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Re: [lwip-users] Problem with NULL pcb->callback_arg

From: address@hidden
Subject: Re: [lwip-users] Problem with NULL pcb->callback_arg
Date: Tue, 04 Aug 2009 15:55:12 +0200
User-agent: Thunderbird (Macintosh/20090605)

Baptiste Chaboud-crousaz wrote:

Sometimes, the face trouble with my callback http_connect - called by the macro TCP_EVENT_SENT - because "arg" is null.

I don't understand that one:
a) there is no function 'http_connect' in the code you posted
b) TCP_EVENT_SENT calls the function set by calling tcp_sent(pcb, fn) - the code you posted doesn't call tcp_sent(). c) I would have thought a connect function would be used with a client, not a server - whereas an accept function (as you posted) is used with a server, not a client)

My understanding is that the http_accept function binds a pcb to an argument by a call to tcp_arg(...). I don't undersatnd why sometimes my callback is called with a NULL arg!!!

This issue seems to be avoided/limited by increasing the size of MEM_SIZE and PBUF_POOL_SIZE.

That could be a hint that you are writing beyond allocated memory somwhere and overwrite the memory where the PCB lies with zeros...

If anybody has an idea, let me knwo about it...

Except for the above, I'm afraid I don't have an idea. Unless you call *tcp_arg(pcb, NULL) somewhere else, of course...*

Does the argument get NULL during the connection or right at the start?


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