golang sendfile_unix_alt 代码
文件路径：/src/net/sendfile_unix_alt.go
/ 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.
/go:build (darwin && !ios) || dragonfly || freebsd || solaris
package net
import (
"internal/poll"
"io"
"os"
)
/ 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, DragonFly and Solaris use 0 as the "until EOF" value.
/ If you pass in more bytes than the file contains, it will
/ loop back to the beginning ad nauseam 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/DragonFly/Solaris'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, io.SeekCurrent)
if err != nil {
return 0, err, false
}
sc, err := f.SyscallConn()
if err != nil {
return 0, nil, false
}
var werr error
err = sc.Read(func(fd uintptr) bool {
written, werr = poll.SendFile(&c.pfd, int(fd), pos, remain)
return true
})
if err == nil {
err = werr
}
if lr != nil {
lr.N = remain - written
}
_, err1 := f.Seek(written, io.SeekCurrent)
if err1 != nil && err == nil {
return written, err1, written > 0
}
return written, wrapSyscallError("sendfile", err), written > 0
}