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
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
|
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>lz4frame 1.7.5 Manual</title>
</head>
<body>
<h1>lz4frame 1.7.5 Manual</h1>
<hr>
<a name="Contents"></a><h2>Contents</h2>
<ol>
<li><a href="#Chapter1">Introduction</a></li>
<li><a href="#Chapter2">Error management</a></li>
<li><a href="#Chapter3">Frame compression types</a></li>
<li><a href="#Chapter4">Simple compression function</a></li>
<li><a href="#Chapter5">Advanced compression functions</a></li>
<li><a href="#Chapter6">Decompression functions</a></li>
</ol>
<hr>
<a name="Chapter1"></a><h2>Introduction</h2><pre>
lz4frame.h implements LZ4 frame specification (doc/lz4_Frame_format.md).
lz4frame.h provides frame compression functions that take care
of encoding standard metadata alongside LZ4-compressed blocks.
<BR></pre>
<a name="Chapter2"></a><h2>Error management</h2><pre></pre>
<pre><b>unsigned LZ4F_isError(LZ4F_errorCode_t code); </b>/**< tells if a `LZ4F_errorCode_t` function result is an error code */<b>
</b></pre><BR>
<pre><b>const char* LZ4F_getErrorName(LZ4F_errorCode_t code); </b>/**< return error code string; useful for debugging */<b>
</b></pre><BR>
<a name="Chapter3"></a><h2>Frame compression types</h2><pre></pre>
<pre><b>typedef enum {
LZ4F_default=0,
LZ4F_max64KB=4,
LZ4F_max256KB=5,
LZ4F_max1MB=6,
LZ4F_max4MB=7
LZ4F_OBSOLETE_ENUM(max64KB)
LZ4F_OBSOLETE_ENUM(max256KB)
LZ4F_OBSOLETE_ENUM(max1MB)
LZ4F_OBSOLETE_ENUM(max4MB)
} LZ4F_blockSizeID_t;
</b></pre><BR>
<pre><b>typedef enum {
LZ4F_blockLinked=0,
LZ4F_blockIndependent
LZ4F_OBSOLETE_ENUM(blockLinked)
LZ4F_OBSOLETE_ENUM(blockIndependent)
} LZ4F_blockMode_t;
</b></pre><BR>
<pre><b>typedef enum {
LZ4F_noContentChecksum=0,
LZ4F_contentChecksumEnabled
LZ4F_OBSOLETE_ENUM(noContentChecksum)
LZ4F_OBSOLETE_ENUM(contentChecksumEnabled)
} LZ4F_contentChecksum_t;
</b></pre><BR>
<pre><b>typedef enum {
LZ4F_frame=0,
LZ4F_skippableFrame
LZ4F_OBSOLETE_ENUM(skippableFrame)
} LZ4F_frameType_t;
</b></pre><BR>
<pre><b>typedef struct {
LZ4F_blockSizeID_t blockSizeID; </b>/* max64KB, max256KB, max1MB, max4MB ; 0 == default */<b>
LZ4F_blockMode_t blockMode; </b>/* blockLinked, blockIndependent ; 0 == default */<b>
LZ4F_contentChecksum_t contentChecksumFlag; </b>/* noContentChecksum, contentChecksumEnabled ; 0 == default */<b>
LZ4F_frameType_t frameType; </b>/* LZ4F_frame, skippableFrame ; 0 == default */<b>
unsigned long long contentSize; </b>/* Size of uncompressed (original) content ; 0 == unknown */<b>
unsigned reserved[2]; </b>/* must be zero for forward compatibility */<b>
} LZ4F_frameInfo_t;
</b><p> makes it possible to supply detailed frame parameters to the stream interface.
It's not required to set all fields, as long as the structure was initially memset() to zero.
All reserved fields must be set to zero.
</p></pre><BR>
<pre><b>typedef struct {
LZ4F_frameInfo_t frameInfo;
int compressionLevel; </b>/* 0 == default (fast mode); values above 16 count as 16; values below 0 count as 0 */<b>
unsigned autoFlush; </b>/* 1 == always flush (reduce usage of tmp buffer) */<b>
unsigned reserved[4]; </b>/* must be zero for forward compatibility */<b>
} LZ4F_preferences_t;
</b><p> makes it possible to supply detailed compression parameters to the stream interface.
It's not required to set all fields, as long as the structure was initially memset() to zero.
All reserved fields must be set to zero.
</p></pre><BR>
<a name="Chapter4"></a><h2>Simple compression function</h2><pre></pre>
<pre><b>size_t LZ4F_compressFrameBound(size_t srcSize, const LZ4F_preferences_t* preferencesPtr);
</b><p> Returns the maximum possible size of a frame compressed with LZ4F_compressFrame() given srcSize content and preferences.
Note : this result is only usable with LZ4F_compressFrame(), not with multi-segments compression.
</p></pre><BR>
<pre><b>size_t LZ4F_compressFrame(void* dstBuffer, size_t dstCapacity, const void* srcBuffer, size_t srcSize, const LZ4F_preferences_t* preferencesPtr);
</b><p> Compress an entire srcBuffer into a valid LZ4 frame, as defined by specification v1.5.1
An important rule is that dstBuffer MUST be large enough (dstCapacity) to store the result in worst case situation.
This value is supplied by LZ4F_compressFrameBound().
If this condition is not respected, LZ4F_compressFrame() will fail (result is an errorCode).
The LZ4F_preferences_t structure is optional : you can provide NULL as argument. All preferences will be set to default.
@return : number of bytes written into dstBuffer.
or an error code if it fails (can be tested using LZ4F_isError())
</p></pre><BR>
<a name="Chapter5"></a><h2>Advanced compression functions</h2><pre></pre>
<pre><b>typedef struct {
unsigned stableSrc; </b>/* 1 == src content will remain present on future calls to LZ4F_compress(); skip copying src content within tmp buffer */<b>
unsigned reserved[3];
} LZ4F_compressOptions_t;
</b></pre><BR>
<pre><b>LZ4F_errorCode_t LZ4F_createCompressionContext(LZ4F_cctx** cctxPtr, unsigned version);
LZ4F_errorCode_t LZ4F_freeCompressionContext(LZ4F_cctx* cctx);
</b><p> The first thing to do is to create a compressionContext object, which will be used in all compression operations.
This is achieved using LZ4F_createCompressionContext(), which takes as argument a version and an LZ4F_preferences_t structure.
The version provided MUST be LZ4F_VERSION. It is intended to track potential version mismatch, notably when using DLL.
The function will provide a pointer to a fully allocated LZ4F_cctx object.
If @return != zero, there was an error during context creation.
Object can release its memory using LZ4F_freeCompressionContext();
</p></pre><BR>
<pre><b>size_t LZ4F_compressBegin(LZ4F_cctx* cctx, void* dstBuffer, size_t dstCapacity, const LZ4F_preferences_t* prefsPtr);
</b><p> will write the frame header into dstBuffer.
dstCapacity must be large enough to store the header. Maximum header size is LZ4F_HEADER_SIZE_MAX bytes.
`prefsPtr` is optional : you can provide NULL as argument, all preferences will then be set to default.
@return : number of bytes written into dstBuffer for the header
or an error code (which can be tested using LZ4F_isError())
</p></pre><BR>
<pre><b>size_t LZ4F_compressBound(size_t srcSize, const LZ4F_preferences_t* prefsPtr);
</b><p> Provides dstCapacity given a srcSize to guarantee operation success in worst case situations.
prefsPtr is optional : you can provide NULL as argument, preferences will be set to cover worst case scenario.
Result is always the same for a srcSize and prefsPtr, so it can be trusted to size reusable buffers.
When srcSize==0, LZ4F_compressBound() provides an upper bound for LZ4F_flush() and LZ4F_compressEnd() operations.
</p></pre><BR>
<pre><b>size_t LZ4F_compressUpdate(LZ4F_cctx* cctx, void* dstBuffer, size_t dstCapacity, const void* srcBuffer, size_t srcSize, const LZ4F_compressOptions_t* cOptPtr);
</b><p> LZ4F_compressUpdate() can be called repetitively to compress as much data as necessary.
An important rule is that dstCapacity MUST be large enough to ensure operation success even in worst case situations.
This value is provided by LZ4F_compressBound().
If this condition is not respected, LZ4F_compress() will fail (result is an errorCode).
LZ4F_compressUpdate() doesn't guarantee error recovery. When an error occurs, compression context must be freed or resized.
`cOptPtr` is optional : NULL can be provided, in which case all options are set to default.
@return : number of bytes written into `dstBuffer` (it can be zero, meaning input data was just buffered).
or an error code if it fails (which can be tested using LZ4F_isError())
</p></pre><BR>
<pre><b>size_t LZ4F_flush(LZ4F_cctx* cctx, void* dstBuffer, size_t dstCapacity, const LZ4F_compressOptions_t* cOptPtr);
</b><p> When data must be generated and sent immediately, without waiting for a block to be completely filled,
it's possible to call LZ4_flush(). It will immediately compress any data buffered within cctx.
`dstCapacity` must be large enough to ensure the operation will be successful.
`cOptPtr` is optional : it's possible to provide NULL, all options will be set to default.
@return : number of bytes written into dstBuffer (it can be zero, which means there was no data stored within cctx)
or an error code if it fails (which can be tested using LZ4F_isError())
</p></pre><BR>
<pre><b>size_t LZ4F_compressEnd(LZ4F_cctx* cctx, void* dstBuffer, size_t dstCapacity, const LZ4F_compressOptions_t* cOptPtr);
</b><p> To properly finish an LZ4 frame, invoke LZ4F_compressEnd().
It will flush whatever data remained within `cctx` (like LZ4_flush())
and properly finalize the frame, with an endMark and a checksum.
`cOptPtr` is optional : NULL can be provided, in which case all options will be set to default.
@return : number of bytes written into dstBuffer (necessarily >= 4 (endMark), or 8 if optional frame checksum is enabled)
or an error code if it fails (which can be tested using LZ4F_isError())
A successful call to LZ4F_compressEnd() makes `cctx` available again for another compression task.
</p></pre><BR>
<a name="Chapter6"></a><h2>Decompression functions</h2><pre></pre>
<pre><b>typedef struct {
unsigned stableDst; </b>/* guarantee that decompressed data will still be there on next function calls (avoid storage into tmp buffers) */<b>
unsigned reserved[3];
} LZ4F_decompressOptions_t;
</b></pre><BR>
<pre><b>LZ4F_errorCode_t LZ4F_createDecompressionContext(LZ4F_dctx** dctxPtr, unsigned version);
LZ4F_errorCode_t LZ4F_freeDecompressionContext(LZ4F_dctx* const dctx);
</b><p> Create an LZ4F_decompressionContext_t object, which will be used to track all decompression operations.
The version provided MUST be LZ4F_VERSION. It is intended to track potential breaking differences between different versions.
The function will provide a pointer to a fully allocated and initialized LZ4F_decompressionContext_t object.
The result is an errorCode, which can be tested using LZ4F_isError().
dctx memory can be released using LZ4F_freeDecompressionContext();
The result of LZ4F_freeDecompressionContext() is indicative of the current state of decompressionContext when being released.
That is, it should be == 0 if decompression has been completed fully and correctly.
</p></pre><BR>
<pre><b>size_t LZ4F_getFrameInfo(LZ4F_dctx* dctx,
LZ4F_frameInfo_t* frameInfoPtr,
const void* srcBuffer, size_t* srcSizePtr);
</b><p> This function decodes frame header information (such as max blockSize, frame checksum, etc.).
Its usage is optional. The objective is to extract frame header information, typically for allocation purposes.
A header size is variable and can length from 7 to 15 bytes. It's possible to provide more input bytes than that.
The number of bytes consumed from srcBuffer will be updated within *srcSizePtr (necessarily <= original value).
Decompression must resume from this point (srcBuffer + *srcSizePtr).
Note that LZ4F_getFrameInfo() can also be used anytime *after* decompression is started, in which case 0 input byte can be enough.
Frame header info is *copied into* an already allocated LZ4F_frameInfo_t structure.
@return : an hint about how many srcSize bytes LZ4F_decompress() expects for next call,
or an error code which can be tested using LZ4F_isError()
(typically, when there is not enough src bytes to fully decode the frame header)
</p></pre><BR>
<pre><b>size_t LZ4F_decompress(LZ4F_dctx* dctx,
void* dstBuffer, size_t* dstSizePtr,
const void* srcBuffer, size_t* srcSizePtr,
const LZ4F_decompressOptions_t* dOptPtr);
</b><p> Call this function repetitively to regenerate data compressed within `srcBuffer`.
The function will attempt to decode up to *srcSizePtr bytes from srcBuffer, into dstBuffer of capacity *dstSizePtr.
The number of bytes regenerated into dstBuffer will be provided within *dstSizePtr (necessarily <= original value).
The number of bytes read from srcBuffer will be provided within *srcSizePtr (necessarily <= original value).
Number of bytes read can be < number of bytes provided, meaning there is some more data to decode.
It typically happens when dstBuffer is not large enough to contain all decoded data.
Remaining data will have to be presented again in a subsequent invocation.
`dstBuffer` content is expected to be flushed between each invocation, as its content will be overwritten.
`dstBuffer` can be changed at will between each consecutive function invocation.
@return is an hint of how many `srcSize` bytes LZ4F_decompress() expects for next call.
Schematically, it's the size of the current (or remaining) compressed block + header of next block.
Respecting the hint provides some boost to performance, since it does skip intermediate buffers.
This is just a hint though, it's always possible to provide any srcSize.
When a frame is fully decoded, @return will be 0 (no more data expected).
If decompression failed, @return is an error code, which can be tested using LZ4F_isError().
After a frame is fully decoded, dctx can be used again to decompress another frame.
</p></pre><BR>
</html>
</body>
|
