Streaming events URL support "not to use cache"

README.md

@@ -39,6 +39,31 @@ You can also build a debian package and install it:
 * See [SONiC telemetry in dial-out mode](./doc/dialout.md) for how to run dial-out mode system telemetry client
 * See [gNMI Usage Examples](./doc/gNMI_usage_examples.md) for gNMI client usage examples.
 
+### Streaming events
+SONiC publishes events of interest via gNMI.
+Sample events could be bgp-state change, link-state change.
+A sample query URL is as below.
+    `gnmi_cli -client_types=gnmi -a 127.0.0.1:50051 -t EVENTS -logtostderr -insecure -v 7 -streaming_type ON_CHANGE -q all -qt s`
+
+The events URL can take the following optional parameters.<br/>
+heartbeat:<br/>
+    `[heartbeat=<N>]`
+<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;The SONiC switch publishes periodic hearbeats when there are no events to publish.<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;The frequency of the heartbeat can be controlled by this parameter as beat in every N seconds.<br/>
+
+usecache:<br/>
+    `[usecache=true/false]`
+<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;The SONiC switch does offline cache when gNMI client is down.<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;The cached events are delivered upon nest gNMI connection<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;Only one client should use the cache service<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;The cached events are delivered upon nest gNMI connection<br/>
+&nbsp;&nbsp;&nbsp;&nbsp;If you are running test clients, use this param to turn off cache use.<br/>
+
+Sample URL: <br/>
+`gnmi_cli -client_types=gnmi -a 127.0.0.1:50051 -t EVENTS -logtostderr -insecure -v 7 -streaming_type ON_CHANGE -q all[heartbeat=5][usecache=false] -qt s`
+
 ## Need Help?
 
 For general questions, setup help, or troubleshooting:

gnmi_server/server_test.go

@@ -2619,7 +2619,7 @@ func TestClient(t *testing.T) {
     rcv_timeout := sdc.SUBSCRIBER_TIMEOUT
     deinit_done := false
 
-    mock1 := gomonkey.ApplyFunc(sdc.C_init_subs, func() unsafe.Pointer {
+    mock1 := gomonkey.ApplyFunc(sdc.C_init_subs, func(use_cache bool) unsafe.Pointer {
         return nil
 	})
 	defer mock1.Reset()
@@ -2672,7 +2672,7 @@ func TestClient(t *testing.T) {
         },
     }
 
-    sdc.C_init_subs()
+    sdc.C_init_subs(true)
 
     for _, tt := range tests {
         heartbeat = 0

sonic_data_client/events_client.go

@@ -56,6 +56,7 @@ const TEST_EVENT = "{\"sonic-host:device-test-event"
 // Path parameter
 const PARAM_HEARTBEAT = "heartbeat"
 const PARAM_QSIZE = "qsize"
+const PARAM_USE_CACHE = "usecache"
 
 type EventClient struct {
 
@@ -90,12 +91,13 @@ func Set_heartbeat(val int) {
     }
 }
 
-func C_init_subs() unsafe.Pointer {
-    return C.events_init_subscriber_wrap(true, C.int(SUBSCRIBER_TIMEOUT))
+func C_init_subs(use_cache bool) unsafe.Pointer {
+    return C.events_init_subscriber_wrap(C.bool(use_cache), C.int(SUBSCRIBER_TIMEOUT))
 }
 
 func NewEventClient(paths []*gnmipb.Path, prefix *gnmipb.Path, logLevel int) (Client, error) {
     var evtc EventClient
+    use_cache := true
     evtc.prefix = prefix
     evtc.pq_max = PQ_DEF_SIZE
     log.V(4).Infof("Events priority Q max set default = %v", evtc.pq_max)
@@ -132,14 +134,19 @@ func NewEventClient(paths []*gnmipb.Path, prefix *gnmipb.Path, logLevel int) (Cl
                     evtc.pq_max = val
                     log.V(7).Infof("Events priority Q max set by qsize param = %v", evtc.pq_max)
                 }
+            } else if (k == PARAM_USE_CACHE) {
+                if strings.ToLower(v) == "false" {
+                    use_cache = false
+                    log.V(7).Infof("Cache use is turned off")
+                }
             }
         }
     }
 
     C.swssSetLogPriority(C.int(logLevel))
 
     /* Init subscriber with cache use and defined time out */
-    evtc.subs_handle = C_init_subs()
+    evtc.subs_handle = C_init_subs(use_cache)
     evtc.stopped = 0
 
     /* Init list & counters */