gcoap: Update example for Observe, including documentation.

examples/gcoap/README.md

@@ -14,13 +14,14 @@ Build with `Makefile.slip`. Follow the setup instructions in README-slip.md, whi
 ## Current Status
 gcoap includes server and client capability. Available features include:
 
+* Message Type: Supports non-confirmable (NON) messaging. Additionally provides a callback on timeout.
+* Observe extension: Provides server-side registration and notifications.
 * Server and Client provide helper functions for writing the response/request. See the CoAP topic in the source documentation for details. See the gcoap example for sample implementations.
 * Server allows an application to register a 'listener', which includes an array of endpoint paths and function callbacks used to write a response.
 * Server listens on a port at startup; defaults to 5683.
-* Client operates asynchronously; sends request and then handles response in a user provided callback. Also executes callback on timeout.
+* Client operates asynchronously; sends request and then handles response in a user provided callback.
 * Client generates token; length defined at compile time.
-* Message Type: Supports non-confirmable (NON) messaging.
-* Options: Supports Content-Format for response payload.
+* Options: Supports Content-Format for payload.
 
 
 ## Example Use

examples/gcoap/gcoap_cli.c

@@ -26,6 +26,9 @@
 #include "od.h"
 #include "fmt.h"
 
+#define ENABLE_DEBUG (0)
+#include "debug.h"
+
 static void _resp_handler(unsigned req_state, coap_pkt_t* pdu);
 static ssize_t _stats_handler(coap_pkt_t* pdu, uint8_t *buf, size_t len);
 
@@ -149,15 +152,33 @@ int gcoap_cli_cmd(int argc, char **argv)
                                                                            argv[4]);
                 }
                 printf("gcoap_cli: sending msg ID %u, %u bytes\n", coap_get_id(&pdu),
-                                                                   (unsigned) len);
+                       (unsigned) len);
                 if (!_send(&buf[0], len, argv[2], argv[3])) {
                     puts("gcoap_cli: msg send failed");
                 }
+                else {
+                    /* send Observe notification for /cli/stats */
+                    switch (gcoap_obs_init(&pdu, &buf[0], GCOAP_PDU_BUF_SIZE,
+                            &_resources[0])) {
+                    case GCOAP_OBS_INIT_OK:
+                        DEBUG("gcoap_cli: creating /cli/stats notification\n");
+                        size_t payload_len = fmt_u16_dec((char *)pdu.payload, req_count);
+                        len = gcoap_finish(&pdu, payload_len, COAP_FORMAT_TEXT);
+                        gcoap_obs_send(&buf[0], len, &_resources[0]);
+                        break;
+                    case GCOAP_OBS_INIT_UNUSED:
+                        DEBUG("gcoap_cli: no observer for /cli/stats\n");
+                        break;
+                    case GCOAP_OBS_INIT_ERR:
+                        DEBUG("gcoap_cli: error initializing /cli/stats notification\n");
+                        break;
+                    }
+                }
                 return 0;
             }
             else {
                 printf("usage: %s <get|post|put> <addr> <port> <path> [data]\n",
-                                                                       argv[0]);
+                       argv[0]);
                 return 1;
             }
         }