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      1 // Copyright 2015 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 package net
      6 
      7 import (
      8 	"io"
      9 	"os"
     10 	"syscall"
     11 )
     12 
     13 // Not strictly needed, but very helpful for debugging, see issue #10221.
     14 //go:cgo_import_dynamic _ _ "libsendfile.so"
     15 //go:cgo_import_dynamic _ _ "libsocket.so"
     16 
     17 // maxSendfileSize is the largest chunk size we ask the kernel to copy
     18 // at a time.
     19 const maxSendfileSize int = 4 << 20
     20 
     21 // sendFile copies the contents of r to c using the sendfile
     22 // system call to minimize copies.
     23 //
     24 // if handled == true, sendFile returns the number of bytes copied and any
     25 // non-EOF error.
     26 //
     27 // if handled == false, sendFile performed no work.
     28 func sendFile(c *netFD, r io.Reader) (written int64, err error, handled bool) {
     29 	// Solaris uses 0 as the "until EOF" value. If you pass in more bytes than the
     30 	// file contains, it will loop back to the beginning ad nauseam until it's sent
     31 	// exactly the number of bytes told to. As such, we need to know exactly how many
     32 	// bytes to send.
     33 	var remain int64 = 0
     34 
     35 	lr, ok := r.(*io.LimitedReader)
     36 	if ok {
     37 		remain, r = lr.N, lr.R
     38 		if remain <= 0 {
     39 			return 0, nil, true
     40 		}
     41 	}
     42 	f, ok := r.(*os.File)
     43 	if !ok {
     44 		return 0, nil, false
     45 	}
     46 
     47 	if remain == 0 {
     48 		fi, err := f.Stat()
     49 		if err != nil {
     50 			return 0, err, false
     51 		}
     52 
     53 		remain = fi.Size()
     54 	}
     55 
     56 	// The other quirk with Solaris's sendfile implementation is that it doesn't
     57 	// use the current position of the file -- if you pass it offset 0, it starts
     58 	// from offset 0. There's no way to tell it "start from current position", so
     59 	// we have to manage that explicitly.
     60 	pos, err := f.Seek(0, os.SEEK_CUR)
     61 	if err != nil {
     62 		return 0, err, false
     63 	}
     64 
     65 	if err := c.writeLock(); err != nil {
     66 		return 0, err, true
     67 	}
     68 	defer c.writeUnlock()
     69 
     70 	dst := c.sysfd
     71 	src := int(f.Fd())
     72 	for remain > 0 {
     73 		n := maxSendfileSize
     74 		if int64(n) > remain {
     75 			n = int(remain)
     76 		}
     77 		pos1 := pos
     78 		n, err1 := syscall.Sendfile(dst, src, &pos1, n)
     79 		if n > 0 {
     80 			pos += int64(n)
     81 			written += int64(n)
     82 			remain -= int64(n)
     83 		}
     84 		if n == 0 && err1 == nil {
     85 			break
     86 		}
     87 		if err1 == syscall.EAGAIN {
     88 			if err1 = c.pd.WaitWrite(); err1 == nil {
     89 				continue
     90 			}
     91 		}
     92 		if err1 == syscall.EINTR {
     93 			continue
     94 		}
     95 		if err1 != nil {
     96 			// This includes syscall.ENOSYS (no kernel
     97 			// support) and syscall.EINVAL (fd types which
     98 			// don't implement sendfile)
     99 			err = err1
    100 			break
    101 		}
    102 	}
    103 	if lr != nil {
    104 		lr.N = remain
    105 	}
    106 	if err != nil {
    107 		err = os.NewSyscallError("sendfile", err)
    108 	}
    109 	return written, err, written > 0
    110 }
    111