Erlang - Parse data from the enclosed curly braces

Question

Erlang experts, I am getting a data like the following from ejabberd server

I(<0.397.0>:mod_http_offline:38) : Data of Fromu {jid,"timok","localhost",
                                              "25636221451404911062246700",
                                              "timok","localhost",
                                              "25636221451404911062246700"}

I am a very much confused about this data type. All I need is to get timok from the enclosed flower braces. {} But not sure how to get the value. Any code to get the value will be much helpful. Currently I am printing the values using the below code

?INFO_MSG("Data of Fromu ~p",[_From]),

Thanks once again for your time and effort.

Berzemus · Accepted Answer · 2014-07-11T07:56:19.350

That's an erlang record (it's a tuple, first element an atom, other elements lists/strings/binaries).

Recommended:

Ejabberd has a jid record definition (line 411):

-record(jid, {user = <<"">> :: binary(),
        server = <<"">> :: binary(),
        resource = <<"">> :: binary(),
        luser = <<"">> :: binary(),
        lserver = <<"">> :: binary(),
        lresource = <<"">> :: binary()}).

It's in the ejabberd/include/jlib.hrl file, so you should be able make it known to your module by including it this way:

 -include_lib("ejabberd/include/jlib.hrl").

Now, in your module to access the (first) "timok" element of your data, you can use the erlang record syntax (assuming JidData contains the data mentioned above):

Out = JidData#jid.user.

Not recommended:

As records are, behind their appearance, tuples, you can also access the nth element of the tuple

Out = element(2,JidData).

Or simply use pattern matching:

{_, Out, _, _, _, _} = JidData.

Use Record Definitions

A record is basically syntaxic sugar on a tuple. It remains a tuple and can be treated as such. They're easy to work with, but you should do what you can to avoid treating a record as a tuple, unless you really know what you're doing.

And because in this case you don't even control the record definition, you really should use it, otherwise changes in the definition, following an update, will invalidate your code.

the above would only work in an erlang shell if the erlang shell already knows of the record definition — bjhaid, Jul 10 '14 at 02:58
Yep. In order to use the record definition in a module, one should include the related ejabberd header file (if there is such thing). — Berzemus, Jul 11 '14 at 07:34
@Berzemus - thanks a lot for the answer. I was able to retrieve the value with the help from your answer. — Timothy Rajan, Jul 14 '14 at 06:08

score 1 · Answer 2 · answered Jul 09 '14 at 13:37

You seem to be trying to access the second item in the tuple stored in variable _From. This can be accessed simply by using pattern matching:

{_, Username, _, _, _, _} = _From

Since you are using the from variable, you should not have a underscore in front of it. In your code change _From to From.

Erlang - Parse data from the enclosed curly braces

2 Answers2