unexpected recursion in restler call (node/js)

Question

I want to get a URI, parse it, and then get another URI based on the parsed data. Using restler, I thought I could do the parsing and the second get call from the .on('complete',...) function of the first get call. It doesn't seem to work as I expect. To investigate, I coded up the following, which is a very simplified version of how my code is structured. It never exits until I hit Ctrl-C.

var sys = require('util');
var rest = require('restler');

function UriCall( uri, handler ) {
    rest.get(uri).on('complete', function(result) {
        if (result instanceof Error) {
            sys.puts('Error: ' + result.message);
        }
        else {
            if (handler) { handler( result ); }
            else { sys.puts('No handler provided.'); }
        }
    });
} 

var uri = "http://www.google.com";

UriCall(uri, function(result) {
   sys.print("@");
   UriCall(uri, function(result) {
      sys.print(".");
   });
});

Output:

$node resttest.js

@@.@..@...@....@.....@......@.......@........@ [deleted error messages] .........@..........@...........@............@.............@..............@...............@................@.................@..................@...................@....................@.....................@......................@.......................@........................@.........................@..........................@...........................@............................@.............................@..............................@...............................@................................@.................................@..................................@...................................  ^C

From the output above it looks like something is getting stacked up with each call and it just gets deeper and deeper. I'm a C/C++ guy who is just getting started with js/node/restler. Why doesn't the program simply call UriCall twice and then exit?

(BTW: The errors messages start with "(node) warning: possible EventEmitter memory leak detected 11 listeners added. Use emitter.setMaxListeners() to increase limit." and then included some trace. The error message doesn't surprise me given what appears to be happening.)

score 1 · Answer 1 · edited May 23 '17 at 11:43

1

When you attach the event listeners to the 'complete' event, they don't go away after the event happens (they will run again with the same callback method you put in originally when any 'complete' is detected). Every successful call to your uri will trigger this event. So you are basically stacking up function calls on the 'complete' event, and the recursive call in the first callback adds more each time the original event is triggered. Does that make sense?

I suggest using .once instead of .on, as was suggested here (Multiple responses on node.js restler call). Or unbind the event upon success.

edited May 23 '17 at 11:43

Community

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answered Sep 06 '13 at 17:20

hiattp

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Thanks. Using rest.get.once did the trick. Output: @. So, every call to rest.get.on appends a new event handler? I assume there is some scope to the event list, that normally the event handler gets unbound, but here because of the nested call it never gets a chance to? – jbirkel Sep 06 '13 at 17:52
@jbirkel. Correct. If you want it to map multiple times, but you might call it more than once, you can name it something like `complete.UriCall` and do an `.off('complete.UriCall')` before you call the `on`. Everything before the period is the event name, and everything afterwards is just for differentiating it later on. – Colin DeClue Sep 06 '13 at 17:56
On/off -- that's good to know. I was thinking of it as "onComplete" Thanks, Colin. – jbirkel Sep 06 '13 at 20:39

unexpected recursion in restler call (node/js)

1 Answers1