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