Step 1: er-coap.c
The file handling server receives data function
static int coap_receive(void)
erbium_status_code = NO_ERROR;//initialization
erbium_status_code=coap_parse_message(message,uip_appdata, uip_datalen());
//for example error messages
if(erbium_status_code == NO_ERROR)
erbium_status_code = NOT_IMPLEMENTED_5_01;
coap_error_message = “NoBlock1Support”;
erbium_status_code = PACKET_SERIALIZATION_ERROR;
erbium_status_code = SERVICE_UNAVAILABLE_5_03;
coap_error_message = “NoFreeTraBuffer”;
}