sendfile_windows.go

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package poll
     6  
     7  import (
     8  	"io"
     9  	"syscall"
    10  )
    11  
    12  // SendFile wraps the TransmitFile call.
    13  func SendFile(fd *FD, src syscall.Handle, n int64) (written int64, err error) {
    14  	defer func() {
    15  		TestHookDidSendFile(fd, 0, written, err, written > 0)
    16  	}()
    17  	if fd.kind == kindPipe {
    18  		// TransmitFile does not work with pipes
    19  		return 0, syscall.ESPIPE
    20  	}
    21  	if ft, _ := syscall.GetFileType(src); ft == syscall.FILE_TYPE_PIPE {
    22  		return 0, syscall.ESPIPE
    23  	}
    24  
    25  	if err := fd.writeLock(); err != nil {
    26  		return 0, err
    27  	}
    28  	defer fd.writeUnlock()
    29  
    30  	o := &fd.wop
    31  	o.handle = src
    32  
    33  	// TODO(brainman): skip calling syscall.Seek if OS allows it
    34  	curpos, err := syscall.Seek(o.handle, 0, io.SeekCurrent)
    35  	if err != nil {
    36  		return 0, err
    37  	}
    38  
    39  	if n <= 0 { // We don't know the size of the file so infer it.
    40  		// Find the number of bytes offset from curpos until the end of the file.
    41  		n, err = syscall.Seek(o.handle, -curpos, io.SeekEnd)
    42  		if err != nil {
    43  			return
    44  		}
    45  		// Now seek back to the original position.
    46  		if _, err = syscall.Seek(o.handle, curpos, io.SeekStart); err != nil {
    47  			return
    48  		}
    49  	}
    50  
    51  	// TransmitFile can be invoked in one call with at most
    52  	// 2,147,483,646 bytes: the maximum value for a 32-bit integer minus 1.
    53  	// See https://docs.microsoft.com/en-us/windows/win32/api/mswsock/nf-mswsock-transmitfile
    54  	const maxChunkSizePerCall = int64(0x7fffffff - 1)
    55  
    56  	for n > 0 {
    57  		chunkSize := maxChunkSizePerCall
    58  		if chunkSize > n {
    59  			chunkSize = n
    60  		}
    61  
    62  		o.qty = uint32(chunkSize)
    63  		o.o.Offset = uint32(curpos)
    64  		o.o.OffsetHigh = uint32(curpos >> 32)
    65  
    66  		nw, err := execIO(o, func(o *operation) error {
    67  			return syscall.TransmitFile(o.fd.Sysfd, o.handle, o.qty, 0, &o.o, nil, syscall.TF_WRITE_BEHIND)
    68  		})
    69  		if err != nil {
    70  			return written, err
    71  		}
    72  
    73  		curpos += int64(nw)
    74  
    75  		// Some versions of Windows (Windows 10 1803) do not set
    76  		// file position after TransmitFile completes.
    77  		// So just use Seek to set file position.
    78  		if _, err = syscall.Seek(o.handle, curpos, io.SeekStart); err != nil {
    79  			return written, err
    80  		}
    81  
    82  		n -= int64(nw)
    83  		written += int64(nw)
    84  	}
    85  
    86  	return
    87  }
    88
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