problems passing payload to AT#XHTTPCREQ in serial_lte_modem

[Michal Vacha]

When working with AT#XHTTPCREQ we have encountered the following provlems:

1. Sending AT Command `AT#XHTTPCREQ="POST","/upload","Content-Length:3357",3357` with the payload of size 3357 in one line, it breaks the serial_lte_modem app. This limit is not mentioned in the docs https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/applications/serial_lte_modem/doc/HTTPC_AT_commands.html I think it is caused by the handling of buffer overflow - it only drops the last character, but the app itself never recovers from it.

2. If we send the payload chunked, we encounter problems with unpaired double quotes - again, the app is deadlocked.

You can reproduce it by sending this: `{"data":"3582e2192900` as payload.

Caused by this line: https://github.com/nrfconnect/sdk-nrf/blob/master/applications/serial_lte_modem/src/slm_at_host.c#L565 

[Martin Lesund]

Hi Michal,

Thank you for your feedback. For further investigation I would like to know:
Which modem firmware version are you running?

Are you running the SLM application from NCS 1.4.0 ?

Could you share the full serial output log as well?

Best regards,
martin L.

[Michal Vacha]

Yes, I'm running the latest version. I can provide the log later this week. Both problems are reproducible from the LTE Link Monitor app.

[Martin Lesund]

Hi Michal,

We are investigating this internally and will update the application in NCS master to include the fix as soon as possible.

[Michal Vacha]

Hi Martin,

do you have any update on the official fix? In the meantime I have found the following workaround:

1) Replace " with ` before passing them to XHTTPCREQ

2) Replace them back in slm_at_httpc_parse like this:

char* replace_char(char* str, char find, char replace){
    char *current_pos = strchr(str,find);
    while (current_pos){
        *current_pos = replace;
        current_pos = strchr(current_pos,find);
    }
    return str;
}

int slm_at_httpc_parse(const char *at_cmd, size_t length)
{
...
	/* Process input data as payload */
	httpc.payload = replace_char((char *)at_cmd, '`', '"');
...
}

BR, Michal V.