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Ask HN: Ways for reading open source code bases?

• nostrademons 17y ago
  Google Code Search: http://www.google.com/codesearch http://www.google.com/codesearch I use it for working my way around Google's codebase, which is a few orders of magnitude bigger than that. Also, there's no substitute for getting your hands dirty and diving into the code. You don't really understand something until you've changed it a few times. Grab a couple of low-priority bugs and write some patches for them; you'll learn far more than if you just sit down and study things.
• patio11 17y ago
  Once upon a time, a client of the day job dropped a substantial Perl codebase on our desk and said "Tell us what this does." My boss gave me the job, and expected me to actually READ all the code, but given that I had no desire to read through 100 kloc of Perl code commented only in Japanese, I went for visualization instead: 1) Inspect several files for commonalities. Thankfully, the author was obsessive compulsive about coding standards. 2) Write a parser for the Perl they used. Use it to glean what pages of the site were connected to each other and what the flow control was like. (a -> b, b -> c, b -> d, etc) 3) Plot that on a graph (all hard work already done for me: http://rgl.rubyforge.org/rgl/index.html http://rgl.rubyforge.org/rgl/index.html ) 4) Visually inspect the graph to learn non-obvious things about the codebase like "Oh, there is an English language version of the site embedded in here. Isn't that TOTALLY UNDOCUMENTED." Do a bit more code to chop the graph into subgraphs by related functionality (signup flow, admin functions, etc etc). 5) Spit out all the code into HTML pages with appropriate autogenerated navigation, inline flow control graphs, and syntax highlighting. Do a bit of quality control, add in some comments about notable things I had learned, burn on CD and hand to customer. 6) Charge customer $X0,000 for the CD. The customer was overjoyed they got it done so cheaply. (Did I mention 100 kloc of Perl?)
  • cperciva 17y ago
    (Did I mention 100 kloc of Perl?) Hey, you got off easy. Just imagine how much more work it would have been if everything had been done in a single line of Perl. :-)
    • skywalker 17y ago
      Yes. When I write anything in Perl I frequently try to compact what would be several lines in just a few obscure expressions. But as the Freebsd security head, what do you do to understand a large code base you probably aren't familiar with and its security implications?
      • cperciva 17y ago
        But as the Freebsd security head, what do you do to understand a large code base you probably aren't familiar with and its security implications? I ask someone to explain it to me. Being FreeBSD Security Officer, I have an uncommon luxury: I have about 200 highly qualified developers available who will stop what they're doing and help me out if I say "so, umm, I sort of need to understand how this code works...".
    • patio11 17y ago
      70 hour workweeks, 3 hour daily commutes, salary below the median for a starting graduate from my alma mater, and debugging code written in India based on instructions translated by Babelfish: all of these I will endure without complaint. But I will not blackbox analyze Perl one-liners. That is just abusive.
      • tptacek 17y ago
        ... why DO you work 70 hour workweeks with 3 hour commutes for below-market wages? "Because, Japan"?
        • mahmud 17y ago
          This happened "once upon a time", he might have done it while learning the ropes and picking up the language.
• xenoterracide 17y ago
  Maybe try this book? http://www.amazon.com/Code-Reading-Open-Source-Perspective/dp/0201799405 http://www.amazon.com/Code-Reading-Open-Source-Perspective/d... I'm not sure how good it is.
• gte910h 17y ago
  Doxygen is great if it understands your language in question
  • tptacek 17y ago
    Doxygen is great when it Just Works, and pretty much useless when it doesn't. Even for languages it groks. The problem with the Big Code Navigation Tools is that when they're wrong, they're misleading.
• cmars232 17y ago
  I used to use pdb.set_trace() liberally to poke around at the internals of Django to figure out what it was doing in undocumented places.
  • forsaken 17y ago
    I recommend ipdb as well. It's IPython's PDB replacement. pip install ipdb
• rajasaur 17y ago
  Itd be good to get a debugger, connect it to the process and run through the code. You will find a pattern emerging when playing with the application, say, for different clicks of a webapp. After a few days, you will know how the flow works. That said, Ive been more successful looking at the forums of an open source project, figure out what problems folks have and trying to solve them. You will be amazed to see how much you can learn about the code base and undocumented features solving those problems.
• tptacek 17y ago
  Is it a web app? Open up Firebug, look for interesting URLs, and grep for segments of the URL. Find the function that implements it, read bottom-up.
• gtani 17y ago
  ruby: http://eigenclass.org/hiki/rcodetools http://eigenclass.org/hiki/rcodetools http://railroad.rubyforge.org/ http://railroad.rubyforge.org/ http://www.pathf.com/blogs/2008/12/read-the-source-luke-a-readers-guide-to-the-rails-source/ http://www.pathf.com/blogs/2008/12/read-the-source-luke-a-re... http://stackoverflow.com/questions/37105/how-do-you-actually-read-source-code http://stackoverflow.com/questions/37105/how-do-you-actually... --------------------------- (you'll see lots of questions on stackoverflow: navigate/inspect/read source repo's) http://stackoverflow.com/questions/1623906/programmatically-inspect-net-code http://stackoverflow.com/questions/1623906/programmatically-... http://stackoverflow.com/questions/935516/how-does-macos-developer-navigate-large-code-base http://stackoverflow.com/questions/935516/how-does-macos-dev... python: http://code.activestate.com/recipes/213898/ http://code.activestate.com/recipes/213898/ http://stackoverflow.com/questions/1568544/given-a-python-class-how-can-i-inspect-and-find-the-place-in-my-code-where-it-is http://stackoverflow.com/questions/1568544/given-a-python-cl... emacs, vim, ctags, etags, http://stackoverflow.com/questions/1220456/navigating-effectively-through-source-code-in-linux http://stackoverflow.com/questions/1220456/navigating-effect...
• ssamuli 17y ago
  I guess you could also take a look at a tool called "LXR Cross Referencer" at http://sourceforge.net/projects/lxr/ http://sourceforge.net/projects/lxr/. Page http://fxr.watson.org http://fxr.watson.org includes LXR-generated cross references for multiple operating systems.