net/http: fix hang in probing for a zero-length request body

Fix a hang that occurs when making a request and all of the following apply:
* The request method is one of GET, HEAD, DELETE, OPTIONS, PROPFIND, or SEARCH.
* The Request.Body is non-nil.
* The content length is not set, or is set to -1.
* Transfer-Encoding: chunked is not set.
* The request body does not respond to a read within 200ms.

In this case, we give up on probing for a zero-length body and send the
request while the probe completes in the background. Fix a bug in the
io.Reader wrapping the in-flight probe: It should return io.EOF after
the probe completes, but does not.

Fixes #47568.

Change-Id: I7f9188c96e1210055df68424081af927006e4816
Reviewed-on: https://go-review.googlesource.com/c/go/+/340256
Trust: Damien Neil <dneil@google.com>
Run-TryBot: Damien Neil <dneil@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ingo Oeser <nightlyone@googlemail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/client_test.go

@@ -2082,3 +2082,47 @@ func (b *issue40382Body) Close() error {
 	}
 	return nil
 }
+
+func TestProbeZeroLengthBody(t *testing.T) {
+	setParallel(t)
+	defer afterTest(t)
+	reqc := make(chan struct{})
+	cst := newClientServerTest(t, false, HandlerFunc(func(w ResponseWriter, r *Request) {
+		close(reqc)
+		if _, err := io.Copy(w, r.Body); err != nil {
+			t.Errorf("error copying request body: %v", err)
+		}
+	}))
+	defer cst.close()
+
+	bodyr, bodyw := io.Pipe()
+	var gotBody string
+	var wg sync.WaitGroup
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		req, _ := NewRequest("GET", cst.ts.URL, bodyr)
+		res, err := cst.c.Do(req)
+		b, err := io.ReadAll(res.Body)
+		if err != nil {
+			t.Error(err)
+		}
+		gotBody = string(b)
+	}()
+
+	select {
+	case <-reqc:
+		// Request should be sent after trying to probe the request body for 200ms.
+	case <-time.After(60 * time.Second):
+		t.Errorf("request not sent after 60s")
+	}
+
+	// Write the request body and wait for the request to complete.
+	const content = "body"
+	bodyw.Write([]byte(content))
+	bodyw.Close()
+	wg.Wait()
+	if gotBody != content {
+		t.Fatalf("server got body %q, want %q", gotBody, content)
+	}
+}

src/net/http/transfer.go

@@ -212,6 +212,7 @@ func (t *transferWriter) probeRequestBody() {
 			rres.b = buf[0]
 		}
 		t.ByteReadCh <- rres
+		close(t.ByteReadCh)
 	}(t.Body)
 	timer := time.NewTimer(200 * time.Millisecond)
 	select {
@@ -1072,6 +1073,9 @@ func (fr finishAsyncByteRead) Read(p []byte) (n int, err error) {
 	if n == 1 {
 		p[0] = rres.b
 	}
+	if err == nil {
+		err = io.EOF
+	}
 	return
 }