aboutsummaryrefslogtreecommitdiff
path: root/vendor/golang.org/x/crypto/ssh/buffer.go
blob: 1ab07d078db1633be8977102b2defc0da0a6d4e8 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
// Copyright 2012 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 ssh

import (
	"io"
	"sync"
)

// buffer provides a linked list buffer for data exchange
// between producer and consumer. Theoretically the buffer is
// of unlimited capacity as it does no allocation of its own.
type buffer struct {
	// protects concurrent access to head, tail and closed
	*sync.Cond

	head *element // the buffer that will be read first
	tail *element // the buffer that will be read last

	closed bool
}

// An element represents a single link in a linked list.
type element struct {
	buf  []byte
	next *element
}

// newBuffer returns an empty buffer that is not closed.
func newBuffer() *buffer {
	e := new(element)
	b := &buffer{
		Cond: newCond(),
		head: e,
		tail: e,
	}
	return b
}

// write makes buf available for Read to receive.
// buf must not be modified after the call to write.
func (b *buffer) write(buf []byte) {
	b.Cond.L.Lock()
	e := &element{buf: buf}
	b.tail.next = e
	b.tail = e
	b.Cond.Signal()
	b.Cond.L.Unlock()
}

// eof closes the buffer. Reads from the buffer once all
// the data has been consumed will receive io.EOF.
func (b *buffer) eof() {
	b.Cond.L.Lock()
	b.closed = true
	b.Cond.Signal()
	b.Cond.L.Unlock()
}

// Read reads data from the internal buffer in buf.  Reads will block
// if no data is available, or until the buffer is closed.
func (b *buffer) Read(buf []byte) (n int, err error) {
	b.Cond.L.Lock()
	defer b.Cond.L.Unlock()

	for len(buf) > 0 {
		// if there is data in b.head, copy it
		if len(b.head.buf) > 0 {
			r := copy(buf, b.head.buf)
			buf, b.head.buf = buf[r:], b.head.buf[r:]
			n += r
			continue
		}
		// if there is a next buffer, make it the head
		if len(b.head.buf) == 0 && b.head != b.tail {
			b.head = b.head.next
			continue
		}

		// if at least one byte has been copied, return
		if n > 0 {
			break
		}

		// if nothing was read, and there is nothing outstanding
		// check to see if the buffer is closed.
		if b.closed {
			err = io.EOF
			break
		}
		// out of buffers, wait for producer
		b.Cond.Wait()
	}
	return
}