sendfile_unix_alt.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 (darwin && !ios) || dragonfly || freebsd || solaris
     6  
     7  package net
     8  
     9  import (
    10  	"internal/poll"
    11  	"io"
    12  	"os"
    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  	// Darwin, FreeBSD, DragonFly and Solaris use 0 as the "until EOF" value.
    24  	// If you pass in more bytes than the file contains, it will
    25  	// loop back to the beginning ad nauseam until it's sent
    26  	// exactly the number of bytes told to. As such, we need to
    27  	// know exactly how many bytes to send.
    28  	var remain int64 = 0
    29  
    30  	lr, ok := r.(*io.LimitedReader)
    31  	if ok {
    32  		remain, r = lr.N, lr.R
    33  		if remain <= 0 {
    34  			return 0, nil, true
    35  		}
    36  	}
    37  	f, ok := r.(*os.File)
    38  	if !ok {
    39  		return 0, nil, false
    40  	}
    41  
    42  	if remain == 0 {
    43  		fi, err := f.Stat()
    44  		if err != nil {
    45  			return 0, err, false
    46  		}
    47  
    48  		remain = fi.Size()
    49  	}
    50  
    51  	// The other quirk with Darwin/FreeBSD/DragonFly/Solaris's sendfile
    52  	// implementation is that it doesn't use the current position
    53  	// of the file -- if you pass it offset 0, it starts from
    54  	// offset 0. There's no way to tell it "start from current
    55  	// position", so we have to manage that explicitly.
    56  	pos, err := f.Seek(0, io.SeekCurrent)
    57  	if err != nil {
    58  		return 0, err, false
    59  	}
    60  
    61  	sc, err := f.SyscallConn()
    62  	if err != nil {
    63  		return 0, nil, false
    64  	}
    65  
    66  	var werr error
    67  	err = sc.Read(func(fd uintptr) bool {
    68  		written, werr, handled = poll.SendFile(&c.pfd, int(fd), pos, remain)
    69  		return true
    70  	})
    71  	if err == nil {
    72  		err = werr
    73  	}
    74  
    75  	if lr != nil {
    76  		lr.N = remain - written
    77  	}
    78  
    79  	_, err1 := f.Seek(written, io.SeekCurrent)
    80  	if err1 != nil && err == nil {
    81  		return written, err1, handled
    82  	}
    83  
    84  	return written, wrapSyscallError("sendfile", err), handled
    85  }
    86
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