Latest revision as of 13:46, 22 October 2017

The $compress identifier performs compression of a disk file or binary variable.

Synopsis[edit]

$compress( <filename | BinaryVariable> ,[b][lN][mN] )

Parameters[edit]

DataFirst parameter can be either a disk file (default) or a Binary Variable
bInforms that first parameter should be treated as a Binary Variable instead of filename.
lNDefault compression level is 6 within the range 0-9. lN overrides to use compression level N, where N is integer 0-9. (l0 does not compress, is not the same as the absence of the l switch)
mNDefault compression method is 2 (zlib). mN overrides to use compression method N, where N = 1 is raw, N = 2 is zlib (the default), and N = 3 is gzip. (0 uses default m2, invalid 4+ uses m3)

Example[edit]

There are patterns that often appear near the beginning, but from observations, it appears you should not assume beyond:

m1 raw: No guaranteed signature because the data is 'raw'. (m1l0 is the same as the input data)
m2 Zlib: The 1st byte is $chr(120) (hex 78) small-x.
m3 gzip: The 1st 4 bytes in hex are: 1F 8B 08 00

Reminder that decompress works without being informed of the lN compression level. Files compressed with non-default m1 or m3 will fail without being informed of the compression method used to compress that file.

Returns 1 if it compressed the file, or 0 if it did not. It will repeatedly process the same file and return 1, even if the attempt to compress an already compressed file slightly increases the filesize. 0 can indicate there's no-such-file, the file wasn't already compressed, or a failure to decompress corrupted data.

//noop | $compress(versions.txt) | echo -a test
//bset -t &snip 1 $read($mircini,ntw,*16777215*) | echo 4 -a / $bvar(&snip,1-) |      $compress(&snip,b) | echo 5 -a \ $bvar(&snip,1-)
//bset -t &snip 1 $read($mircini,ntw,*16777215*) | echo 4 -a / $bvar(&snip,1-) | noop $compress(&snip,b) | echo 5 -a \ $bvar(&snip,1-)

In the above example, the first 2 lines are incorrect usage, and fail to alter the filename or binary variable, nor do they display the following echo. You must use $compress an argument to something else, which should be done in order to determine success or failure.

alias compress-then-send {
  if (!$comchan($1,1)) { echo 5 -a no shared channels with nick $1 | return }
  if (!$isfile($2-)) { echo 5 -a filename does not exist: $2- | return }
  bread $qt($2-) 0 1 &snip
  if ($bvar(&snip,1) != 120) { var %i $compress($2-) | if (%i == 0) echo 5 -a warning failure to zlib compress $1- }
  dcc send $1 $2-
}

Note: Before making a script which automatically compresses all files before sending them and decompressing them when they finish, you should take several issues into account.

1. You shouldn't automatically decompress or compress files without making certain that the same file isn't also being transferred to/from someone else.
2. Besides ON FILESENT, Transfers can also terminate with ON SENDFAIL, clicking to close the send window, using the /close command with the -s switch, mIRC crashing, etc.
3. To make certain all files get safely decompressed, the script should probably work from a file listing that doesn't remove lines until the file has been determined to be decompressed.
4. Now that $compress supports gzip compression, a script must first determine which method was used to compress the file in order to successfully decompress the file.

Compatibility[edit]

Added: mIRC v6.1
Added on: 29 Aug 2003
Note: Unless otherwise stated, this was the date of original functionality.
Further enhancements may have been made in later versions.

version 7.51 expanded lN from 1-6 to 0-9, and introduced mN

See also[edit]

• $decompress