Test tools - logging and validation

Imported from previous forum

[ original email was from John Hardman - yiq12@dial.pipex.com ]
For testing purposes I need a utility that intercepts TCP/IP traffic between my client and server, logs that traffic in binary files or as a hex dump, then decodes and validates FIX messages stored therein. Does anyone know of such a tool, ideally but not necessarily freeware ?

Many thanks in advance,

John Hardman.