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
7package net
8
9import (
10	"internal/poll"
11	"io"
12	"io/fs"
13	"syscall"
14)
15
16const 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.
25func 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
57		remain = fi.Size()
58	}
59
60	// The other quirk with Darwin/FreeBSD/DragonFly/Solaris's sendfile
61	// implementation is that it doesn't use the current position
62	// of the file -- if you pass it offset 0, it starts from
63	// offset 0. There's no way to tell it "start from current
64	// position", so we have to manage that explicitly.
65	pos, err := f.Seek(0, io.SeekCurrent)
66	if err != nil {
67		return 0, err, false
68	}
69
70	sc, err := f.SyscallConn()
71	if err != nil {
72		return 0, nil, false
73	}
74
75	var werr error
76	err = sc.Read(func(fd uintptr) bool {
77		written, werr, handled = poll.SendFile(&c.pfd, int(fd), pos, remain)
78		return true
79	})
80	if err == nil {
81		err = werr
82	}
83
84	if lr != nil {
85		lr.N = remain - written
86	}
87
88	_, err1 := f.Seek(written, io.SeekCurrent)
89	if err1 != nil && err == nil {
90		return written, err1, handled
91	}
92
93	return written, wrapSyscallError("sendfile", err), handled
94}
95