Network Programming with Perl

Summary

TCP urgent data provides a way for one process to signal another via a TCP stream that some time-critical event has occurred. Although the urgent signal is transmitted "out of band," meaning that it is delivered to the remote host in a priority fashion, the urgent data itself is not truly out of band but is subject to the same sequencing and flow-control rules as ordinary TCP data. To read the contents of the urgent data, it may be necessary to read (and possibly discard) normal data until the urgent data becomes available. Hence, urgent data is easiest to work with when it is the existence of the data that counts and not its actual contents.

In addition to reading the contents of the urgent data byte, you can discover its position in ...