sendfile_windows.go

Documentation: internal/poll

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