Gzip (String function)

Compress a longstring with GZIP (String class)

[Introduced in Sirius Mods 7.4]

This function compresses a longstring using the "deflate" algorithm, which is described completely in RFC 1951. The GZIP format is described in RFC 1952. It is very effective with HTML and XML data.

Syntax

%outString = string:Gzip[( [FixedCode= boolean], [LazyMatch= boolean], - [MaxChain= number], [Filename= string], - [LastModified= number])]

Syntax terms

%outString	The result of the GZIP operation, compressing the method object string.
string	The string to be compressed by the GZIP operation.
FixedCode	FixedCode is an optional, name required, parameter that is a Boolean value that specifies whether the compression uses fixed codes or is dynamic, based on the contents of the input string. With fixed code compression (fixedCode=true), the tables used for compression (defined as part of RFC 1951) are somewhat optimized for ASCII character data, but they slightly decrease the amount of CPU required to perform compression. Also, since the codes are already defined as part of the specification, they are not included in the compressed data. With dynamic compression (fixedCode=false), the compression code tables are generated based on the input data. Dynamic tables typically provide somewhat better compression on most types of data. There is a very slight CPU overhead in computing the frequencies of byte values in the input data. Also, since the code tables are dynamic, they are included as part of the compressed data. This will increase the size of the compressed longstring, but these tables are small, since they are also stored in a compressed form. The default value for this argument is False (use dynamic compression).
LazyMatch	LazyMatch is an optional, name required, parameter that is a Boolean value that specifies whether to use "lazy match" compression, as specified in RFC 1951. The default value for this argument is False (do not use "lazy match" compression).
MaxChain	MaxChain is an optional, name required, parameter that is a numeric value that specifies the maximum hash chain length, as explained in RFC 1951. The default value for this argument is 0. If specified, it must be between 0 and 99, inclusive.
Filename	Filename is an optional, name required, parameter that is a string to be stored as the internal name of the compressed string. Decompression programs will use this name for the output file when the string is un-zipped. The maximum length of the file name is 32 bytes.
LastModified	The date/time stamp to be stored as a component of %outString, expressed as the number of milliseconds since 12:00 AM, Jan 1, 1900. The default is the current date and time (that is, %(System):CurrentTimeMilliseconds). After Gzip stores a value into %outString, the LastModified date/time stamp can be obtained with the GunzipDatetimeNS function, but note that its output is in seconds, not milliseconds.

Usage notes

• The NCMPBUF parameter must be set by User 0 before Gzip can be used. If Gzip is called and the NCMPBUF value is 0, the request is cancelled.

See also

• The inverse of Gzip is Gunzip.
• Other related methods:
  • GunzipDatetimeNS
  • GunzipFilename
  • Zip
  • Deflate
  • Inflate

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