08-19-2008
UDP File Transfer Validation and Checksum
Dear All
I have written a client server program for file transmission from one system to other using UDP.
Can i use the cksum number in the udp header to validate if the received packet is corrupted or not? If yes, how can i extract the header and validate it..
Also is there any way that i can call cksum in c program? Except popen("cksum","r")
Any inputs will be of great help
Thanks in advance
Collins
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cksum(n) Cyclic Redundancy Checks cksum(n)
__________________________________________________________________________________________________________________________________________________
NAME
cksum - Calculate a cksum(1) compatible checksum
SYNOPSIS
package require Tcl 8.2
package require cksum ?1.1.3?
::crc::cksum ?-format format? ?-chunksize size? [ -channel chan | -filename file | string ]
::crc::CksumInit
::crc::CksumUpdate token data
::crc::CksumFinal token
_________________________________________________________________
DESCRIPTION
This package provides a Tcl implementation of the cksum(1) algorithm based upon information provided at in the GNU implementation of this
program as part of the GNU Textutils 2.0 package.
COMMANDS
::crc::cksum ?-format format? ?-chunksize size? [ -channel chan | -filename file | string ]
The command takes string data or a channel or file name and returns a checksum value calculated using the cksum(1) algorithm. The
result is formatted using the format(n) specifier provided or as an unsigned integer (%u) by default.
OPTIONS
-channel name
Return a checksum for the data read from a channel. The command will read data from the channel until the eof is true. If you need
to be able to process events during this calculation see the PROGRAMMING INTERFACE section
-filename name
This is a convenience option that opens the specified file, sets the encoding to binary and then acts as if the -channel option had
been used. The file is closed on completion.
-format string
Return the checksum using an alternative format template.
PROGRAMMING INTERFACE
The cksum package implements the checksum using a context variable to which additional data can be added at any time. This is expecially
useful in an event based environment such as a Tk application or a web server package. Data to be checksummed may be handled incrementally
during a fileevent handler in discrete chunks. This can improve the interactive nature of a GUI application and can help to avoid excessive
memory consumption.
::crc::CksumInit
Begins a new cksum context. Returns a token ID that must be used for the remaining functions. An optional seed may be specified if
required.
::crc::CksumUpdate token data
Add data to the checksum identified by token. Calling CksumUpdate $token "abcd" is equivalent to calling CksumUpdate $token "ab"
followed by CksumUpdate $token "cb". See EXAMPLES.
::crc::CksumFinal token
Returns the checksum value and releases any resources held by this token. Once this command completes the token will be invalid. The
result is a 32 bit integer value.
EXAMPLES
% crc::cksum "Hello, World!"
2609532967
% crc::cksum -format 0x%X "Hello, World!"
0x9B8A5027
% crc::cksum -file cksum.tcl
1828321145
% set tok [crc::CksumInit]
% crc::CksumUpdate $tok "Hello, "
% crc::CksumUpdate $tok "World!"
% crc::CksumFinal $tok
2609532967
AUTHORS
Pat Thoyts
BUGS, IDEAS, FEEDBACK
This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category crc of
the Tcllib SF Trackers [http://sourceforge.net/tracker/?group_id=12883]. Please also report any ideas for enhancements you may have for
either package and/or documentation.
SEE ALSO
crc32(n), sum(n)
KEYWORDS
checksum, cksum, crc, crc32, cyclic redundancy check, data integrity, security
CATEGORY
Hashes, checksums, and encryption
COPYRIGHT
Copyright (c) 2002, Pat Thoyts
crc 1.1.3 cksum(n)