Crawler

Problem domain: You want to crawl a non-trivial amount of webpages using only your personal computer.

This crawler offers:

• integrated duplicate detection, only process each unique line once
• modest memory and cpu requirements: 400.000.000+ line duplicate cache 128 different domains in parallel 10 MBit/s download speed (before removal of duplicates) => 1 GB RAM + ~10% of a single core
• stores results into a single stream file, optimal for later batch processing
• short pauses between requests to the same server
• a simplistic HTML "parser"
• asynchronous DNS resolution via libadns
• short an concise program code
• liberal licencing terms

= "Architecture" (i.e. what I wrote before the code) =

Input: List of URLs

Create Bloom filter for seen URLs Create Bloom filter for seen Lines

For each domain: Open output stream Fetch robots.txt, parse into patterns

Create client socket and read / write buffers Fetch page Parse into lines, check with filter Put surviving lines into output stream

Parse target URLs, check with filter Put surviving URLs into search front if search front limit per domain has been reached, drop URL

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