1TclZlib(3) Tcl Library Procedures TclZlib(3)
2______________________________________________________________________________
6
8 Tcl_ZlibAdler32, Tcl_ZlibCRC32, Tcl_ZlibDeflate, Tcl_ZlibInflate,
9 Tcl_ZlibStreamChecksum, Tcl_ZlibStreamClose, Tcl_ZlibStreamEof,
10 Tcl_ZlibStreamGet, Tcl_ZlibStreamGetCommandName, Tcl_ZlibStreamInit,
11 Tcl_ZlibStreamPut - compression and decompression functions
12
14 #include <tcl.h>
15 int
17 Tcl_ZlibDeflate(interp, format, dataObj, level, dictObj)
18 int
20 Tcl_ZlibInflate(interp, format, dataObj, dictObj)
21 unsigned int
23 Tcl_ZlibCRC32(initValue, bytes, length)
24 unsigned int
26 Tcl_ZlibAdler32(initValue, bytes, length)
27 int
29 Tcl_ZlibStreamInit(interp, mode, format, level, dictObj, zshandlePtr)
30 Tcl_Obj *
32 Tcl_ZlibStreamGetCommandName(zshandle)
33 int
35 Tcl_ZlibStreamEof(zshandle)
36 int
38 Tcl_ZlibStreamClose(zshandle)
39 int
41 Tcl_ZlibStreamReset(zshandle)
42 int
44 Tcl_ZlibStreamChecksum(zshandle)
45 int
47 Tcl_ZlibStreamPut(zshandle, dataObj, flush)
48 int
50 Tcl_ZlibStreamGet(zshandle, dataObj, count)
51 Tcl_ZlibStreamSetCompressionDictionary(zshandle, compDict)
53
55 Tcl_Interp *interp (in) The interpreter to store result‐
56 ing compressed or uncompressed
57 data in. Also where any error
58 messages are written. For
59 Tcl_ZlibStreamInit, this can be
60 NULL to create a stream that is
61 not bound to a command.
62 int format (in) What format of compressed data to
64 work with. Must be one of
65 TCL_ZLIB_FORMAT_ZLIB for zlib-
66 format data, TCL_ZLIB_FORMAT_GZIP
67 for gzip-format data, or
68 TCL_ZLIB_FORMAT_RAW for raw com‐
69 pressed data. In addition, for
70 decompression only, TCL_ZLIB_FOR‐
71 MAT_AUTO may also be chosen which
72 can automatically detect whether
73 the compressed data was in zlib
74 or gzip format.
75 Tcl_Obj *dataObj (in/out) A byte-array value containing the
77 data to be compressed or decom‐
78 pressed, or to which the data
79 extracted from the stream is
80 appended when passed to Tcl_Zlib‐
81 StreamGet.
82 int level (in) What level of compression to use.
84 Should be a number from 0 to 9 or
85 one of the following:
86 TCL_ZLIB_COMPRESS_NONE for no
87 compression, TCL_ZLIB_COM‐
88 PRESS_FAST for fast but ineffi‐
89 cient compression, TCL_ZLIB_COM‐
90 PRESS_BEST for slow but maximal
91 compression, or TCL_ZLIB_COM‐
92 PRESS_DEFAULT for the level rec‐
93 ommended by the zlib library.
94 Tcl_Obj *dictObj (in/out) A dictionary that contains, or
96 which will be updated to contain,
97 a description of the gzip header
98 associated with the compressed
99 data. Only useful when the format
100 is TCL_ZLIB_FORMAT_GZIP or
101 TCL_ZLIB_FORMAT_AUTO. If a NULL
102 is passed, a default header will
103 be used on compression and the
104 header will be ignored (apart
105 from integrity checks) on decom‐
106 pression. See the section GZIP
107 OPTIONS DICTIONARY for details
108 about the contents of this dic‐
109 tionary.
110 unsigned int initValue (in) The initial value for the check‐
112 sum algorithm.
113 unsigned char *bytes (in) An array of bytes to run the
115 checksum algorithm over, or NULL
116 to get the recommended initial
117 value for the checksum algorithm.
118 int length (in) The number of bytes in the array.
120 int mode (in) What mode to operate the stream
122 in. Should be either
123 TCL_ZLIB_STREAM_DEFLATE for a
124 compressing stream or
125 TCL_ZLIB_STREAM_INFLATE for a
126 decompressing stream.
127 Tcl_ZlibStream *zshandlePtr (out) A pointer to a variable in which
129 to write the abstract token for
130 the stream upon successful cre‐
131 ation.
132 Tcl_ZlibStream zshandle (in) The abstract token for the stream
134 to operate on.
135 int flush (in) Whether and how to flush the
137 stream after writing the data to
138 it. Must be one of:
139 TCL_ZLIB_NO_FLUSH if no flushing
140 is to be done, TCL_ZLIB_FLUSH if
141 the currently compressed data
142 must be made available for access
143 using Tcl_ZlibStreamGet,
144 TCL_ZLIB_FULLFLUSH if the stream
145 must be put into a state where
146 the decompressor can recover from
147 on corruption, or TCL_ZLIB_FINAL‐
148 IZE to ensure that the stream is
149 finished and that any trailer
150 demanded by the format is writ‐
151 ten.
152 int count (in) The maximum number of bytes to
154 get from the stream, or -1 to get
155 all remaining bytes from the
156 stream's buffers.
157 Tcl_Obj *compDict (in) A byte array value that is the
159 compression dictionary to use
160 with the stream. Note that this
161 is not a Tcl dictionary, and it
162 is recommended that this only
163 ever be used with streams that
164 were created with their format
165 set to TCL_ZLIB_FORMAT_ZLIB
166 because the other formats have no
167 mechanism to indicate whether a
168 compression dictionary was
169 present other than to fail on
170 decompression.
171______________________________________________________________________________
172
174 These functions form the interface from the Tcl library to the Zlib
175 library by Jean-loup Gailly and Mark Adler.
176 Tcl_ZlibDeflate and Tcl_ZlibInflate respectively compress and decom‐
178 press the data contained in the dataObj argument, according to the for‐
179 mat and, for compression, level arguments. The dictionary in the dic‐
180 tObj parameter is used to convey additional header information about
181 the compressed data when the compression format supports it; currently,
182 the dictionary is only used when the format parameter is TCL_ZLIB_FOR‐
183 MAT_GZIP or TCL_ZLIB_FORMAT_AUTO. For details of the contents of the
184 dictionary, see the GZIP OPTIONS DICTIONARY section below. Upon suc‐
185 cess, both functions leave the resulting compressed or decompressed
186 data in a byte-array value that is the Tcl interpreter's result; the
187 returned value is a standard Tcl result code.
188 Tcl_ZlibAdler32 and Tcl_ZlibCRC32 compute checksums on arrays of bytes,
190 returning the computed checksum. Checksums are computed incrementally,
191 allowing data to be processed one block at a time, but this requires
192 the caller to maintain the current checksum and pass it in as the init‐
193 Value parameter; the initial value to use for this can be obtained by
194 using NULL for the bytes parameter instead of a pointer to the array of
195 bytes to compute the checksum over. Thus, typical usage in the single
196 data block case is like this:
197 checksum = Tcl_ZlibCRC32(Tcl_ZlibCRC32(0,NULL,0), data, length);
199 Note that the Adler-32 algorithm is not a real checksum, but instead is
201 a related type of hash that works best on longer data.
202 ZLIB STREAMS
204 Tcl_ZlibStreamInit creates a compressing or decompressing stream that
205 is linked to a Tcl command, according to its arguments, and provides an
206 abstract token for the stream and returns a normal Tcl result code;
207 Tcl_ZlibStreamGetCommandName returns the name of that command given the
208 stream token, or NULL if the stream has no command. Streams are not
209 designed to be thread-safe; each stream should only ever be used from
210 the thread that created it. When working with gzip streams, a dictio‐
211 nary (fields as given in the GZIP OPTIONS DICTIONARY section below) can
212 be given via the dictObj parameter that on compression allows control
213 over the generated headers, and on decompression allows discovery of
214 the existing headers. Note that the dictionary will be written to on
215 decompression once sufficient data has been read to have a complete
216 header. This means that the dictionary must be an unshared value in
217 that case; a blank value created with Tcl_NewObj is suggested.
218 Once a stream has been constructed, Tcl_ZlibStreamPut is used to add
220 data to the stream and Tcl_ZlibStreamGet is used to retrieve data from
221 the stream after processing. Both return normal Tcl result codes and
222 leave an error message in the result of the interpreter that the stream
223 is registered with in the error case (if such a registration has been
224 performed). With Tcl_ZlibStreamPut, the data buffer value passed to it
225 should not be modified afterwards. With Tcl_ZlibStreamGet, the data
226 buffer value passed to it will have the data bytes appended to it.
227 Internally to the stream, data is kept compressed so as to minimize the
228 cost of buffer space.
229 Tcl_ZlibStreamChecksum returns the checksum computed over the uncom‐
231 pressed data according to the format, and Tcl_ZlibStreamEof returns a
232 boolean value indicating whether the end of the uncompressed data has
233 been reached.
234 Tcl_ZlibStreamSetCompressionDictionary is used to control the compres‐
236 sion dictionary used with the stream, a compression dictionary being an
237 array of bytes (such as might be created with Tcl_NewByteArrayObj) that
238 is used to initialize the compression engine rather than leaving it to
239 create it on the fly from the data being compressed. Setting a compres‐
240 sion dictionary allows for more efficient compression in the case where
241 the start of the data is highly regular, but it does require both the
242 compressor and the decompressor to agreee on the value to use. Compres‐
243 sion dictionaries are only fully supported for zlib-format data; on
244 compression, they must be set before any data is sent in with Tcl_Zlib‐
245 StreamPut, and on decompression they should be set when Tcl_Zlib‐
246 StreamGet produces an error with its -errorcode set to “ZLIB NEED_DICT
247 code”; the code will be the Adler-32 checksum (see Tcl_ZlibAdler32) of
248 the compression dictionary sought. (Note that this is only true for
249 zlib-format streams; gzip streams ignore compression dictionaries as
250 the format specification doesn't permit them, and raw streams just pro‐
251 duce a data error if the compression dictionary is missing or incor‐
252 rect.)
253 If you wish to clear a stream and reuse it for a new compression or
255 decompression action, Tcl_ZlibStreamReset will do this and return a
256 normal Tcl result code to indicate whether it was successful; if the
257 stream is registered with an interpreter, an error message will be left
258 in the interpreter result when this function returns TCL_ERROR.
259 Finally, Tcl_ZlibStreamClose will clean up the stream and delete the
260 associated command: using Tcl_DeleteCommand on the stream's command is
261 equivalent (when such a command exists).
262
264 The dictObj parameter to Tcl_ZlibDeflate, Tcl_ZlibInflate and Tcl_Zlib‐
265 StreamInit is used to pass a dictionary of options about that is used
266 to describe the gzip header in the compressed data. When creating com‐
267 pressed data, the dictionary is read and when unpacking compressed data
268 the dictionary is written (in which case the dictObj parameter must
269 refer to an unshared dictionary value).
270 The following fields in the dictionary value are understood. All other
272 fields are ignored. No field is required when creating a gzip-format
273 stream.
274 comment
276 This holds the comment field of the header, if present. If
277 absent, no comment was supplied (on decompression) or will be
278 created (on compression).
279 crc A boolean value describing whether a CRC of the header is com‐
281 puted. Note that the gzip program does not use or allow a CRC on
282 the header.
283 filename
285 The name of the file that held the uncompressed data. This
286 should not contain any directory separators, and should be sani‐
287 tized before use on decompression with file tail.
288 os The operating system type code field from the header (if not the
290 “unknown” value). See RFC 1952 for the meaning of these codes.
291 On compression, if this is absent then the field will be set to
292 the “unknown” value.
293 size The size of the uncompressed data. This is ignored on compres‐
295 sion; the size of the data compressed depends on how much data
296 is supplied to the compression engine.
297 time The time field from the header if non-zero, expected to be the
299 time that the file named by the filename field was modified.
300 Suitable for use with clock format. On creation, the right value
301 to use is that from clock seconds or file mtime.
302 type The type of the uncompressed data (either binary or text) if
304 known.
305
307 These functions will fail gracefully if Tcl is not linked with the zlib
308 library.
309
311 Tcl_NewByteArrayObj(3), zlib(n)
312
314 compress, decompress, deflate, gzip, inflate
315Tcl 8.6 TclZlib(3)