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  	"io/fs"
    13  	"syscall"
    14  )
    15  
    16  const supportsSendfile = true
    17  
    18  // sendFile copies the contents of r to c using the sendfile
    19  // system call to minimize copies.
    20  //
    21  // if handled == true, sendFile returns the number (potentially zero) of bytes
    22  // copied and any non-EOF error.
    23  //
    24  // if handled == false, sendFile performed no work.
    25  func sendFile(c *netFD, r io.Reader) (written int64, err error, handled bool) {
    26  	// Darwin, FreeBSD, DragonFly and Solaris use 0 as the "until EOF" value.
    27  	// If you pass in more bytes than the file contains, it will
    28  	// loop back to the beginning ad nauseam until it's sent
    29  	// exactly the number of bytes told to. As such, we need to
    30  	// know exactly how many bytes to send.
    31  	var remain int64 = 0
    32  
    33  	lr, ok := r.(*io.LimitedReader)
    34  	if ok {
    35  		remain, r = lr.N, lr.R
    36  		if remain <= 0 {
    37  			return 0, nil, true
    38  		}
    39  	}
    40  	// r might be an *os.File or an os.fileWithoutWriteTo.
    41  	// Type assert to an interface rather than *os.File directly to handle the latter case.
    42  	f, ok := r.(interface {
    43  		fs.File
    44  		io.Seeker
    45  		syscall.Conn
    46  	})
    47  	if !ok {
    48  		return 0, nil, false
    49  	}
    50  
    51  	if remain == 0 {
    52  		fi, err := f.Stat()
    53  		if err != nil {
    54  			return 0, err, false
    55  		}
    56  
    57  		remain = fi.Size()
    58  	}
    59  
    60  	// The other quirk with Darwin/FreeBSD/DragonFly/Solaris's sendfile
    61  	// implementation is that it doesn't use the current position
    62  	// of the file -- if you pass it offset 0, it starts from
    63  	// offset 0. There's no way to tell it "start from current
    64  	// position", so we have to manage that explicitly.
    65  	pos, err := f.Seek(0, io.SeekCurrent)
    66  	if err != nil {
    67  		return 0, err, false
    68  	}
    69  
    70  	sc, err := f.SyscallConn()
    71  	if err != nil {
    72  		return 0, nil, false
    73  	}
    74  
    75  	var werr error
    76  	err = sc.Read(func(fd uintptr) bool {
    77  		written, werr, handled = poll.SendFile(&c.pfd, int(fd), pos, remain)
    78  		return true
    79  	})
    80  	if err == nil {
    81  		err = werr
    82  	}
    83  
    84  	if lr != nil {
    85  		lr.N = remain - written
    86  	}
    87  
    88  	_, err1 := f.Seek(written, io.SeekCurrent)
    89  	if err1 != nil && err == nil {
    90  		return written, err1, handled
    91  	}
    92  
    93  	return written, wrapSyscallError("sendfile", err), handled
    94  }
    95
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