net/http: omit forbidden Trailer headers from response

Use the vendored ValidTrailerHeader function from x/net/http/httpguts to
check Trailer headers according to RFC 7230. The previous implementation
only omitted illegal Trailer headers defined in RFC 2616.

This CL adds x/net/http/httpguts from CL 104042 (git rev a35a21de97)

Fixes #23908

Change-Id: Ib2329a384040494093c18e209db9b62aaf86e921
Reviewed-on: https://go-review.googlesource.com/104075
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/go/build/deps_test.go

@@ -400,6 +400,7 @@ var pkgDeps = map[string][]string{
 		"context",
 		"crypto/rand",
 		"crypto/tls",
+		"golang_org/x/net/http/httpguts",
 		"golang_org/x/net/http2/hpack",
 		"golang_org/x/net/idna",
 		"golang_org/x/net/lex/httplex",
@@ -419,7 +420,10 @@ var pkgDeps = map[string][]string{
 	"net/http/cgi":       {"L4", "NET", "OS", "crypto/tls", "net/http", "regexp"},
 	"net/http/cookiejar": {"L4", "NET", "net/http"},
 	"net/http/fcgi":      {"L4", "NET", "OS", "context", "net/http", "net/http/cgi"},
-	"net/http/httptest":  {"L4", "NET", "OS", "crypto/tls", "flag", "net/http", "net/http/internal", "crypto/x509"},
+	"net/http/httptest": {
+		"L4", "NET", "OS", "crypto/tls", "flag", "net/http", "net/http/internal", "crypto/x509",
+		"golang_org/x/net/http/httpguts",
+	},
 	"net/http/httputil": {"L4", "NET", "OS", "context", "net/http", "net/http/internal"},
 	"net/http/pprof":    {"L4", "OS", "html/template", "net/http", "runtime/pprof", "runtime/trace"},
 	"net/rpc":           {"L4", "NET", "encoding/gob", "html/template", "net/http"},

src/net/http/httptest/recorder.go

@@ -11,6 +11,8 @@ import (
 	"net/http"
 	"strconv"
 	"strings"
+
+	"golang_org/x/net/http/httpguts"
 )
 
 // ResponseRecorder is an implementation of http.ResponseWriter that
@@ -186,16 +188,11 @@ func (rw *ResponseRecorder) Result() *http.Response {
 	if trailers, ok := rw.snapHeader["Trailer"]; ok {
 		res.Trailer = make(http.Header, len(trailers))
 		for _, k := range trailers {
-			// TODO: use http2.ValidTrailerHeader, but we can't
-			// get at it easily because it's bundled into net/http
-			// unexported. This is good enough for now:
-			switch k {
-			case "Transfer-Encoding", "Content-Length", "Trailer":
-				// Ignore since forbidden by RFC 2616 14.40.
-				// TODO: inconsistent with RFC 7230, section 4.1.2.
+			k = http.CanonicalHeaderKey(k)
+			if !httpguts.ValidTrailerHeader(k) {
+				// Ignore since forbidden by RFC 7230, section 4.1.2.
 				continue
 			}
-			k = http.CanonicalHeaderKey(k)
 			vv, ok := rw.HeaderMap[k]
 			if !ok {
 				continue

src/net/http/server.go

@@ -28,6 +28,7 @@ import (
 	"sync/atomic"
 	"time"
 
+	"golang_org/x/net/http/httpguts"
 	"golang_org/x/net/lex/httplex"
 )
 
@@ -510,10 +511,8 @@ func (b *atomicBool) setTrue()    { atomic.StoreInt32((*int32)(b), 1) }
 // written in the trailers at the end of the response.
 func (w *response) declareTrailer(k string) {
 	k = CanonicalHeaderKey(k)
-	switch k {
-	case "Transfer-Encoding", "Content-Length", "Trailer":
-		// Forbidden by RFC 2616 14.40.
-		// TODO: inconsistent with RFC 7230, section 4.1.2
+	if !httpguts.ValidTrailerHeader(k) {
+		// Forbidden by RFC 7230, section 4.1.2
 		return
 	}
 	w.trailers = append(w.trailers, k)

src/vendor/golang_org/x/net/http/httpguts/guts.go

@@ -0,0 +1,50 @@
+// 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.
+
+// Package httpguts provides functions implementing various details
+// of the HTTP specification.
+//
+// This package is shared by the standard library (which vendors it)
+// and x/net/http2. It comes with no API stability promise.
+package httpguts
+
+import (
+	"net/textproto"
+	"strings"
+)
+
+// ValidTrailerHeader reports whether name is a valid header field name to appear
+// in trailers.
+// See RFC 7230, Section 4.1.2
+func ValidTrailerHeader(name string) bool {
+	name = textproto.CanonicalMIMEHeaderKey(name)
+	if strings.HasPrefix(name, "If-") || badTrailer[name] {
+		return false
+	}
+	return true
+}
+
+var badTrailer = map[string]bool{
+	"Authorization":       true,
+	"Cache-Control":       true,
+	"Connection":          true,
+	"Content-Encoding":    true,
+	"Content-Length":      true,
+	"Content-Range":       true,
+	"Content-Type":        true,
+	"Expect":              true,
+	"Host":                true,
+	"Keep-Alive":          true,
+	"Max-Forwards":        true,
+	"Pragma":              true,
+	"Proxy-Authenticate":  true,
+	"Proxy-Authorization": true,
+	"Proxy-Connection":    true,
+	"Range":               true,
+	"Realm":               true,
+	"Te":                  true,
+	"Trailer":             true,
+	"Transfer-Encoding":   true,
+	"Www-Authenticate":    true,
+}