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  		if fi.Mode()&(fs.ModeSymlink|fs.ModeDevice|fs.ModeCharDevice|fs.ModeIrregular) != 0 {
    57  			return 0, nil, false
    58  		}
    59  
    60  		remain = fi.Size()
    61  	}
    62  
    63  	// The other quirk with Darwin/FreeBSD/DragonFly/Solaris's sendfile
    64  	// implementation is that it doesn't use the current position
    65  	// of the file -- if you pass it offset 0, it starts from
    66  	// offset 0. There's no way to tell it "start from current
    67  	// position", so we have to manage that explicitly.
    68  	pos, err := f.Seek(0, io.SeekCurrent)
    69  	if err != nil {
    70  		return 0, err, false
    71  	}
    72  
    73  	sc, err := f.SyscallConn()
    74  	if err != nil {
    75  		return 0, nil, false
    76  	}
    77  
    78  	var werr error
    79  	err = sc.Read(func(fd uintptr) bool {
    80  		written, werr, handled = poll.SendFile(&c.pfd, int(fd), pos, remain)
    81  		return true
    82  	})
    83  	if err == nil {
    84  		err = werr
    85  	}
    86  
    87  	if lr != nil {
    88  		lr.N = remain - written
    89  	}
    90  
    91  	_, err1 := f.Seek(written, io.SeekCurrent)
    92  	if err1 != nil && err == nil {
    93  		return written, err1, handled
    94  	}
    95  
    96  	return written, wrapSyscallError("sendfile", err), handled
    97  }
    98
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