[erlang-questions] Peername of a closed TCP socket

Cameron Kerr ckerr@REDACTED
Wed Jun 3 20:08:13 CEST 2009

In your C server, what happens if you put a sleep(1) between the  
accept(socket, NULL, ...) and the getpeername()?

I'm [still a relative Erlang newbie, but an experienced socket  
programmer] thinking it's basically a race condition. What you really  
want in this case is the form of accept(2) that gives you the  
peername. That way this case cannot occur. Unfortunately, there is no  
suitable inet:accept variant that gives you this information, as far  
as I can tell. (Would love to be corrected about that).

On 3/06/2009, at 11:19 PM, Dowse, Malcolm wrote:

> Hi,
> Thanks for the tip, but unfortunately it didn't help. After some more
> investigation I managed to reproduce the issue. The client was closing
> its connection immediately after opening with the SO_LINGER option
> enabled, and a timeout of 0 seconds. This resulted in a RST with no  
> FIN.
> So, even if I called peername immediately after accept, with option
> {exit_on_close, false} set, it always returned enotconn.
> However, when I wrote a server in C I had no problem getting the  
> remote
> address. The 'accept' C call returns a socket address along with the  
> new
> file descriptor. This is also the interface given by the 'accept' call
> in python's socket module.
> Would it be possible to get a similar accept interface in Erlang, in  
> the
> future?
> best regards,
> malcolm
> -----Original Message-----
> From: Tony Rogvall [mailto:tony@REDACTED]
> Sent: 26 May 2009 22:06
> To: Dowse, Malcolm
> Cc: Erlang Questions
> Subject: Re: [erlang-questions] Peername of a closed TCP socket
> You can try the inet option:
> 	{exit_on_close, false}
> This will keep the port and the socket active so you can read
> statistics,
> continue write data to a half open socket and possibly get the
> peername, if that is available
> by the underlying operating system.
> You must then call gen_tcp:close to terminate the port/socket
> /Tony
> On 26 maj 2009, at 17.39, Malcolm Dowse wrote:
>> Hello,
>> When a TCP client disconnects very soon after connecting to an
>> Erlang server, is there any reliable way of getting the client's
>> remote address?
>> The inet:peername/1 function returns an error if the socket in
>> question has closed. As a result, I can't find any better solution
>> than to refactor the code so that inet:peername/1 is called as soon
>> as possible after the gen_tcp:accept/1.
>> Thanks in advance,
>> malcolm
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