _, c := range p {
+		if _, exist := mux.m[c+"/"]; exist {
+			return path[n-1] != '/'
+		}
+	}
+
+	return false
+}

src/net/http/server.go

@@ -33,6 +33,8 @@ import (
 	"golang.org/x/net/http/httpguts"
 )
 
+// TODO(jba): test
+
 // Errors used by the HTTP server.
 var (
 	// ErrBodyNotAllowed is returned by ResponseWriter.Write calls
@@ -2348,7 +2350,8 @@ type ServeMux struct {
 	mu       sync.RWMutex
 	tree     routingNode
 	index    routingIndex
-	patterns []*pattern // TODO(jba): remove if possible
+	patterns []*pattern  // TODO(jba): remove if possible
+	mux121   serveMux121 // used only when GODEBUG=httpmuxgo121=1
 }
 
 // NewServeMux allocates and returns a new ServeMux.
@@ -2412,6 +2415,9 @@ func stripHostPort(h string) string {
 // If there is no registered handler that applies to the request,
 // Handler returns a “page not found” handler and an empty pattern.
 func (mux *ServeMux) Handler(r *Request) (h Handler, pattern string) {
+	if use121 {
+		return mux.mux121.findHandler(r)
+	}
 	h, p, _, _ := mux.findHandler(r)
 	return h, p
 }
@@ -2585,9 +2591,12 @@ func (mux *ServeMux) ServeHTTP(w ResponseWriter, r *Request) {
 		w.WriteHeader(StatusBadRequest)
 		return
 	}
-	h, _, pat, matches := mux.findHandler(r)
-	r.pat = pat
-	r.matches = matches
+	var h Handler
+	if use121 {
+		h, _ = mux.mux121.findHandler(r)
+	} else {
+		h, _, r.pat, r.matches = mux.findHandler(r)
+	}
 	h.ServeHTTP(w, r)
 }
 
@@ -2597,23 +2606,35 @@ func (mux *ServeMux) ServeHTTP(w ResponseWriter, r *Request) {
 // Handle registers the handler for the given pattern.
 // If a handler already exists for pattern, Handle panics.
 func (mux *ServeMux) Handle(pattern string, handler Handler) {
+	if use121 {
+		mux.mux121.handle(pattern, handler)
+	}
 	mux.register(pattern, handler)
 }
 
 // HandleFunc registers the handler function for the given pattern.
 func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
+	if use121 {
+		mux.mux121.handleFunc(pattern, handler)
+	}
 	mux.register(pattern, HandlerFunc(handler))
 }
 
 // Handle registers the handler for the given pattern in [DefaultServeMux].
 // The documentation for [ServeMux] explains how patterns are matched.
 func Handle(pattern string, handler Handler) {
+	if use121 {
+		DefaultServeMux.mux121.handle(pattern, handler)
+	}
 	DefaultServeMux.register(pattern, handler)
 }
 
 // HandleFunc registers the handler function for the given pattern in [DefaultServeMux].
 // The documentation for [ServeMux] explains how patterns are matched.
 func HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
+	if use121 {
+		DefaultServeMux.mux121.handleFunc(pattern, handler)
+	}
 	DefaultServeMux.register(pattern, HandlerFunc(handler))
 }
 

src/net/http/server_test.go

@@ -174,6 +174,68 @@ func TestExactMatch(t *testing.T) {
 	}
 }
 
+func TestEscapedPathsAndPatterns(t *testing.T) {
+	matches := []struct {
+		pattern  string
+		paths    []string // paths that match the pattern
+		paths121 []string // paths that matched the pattern in Go 1.21.
+	}{
+		{
+			"/a", // this pattern matches a path that unescapes to "/a"
+			[]string{"/a", "/%61"},
+			[]string{"/a", "/%61"},
+		},
+		{
+			"/%62", // patterns are unescaped by segment; matches paths that unescape to "/b"
+			[]string{"/b", "/%62"},
+			[]string{"/%2562"}, // In 1.21, patterns were not unescaped but paths were.
+		},
+		{
+			"/%7B/%7D", // the only way to write a pattern that matches '{' or '}'
+			[]string{"/{/}", "/%7b/}", "/{/%7d", "/%7B/%7D"},
+			[]string{"/%257B/%257D"}, // In 1.21, patterns were not unescaped.
+		},
+		{
+			"/%x", // patterns that do not unescape are left unchanged
+			[]string{"/%25x"},
+			[]string{"/%25x"},
+		},
+	}
+
+	run := func(t *testing.T, test121 bool) {
+		defer func(u bool) { use121 = u }(use121)
+		use121 = test121
+
+		mux := NewServeMux()
+		for _, m := range matches {
+			mux.HandleFunc(m.pattern, func(w ResponseWriter, r *Request) {})
+		}
+
+		for _, m := range matches {
+			paths := m.paths
+			if use121 {
+				paths = m.paths121
+			}
+			for _, p := range paths {
+				u, err := url.ParseRequestURI(p)
+				if err != nil {
+					t.Fatal(err)
+				}
+				req := &Request{
+					URL: u,
+				}
+				_, gotPattern := mux.Handler(req)
+				if g, w := gotPattern, m.pattern; g != w {
+					t.Errorf("%s: pattern: got %q, want %q", p, g, w)
+				}
+			}
+		}
+	}
+
+	t.Run("latest", func(t *testing.T) { run(t, false) })
+	t.Run("1.21", func(t *testing.T) { run(t, true) })
+}
+
 func BenchmarkServerMatch(b *testing.B) {
 	fn := func(w ResponseWriter, r *Request) {
 		fmt.Fprintf(w, "OK")

src/runtime/metrics/doc.go

@@ -259,6 +259,10 @@ Below is the full list of supported metrics, ordered lexicographically.
 		package due to a non-default GODEBUG=httplaxcontentlength=...
 		setting.
 
+	/godebug/non-default-behavior/httpmuxgo121:events
+		The number of non-default behaviors executed by the net/http
+		package due to a non-default GODEBUG=httpmuxgo121=... setting.
+
 	/godebug/non-default-behavior/installgoroot:events
 		The number of non-default behaviors executed by the go/build
 		package due to a non-default GODEBUG=installgoroot=... setting.