Programming Assignment 3 - HTTP Proxy

HTTP proxy that supports caching and link prefetching.
This proxy only support HTTP GET method.
This program is an academic exercise.

what does it do?

run server executable with arguments: <port#> <cached-file-ttl-seconds>
optionally support a blocklist file where blocked hosts are listed as <domain> or <domain>:<port> or <ip>:<port>
This blocklist file needs to be in the working directory of the server executable.

Overview

what is in the makefile?

• do make server to compile server executable. The finished binary will be at ./executables/server the default cache root is ./executables/cache
• there are some non-automated unit tests, do make tests to compile them.
• there are some small scale experiments I used to learn about the behaviour HTTP. do make experiments to compile them.

few thing to note

• most comments and documentations are in .h files
• client request / response and prefetch uses pretty much the same code path and same objects for ease of development.
• While a resource is being retrieved for the first time from server, before it is finished. The cache_record_get_or_create will return an unavailable status when another thread checks the same resource. This means if a resource is requested in quick succession, the first few requests will trigger a server get. The rationale behind this is that coordinating reading incomplete cache file is risky and blocking subsequent requests untill the first one finishes is bad for responsiveness to interactive users.
• While the cache files are stored on disk, the cache record used for retrieving and coordinating multiple reader / writer thread lives in memory and will be lost after server shutdown. This means cached responses do not persist past the lifetime of the server program.
• During cache_record_get_or_create this program will user popen to execute md5sum in the terminal. This seems pretty dangerous but given the time constraint and the scope of the assignment it seems reasonable. This is not how I live my life normally.

want to see extra printout?

• files such as thread-safe-job-stack.c and worker.c have DEBUG flags that will enable more printouts.

Library / works cited

• uthash.h is a hash table library maintained by Troy D. Hanson see https://troydhanson.github.io/uthash/
• request.c is an HTTP test client made by Prof.Schreuder. The server does not include any code from it.