net: implement Buffers on windows

Updates #13451

Change-Id: I2c3c66d9532c16e616c476e2afe31b3ddc0a8d79
Reviewed-on: https://go-review.googlesource.com/32371Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>

src/net/fd_windows.go

@@ -96,6 +96,7 @@ type operation struct {
 	rsan   int32
 	handle syscall.Handle
 	flags  uint32
+	bufs   []syscall.WSABuf
 }
 
 func (o *operation) InitBuf(buf []byte) {
@@ -106,6 +107,30 @@ func (o *operation) InitBuf(buf []byte) {
 	}
 }
 
+func (o *operation) InitBufs(buf *Buffers) {
+	if o.bufs == nil {
+		o.bufs = make([]syscall.WSABuf, 0, len(*buf))
+	} else {
+		o.bufs = o.bufs[:0]
+	}
+	for _, b := range *buf {
+		var p *byte
+		if len(b) > 0 {
+			p = &b[0]
+		}
+		o.bufs = append(o.bufs, syscall.WSABuf{uint32(len(b)), p})
+	}
+}
+
+// ClearBufs clears all pointers to Buffers parameter captured
+// by InitBufs, so it can be released by garbage collector.
+func (o *operation) ClearBufs() {
+	for i := range o.bufs {
+		o.bufs[i].Buf = nil
+	}
+	o.bufs = o.bufs[:0]
+}
+
 // ioSrv executes net IO requests.
 type ioSrv struct {
 	req chan ioSrvReq
@@ -484,6 +509,42 @@ func (fd *netFD) Write(buf []byte) (int, error) {
 	return n, err
 }
 
+func (c *conn) writeBuffers(v *Buffers) (int64, error) {
+	if !c.ok() {
+		return 0, syscall.EINVAL
+	}
+	n, err := c.fd.writeBuffers(v)
+	if err != nil {
+		return n, &OpError{Op: "WSASend", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
+	}
+	return n, nil
+}
+
+func (fd *netFD) writeBuffers(buf *Buffers) (int64, error) {
+	if len(*buf) == 0 {
+		return 0, nil
+	}
+	if err := fd.writeLock(); err != nil {
+		return 0, err
+	}
+	defer fd.writeUnlock()
+	if race.Enabled {
+		race.ReleaseMerge(unsafe.Pointer(&ioSync))
+	}
+	o := &fd.wop
+	o.InitBufs(buf)
+	n, err := wsrv.ExecIO(o, "WSASend", func(o *operation) error {
+		return syscall.WSASend(o.fd.sysfd, &o.bufs[0], uint32(len(*buf)), &o.qty, 0, &o.o, nil)
+	})
+	o.ClearBufs()
+	if _, ok := err.(syscall.Errno); ok {
+		err = os.NewSyscallError("wsasend", err)
+	}
+	testHookDidWritev(n)
+	buf.consume(int64(n))
+	return int64(n), err
+}
+
 func (fd *netFD) writeTo(buf []byte, sa syscall.Sockaddr) (int, error) {
 	if len(buf) == 0 {
 		return 0, nil

src/net/writev_test.go

@@ -150,18 +150,27 @@ func testBuffer_writeTo(t *testing.T, chunks int, useCopy bool) {
 		}
 
 		var wantSum int
-		var wantMinCalls int
 		switch runtime.GOOS {
 		case "darwin", "dragonfly", "freebsd", "linux", "netbsd", "openbsd":
+			var wantMinCalls int
 			wantSum = want.Len()
 			v := chunks
 			for v > 0 {
 				wantMinCalls++
 				v -= 1024
 			}
-		}
-		if len(writeLog.log) < wantMinCalls {
-			t.Errorf("write calls = %v < wanted min %v", len(writeLog.log), wantMinCalls)
+			if len(writeLog.log) < wantMinCalls {
+				t.Errorf("write calls = %v < wanted min %v", len(writeLog.log), wantMinCalls)
+			}
+		case "windows":
+			var wantCalls int
+			wantSum = want.Len()
+			if wantSum > 0 {
+				wantCalls = 1 // windows will always do 1 syscall, unless sending empty buffer
+			}
+			if len(writeLog.log) != wantCalls {
+				t.Errorf("write calls = %v; want %v", len(writeLog.log), wantCalls)
+			}
 		}
 		if gotSum != wantSum {
 			t.Errorf("writev call sum  = %v; want %v", gotSum, wantSum)
@@ -171,6 +180,10 @@ func testBuffer_writeTo(t *testing.T, chunks int, useCopy bool) {
 }
 
 func TestWritevError(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skipf("skipping the test: windows does not have problem sending large chunks of data")
+	}
+
 	ln, err := newLocalListener("tcp")
 	if err != nil {
 		t.Fatal(err)