1 files changed, 81 insertions, 0 deletions
diff --git a/src/internal/poll/sendfile_windows.go b/src/internal/poll/sendfile_windows.go
new file mode 100644
index 0000000..50c3ee8
--- /dev/null
+++ b/src/internal/poll/sendfile_windows.go
@@ -0,0 +1,81 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package poll
+
+import (
+	"io"
+	"syscall"
+)
+
+// SendFile wraps the TransmitFile call.
+func SendFile(fd *FD, src syscall.Handle, n int64) (written int64, err error) {
+	if fd.kind == kindPipe {
+		// TransmitFile does not work with pipes
+		return 0, syscall.ESPIPE
+	}
+
+	if err := fd.writeLock(); err != nil {
+		return 0, err
+	}
+	defer fd.writeUnlock()
+
+	o := &fd.wop
+	o.handle = src
+
+	// TODO(brainman): skip calling syscall.Seek if OS allows it
+	curpos, err := syscall.Seek(o.handle, 0, io.SeekCurrent)
+	if err != nil {
+		return 0, err
+	}
+
+	if n <= 0 { // We don't know the size of the file so infer it.
+		// Find the number of bytes offset from curpos until the end of the file.
+		n, err = syscall.Seek(o.handle, -curpos, io.SeekEnd)
+		if err != nil {
+			return
+		}
+		// Now seek back to the original position.
+		if _, err = syscall.Seek(o.handle, curpos, io.SeekStart); err != nil {
+			return
+		}
+	}
+
+	// TransmitFile can be invoked in one call with at most
+	// 2,147,483,646 bytes: the maximum value for a 32-bit integer minus 1.
+	// See https://docs.microsoft.com/en-us/windows/win32/api/mswsock/nf-mswsock-transmitfile
+	const maxChunkSizePerCall = int64(0x7fffffff - 1)
+
+	for n > 0 {
+		chunkSize := maxChunkSizePerCall
+		if chunkSize > n {
+			chunkSize = n
+		}
+
+		o.qty = uint32(chunkSize)
+		o.o.Offset = uint32(curpos)
+		o.o.OffsetHigh = uint32(curpos >> 32)
+
+		nw, err := 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 {
+			return written, err
+		}
+
+		curpos += int64(nw)
+
+		// Some versions of Windows (Windows 10 1803) do not set
+		// file position after TransmitFile completes.
+		// So just use Seek to set file position.
+		if _, err = syscall.Seek(o.handle, curpos, io.SeekStart); err != nil {
+			return written, err
+		}
+
+		n -= int64(nw)
+		written += int64(nw)
+	}
+
+	return
+}