// 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 ft, _ := syscall.GetFileType(src); ft == syscall.FILE_TYPE_PIPE { 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 }