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2 '\" Copyright (c) 2008 Donal K. Fellows
4 '\" See the file "license.terms" for information on usage and redistribution
5 '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
7 .TH TclZlib 3 8.6 Tcl "Tcl Library Procedures"
8 .so man.macros
10 '\" Note: do not modify the .SH NAME line immediately below!
11 .SH NAME
12 Tcl_ZlibAdler32, Tcl_ZlibCRC32, Tcl_ZlibDeflate, Tcl_ZlibInflate, Tcl_ZlibStreamChecksum, Tcl_ZlibStreamClose, Tcl_ZlibStreamEof, Tcl_ZlibStreamGet, Tcl_ZlibStreamGetCommandName, Tcl_ZlibStreamInit, Tcl_ZlibStreamPut \- compression and decompression functions
13 .SH SYNOPSIS
15 #include <tcl.h>
18 \fBTcl_ZlibDeflate\fR(\fIinterp, format, dataObj, level, dictObj\fR)
21 \fBTcl_ZlibInflate\fR(\fIinterp, format, dataObj, dictObj\fR)
23 unsigned int
24 \fBTcl_ZlibCRC32\fR(\fIinitValue, bytes, length\fR)
26 unsigned int
27 \fBTcl_ZlibAdler32\fR(\fIinitValue, bytes, length\fR)
30 \fBTcl_ZlibStreamInit\fR(\fIinterp, mode, format, level, dictObj, zshandlePtr\fR)
32 Tcl_Obj *
48 \fBTcl_ZlibStreamPut\fR(\fIzshandle, dataObj, flush\fR)
51 \fBTcl_ZlibStreamGet\fR(\fIzshandle, dataObj, count\fR)
53 \fBTcl_ZlibStreamSetCompressionDictionary\fR(\fIzshandle, compDict\fR)
55 .SH ARGUMENTS
56 .AS Tcl_ZlibStream zshandle in
57 .AP Tcl_Interp *interp in
58 The interpreter to store resulting compressed or uncompressed data in. Also
59 where any error messages are written. For \fBTcl_ZlibStreamInit\fR, this can
60 be NULL to create a stream that is not bound to a command.
61 .AP int format in
62 What format of compressed data to work with. Must be one of
63 \fBTCL_ZLIB_FORMAT_ZLIB\fR for zlib-format data, \fBTCL_ZLIB_FORMAT_GZIP\fR
64 for gzip-format data, or \fBTCL_ZLIB_FORMAT_RAW\fR for raw compressed data. In
65 addition, for decompression only, \fBTCL_ZLIB_FORMAT_AUTO\fR may also be
66 chosen which can automatically detect whether the compressed data was in zlib
67 or gzip format.
68 .AP Tcl_Obj *dataObj in/out
69 A byte-array value containing the data to be compressed or decompressed, or
70 to which the data extracted from the stream is appended when passed to
72 .AP int level in
73 What level of compression to use. Should be a number from 0 to 9 or one of the
74 following: \fBTCL_ZLIB_COMPRESS_NONE\fR for no compression,
75 \fBTCL_ZLIB_COMPRESS_FAST\fR for fast but inefficient compression,
76 \fBTCL_ZLIB_COMPRESS_BEST\fR for slow but maximal compression, or
77 \fBTCL_ZLIB_COMPRESS_DEFAULT\fR for the level recommended by the zlib library.
78 .AP Tcl_Obj *dictObj in/out
79 A dictionary that contains, or which will be updated to contain, a description
80 of the gzip header associated with the compressed data. Only useful when the
81 \fIformat\fR is \fBTCL_ZLIB_FORMAT_GZIP\fR or \fBTCL_ZLIB_FORMAT_AUTO\fR. If
82 a NULL is passed, a default header will be used on compression and the header
83 will be ignored (apart from integrity checks) on decompression. See the
84 section \fBGZIP OPTIONS DICTIONARY\fR for details about the contents of this
86 .AP "unsigned int" initValue in
87 The initial value for the checksum algorithm.
88 .AP "unsigned char" *bytes in
89 An array of bytes to run the checksum algorithm over, or NULL to get the
90 recommended initial value for the checksum algorithm.
91 .AP int length in
92 The number of bytes in the array.
93 .AP int mode in
94 What mode to operate the stream in. Should be either
95 \fBTCL_ZLIB_STREAM_DEFLATE\fR for a compressing stream or
96 \fBTCL_ZLIB_STREAM_INFLATE\fR for a decompressing stream.
97 .AP Tcl_ZlibStream *zshandlePtr out
98 A pointer to a variable in which to write the abstract token for the stream
99 upon successful creation.
100 .AP Tcl_ZlibStream zshandle in
101 The abstract token for the stream to operate on.
102 .AP int flush in
103 Whether and how to flush the stream after writing the data to it. Must be one
104 of: \fBTCL_ZLIB_NO_FLUSH\fR if no flushing is to be done, \fBTCL_ZLIB_FLUSH\fR
105 if the currently compressed data must be made available for access using
106 \fBTcl_ZlibStreamGet\fR, \fBTCL_ZLIB_FULLFLUSH\fR if the stream must be put
107 into a state where the decompressor can recover from on corruption, or
108 \fBTCL_ZLIB_FINALIZE\fR to ensure that the stream is finished and that any
109 trailer demanded by the format is written.
110 .AP int count in
111 The maximum number of bytes to get from the stream, or -1 to get all remaining
112 bytes from the stream's buffers.
113 .AP Tcl_Obj *compDict in
114 A byte array value that is the compression dictionary to use with the stream.
115 Note that this is \fInot a Tcl dictionary\fR, and it is recommended that this
116 only ever be used with streams that were created with their \fIformat\fR set
117 to \fBTCL_ZLIB_FORMAT_ZLIB\fR because the other formats have no mechanism to
118 indicate whether a compression dictionary was present other than to fail on
121 .SH DESCRIPTION
122 These functions form the interface from the Tcl library to the Zlib
123 library by Jean-loup Gailly and Mark Adler.
125 \fBTcl_ZlibDeflate\fR and \fBTcl_ZlibInflate\fR respectively compress and
126 decompress the data contained in the \fIdataObj\fR argument, according to the
127 \fIformat\fR and, for compression, \fIlevel\fR arguments. The dictionary in
128 the \fIdictObj\fR parameter is used to convey additional header information
129 about the compressed data when the compression format supports it; currently,
130 the dictionary is only used when the \fIformat\fR parameter is
131 \fBTCL_ZLIB_FORMAT_GZIP\fR or \fBTCL_ZLIB_FORMAT_AUTO\fR. For details of the
132 contents of the dictionary, see the \fBGZIP OPTIONS DICTIONARY\fR section
133 below. Upon success, both functions leave the resulting compressed or
134 decompressed data in a byte-array value that is the Tcl interpreter's result;
135 the returned value is a standard Tcl result code.
137 \fBTcl_ZlibAdler32\fR and \fBTcl_ZlibCRC32\fR compute checksums on arrays of
138 bytes, returning the computed checksum. Checksums are computed incrementally,
139 allowing data to be processed one block at a time, but this requires the
140 caller to maintain the current checksum and pass it in as the \fIinitValue\fR
141 parameter; the initial value to use for this can be obtained by using NULL for
142 the \fIbytes\fR parameter instead of a pointer to the array of bytes to
143 compute the checksum over. Thus, typical usage in the single data block case
144 is like this:
147 checksum = \fBTcl_ZlibCRC32\fR(\fBTcl_ZlibCRC32\fR(0,NULL,0), data, length);
150 Note that the Adler-32 algorithm is not a real checksum, but instead is a
151 related type of hash that works best on longer data.
152 .SS "ZLIB STREAMS"
154 \fBTcl_ZlibStreamInit\fR creates a compressing or decompressing stream that is
155 linked to a Tcl command, according to its arguments, and provides an abstract
156 token for the stream and returns a normal Tcl result code;
157 \fBTcl_ZlibStreamGetCommandName\fR returns the name of that command given the
158 stream token, or NULL if the stream has no command. Streams are not designed
159 to be thread-safe; each stream should only ever be used from the thread that
160 created it. When working with gzip streams, a dictionary (fields as given in
161 the \fBGZIP OPTIONS DICTIONARY\fR section below) can be given via the
162 \fIdictObj\fR parameter that on compression allows control over the generated
163 headers, and on decompression allows discovery of the existing headers. Note
164 that the dictionary will be written to on decompression once sufficient data
165 has been read to have a complete header. This means that the dictionary must
166 be an unshared value in that case; a blank value created with
167 \fBTcl_NewObj\fR is suggested.
169 Once a stream has been constructed, \fBTcl_ZlibStreamPut\fR is used to add
170 data to the stream and \fBTcl_ZlibStreamGet\fR is used to retrieve data from
171 the stream after processing. Both return normal Tcl result codes and leave an
172 error message in the result of the interpreter that the stream is registered
173 with in the error case (if such a registration has been performed). With
174 \fBTcl_ZlibStreamPut\fR, the data buffer value passed to it should not be
175 modified afterwards. With \fBTcl_ZlibStreamGet\fR, the data buffer value
176 passed to it will have the data bytes appended to it. Internally to the
177 stream, data is kept compressed so as to minimize the cost of buffer space.
179 \fBTcl_ZlibStreamChecksum\fR returns the checksum computed over the
180 uncompressed data according to the format, and \fBTcl_ZlibStreamEof\fR returns
181 a boolean value indicating whether the end of the uncompressed data has been
184 \fBTcl_ZlibStreamSetCompressionDictionary\fR is used to control the
185 compression dictionary used with the stream, a compression dictionary being an
186 array of bytes (such as might be created with \fBTcl_NewByteArrayObj\fR) that
187 is used to initialize the compression engine rather than leaving it to create
188 it on the fly from the data being compressed. Setting a compression dictionary
189 allows for more efficient compression in the case where the start of the data
190 is highly regular, but it does require both the compressor and the
191 decompressor to agreee on the value to use. Compression dictionaries are only
192 fully supported for zlib-format data; on compression, they must be set before
193 any data is sent in with \fBTcl_ZlibStreamPut\fR, and on decompression they
194 should be set when \fBTcl_ZlibStreamGet\fR produces an \fBerror\fR with its
195 \fB\-errorcode\fR set to
196 .QW "\fBZLIB NEED_DICT\fI code\fR" ;
197 the \fIcode\fR will be the Adler-32 checksum (see \fBTcl_ZlibAdler32\fR) of
198 the compression dictionary sought. (Note that this is only true for
199 zlib-format streams; gzip streams ignore compression dictionaries as the
200 format specification doesn't permit them, and raw streams just produce a data
201 error if the compression dictionary is missing or incorrect.)
203 If you wish to clear a stream and reuse it for a new compression or
204 decompression action, \fBTcl_ZlibStreamReset\fR will do this and return a
205 normal Tcl result code to indicate whether it was successful; if the stream is
206 registered with an interpreter, an error message will be left in the
207 interpreter result when this function returns TCL_ERROR.
208 Finally, \fBTcl_ZlibStreamClose\fR will clean up the stream and delete the
209 associated command: using \fBTcl_DeleteCommand\fR on the stream's command is
210 equivalent (when such a command exists).
211 .SH "GZIP OPTIONS DICTIONARY"
213 The \fIdictObj\fR parameter to \fBTcl_ZlibDeflate\fR, \fBTcl_ZlibInflate\fR
214 and \fBTcl_ZlibStreamInit\fR is used to pass a dictionary of options about
215 that is used to describe the gzip header in the compressed data. When creating
216 compressed data, the dictionary is read and when unpacking compressed data the
217 dictionary is written (in which case the \fIdictObj\fR parameter must refer to
218 an unshared dictionary value).
220 The following fields in the dictionary value are understood. All other fields
221 are ignored. No field is required when creating a gzip-format stream.
225 This holds the comment field of the header, if present. If absent, no comment
226 was supplied (on decompression) or will be created (on compression).
230 A boolean value describing whether a CRC of the header is computed. Note that
231 the \fBgzip\fR program does \fInot\fR use or allow a CRC on the header.
235 The name of the file that held the uncompressed data. This should not contain
236 any directory separators, and should be sanitized before use on decompression
237 with \fBfile tail\fR.
241 The operating system type code field from the header (if not the
242 .QW unknown
243 value). See RFC 1952 for the meaning of these codes. On compression, if this
244 is absent then the field will be set to the
245 .QW unknown
250 The size of the uncompressed data. This is ignored on compression; the size
251 of the data compressed depends on how much data is supplied to the
252 compression engine.
256 The time field from the header if non-zero, expected to be the time that the
257 file named by the \fBfilename\fR field was modified. Suitable for use with
258 \fBclock format\fR. On creation, the right value to use is that from
259 \fBclock seconds\fR or \fBfile mtime\fR.
263 The type of the uncompressed data (either \fBbinary\fR or \fBtext\fR) if
265 .SH "PORTABILITY NOTES"
266 These functions will fail gracefully if Tcl is not linked with the zlib
268 .SH "SEE ALSO"
269 Tcl_NewByteArrayObj(3), zlib(n)
271 .SH "KEYWORDS"
272 compress, decompress, deflate, gzip, inflate
273 '\" Local Variables:
274 '\" mode: nroff
275 '\" fill-column: 78
276 '\" End: