re-entrancy of httpd_ws_recv_frame (IDFGH-4619)

[oclyke]

Thanks for the addition of websocket support in the IDF! Overall it is making my job far easier. The problem I am facing is that I am forced to use a local buffer with a fixed size to receive the packet payload.

I would like to use httpd_ws_recv_frame (or another high level idf function) to measure the message length of the websocket packet before allocating memory to use for the payload, thus allowing me to handle any size packet. For example:

httpd_ws_frame_t ws_pkt = {0};

// determine the length of the message
httpd_ws_recv_frame(req, &ws_pkt, 0); // <-- ignore length error, we are just getting needed length
ESP_LOGI(TAG, "frame recvd with length: %d", ws_pkt.len);

// allocate enough memory for the data
void* data = malloc(ws_pkt.len);
ws_pkt.payload = (uint8_t*)data;

// receive the data
esp_err_t ret = httpd_ws_recv_frame(req, &ws_pkt, ws_pkt.len);
if(ret != ESP_OK){
  ESP_LOGE(TAG, "could not receive frame data - error (%d)", ret);
}

However from experience I have deduced that one cannot call httpd_ws_recv_frame more than once for a particular httpd request. When I do I always get the error ESP_ERR_INVALID_SIZE ("WS Message too long")

An example of a similar api is that of snprintf which, when the output buffer is NULL will return the number of characters that would have been necessary to store the output.

(p.s. if there is an existing API to get this information I would be happy to hear about it. I have tried searching the IDF docs but info concerning the httpd_ws_recv_frame function seems sparse)

[yuanjianmin]

0001-esp_http_server-support-dynamic-payload-len-for-ws-s.zip
@oclyke hi oclyke， Thank you for your suggestions, requirements and interface call ideas. I offer a patch to satisfy your requirements. Could you please help me to check this patch whether could meet your functions.
Thanks！
Wait for your reply.

[NikLeberg]

Hi @yuanjianmin
I'm not the original issue opener but I'm using your patch for a few days now. It works flawlessly!
Having this feature is very key for the app I'm building.
Thanks for the patch!
Nik

[oclyke]

Hi @yuanjianmin, thanks for writing that patch! I have just reviewed it and agree with NikLeberg that it is quite useful. Hoping that Espressif will be able to accept the changes so that I can rely on them in my application.

[yuanjianmin]

@NikLeberg @oclyke hi guys, the patch has been merged and will be synchronized to Github later. I will notify you as soon as synchronized to github. Thanks.