setting a backlog, response issue with TCP Raw Socket Server

[VSomasekhar]

1. How to set the number of simultaneous connections (backlog) in the Raw Socket Listen API? This is the relevant code snippet: /* start tcp listening for echo_pcb */ tcp_echoserver_pcb = tcp_listen( tcp_echoserver_pcb ); In contrast, the BSD/LWIP Sockets Listen API is: int lwip_listen(int s, int backlog)
2. Do I have to enable this macro in opt.h for the above purpose? #define TCP_LISTEN_BACKLOG
3. I am running a modified TCP Echo Server on the Board and sending continuous sequence of Modbus requests from the Modscan32 tool to the Modbus server running on the Board with STM32H723Zet6 MCU. But the response is given only to the first Request. The TCP Server is based on the source in the webpage: https://community.st.com/t5/stm32-mcus-embedded-software/how-to-send-data-lwip-tcp-server-to-client/td-p/119556
4. How to modify the TCP Raw Socket Server mentioned above to send the response for all the request packets? As mentioned, the TCP Raw Socket Server is responding only once, that too after restart.

[STea]

Hello @VSomasekhar ,

I think that the server stops responding because you are running out of memory as you allocate a packet each time you try to send a response and then this packet should be free afterwards.
you need also to set the pointer back to NULL after sending the response to make sure you are not holding the received buffer value in your send buffer.

ideally you should implement proper buffer management for this to work properly and ensure that you have sufficient space in the pool for handling data in LWIP.
Regards

 

[VSomasekhar]

Hi,

Thanks for the suggestion. I've created a packet buffer in ModbusIxFace(struct pbuf *p), using pbuf_alloc(). I've freed it in tcp_echoserver_recv(..), using pbuf_free(), where:

es->state == ES_CLOSING

But now the server is responding 4-5 times only and then stopping responses. The file is attached. Please check and suggest. I've tried the same at other locations also, where pbuf_free(p) was called and where: es->state = ES_CLOSING_SERVER;

In the program, I've created only one packet buffer, and tried to free it. But it doesn't seem to improve - hardly 4-5 responses.