[comment {-*- tcl -*- doctools manpage}]
[manpage_begin tcl::transform::crc32 n 1]
[keywords {channel transformation}]
[keywords checksum]
[keywords crc32]
[keywords {reflected channel}]
[keywords {tip 230}]
[keywords transformation]
[keywords {virtual channel}]
[copyright {2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>}]
[moddesc   {Reflected/virtual channel support}]
[category  Channels]
[titledesc {Crc32 transformation}]
[require Tcl 8.6]
[require tcl::transform::core [opt 1]]
[require tcl::transform::crc32 [opt 1]]
[description]
[para]

The [package tcl::transform::crc32] package provides a command
creating a channel transformation which passes the read and written
bytes through unchanged (like [package tcl::transform::identity]), but
additionally continuously computes the crc32 checksums of the data it
has seen for each direction and stores them in Tcl variables specified
at construction time. The checksum in question is zlib's crc32.

[para] Related transformations in this module are
[package tcl::transform::adler32],
[package tcl::transform::counter],
[package tcl::transform::identity], and
[package tcl::transform::observe].

[para] The internal [package TclOO] class implementing the transform
handler is a sub-class of the [package tcl::transform::core]
framework.

[section API]

[list_begin definitions]

[call [cmd ::tcl::transform::crc32] [arg chan] [option -option] [arg value]...]

This command creates a crc32 checksumming transformation on top of
the channel [arg chan] and returns its handle. The accepted options are

[list_begin options]
[opt_def -read-variable varname]

The value of the option is the name of a global or namespaced
variable, the location where the transformation has to store the
crc32 checksum of the data read from the channel.

[para] If not specified, or the empty string, the checksum of the read
direction is not saved.

[opt_def -write-variable varname]

The value of the option is the name of a global or namespaced
variable, the location where the transformation has to store the
crc32 checksum of the data written to the channel.

[para] If not specified, or the empty string, the checksum of the
write direction is not saved.

[list_end]
[list_end]

[vset CATEGORY virtchannel]
[include ../common-text/feedback.inc]
[manpage_end]