[lwip-users] Issue with TCP raw API and messages larger than TCP_MSS

[David Perlaza]

Hi,

 

I am currently writing a raw-API-based HTTP client to request and receive a still image from an IP camera. The HTTP response from the camera is about 7 kB in size, and because of the fact the image is in the JPEG format, the size of the message varies between messages. The problem I am experiencing is that I am receiving each TCP segment (1024 bytes) as a single pbuf instead of a pbuf chain, complicating the reception of a single HTTP response. Based on some messages posted to the mailing list, my application uses the function pbuf_copy_partial() and acknowledges the data received using p->tot_len; however, I have noticed that  p->len is always equal to p->tot_len (i.e. 1024) and p->next is always NULL. Am I missing any configuration settings to enable the buffering of the entire HTTP data before it gets processed in my tcp_recv callback? I have attached a Wireshark capture of the packets sent by the camera (IP address 10.77.0.60) to the microprocessor running my application (IP address 10.77.0.57).

 

Thank you,

 

David

 

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