Stack overflow when IOT_DEBUG is enabled

[lkaino]

When IOT_DEBUG is enabled, iot_tls_connect declares a stack variable of 16 kB:

#ifdef IOT_DEBUG
	unsigned char buf[MBEDTLS_SSL_MAX_CONTENT_LEN + 1];
#endif

This will easily cause stack overflow on many embedded devices.

I suggest to declare the buf global instead.

[lkaino]

In addition, I think above should be wrapped inside

#ifdef ENABLE_IOT_DEBUG
instead of
#ifdef IOT_DEBUG
as IOT_DEBUG is always defined.

[chaurah]

Hi @lkaino,
Thank you for the suggestion. We are looking into optimizing the SDK so it can be used on smaller devices. I have made a note of this suggestion in our internal tracker. We will definitely look into optimizing the debug memory allocations as well for the next release.

Please do let us know if you have further suggestions.

Rahul