51 lines
2.2 KiB
Markdown
51 lines
2.2 KiB
Markdown
For a Haskell programmer, and day where a big thing is implemented
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without the least scrap of code that touches the IO monad is a good day.
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And this was a good day for me!
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Implemented the p2p protocol for tor hidden services. Its needs are somewhat
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similar to the external special remote protocol, but the two protocols are
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not fully overlapping with one-another. Rather than try to unify them, and
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so complicate both cases, I prefer to reuse as much code as possible between
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separate protocol implementations. The generating and parsing of messages
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is largely shared between them. I let the new p2p protocol otherwise
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develop in its own direction.
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But, I *do* want to make this p2p protocol reusable for other types of p2p
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networks than tor hidden services. This was an opportunity to use the Free
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monad, which I'd never used before. It worked out great, letting me write
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monadic code to handle requests and responses in the protocol, that reads
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the content of files and resumes transfers and so on, all independent
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of any concrete implementation.
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The whole implementation of the protocol only needed 74 lines of monadic code.
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It helped that I was able to factor out functions like this one, that is used
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both for handling a download, and by the remote when an upload is sent to it:
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receiveContent :: Key -> Offset -> Len -> Proto Bool
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receiveContent key offset len = do
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content <- receiveBytes len
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ok <- writeKeyFile key offset content
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sendMessage $ if ok then SUCCESS else FAILURE
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return ok
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To get transcripts of the protocol in action, the Free monad can be evaluated
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purely, providing the other side of the conversation:
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ghci> putStrLn $ protoDump $ runPure (put (fromJust $ file2key "WORM--foo")) [PUT_FROM (Offset 10), SUCCESS]
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> PUT WORM--foo
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< PUT-FROM 10
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> DATA 90
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> bytes
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< SUCCESS
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result: True
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ghci> putStrLn $ protoDump $ runPure (serve (toUUID "myuuid")) [GET (Offset 0) (fromJust $ file2key "WORM--foo")]
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< GET 0 WORM--foo
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> PROTO-ERROR must AUTH first
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result: ()
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Am very happy with all this pure code and that I'm finally using Free monads.
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Next I need to get down the the dirty business of wiring this up to
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actual IO actions, and an actual network connection.
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Today's work was sponsored by Jake Vosloo on Patreon.
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