net/http: limit Transport's reading of response header bytes from servers

The default is 10MB, like http2, but can be configured with a new
field http.Transport.MaxResponseHeaderBytes.

Fixes #9115

Change-Id: I01808ac631ce4794ef2b0dfc391ed51cf951ceb1
Reviewed-on: https://go-review.googlesource.com/21329
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>

src/net/http/http.go

+// Copyright 2016 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
+
+// maxInt64 is the effective "infinite" value for the Server and
+// Transport's byte-limiting readers.
+const maxInt64 = 1<<63 - 1
+
+// TODO(bradfitz): move common stuff here. The other files have accumulated
+// generic http stuff in random places.

src/net/http/server.go

@@ -497,7 +497,7 @@ type connReader struct {
 }
 
 func (cr *connReader) setReadLimit(remain int64) { cr.remain = remain }
-func (cr *connReader) setInfiniteReadLimit()     { cr.remain = 1<<63 - 1 }
+func (cr *connReader) setInfiniteReadLimit()     { cr.remain = maxInt64 }
 func (cr *connReader) hitReadLimit() bool        { return cr.remain <= 0 }
 
 func (cr *connReader) Read(p []byte) (n int, err error) {

src/net/http/transport.go

@@ -146,6 +146,13 @@ type Transport struct {
 	// If TLSNextProto is nil, HTTP/2 support is enabled automatically.
 	TLSNextProto map[string]func(authority string, c *tls.Conn) RoundTripper
 
+	// MaxResponseHeaderBytes specifies a limit on how many
+	// response bytes are allowed in the server's response
+	// header.
+	//
+	// Zero means to use a default limit.
+	MaxResponseHeaderBytes int64
+
 	// nextProtoOnce guards initialization of TLSNextProto and
 	// h2transport (via onceSetNextProtoDefaults)
 	nextProtoOnce sync.Once
@@ -188,8 +195,23 @@ func (t *Transport) onceSetNextProtoDefaults() {
 	t2, err := http2configureTransport(t)
 	if err != nil {
 		log.Printf("Error enabling Transport HTTP/2 support: %v", err)
-	} else {
-		t.h2transport = t2
+		return
+	}
+	t.h2transport = t2
+
+	// Auto-configure the http2.Transport's MaxHeaderListSize from
+	// the http.Transport's MaxResponseHeaderBytes. They don't
+	// exactly mean the same thing, but they're close.
+	//
+	// TODO: also add this to x/net/http2.Configure Transport, behind
+	// a +build go1.7 build tag:
+	if limit1 := t.MaxResponseHeaderBytes; limit1 != 0 && t2.MaxHeaderListSize == 0 {
+		const h2max = 1<<32 - 1
+		if limit1 >= h2max {
+			t2.MaxHeaderListSize = h2max
+		} else {
+			t2.MaxHeaderListSize = uint32(limit1)
+		}
 	}
 }
 
@@ -351,7 +373,8 @@ func (t *Transport) RoundTrip(req *Request) (*Response, error) {
 // resent on a new connection. The non-nil input error is the error from
 // roundTrip, which might be wrapped in a beforeRespHeaderError error.
 //
-// The return value is err or the unwrapped error inside a
+// The return value is either nil to retry the request, the provided
+// err unmodified, or the unwrapped error inside a
 // beforeRespHeaderError.
 func checkTransportResend(err error, req *Request, pconn *persistConn) error {
 	brhErr, ok := err.(beforeRespHeaderError)
@@ -864,7 +887,7 @@ func (t *Transport) dialConn(cm connectMethod) (*persistConn, error) {
 		}
 	}
 
-	pconn.br = bufio.NewReader(noteEOFReader{pconn.conn, &pconn.sawEOF})
+	pconn.br = bufio.NewReader(pconn)
 	pconn.bw = bufio.NewWriter(pconn.conn)
 	go pconn.readLoop()
 	go pconn.writeLoop()
@@ -998,17 +1021,18 @@ type persistConn struct {
 	// If it's non-nil, the rest of the fields are unused.
 	alt RoundTripper
 
-	t        *Transport
-	cacheKey connectMethodKey
-	conn     net.Conn
-	tlsState *tls.ConnectionState
-	br       *bufio.Reader       // from conn
-	sawEOF   bool                // whether we've seen EOF from conn; owned by readLoop
-	bw       *bufio.Writer       // to conn
-	reqch    chan requestAndChan // written by roundTrip; read by readLoop
-	writech  chan writeRequest   // written by roundTrip; read by writeLoop
-	closech  chan struct{}       // closed when conn closed
-	isProxy  bool
+	t         *Transport
+	cacheKey  connectMethodKey
+	conn      net.Conn
+	tlsState  *tls.ConnectionState
+	br        *bufio.Reader       // from conn
+	bw        *bufio.Writer       // to conn
+	reqch     chan requestAndChan // written by roundTrip; read by readLoop
+	writech   chan writeRequest   // written by roundTrip; read by writeLoop
+	closech   chan struct{}       // closed when conn closed
+	isProxy   bool
+	sawEOF    bool  // whether we've seen EOF from conn; owned by readLoop
+	readLimit int64 // bytes allowed to be read; owned by readLoop
 	// writeErrCh passes the request write error (usually nil)
 	// from the writeLoop goroutine to the readLoop which passes
 	// it off to the res.Body reader, which then uses it to decide
@@ -1027,6 +1051,28 @@ type persistConn struct {
 	mutateHeaderFunc func(Header)
 }
 
+func (pc *persistConn) maxHeaderResponseSize() int64 {
+	if v := pc.t.MaxResponseHeaderBytes; v != 0 {
+		return v
+	}
+	return 10 << 20 // conservative default; same as http2
+}
+
+func (pc *persistConn) Read(p []byte) (n int, err error) {
+	if pc.readLimit <= 0 {
+		return 0, fmt.Errorf("read limit of %d bytes exhausted", pc.maxHeaderResponseSize())
+	}
+	if int64(len(p)) > pc.readLimit {
+		p = p[:pc.readLimit]
+	}
+	n, err = pc.conn.Read(p)
+	if err == io.EOF {
+		pc.sawEOF = true
+	}
+	pc.readLimit -= int64(n)
+	return
+}
+
 // isBroken reports whether this connection is in a known broken state.
 func (pc *persistConn) isBroken() bool {
 	pc.mu.Lock()
@@ -1082,6 +1128,7 @@ func (pc *persistConn) readLoop() {
 
 	alive := true
 	for alive {
+		pc.readLimit = pc.maxHeaderResponseSize()
 		_, err := pc.br.Peek(1)
 		if err != nil {
 			err = beforeRespHeaderError{err}
@@ -1103,6 +1150,9 @@ func (pc *persistConn) readLoop() {
 		}
 
 		if err != nil {
+			if pc.readLimit <= 0 {
+				err = fmt.Errorf("net/http: server response headers exceeded %d bytes; aborted", pc.maxHeaderResponseSize())
+			}
 			// If we won't be able to retry this request later (from the
 			// roundTrip goroutine), mark it as done now.
 			// BEFORE the send on rc.ch, as the client might re-use the
@@ -1120,6 +1170,7 @@ func (pc *persistConn) readLoop() {
 			}
 			return
 		}
+		pc.readLimit = maxInt64 // effictively no limit for response bodies
 
 		pc.mu.Lock()
 		pc.numExpectedResponses--
@@ -1251,6 +1302,7 @@ func (pc *persistConn) readResponse(rc requestAndChan) (resp *Response, err erro
 		}
 	}
 	if resp.StatusCode == 100 {
+		pc.readLimit = pc.maxHeaderResponseSize() // reset the limit
 		resp, err = ReadResponse(pc.br, rc.req)
 		if err != nil {
 			return
@@ -1706,19 +1758,6 @@ func (tlsHandshakeTimeoutError) Timeout() bool   { return true }
 func (tlsHandshakeTimeoutError) Temporary() bool { return true }
 func (tlsHandshakeTimeoutError) Error() string   { return "net/http: TLS handshake timeout" }
 
-type noteEOFReader struct {
-	r      io.Reader
-	sawEOF *bool
-}
-
-func (nr noteEOFReader) Read(p []byte) (n int, err error) {
-	n, err = nr.r.Read(p)
-	if err == io.EOF {
-		*nr.sawEOF = true
-	}
-	return
-}
-
 // fakeLocker is a sync.Locker which does nothing. It's used to guard
 // test-only fields when not under test, to avoid runtime atomic
 // overhead.

src/net/http/transport_test.go

@@ -3090,6 +3090,42 @@ func testTransportReuseConnection_Gzip(t *testing.T, chunked bool) {
 	}
 }
 
+func TestTransportResponseHeaderLength(t *testing.T) {
+	defer afterTest(t)
+	ts := httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {
+		if r.URL.Path == "/long" {
+			w.Header().Set("Long", strings.Repeat("a", 1<<20))
+		}
+	}))
+	defer ts.Close()
+
+	tr := &Transport{
+		MaxResponseHeaderBytes: 512 << 10,
+	}
+	defer tr.CloseIdleConnections()
+	c := &Client{Transport: tr}
+	if res, err := c.Get(ts.URL); err != nil {
+		t.Fatal(err)
+	} else {
+		res.Body.Close()
+	}
+
+	res, err := c.Get(ts.URL + "/long")
+	if err == nil {
+		defer res.Body.Close()
+		var n int64
+		for k, vv := range res.Header {
+			for _, v := range vv {
+				n += int64(len(k)) + int64(len(v))
+			}
+		}
+		t.Fatalf("Unexpected success. Got %v and %d bytes of response headers", res.Status, n)
+	}
+	if want := "server response headers exceeded 524288 bytes"; !strings.Contains(err.Error(), want) {
+		t.Errorf("got error: %v; want %q", err, want)
+	}
+}
+
 var errFakeRoundTrip = errors.New("fake roundtrip")
 
 type funcRoundTripper func()