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1 /* | |
2 * Copyright 2013 Google Inc. | |
3 * | |
4 * Use of this source code is governed by a BSD-style license that can be | |
5 * found in the LICENSE file. | |
6 */ | |
7 | |
8 #include "SkFrontBufferedStream.h" | |
9 | |
10 SkFrontBufferedStream* SkFrontBufferedStream::Create(SkStream* stream, size_t bu fferSize) { | |
11 if (NULL == stream) { | |
12 return NULL; | |
13 } | |
14 return SkNEW_ARGS(SkFrontBufferedStream, (stream, bufferSize)); | |
15 } | |
16 | |
17 SkFrontBufferedStream::SkFrontBufferedStream(SkStream* stream, size_t bufferSize ) | |
18 : fStream(SkRef(stream)) | |
19 , fOffset(0) | |
20 , fBufferedSoFar(0) | |
21 , fBufferSize(bufferSize) | |
22 , fBuffer(bufferSize) {} | |
23 | |
24 bool SkFrontBufferedStream::isAtEnd() const { | |
25 if (fOffset < fBufferedSoFar) { | |
26 // Even if the underlying stream is at the end, this stream has been | |
27 // rewound after buffering, so it is not at the end. | |
28 return false; | |
29 } | |
30 | |
31 return fStream->isAtEnd(); | |
32 } | |
33 | |
34 bool SkFrontBufferedStream::rewind() { | |
35 // Only allow a rewind if we have not exceeded the buffer. | |
36 if (fOffset <= fBufferSize) { | |
37 fOffset = 0; | |
38 return true; | |
39 } | |
40 return false; | |
41 } | |
42 | |
43 bool SkFrontBufferedStream::hasLength() const { | |
44 return fStream->hasLength(); | |
45 } | |
46 | |
47 size_t SkFrontBufferedStream::getLength() const { | |
48 return fStream->getLength(); | |
49 } | |
50 | |
51 size_t SkFrontBufferedStream::read(void* voidDst, size_t size) { | |
52 // Cast voidDst to a char* for easy addition. | |
53 char* dst = reinterpret_cast<char*>(voidDst); | |
54 SkDEBUGCODE(const size_t totalSize = size;) | |
55 size_t readSoFar = 0; | |
56 | |
57 // First, read any data that was previously buffered. | |
mtklein
2013/09/19 18:56:53
I think this wants to be three method calls, one t
scroggo
2013/09/25 17:36:01
FWIW, I think there are two camps for whether to r
| |
58 if (fOffset < fBufferedSoFar) { | |
59 // Some data has already been copied to fBuffer. Read up to the | |
60 // lesser of the size requested and the remainder of the buffered | |
61 // data. | |
62 const size_t bytesToCopy = SkTMin(size, fBufferedSoFar - fOffset); | |
63 if (dst != NULL) { | |
64 memcpy(dst, this->getBufferAtOffset(), bytesToCopy); | |
65 } | |
66 | |
67 // Update fOffset to the new position. It is guaranteed to be | |
68 // within the buffered data. | |
69 fOffset += bytesToCopy; | |
70 SkASSERT(fOffset <= fBufferedSoFar); | |
71 | |
72 if (bytesToCopy == size) { | |
73 // The entire requested read was inside the already buffered | |
74 // data. | |
75 SkASSERT(fOffset <= fBufferedSoFar); | |
76 return size; | |
77 } | |
78 | |
79 // The requested read extends beyond the buffered data. Update | |
80 // the remaining number of bytes needed to read, the number of | |
81 // bytes read so far, and the destination buffer. | |
82 size -= bytesToCopy; | |
83 readSoFar += bytesToCopy; | |
84 SkASSERT(size + readSoFar == totalSize); | |
85 if (dst != NULL) { | |
86 dst += bytesToCopy; | |
87 } | |
88 } | |
89 | |
90 // If we got here, we have read everything that was already buffered. | |
91 SkASSERT(fOffset >= fBufferedSoFar); | |
92 | |
93 // Buffer any more data that should be buffered, and copy it to the | |
94 // destination. | |
95 if (fBufferedSoFar < fBufferSize) { | |
96 // Data needs to be buffered. Buffer up to the lesser of the size reques ted | |
97 // and the remainder of the max buffer size. | |
98 const size_t bytesToBuffer = SkTMin(size, fBufferSize - fBufferedSoFar); | |
99 char* buffer = this->getBufferAtOffset(); | |
100 const size_t buffered = fStream->read(buffer, bytesToBuffer); | |
101 fBufferedSoFar += buffered; | |
102 fOffset = fBufferedSoFar; | |
103 | |
104 // Copy the buffer to the destination buffer and update the amount read. | |
105 if (dst != NULL) { | |
106 memcpy(dst, buffer, buffered); | |
107 } | |
108 readSoFar += buffered; | |
109 | |
110 if (buffered == size || fStream->isAtEnd()) { | |
111 // We were able to buffer all of the data requested (or all the data | |
112 // remaining in the stream) and provide it to the caller. | |
113 SkASSERT(fBufferedSoFar <= fBufferSize); | |
114 SkASSERT(totalSize == readSoFar || fStream->isAtEnd()); | |
115 return readSoFar; | |
116 } | |
117 | |
118 // The requested read extends beyond the length of the buffer. Update | |
119 // the remaining number of bytes needed to read and the destination | |
120 // buffer. | |
121 size -= buffered; | |
122 SkASSERT(size + readSoFar == totalSize); | |
123 if (dst != NULL) { | |
124 dst += buffered; | |
125 } | |
126 } | |
127 | |
128 // If we get here, we have buffered all that can be buffered. | |
129 SkASSERT(fBufferSize == fBufferedSoFar && fOffset >= fBufferSize); | |
130 | |
131 // Read directly from the stream. | |
132 const size_t bytesReadDirectly = fStream->read(dst, size); | |
133 fOffset += bytesReadDirectly; | |
134 if (bytesReadDirectly > 0) { | |
135 sk_free(fBuffer.detach()); | |
136 } | |
137 return bytesReadDirectly + readSoFar; | |
138 } | |
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