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Re: [lwip-users] Sockopt SND_TIMEO

From: address@hidden
Subject: Re: [lwip-users] Sockopt SND_TIMEO
Date: Thu, 14 Jan 2010 21:32:29 +0100
User-agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; de; rv: Gecko/20091204 Thunderbird/3.0

Just one more thing about the send timeout - I've written it in bug #28605, too: What do you want to do on a timeout? With the suggested implementation below, you don't know how much data has already been sent when send() returns with an error... And there's not a simple solution for that aside from only allowing single-write in send-timeout mode (i.e. in do_writemore, skip the if (available < len) - send all or nothing).


Fabian Koch wrote:

address@hidden wrote on 13.01.2010 17:41:54:
> A more sophisticated way to implement this (which might even have
> the potential to be included in CVS?) would be to have a timstamp
> when write was started and let poll_tcp() or do_writemore() check
> whether the operation timed out (using sys_now() to get the
> timestamp and compare it). If you do that, it would be nice to share
> the work as a patch entry on savannah.

Hey Simon,

sys_now() is only used when LWIP_TCP_TIMESTAMPS is 1 and it's implementation is up to the user (probably in sys_arch.c), correct?
It would be great to document that at the appropriate places (release notes and Wiki) so that people don't trip over the missing function, when I use that as a timestamp provider. (Maybe I just missed it, but in "porting for an OS" it's not documented)

Also, I would make the feature optional and disabled in the standard version (just like the UDP Infos).
And maybe create the sockopt for it.

So in short:

1) create a timestamp in do_write() via sys_now() and save it in msg->conn->write_timestamp
2) at the beginning of do_writemore() get a current timestamp via sys_now() and compare it to msg->conn->write_timestamp
3) if the difference is greater than conn->pcb.tcp->snd_timeo then clear write_msg,_offset and state and signal op_complete (with ERR_* set)
4) have a reasonable default value for conn->pcb.tcp->snd_timeo in the area of 10-30 sec.?
[5) add the parsing of SOCKET_SO_SNDTIMEO to the socket API. I might not do that because I don't use that API]

Would that be okay with you guys and are there plans to release another 1.3.x Version before 1.4.0?
As I said before, we treat LwIP as an external Blob of Software that we don't change, so I'd need my own Patch included in an official Version "soon".

kind regards,
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