NOTE: maintenance of BERT has been taken over by Roman Cheplyaka; its new location is https://github.com/feuerbach/bert

BERT[-RPC] for Haskell

by marius a. eriksen (marius@monkey.org)

This is a BERT serializer/deserializer and BERT-RPC client and server for Haskell. BERT-RPC currently supports synchronous (call) requests.

The primitives provided are fairly elementary: for the client, call provides the capability to perform the RPC call, while the server's serve is provided with a dispatch function providing the dispatching logic for the server. Thus, one can imagine building higher level abstractions on top of these primitives.

Installation

It's a cabal package, so

$ cabal configure && cabal install

should do the trick.

BERT

import qualified Data.ByteString.Lazy.Char8 as C
import Data.BERT

Creating BERT terms is simple.

TupleTerm [BytelistTerm (C.pack "hello"), IntTerm 123]

Or by using the BERT typeclass.

showBERT $ ("hello", 123)

The BERT class can also read terms back.

Right ("hello", 123) = readBERT . showBERT $ ("hello", 123)

BERT-RPC client

import Data.BERT
import Network.BERT.Client

Create a transport to the server endpoint, and issue a (synchronous) call with it.

t <- fromURI "bert://localhost:8000"
r <- call t "calc" "add" ([123, 3000]::[Int])
case r of
  Right res -> print (res :: Int)
  Left _    -> putStrLn "error"

BERT-RPC server

import Data.BERT
import Network.BERT.Server

Create a transport from which to accept connections, and provide a dispatch function for incoming RPCs. The dispatch function is issued in a new thread for each incoming request.

main = do
  t <- fromHostPort "" 8080
  serve t dispatch

dispatch "calc" "add" [IntTerm a, IntTerm b] = 
  return $ Success $ IntTerm (a + b)
dispatch "calc" _ _ =
  return NoSuchFunction
dispatch _ _ _ = 
  return NoSuchModule

Command line tool

Also included is a tool, bert that is able to parse terms in the erlang grammar and issue requests.

$ bert call bert://localhost:8000 calc add 123 456 
reply: 579 
$ bert call bert://localhost:8000 errorcalc add 123 456 
error: ServerError {error, {user, 0, <<"RuntimeError">>, 
<<"abandon hope!">>, [<<"/Users/marius/Loc.. 
$ bert call bert://localhost:8000 calc add "{1, test, [5,6,7]}" 456 
error: ServerError {error, {user, 0, <<"TypeError">>, 
<<"can't convert Fixnum into Array">>, ..