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      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 package net
      6 
      7 import (
      8 	"io"
      9 	"os"
     10 	"syscall"
     11 )
     12 
     13 // maxSendfileSize is the largest chunk size we ask the kernel to copy
     14 // at a time.
     15 const maxSendfileSize int = 4 << 20
     16 
     17 // sendFile copies the contents of r to c using the sendfile
     18 // system call to minimize copies.
     19 //
     20 // if handled == true, sendFile returns the number of bytes copied and any
     21 // non-EOF error.
     22 //
     23 // if handled == false, sendFile performed no work.
     24 func sendFile(c *netFD, r io.Reader) (written int64, err error, handled bool) {
     25 	var remain int64 = 1 << 62 // by default, copy until EOF
     26 
     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 	f, ok := r.(*os.File)
     35 	if !ok {
     36 		return 0, nil, false
     37 	}
     38 
     39 	if err := c.writeLock(); err != nil {
     40 		return 0, err, true
     41 	}
     42 	defer c.writeUnlock()
     43 
     44 	dst := c.sysfd
     45 	src := int(f.Fd())
     46 	for remain > 0 {
     47 		n := maxSendfileSize
     48 		if int64(n) > remain {
     49 			n = int(remain)
     50 		}
     51 		n, err1 := syscall.Sendfile(dst, src, nil, n)
     52 		if n > 0 {
     53 			written += int64(n)
     54 			remain -= int64(n)
     55 		}
     56 		if n == 0 && err1 == nil {
     57 			break
     58 		}
     59 		if err1 == syscall.EAGAIN {
     60 			if err1 = c.pd.WaitWrite(); err1 == nil {
     61 				continue
     62 			}
     63 		}
     64 		if err1 != nil {
     65 			// This includes syscall.ENOSYS (no kernel
     66 			// support) and syscall.EINVAL (fd types which
     67 			// don't implement sendfile)
     68 			err = err1
     69 			break
     70 		}
     71 	}
     72 	if lr != nil {
     73 		lr.N = remain
     74 	}
     75 	if err != nil {
     76 		err = os.NewSyscallError("sendfile", err)
     77 	}
     78 	return written, err, written > 0
     79 }
     80