CODEWITHSUNDEEP
error-handlingexceptionerlangejabberd
Gopal S Rathore
Gopal S Rathore

Reputation: 9995

Exception handling in Erlang to Continue execution

What I am trying to do is mochijson2:decode(Ccode) generates any exception or error, program execution should not stop and case branch {error, Reason} should get executed.

But when I am trying to get it implemented, it generates error at first line while checking and code doesn't continue execution for lines below it. 

SCustomid = case mochijson2:decode(Ccode) of
  {struct, JsonDataa} -> 
       {struct, JsonData} = mochijson2:decode(Ccode),
       Mvalll = proplists:get_value(<<"customid">>, JsonData),
       Pcustomid = erlang:binary_to_list(Mvalll),
       "'" ++ Pcustomid ++ "'";
  {error, Reason} -> escape_str(LServer, Msg#archive_message.customid)


end,

You could suggest if I need to use Try Catch. I am a bit experienced with Ejabberd but newbie for Erlang. Any help is appreciated.

Upvotes: 0

Views: 190

Answers (2)

P_A
P_A

Reputation: 1818

You can use this:

    SCustomid = try
                    {struct, JsonData} = mochijson2:decode(Ccode),
                    Mvalll = proplists:get_value(<<"customid">>, JsonData),
                    Pcustomid = erlang:binary_to_list(Mvalll),
                    "'" ++ Pcustomid ++ "'"
                catch _:_ -> escape_str(LServer, Msg#archive_message.customid)
                end

Upvotes: 1

Danil Onishchenko
Danil Onishchenko

Reputation: 2040

Seems the reason is an exception happens in mochijson2:decode/1. The function doesn't return a error as a tuple, instead the process crashes. There isn't enough information to tell what exactly the reason is. However I guess that the data format of Ccode might be wrong. You can handle exception using try ... catch statement:

SCustomid = try
  case mochijson2:decode(Ccode) of
    {struct, JsonDataa} -> 
       {struct, JsonData} = mochijson2:decode(Ccode),
       Mvalll = proplists:get_value(<<"customid">>, JsonData),
       Pcustomid = erlang:binary_to_list(Mvalll),
       "'" ++ Pcustomid ++ "'";
    {error, Reason} -> 
       escape_str(LServer, Msg#archive_message.customid) 
  end   
catch
  What:Reason ->
    escape_str(LServer, Msg#archive_message.customid)
end,

Or just catch:

SCustomid = case catch(mochijson2:decode(Ccode)) of
  {struct, JsonDataa} -> 
       {struct, JsonData} = mochijson2:decode(Ccode),
       Mvalll = proplists:get_value(<<"customid">>, JsonData),
       Pcustomid = erlang:binary_to_list(Mvalll),
       "'" ++ Pcustomid ++ "'";
  {error, Reason} -> 
     escape_str(LServer, Msg#archive_message.customid);
  {What, Reason} ->
    escape_str(LServer, Msg#archive_message.customid)
end,

Upvotes: 1

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