callback of failed listen call wrongly invoked after successful call

[vincentcr]

with node 0.6.5 on a mac:

it seems that if one retries a listen on a server after the first one failed (because, eg, we're trying to find a free port), the callbacks will be invoked both for the first, failed, call, and the second, successful call.

here's a sample that explains it better, i hope:

var http = require('http');

var port = 12345;

var s1 = http.createServer();

s1.listen(port, function(){
    console.log('s1 listen successful:', s1.address().port);
});

var s2 = http.createServer();

s2.on('error', function(err) {
    if (err.code !== 'EADDRINUSE') throw err;

    //retry next port
    s2.listen(port + 1, function(){
        console.log('s2 listen # 2 successful:', s2.address().port);
    });
});

s2.listen(port, function(){
    console.log('s2 listen # 1 successful:', s2.address().port);
});

this outputs:

s1 listen successful: 12345
s2 listen # 1 successful: 12346
s2 listen # 2 successful: 12346

's2 listen # 1' should not happen because it wasn't, in fact, sucessful as the port was busy with s1.

[bnoordhuis]

What happens is that both calls to s2.listen() register their own 'listening' event handler. When the second listen attempt succeeds, both handlers fire. If you explicitly register the handler it works as expected:

var http = require('http');

var port = 12345;

var s1 = http.createServer();

s1.listen(port, function(){
    console.log('s1 listen successful:', s1.address().port);
});

var s2 = http.createServer();

// REGISTER HANDLER
s2.on('listening', function() {
    console.log('s2 listen # 1 successful:', s2.address().port);
});

s2.on('error', function(err) {
    if (err.code !== 'EADDRINUSE') throw err;

    //retry next port
    s2.listen(port + 1);
});

s2.listen(port);

I agree it's somewhat confusing behaviour, we should probably fix it.

[vincentcr]

thanks for the workaround.

[vincentcr]

btw i would like to point out that this is mostly a documentation issue.

the doc for net.listen makes clear what is happening and, if i had read it, i would not have thought of this behavior as a bug.

however, the doc for http.listen (which is what i read) is more ambiguous. also it's not mentioned that http extends net (however obvious this seems once you know), and so that http.listen is in fact net.listen.

[koichik]

@vincentcr: I agree.

@bnoordhuis: Can you review koichik/node@4d954b8?

[bnoordhuis]

@koichik: LGTM

[koichik]

@bnoordhuis: Thanks!