github.com/JimmyHuang454/JLS-go@v0.0.0-20230831150107-90d536585ba0/internal/poll/sendfile_bsd.go (about)

     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  //go:build darwin || dragonfly || freebsd
     6  
     7  package poll
     8  
     9  import "syscall"
    10  
    11  // maxSendfileSize is the largest chunk size we ask the kernel to copy
    12  // at a time.
    13  const maxSendfileSize int = 4 << 20
    14  
    15  // SendFile wraps the sendfile system call.
    16  func SendFile(dstFD *FD, src int, pos, remain int64) (int64, error) {
    17  	if err := dstFD.writeLock(); err != nil {
    18  		return 0, err
    19  	}
    20  	defer dstFD.writeUnlock()
    21  	if err := dstFD.pd.prepareWrite(dstFD.isFile); err != nil {
    22  		return 0, err
    23  	}
    24  
    25  	dst := dstFD.Sysfd
    26  	var written int64
    27  	var err error
    28  	for remain > 0 {
    29  		n := maxSendfileSize
    30  		if int64(n) > remain {
    31  			n = int(remain)
    32  		}
    33  		pos1 := pos
    34  		n, err1 := syscall.Sendfile(dst, src, &pos1, n)
    35  		if n > 0 {
    36  			pos += int64(n)
    37  			written += int64(n)
    38  			remain -= int64(n)
    39  		} else if n == 0 && err1 == nil {
    40  			break
    41  		}
    42  		if err1 == syscall.EINTR {
    43  			continue
    44  		}
    45  		if err1 == syscall.EAGAIN {
    46  			if err1 = dstFD.pd.waitWrite(dstFD.isFile); err1 == nil {
    47  				continue
    48  			}
    49  		}
    50  		if err1 != nil {
    51  			// This includes syscall.ENOSYS (no kernel
    52  			// support) and syscall.EINVAL (fd types which
    53  			// don't implement sendfile)
    54  			err = err1
    55  			break
    56  		}
    57  	}
    58  	return written, err
    59  }