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
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
|
/*
* Copyright (C) 2003-2015 The Music Player Daemon Project
* http://www.musicpd.org
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include "config.h"
#include "RewindInputPlugin.hxx"
#include "../ProxyInputStream.hxx"
#include <assert.h>
#include <string.h>
class RewindInputStream final : public ProxyInputStream {
/**
* The read position within the buffer. Undefined as long as
* ReadingFromBuffer() returns false.
*/
size_t head;
/**
* The write/append position within the buffer.
*/
size_t tail;
/**
* The size of this buffer is the maximum number of bytes
* which can be rewinded cheaply without passing the "seek"
* call to CURL.
*
* The origin of this buffer is always the beginning of the
* stream (offset 0).
*/
char buffer[64 * 1024];
public:
RewindInputStream(InputStream *_input)
:ProxyInputStream(_input),
tail(0) {
}
/* virtual methods from InputStream */
void Update() override {
if (!ReadingFromBuffer())
ProxyInputStream::Update();
}
bool IsEOF() override {
return !ReadingFromBuffer() && ProxyInputStream::IsEOF();
}
size_t Read(void *ptr, size_t size, Error &error) override;
bool Seek(offset_type offset, Error &error) override;
private:
/**
* Are we currently reading from the buffer, and does the
* buffer contain more data for the next read operation?
*/
bool ReadingFromBuffer() const {
return tail > 0 && offset < input.GetOffset();
}
};
size_t
RewindInputStream::Read(void *ptr, size_t read_size, Error &error)
{
if (ReadingFromBuffer()) {
/* buffered read */
assert(head == (size_t)offset);
assert(tail == (size_t)input.GetOffset());
if (read_size > tail - head)
read_size = tail - head;
memcpy(ptr, buffer + head, read_size);
head += read_size;
offset += read_size;
return read_size;
} else {
/* pass method call to underlying stream */
size_t nbytes = input.Read(ptr, read_size, error);
if (input.GetOffset() > (offset_type)sizeof(buffer))
/* disable buffering */
tail = 0;
else if (tail == (size_t)offset) {
/* append to buffer */
memcpy(buffer + tail, ptr, nbytes);
tail += nbytes;
assert(tail == (size_t)input.GetOffset());
}
CopyAttributes();
return nbytes;
}
}
bool
RewindInputStream::Seek(offset_type new_offset,
Error &error)
{
assert(IsReady());
if (tail > 0 && new_offset <= (offset_type)tail) {
/* buffered seek */
assert(!ReadingFromBuffer() ||
head == (size_t)offset);
assert(tail == (size_t)input.GetOffset());
head = (size_t)new_offset;
offset = new_offset;
return true;
} else {
/* disable the buffer, because input has left the
buffered range now */
tail = 0;
return ProxyInputStream::Seek(new_offset, error);
}
}
InputStream *
input_rewind_open(InputStream *is)
{
assert(is != nullptr);
assert(!is->IsReady() || is->GetOffset() == 0);
if (is->IsReady() && is->IsSeekable())
/* seekable resources don't need this plugin */
return is;
return new RewindInputStream(is);
}
|
