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1 | // Copyright 2012 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 ssh | |
6 | ||
7 | import ( | |
8 | "io" | |
9 | "sync" | |
10 | ) | |
11 | ||
12 | // buffer provides a linked list buffer for data exchange | |
13 | // between producer and consumer. Theoretically the buffer is | |
14 | // of unlimited capacity as it does no allocation of its own. | |
15 | type buffer struct { | |
16 | // protects concurrent access to head, tail and closed | |
17 | *sync.Cond | |
18 | ||
19 | head *element // the buffer that will be read first | |
20 | tail *element // the buffer that will be read last | |
21 | ||
22 | closed bool | |
23 | } | |
24 | ||
25 | // An element represents a single link in a linked list. | |
26 | type element struct { | |
27 | buf []byte | |
28 | next *element | |
29 | } | |
30 | ||
31 | // newBuffer returns an empty buffer that is not closed. | |
32 | func newBuffer() *buffer { | |
33 | e := new(element) | |
34 | b := &buffer{ | |
35 | Cond: newCond(), | |
36 | head: e, | |
37 | tail: e, | |
38 | } | |
39 | return b | |
40 | } | |
41 | ||
42 | // write makes buf available for Read to receive. | |
43 | // buf must not be modified after the call to write. | |
44 | func (b *buffer) write(buf []byte) { | |
45 | b.Cond.L.Lock() | |
46 | e := &element{buf: buf} | |
47 | b.tail.next = e | |
48 | b.tail = e | |
49 | b.Cond.Signal() | |
50 | b.Cond.L.Unlock() | |
51 | } | |
52 | ||
53 | // eof closes the buffer. Reads from the buffer once all | |
54 | // the data has been consumed will receive os.EOF. | |
55 | func (b *buffer) eof() error { | |
56 | b.Cond.L.Lock() | |
57 | b.closed = true | |
58 | b.Cond.Signal() | |
59 | b.Cond.L.Unlock() | |
60 | return nil | |
61 | } | |
62 | ||
63 | // Read reads data from the internal buffer in buf. Reads will block | |
64 | // if no data is available, or until the buffer is closed. | |
65 | func (b *buffer) Read(buf []byte) (n int, err error) { | |
66 | b.Cond.L.Lock() | |
67 | defer b.Cond.L.Unlock() | |
68 | ||
69 | for len(buf) > 0 { | |
70 | // if there is data in b.head, copy it | |
71 | if len(b.head.buf) > 0 { | |
72 | r := copy(buf, b.head.buf) | |
73 | buf, b.head.buf = buf[r:], b.head.buf[r:] | |
74 | n += r | |
75 | continue | |
76 | } | |
77 | // if there is a next buffer, make it the head | |
78 | if len(b.head.buf) == 0 && b.head != b.tail { | |
79 | b.head = b.head.next | |
80 | continue | |
81 | } | |
82 | ||
83 | // if at least one byte has been copied, return | |
84 | if n > 0 { | |
85 | break | |
86 | } | |
87 | ||
88 | // if nothing was read, and there is nothing outstanding | |
89 | // check to see if the buffer is closed. | |
90 | if b.closed { | |
91 | err = io.EOF | |
92 | break | |
93 | } | |
94 | // out of buffers, wait for producer | |
95 | b.Cond.Wait() | |
96 | } | |
97 | return | |
98 | } |