net/http: rewind request body unconditionally

When http2 fails with ErrNoCachedConn the request is retried with body
that has already been read.

Fixes #25009

Change-Id: I51ed5c8cf469dd8b17c73fff6140ab80162bf267
Reviewed-on: https://go-review.googlesource.com/c/131755
Run-TryBot: Iskander Sharipov <iskander.sharipov@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/transport.go

@@ -478,9 +478,8 @@ func (t *Transport) roundTrip(req *Request) (*Response, error) {
 		}
 		testHookRoundTripRetried()
 
-		// Rewind the body if we're able to.  (HTTP/2 does this itself so we only
-		// need to do it for HTTP/1.1 connections.)
-		if req.GetBody != nil && pconn.alt == nil {
+		// Rewind the body if we're able to.
+		if req.GetBody != nil {
 			newReq := *req
 			var err error
 			newReq.Body, err = req.GetBody()

src/net/http/transport_internal_test.go

@@ -7,8 +7,13 @@
 package http
 
 import (
+	"bytes"
+	"crypto/tls"
 	"errors"
+	"io"
+	"io/ioutil"
 	"net"
+	"net/http/internal"
 	"strings"
 	"testing"
 )
@@ -178,3 +183,81 @@ func TestTransportShouldRetryRequest(t *testing.T) {
 		}
 	}
 }
+
+type roundTripFunc func(r *Request) (*Response, error)
+
+func (f roundTripFunc) RoundTrip(r *Request) (*Response, error) {
+	return f(r)
+}
+
+// Issue 25009
+func TestTransportBodyAltRewind(t *testing.T) {
+	cert, err := tls.X509KeyPair(internal.LocalhostCert, internal.LocalhostKey)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ln := newLocalListener(t)
+	defer ln.Close()
+
+	go func() {
+		tln := tls.NewListener(ln, &tls.Config{
+			NextProtos:   []string{"foo"},
+			Certificates: []tls.Certificate{cert},
+		})
+		for i := 0; i < 2; i++ {
+			sc, err := tln.Accept()
+			if err != nil {
+				t.Error(err)
+				return
+			}
+			if err := sc.(*tls.Conn).Handshake(); err != nil {
+				t.Error(err)
+				return
+			}
+			sc.Close()
+		}
+	}()
+
+	addr := ln.Addr().String()
+	req, _ := NewRequest("POST", "https://example.org/", bytes.NewBufferString("request"))
+	roundTripped := false
+	tr := &Transport{
+		DisableKeepAlives: true,
+		TLSNextProto: map[string]func(string, *tls.Conn) RoundTripper{
+			"foo": func(authority string, c *tls.Conn) RoundTripper {
+				return roundTripFunc(func(r *Request) (*Response, error) {
+					n, _ := io.Copy(ioutil.Discard, r.Body)
+					if n == 0 {
+						t.Error("body length is zero")
+					}
+					if roundTripped {
+						return &Response{
+							Body:       NoBody,
+							StatusCode: 200,
+						}, nil
+					}
+					roundTripped = true
+					return nil, http2noCachedConnError{}
+				})
+			},
+		},
+		DialTLS: func(_, _ string) (net.Conn, error) {
+			tc, err := tls.Dial("tcp", addr, &tls.Config{
+				InsecureSkipVerify: true,
+				NextProtos:         []string{"foo"},
+			})
+			if err != nil {
+				return nil, err
+			}
+			if err := tc.Handshake(); err != nil {
+				return nil, err
+			}
+			return tc, nil
+		},
+	}
+	c := &Client{Transport: tr}
+	_, err = c.Do(req)
+	if err != nil {
+		t.Error(err)
+	}
+}