[rabbitmq-discuss] custom plugin debugging

[Tim Watson]

Hi

On 8 Nov 2012, at 23:22, Prabodh Upreti wrote:

> I got over the crash problem.
> 
> Now where I try to connect via my java client I get
> 
> =ERROR REPORT==== 8-Nov-2012::18:16:57 ===
> closing AMQP connection <0.246.0> (127.0.0.1:52094 -> 127.0.0.1:5672):
> {channel0_error,starting,
>    {error,function_clause,'connection.start_ok',
>        [{rabbitmq_cas_authen,q,
>             [user_path,
>              [{ticket,<<"ST-2-VYPDk5OF0y7SCDe9LGCO-cas01.example.org">>},
>               {password,<<>>}]],
>             []},

This error specifically means that the function 'q' in the rabbitmq_cas_authen module was called with the arguments given (i.e., q(user_path, [{ticket, _}, {password, <<>>}]) and there was no function clause matching those inputs, therefore the process executing that code crashed. This is probably because according to your subsequent post, you've defined q/2 as 

q(PathName, token) ->
   {ok, Path} = application:get_env(rabbitmq_cas_authen, PathName),
   R = Path ++ "?ticket=" ++ token,
   R.

So I think what you're probably getting confused about here is that in Erlang, variable names begin with a capital letter, so you'd want something more like `q(PathName, Token)` - the lowercase 'token' is an atom (i.e., like an interned string) and that's clearly not what's getting passed. I'd be remiss if I didn't strongly suggest spending some quality time with http://www.erlang.org/doc/reference_manual/users_guide.html at this point.

Now, you're trying to return `Path ++ "?ticket=" ++ Token` but the ++ operator is used to concatenate lists (which strings are represented as in Erlang) so even that's going to go wrong when you call it as `q(user_path, [{ticket, Username}|AuthProps])` because you've got a list of tuples there in that second parameter, not a string.

So..... What exactly are you trying to do here? It seems you want to append this *Token* to the URL you're doing a 'GET' on to authenticate, but where exactly is this Token data meant to be coming from? Is it in a header, or a cookie, or what? In Simon's code he appends the tuple {username, Username} to the AuthProps list, then takes all the {Key, Value} pairs in that list and formats them into a query string. But your 'token' seems to have appeared from nowhere!? At this point, even getting the syntax right isn't going to help! ;)

If you let us know where the token is meant to be coming from then I'm sure we can steer you in the right direction anyway.

Cheers,
Tim