net/http: don't reuse conns after incomplete 100-continue requests

If we receive an HTTP request with "Expect: 100-continue" and the
Handler never read to EOF, the conn is in an unknown state.
Don't reuse that connection.

Fixes #11549

Change-Id: I5be93e7a54e899d615b05f72bdcf12b25304bc60
Reviewed-on: https://go-review.googlesource.com/12262Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/serve_test.go

@@ -2991,6 +2991,49 @@ func TestTolerateCRLFBeforeRequestLine(t *testing.T) {
 	}
 }
 
+func TestIssue11549_Expect100(t *testing.T) {
+	req := reqBytes(`PUT /readbody HTTP/1.1
+User-Agent: PycURL/7.22.0
+Host: 127.0.0.1:9000
+Accept: */*
+Expect: 100-continue
+Content-Length: 10
+
+HelloWorldPUT /noreadbody HTTP/1.1
+User-Agent: PycURL/7.22.0
+Host: 127.0.0.1:9000
+Accept: */*
+Expect: 100-continue
+Content-Length: 10
+
+GET /should-be-ignored HTTP/1.1
+Host: foo
+
+`)
+	var buf bytes.Buffer
+	conn := &rwTestConn{
+		Reader: bytes.NewReader(req),
+		Writer: &buf,
+		closec: make(chan bool, 1),
+	}
+	ln := &oneConnListener{conn: conn}
+	numReq := 0
+	go Serve(ln, HandlerFunc(func(w ResponseWriter, r *Request) {
+		numReq++
+		if r.URL.Path == "/readbody" {
+			ioutil.ReadAll(r.Body)
+		}
+		io.WriteString(w, "Hello world!")
+	}))
+	<-conn.closec
+	if numReq != 2 {
+		t.Errorf("num requests = %d; want 2", numReq)
+	}
+	if !strings.Contains(buf.String(), "Connection: close\r\n") {
+		t.Errorf("expected 'Connection: close' in response; got: %s", buf.String())
+	}
+}
+
 func BenchmarkClientServer(b *testing.B) {
 	b.ReportAllocs()
 	b.StopTimer()

src/net/http/server.go

@@ -554,6 +554,7 @@ type expectContinueReader struct {
 	resp       *response
 	readCloser io.ReadCloser
 	closed     bool
+	sawEOF     bool
 }
 
 func (ecr *expectContinueReader) Read(p []byte) (n int, err error) {
@@ -565,7 +566,11 @@ func (ecr *expectContinueReader) Read(p []byte) (n int, err error) {
 		ecr.resp.conn.buf.WriteString("HTTP/1.1 100 Continue\r\n\r\n")
 		ecr.resp.conn.buf.Flush()
 	}
-	return ecr.readCloser.Read(p)
+	n, err = ecr.readCloser.Read(p)
+	if err == io.EOF {
+		ecr.sawEOF = true
+	}
+	return
 }
 
 func (ecr *expectContinueReader) Close() error {
@@ -846,6 +851,22 @@ func (cw *chunkWriter) writeHeader(p []byte) {
 		w.closeAfterReply = true
 	}
 
+	// If the client wanted a 100-continue but we never sent it to
+	// them (or, more strictly: we never finished reading their
+	// request body), don't reuse this connection because it's now
+	// in an unknown state: we might be sending this response at
+	// the same time the client is now sending its request body
+	// after a timeout.  (Some HTTP clients send Expect:
+	// 100-continue but knowing that some servers don't support
+	// it, the clients set a timer and send the body later anyway)
+	// If we haven't seen EOF, we can't skip over the unread body
+	// because we don't know if the next bytes on the wire will be
+	// the body-following-the-timer or the subsequent request.
+	// See Issue 11549.
+	if ecr, ok := w.req.Body.(*expectContinueReader); ok && !ecr.sawEOF {
+		w.closeAfterReply = true
+	}
+
 	// Per RFC 2616, we should consume the request body before
 	// replying, if the handler hasn't already done so.  But we
 	// don't want to do an unbounded amount of reading here for