internal/poll: do not use Windows TransmitFile with pipes

It appears that TransmitFile Windows API does not work with Windows
pipes. So just copy data from pipe and into TCP connection manually.

Fixes #22278

Change-Id: I4810caca5345eac5bffb3176956689b8ae993256
Reviewed-on: https://go-review.googlesource.com/79775
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/internal/poll/sendfile_windows.go

@@ -8,6 +8,15 @@ import "syscall"
 
 // SendFile wraps the TransmitFile call.
 func SendFile(fd *FD, src syscall.Handle, n int64) (int64, error) {
+	ft, err := syscall.GetFileType(src)
+	if err != nil {
+		return 0, err
+	}
+	// TransmitFile does not work with pipes
+	if ft == syscall.FILE_TYPE_PIPE {
+		return 0, syscall.ESPIPE
+	}
+
 	if err := fd.writeLock(); err != nil {
 		return 0, err
 	}

src/net/tcpsock_test.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"internal/testenv"
 	"io"
+	"os"
 	"reflect"
 	"runtime"
 	"sync"
@@ -722,3 +723,74 @@ func TestTCPBig(t *testing.T) {
 		})
 	}
 }
+
+func TestCopyPipeIntoTCP(t *testing.T) {
+	ln, err := newLocalListener("tcp")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer ln.Close()
+
+	errc := make(chan error, 1)
+	defer func() {
+		if err := <-errc; err != nil {
+			t.Error(err)
+		}
+	}()
+	go func() {
+		c, err := ln.Accept()
+		if err != nil {
+			errc <- err
+			return
+		}
+		defer c.Close()
+
+		buf := make([]byte, 100)
+		n, err := io.ReadFull(c, buf)
+		if err != io.ErrUnexpectedEOF || n != 2 {
+			errc <- fmt.Errorf("got err=%q n=%v; want err=%q n=2", err, n, io.ErrUnexpectedEOF)
+			return
+		}
+
+		errc <- nil
+	}()
+
+	c, err := Dial("tcp", ln.Addr().String())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer c.Close()
+
+	r, w, err := os.Pipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer r.Close()
+
+	errc2 := make(chan error, 1)
+	defer func() {
+		if err := <-errc2; err != nil {
+			t.Error(err)
+		}
+	}()
+
+	defer w.Close()
+
+	go func() {
+		_, err := io.Copy(c, r)
+		errc2 <- err
+	}()
+
+	// Split write into 2 packets. That makes Windows TransmitFile
+	// drop second packet.
+	packet := make([]byte, 1)
+	_, err = w.Write(packet)
+	if err != nil {
+		t.Fatal(err)
+	}
+	time.Sleep(100 * time.Millisecond)
+	_, err = w.Write(packet)
+	if err != nil {
+		t.Fatal(err)
+	}
+}