Universal Binary Format and JSON-RPC

Authors: Joseph Wayne Norton (norton@alum.mit.edu).

This is UBF-JSONRPC, a framework for integrating UBF, JSF and JSON-RPC. This repository depends on the UBF and MOCHIWEB (actually only the mochijson2.erl module) open source repositories.

This repository is intended for production deployment and is deployed in carrier-grade systems.

Quick Start Recipe

To download, build, and test the ubf_jsonrpc application in one shot, please follow this recipe:

$ mkdir working-directory-name
$ cd working-directory-name
$ git clone https://github.com/ubf/ubf-jsonrpc.git ubf_jsonrpc
$ cd ubf_jsonrpc
$ make deps clean compile test

Documentation

Where should I start?

This README is a good first step.

The UBF User's Guide is the best next step. Check out http://ubf.github.com/ubf/ubf-user-guide.en.html for further detailed information.

Eunit tests can be found in the test/eunit directory. These tests illustrate an inets-based httpd module that uses UBF's contract manager for checking JSON-RPC requests and responses.

What is UBF?

UBF is the "Universal Binary Format", designed and implemented by Joe Armstrong. UBF is a language for transporting and describing complex data structures across a network. It has three components:

UBF(a) is a "language neutral" data transport format, roughly equivalent to well-formed XML.
UBF(b) is a programming language for describing types in UBF(a) and protocols between clients and servers. This layer is typically called the "protocol contract". UBF(b) is roughly equivalent to Verified XML, XML-schemas, SOAP and WDSL.
UBF(c) is a meta-level protocol used between a UBF client and a UBF server.

See http://ubf.github.com/ubf for further details.

What is JSF?

JSF is an implementation of UBF(b) but does not use UBF(a) for client-server communication. Instead, JSON (RFC 4627) is used.

"JSF" is short for "JavaScript Format".

There is no agreed-upon convention for converting Erlang terms to JSON objects. This library uses the convention set forth by MochiWeb's JSON library (see URL above). In addition, there are a couple of other conventions layered on top of MochiWeb's implementation.

The UBF(b) contract checker has been modified to make a distinction between an Erlang record and an arbitrary Erlang tuple. An experience Erlang developer would view such a distinction either with skepticism or with approval.

For the skeptics, the contract author has the option of having the UBF(b) contract compiler automatically generate Erlang -record() definitions for appropriate tuples within the contract. Such record definitions are very convenient for developers on the Erlang side of the world, but they introduce more complication to the JavaScript side of the world. For example, JavaScript does not have a concept of an arbitrary atom, as Erlang does. Also, the JavaScript side must make a distinction between {foo, 42} and {bar, 42} when #foo is a record on the Erlang side but #bar is not.

This extra convention creates something slightly messy-looking, if you look at the raw JSON passed back-and-forth. The examples of the Erlang record {foo, 42} and the general tuple {bar, 42} would look like this:

record (defined in the contract as "foo() = #foo{attribute1 = term()};")

   {"$R":"foo", "attribute1":42}

general tuple

   {"$T":[{"$A":"bar"}, 42]}

However, it requires very little JavaScript code to convert objects with the "!$R", "$T", and "$A" notation (for records, tuples, and atoms) into whatever object is most convenient.

Tip

Gemini Mobile Technologies, Inc. has implemented a module for classifying the input character set< to detect non-UTF8 JSON inputs. This module has been released to the open-source world (http://github.com/hibari/gmt-util/blob/master/src/gmt_charset.erl) and copied to this repository as the jsf_charset.erl module.

What is JSON-RPC?

JSON-RPC is a remote procedure call protocol encoded in JSON. See http://json-rpc.org/ for full details.

Tools

For further information and help for related tools, please refer to the following links:

Erlang - http://www.erlang.org/
- R15B01 or newer, 17.0 has been tested most recently
Git - http://git-scm.com/
- Git 1.5.4 or newer, Git 1.9.3 has been tested most recently
GitHub - https://github.com