[release-branch.go1.11] internal/poll: advance file position in windows sendfile

Some versions of Windows (Windows 10 1803) do not set file
position after TransmitFile completes. So just use Seek
to set file position before returning from sendfile.

Fixes #27411

Change-Id: I7a49be10304b5db19dda707b13ac93d338aeb190
Reviewed-on: https://go-review.googlesource.com/131976
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Yasuhiro MATSUMOTO <mattn.jp@gmail.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-on: https://go-review.googlesource.com/c/145779
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>

diff --git a/src/internal/poll/sendfile_windows.go b/src/internal/poll/sendfile_windows.go
index dc93e851d63a459fa599e8307eb48dedf6a188db..17a3681064b66df8da5a3f2f3a25f5fd2076c5b8 100644 (file)
--- a/src/internal/poll/sendfile_windows.go
+++ b/src/internal/poll/sendfile_windows.go
@@ -38,5 +38,11 @@ func SendFile(fd *FD, src syscall.Handle, n int64) (int64, error) {
        done, err := wsrv.ExecIO(o, func(o *operation) error {
                return syscall.TransmitFile(o.fd.Sysfd, o.handle, o.qty, 0, &o.o, nil, syscall.TF_WRITE_BEHIND)
        })
+       if err == nil {
+               // Some versions of Windows (Windows 10 1803) do not set
+               // file position after TransmitFile completes.
+               // So just use Seek to set file position.
+               _, err = syscall.Seek(o.handle, curpos+int64(done), 0)
+       }
        return int64(done), err
 }