@Jens: many thanks
On Tue, May 7, 2013 at 6:02 PM, Jens Jorgensen <jbj1 at ultraemail.net> wrote:
> One thing I didn't mention before will perhaps make you feel better. The
> OS will not object to the client send()ing on a socket when FIN has been
> received on it. On the server end though is another story. If the file
> handle for the socket has been closed (it wouldn't /have/ to be, the server
> code could have called shutdown() with SHUT_WR and that would have also
> triggered FIN) then when new data is received an RST will be sent back to
> the client. Now on the client end if you try to call send() when the OS has
> received RST you will indeed get an error... a second way you will detect
> that the socket has closed. I attach a real working Python script that will
> demonstrate the behavior (the second time the client calls send() a Python
> exception will result).
>
> There are lots of subtleties to how TCP works ;-)
>
>
> On 5/7/13 6:46 PM, Khoa Pham wrote:
>
> @Jens. thanks
>
> If we can read/write packets to detect closed socket, why is there TCP
> keep alive ??
>
>
> On Tue, May 7, 2013 at 2:07 PM, Jens Jorgensen <jbj1 at ultraemail.net>wrote:
>
>> Well the thing is just because you sniffed the packet off the wire
>> doesn't in any way mean the "client" (i.e. the SIP software) has actually
>> received it. In fact, a pretty reasonable piece of SIP code (I'll just
>> write Python pseudo-code for brevity) might look something like:
>>
>> s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
>> s.connect( (server, port) )
>> s.send('REGISTER ....')
>> while True :
>> bytes = s.recv(256)
>> if len(bytes) == 0 :
>> # uh-oh, the remote end closed the socket
>>
>> And in fact even if the OS has received the [FIN,ACK] already when
>> s.send() is called, this will *not* cause an error. The send() will
>> complete successfully. Try it!
>>
>>
>> On 5/7/13 2:58 PM, Khoa Pham wrote:
>>
>> @Jens, thanks for reply
>>
>> But client already received the [FIN,ACK] from server, it should know
>> that sending REGISTER does not make sense anymore
>>
>>
>> On Tue, May 7, 2013 at 12:13 PM, Jens Jorgensen <jbj1 at ultraemail.net>wrote:
>>
>>> You make it sound like you want the client to hang up?! As you know,
>>> the primary way a program finds out if a socket is closed is to try reading
>>> or writing on it. In this case the server has closed its end of the socket
>>> but the client probably doesn't know that (yet)--evidently because it
>>> thought it would get the chance to REGISTER
>>>
>>> On 5/6/13 5:15 PM, Khoa Pham wrote:
>>>
>>> Hi pjsip team,
>>>
>>> When I make REGISTER request to server, I often receive this
>>>
>>> 1. client: SYN
>>> 2. server: SYN, ACK
>>> 3. client: ACK
>>> 4. server: FIN, ACK
>>> 5. client: REGISTER
>>> 6. server: RST
>>>
>>> Why in step 5 does client not send FIN, ACK ??
>>>
>>> --
>>> Khoa Pham
>>> HCMC University of Science
>>> Faculty of Information Technology
>>>
>>>
>>> _______________________________________________
>>> Visit our blog: http://blog.pjsip.org
>>>
>>> pjsip mailing listpjsip at lists.pjsip.orghttp://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org
>>>
>>>
>>> --
>>> Jens B. Jorgensenjbj1 at ultraemail.net
>>>
>>>
>>> _______________________________________________
>>> Visit our blog: http://blog.pjsip.org
>>>
>>> pjsip mailing list
>>> pjsip at lists.pjsip.org
>>> http://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org
>>>
>>>
>>
>>
>> --
>> Khoa Pham
>> HCMC University of Science
>> Faculty of Information Technology
>>
>>
>> _______________________________________________
>> Visit our blog: http://blog.pjsip.org
>>
>> pjsip mailing listpjsip at lists.pjsip.orghttp://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org
>>
>>
>> --
>> Jens B. Jorgensenjbj1 at ultraemail.net
>>
>>
>> _______________________________________________
>> Visit our blog: http://blog.pjsip.org
>>
>> pjsip mailing list
>> pjsip at lists.pjsip.org
>> http://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org
>>
>>
>
>
> --
> Khoa Pham
> HCMC University of Science
> Faculty of Information Technology
>
>
> _______________________________________________
> Visit our blog: http://blog.pjsip.org
>
> pjsip mailing listpjsip at lists.pjsip.orghttp://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org
>
>
> --
> Jens B. Jorgensenjbj1 at ultraemail.net
>
>
> _______________________________________________
> Visit our blog: http://blog.pjsip.org
>
> pjsip mailing list
> pjsip at lists.pjsip.org
> http://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org
>
>
--
Khoa Pham
HCMC University of Science
Faculty of Information Technology
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