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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package net
import (
"io"
"os"
"syscall"
)
// maxSendfileSize is the largest chunk size we ask the kernel to copy
// at a time.
const maxSendfileSize int = 4 << 20
// sendFile copies the contents of r to c using the sendfile
// system call to minimize copies.
//
// if handled == true, sendFile returns the number of bytes copied and any
// non-EOF error.
//
// if handled == false, sendFile performed no work.
func sendFile(c *netFD, r io.Reader) (written int64, err error, handled bool) {
// FreeBSD uses 0 as the "until EOF" value. If you pass in more bytes than the
// file contains, it will loop back to the beginning ad nauseum until it's sent
// exactly the number of bytes told to. As such, we need to know exactly how many
// bytes to send.
var remain int64 = 0
lr, ok := r.(*io.LimitedReader)
if ok {
remain, r = lr.N, lr.R
if remain <= 0 {
return 0, nil, true
}
}
f, ok := r.(*os.File)
if !ok {
return 0, nil, false
}
if remain == 0 {
fi, err := f.Stat()
if err != nil {
return 0, err, false
}
remain = fi.Size()
}
// The other quirk with FreeBSD's sendfile implementation is that it doesn't
// use the current position of the file -- if you pass it offset 0, it starts
// from offset 0. There's no way to tell it "start from current position", so
// we have to manage that explicitly.
pos, err := f.Seek(0, os.SEEK_CUR)
if err != nil {
return 0, err, false
}
c.wio.Lock()
defer c.wio.Unlock()
if err := c.incref(false); err != nil {
return 0, err, true
}
defer c.decref()
dst := c.sysfd
src := int(f.Fd())
for remain > 0 {
n := maxSendfileSize
if int64(n) > remain {
n = int(remain)
}
pos1 := pos
n, err1 := syscall.Sendfile(dst, src, &pos1, n)
if n > 0 {
pos += int64(n)
written += int64(n)
remain -= int64(n)
}
if n == 0 && err1 == nil {
break
}
if err1 == syscall.EAGAIN {
if err1 = c.pollServer.WaitWrite(c); err1 == nil {
continue
}
}
if err1 == syscall.EINTR {
continue
}
if err1 != nil {
// This includes syscall.ENOSYS (no kernel
// support) and syscall.EINVAL (fd types which
// don't implement sendfile together)
err = &OpError{"sendfile", c.net, c.raddr, err1}
break
}
}
if lr != nil {
lr.N = remain
}
return written, err, written > 0
}
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