diff options
Diffstat (limited to 'doc/TclZlib.3')
| -rw-r--r-- | doc/TclZlib.3 | 30 |
1 files changed, 29 insertions, 1 deletions
diff --git a/doc/TclZlib.3 b/doc/TclZlib.3 index 1b5e892..ebd294b 100644 --- a/doc/TclZlib.3 +++ b/doc/TclZlib.3 @@ -49,9 +49,11 @@ int .sp int \fBTcl_ZlibStreamGet\fR(\fIzshandle, dataObj, count\fR) +.sp +\fBTcl_ZlibStreamSetCompressionDictionary\fR(\fIzshandle, compDict\fR) .fi .SH ARGUMENTS -.AS Tcl_ZlibStream *zshandlePtr out +.AS Tcl_ZlibStream zshandle in .AP Tcl_Interp *interp in The interpreter to store resulting compressed or uncompressed data in. Also where any error messages are written. For \fBTcl_ZlibStreamInit\fR, this can @@ -108,6 +110,13 @@ trailer demanded by the format is written. .AP int count in The maximum number of bytes to get from the stream, or -1 to get all remaining bytes from the stream's buffers. +.AP Tcl_Obj *compDict in +A byte array object that is the compression dictionary to use with the stream. +Note that this is \fInot a Tcl dictionary\fR, and it is recommended that this +only ever be used with streams that were created with their \fIformat\fR set +to \fBTCL_ZLIB_FORMAT_ZLIB\fR because the other formats have no mechanism to +indicate whether a compression dictionary was present other than to fail on +decompression. .BE .SH DESCRIPTION These functions form the interface from the Tcl library to the Zlib @@ -172,6 +181,25 @@ uncompressed data according to the format, and \fBTcl_ZlibStreamEof\fR returns a boolean value indicating whether the end of the uncompressed data has been reached. .PP +\fBTcl_ZlibStreamSetCompressionDictionary\fR is used to control the +compression dictionary used with the stream, a compression dictionary being an +array of bytes (such as might be created with \fBTcl_NewByteArrayObj\fR) that +is used to initialize the compression engine rather than leaving it to create +it on the fly from the data being compressed. Setting a compression dictionary +allows for more efficient compression in the case where the start of the data +is highly regular, but it does require both the compressor and the +decompressor to agreee on the value to use. Compression dictionaries are only +fully supported for zlib-format data; on compression, they must be set before +any data is sent in with \fBTcl_ZlibStreamPut\fR, and on decompression they +should be set when \fBTcl_ZlibStreamGet\fR produces an \fBerror\fR with its +\fB\-errorcode\fR set to +.QW "\fBZLIB NEED_DICT\fI code\fR" ; +the \fIcode\fR will be the Adler-32 checksum (see \fBTcl_ZlibAdler32\fR) of +the compression dictionary sought. (Note that this is only true for +zlib-format streams; gzip streams ignore compression dictionaries as the +format specification doesn't permit them, and raw streams just produce a data +error if the compression dictionary is missing or incorrect.) +.PP If you wish to clear a stream and reuse it for a new compression or decompression action, \fBTcl_ZlibStreamReset\fR will do this and return a normal Tcl result code to indicate whether it was successful; if the stream is |