Erlang Examples

It’s been a long time I haven’t blogged anything about erlang … damn… too many cool stuff but too little time. Actually my works are getting heavily busy these days + 4-month-old kid … lots of excuses huh?

Good news is I’ve been back to my Erling (AMF Implementation) recently. While spending sometimes to see what progress I have made so far, I came across OMS (OneTeam Media Server) release announcement.

OneTeam Media Server, or OMS for short, is a new Flash server implementation, written in erlang, by ProcessOne. This will enable your users to broadcast voice and/or video streams to multiple subscribers.

Wow, this is a great news … it’s greater to see more and more heavy task back-end services written in Erlang. I’ve registered an account with ProcessOne Git Repository just to fork the project. Lots of thing can learn from OMS. Many thanks to ProcessOne for open source this project.

Trung AMF AMF, erling, media server, oms, processone

For AMF implementation, I have to define the mapping between Actionscript classes with something equivalent in Erlang. First thing came into my mind is record. However, I immediately encountered some of the difficulties when using records in Erlang

1. Read: can’t use reflection easily after parsing AMF, I received the object with properties/values and I need to map to the corresponding record
2. Write: Need to introspect the record and write its properties into binaries

I found this post from trapexit. However, I need specifically more than that.

Normally records are defined in a header file “.hrl”. And the idea is to generate utility codes (getter, setter, record meta data ….) at compile time. The heart of it is epp:parse_file/3 function. The generator (or the helper) reads header files, parses all records and create a compilable .erl file which contains all functions you need to do all magic with records:

1. set(Obj, PropertyName, Value) -> {ok, NewObj, {PropertyName, Value}}
2. get(Obj, PropertyName) -> {ok, Value}
3. fields(record_name) -> Fields = [string()]
4. fields_atom(record_name) -> Fields = [term()]
5. type(Obj) -> record_name

messages.hrl – the source

record_helper.erl – the generator

record_utils.erl – the generated source

Below is the demonstration of how to generate and use the record utils

1> c(record_helper.erl).
{ok,record_helper}
2> record_helper:make(["messages.hrl"], ".").
ok
3> ls().
messages.hrl            record_helper.beam
record_helper.erl      record_utils.erl
ok
6> c(record_utils).
{ok,record_utils}
7> rr("messages.hrl").
[abstract_message,async_message]
8> Obj = #async_message{}.
#async_message{
    parent =
        #abstract_message{
            clientId = undefined,destination = undefined,
            messageId = undefined,timestamp = undefined,
            timeToLive = undefined,headers = undefined,body = undefined},
    correlationId = undefined,correlationIdBytes = undefined}
9> record_utils:set(Obj, correlationId, "ADF-123-DDF-543").
{ok,#async_message{
        parent =
            #abstract_message{
                clientId = undefined,destination = undefined,
                messageId = undefined,timestamp = undefined,
                timeToLive = undefined,headers = undefined,body = undefined},
        correlationId = "ADF-123-DDF-543",
        correlationIdBytes = undefined},
    {correlationId,"ADF-123-DDF-543"}}
10> {ok,NewObj, _} = record_utils:set(Obj, correlationId, "ADF-123-DDF-543").
{ok,#async_message{
        parent =
            #abstract_message{
                clientId = undefined,destination = undefined,
                messageId = undefined,timestamp = undefined,
                timeToLive = undefined,headers = undefined,body = undefined},
        correlationId = "ADF-123-DDF-543",
        correlationIdBytes = undefined},
    {correlationId,"ADF-123-DDF-543"}}
11> record_utils:get(NewObj, correlationId).
{ok,"ADF-123-DDF-543"}
12> record_utils:type(NewObj).
async_message

record_helper.erl is not so clean as there’re all string concatenations … further improvements can be:

1. Using template language like ErlyDTL or ErlTL …
2. Clean up code to have more friendly arguments
3. You add ….

Trung AMF, Basic, Record autogenerate, instrospection, Record

I just restarted a long sleep idea to implement AMF using Erlang, the project, codenamed Erling, is hosted in github. There’s nothing much yet except amf0 and amf3 implementation, i’m working on the unit test for whatever I’ve written so far to make sure it won’t go messy as the code evolved.
Everyday I’m learning new thing along with Erling and therefore more Erlang examples to come …

Trung AMF AMF, erling, git, github