4.4.1 Proxy Architecture Overview 

The client side proxy that is used to analyse HTTP requests is based on Jigsaw. Jigsaw is the 

W3C reference server

. 

Its main purpose is to demonstrate new protocol features as they are 

defined (such as HTTP/1.1), and to provide the basis for experimentations in the field of 

server software [20].  

Jigsaw is written in Java to take advantage of threads and garbage collection, which allows 

for very dynamic and flexible server architecture. The primary reason that Jigsaw was 

chosen for the client side proxy architecture is that it is highly extensible and allows what 

are referred to as Frames, which control how Resources (objects exported and made 

accessible to the outside world) are served using a specific protocol. It also allows what are 

referred to as filters, to be attached to the Protocol Frame (such as a HTTPFrame) of a 

Resource. A Filter is a full Java Object, associated to a Frame, which can modify the 

Request and/or the Reply. Usually filters are called before and after serving a Resource.  

One of the frames that Jigsaw provides is a ProxyFrame. The Jigsaw ProxyFrame 

implements a full blown proxy module for Jigsaw so that it can be configured to run as an 

HTTP proxy. It relies on the W3C s HTTP client side API to handle both request forwarding 

and reply caching on the end users behalf. The client side API emulates the interactions with 

the origin server that the end user's browser would normally make. The HTTPD component 

of Jigsaw accepts the requests from and sends replies to the end user's browser. 

Filters in Jigsaw can be classified in two types, server side and the client side filters. Server 

side filters are applied to requests to the whole server if it is running as a Web server or 

proxy.  A client side filter applies to the use of W3C s HTTP client side API in Jigsaw.