sendfile.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  //go:build linux || (darwin && !ios) || dragonfly || freebsd || solaris || windows
     6  
     7  package net
     8  
     9  import (
    10  	"internal/poll"
    11  	"io"
    12  	"syscall"
    13  )
    14  
    15  // sendFile copies the contents of r to c using the sendfile
    16  // system call to minimize copies.
    17  //
    18  // if handled == true, sendFile returns the number (potentially zero) of bytes
    19  // copied and any non-EOF error.
    20  //
    21  // if handled == false, sendFile performed no work.
    22  func sendFile(c *netFD, r io.Reader) (written int64, err error, handled bool) {
    23  	if !supportsSendfile() {
    24  		return 0, nil, false
    25  	}
    26  	var remain int64 = 0 // 0 writes the entire file
    27  	lr, ok := r.(*io.LimitedReader)
    28  	if ok {
    29  		remain, r = lr.N, lr.R
    30  		if remain <= 0 {
    31  			return 0, nil, true
    32  		}
    33  	}
    34  	// r might be an *os.File or an os.fileWithoutWriteTo.
    35  	// Type assert to an interface rather than *os.File directly to handle the latter case.
    36  	f, ok := r.(syscall.Conn)
    37  	if !ok {
    38  		return 0, nil, false
    39  	}
    40  
    41  	sc, err := f.SyscallConn()
    42  	if err != nil {
    43  		return 0, nil, false
    44  	}
    45  
    46  	var werr error
    47  	err = sc.Read(func(fd uintptr) bool {
    48  		written, werr, handled = poll.SendFile(&c.pfd, fd, remain)
    49  		return true
    50  	})
    51  	if err == nil {
    52  		err = werr
    53  	}
    54  
    55  	if lr != nil {
    56  		lr.N = remain - written
    57  	}
    58  
    59  	return written, wrapSyscallError("sendfile", err), handled
    60  }
    61
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