Re: [lwip-users] UDP bind error due to address and port reuse

[Surya Chaitanya]

Hi Noam,

On the recipients side, they are using the same port for send and receive. And 
yeah, 
like you mentioned, we do have a way(an ID) to recognize from which port, the 
data 
has arrived. 

What I would like to know is after sending 5 messages from the application at 
the 
embedded side using one port and one UDP PCB, can I listen to all the 5 ports 
of the 
destination using the same one UDP PCB? Thanks.

Regards,
Surya 

On Wed, 7 Dec 2016 10:56:08 +0000, Noam Weissman wrote
> Hi,
> 
> Dirk, if the application is creating a different port on every reply you 
> cannot rely on that.
> 
> You must have control over the data
> 
> Surya,
> 
> Yes you can listen on a single UDP but you need to get some kind of data that 
> will let you know who
> 
> Responded.
> 
> If you have a processing issue, meaning you send 5 messages and applications 
> send the replies
> 
> more or less at the same time, you may need to first to add the received data 
> to some kind of
> 
> temporary buffering mechanism and in the background process one message at a 
> time.
> 
> The above buffering mechanism ensures that you do not loos any [UTF-8?]data…
> 
> This is how I would have done it.
> 
> BR,
> 
> Noam.
> 
> From: lwip-users [mailto:address@hidden On 
> Behalf Of Dirk Ziegelmeier
 Sent: Wednesday, December 07, 2016 12:44 PM
 To: 
> Mailing list for lwIP users
 Subject: Re: [lwip-users] UDP bind error due to 
> address and port reuse
> 
> Use one UDP PCB, bind it to IPADDR_ANY and port x.
> Use udp_sendto() to send to any IP/port combination.
> http://www.nongnu.org/lwip/2_0_0/group__udp__raw.html
> 
> You get the src address/port of any request in your receive callback:
> 
> void my_udp_recv_fn (void *arg, struct 
> udp_pcb<http://www.nongnu.org/lwip/2_0_0/structudp__pcb.html> *pcb, struct 
> pbuf<http://www.nongnu.org/lwip/2_0_0/structpbuf.html> *p, const 
> 
ip_addr_t<http://www.nongnu.org/lwip/2_0_0/group__ipaddr.html#ga44f9ada14c65d17aecf8
02d82eb273c5> *addr, u16_t port)
 {
   [create new pbuf with response]
   udp_sendto(pcb, response_pbuf, addr, port);
 [UTF-8?]​}
 [UTF-8?]​Dirk
 [UTF-8?]​


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