Parsing a stream of JSON with pipes-aeson

Question

Given a simple example JSON type:

data Test = Test
  { name :: Text
  , age  :: Int
  } deriving (Show, Generic)

instance FromJSON Test

How can I use pipes-aeson to decode a stream of JSON messages coming over a socket using the decoded lens? As an example I'd like to just print them out as they're parsed:

main = connect "127.0.0.1" "8000" $ \(socket, _) -> $ runEffect $
  some use of zoom decoded? view decoded? >-> P.print

danidiaz danidiaz · Accepted Answer · 2015-03-16T07:56:08

decoded (the one from Pipes.Aeson.Unchecked) is a lens than transforms a Producer of raw bytes into a Producer of parsed FromJSON values.

So, we must first create the Producer of bytes out of the socket using the fromSocket function from the pipes-network package. Something like this:

-- to help with type inference
printTest :: (MonadIO m) => Consumer' Test m r
printTest = P.print

main = do
    connect "127.0.0.1" "8000" $ \(socket, _) -> $ runEffect $
        view decoded (fromSocket socket 4096) >-> printTest
    return ()

Parsing a stream of JSON with pipes-aeson

1 Answers