[Vm-dev] Socket listening

Bert Freudenberg bert at freudenbergs.de
Tue Jul 1 13:35:23 UTC 2008

Ian, and folks,

I'm trying to write a more robust Etoys server for OLPC, and found  
some surprising listening behavior.

The snippet below tries to listen on the same port twice. I'd have  
expected to get an error on the second listening attempt. However, on  
both Linux and Mac OS X (John's VM) I get back

	#(6060 57855)

which means the second socket listens successfully, but on a random  
port. I verified it is actually listening there using lsof. The  
SO_REUSEADDR option does not make any difference, btw.

So, is this intended behavior? If not, will we change it?

In my actual use case I would have tried to iterate through some ports  
to find an unbound one, so in this particular case the behavior is  
convenient for me. But I think I should not rely on it. Also, the same  
code gives an error (as expected) on Windows.

- Bert -

         p := 6060.

         s1 := Socket newTCP.
         s1 setOption: 'SO_REUSEADDR' value: 0.
         s1 listenOn: p.

         s2 := Socket newTCP.
         s2 setOption: 'SO_REUSEADDR' value: 0.
         s2 listenOn: p.

		s1 isValid ifTrue: [s1 port].
         	s2 isValid ifTrue: [s2 port]
] ensure: [
         s1 destroy.
         s2 destroy.

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