feat: add IM service health and metrics endpoints

server/stats.go

@@ -77,18 +77,27 @@ func statsInit(mux *http.ServeMux, path string) {
 
 func statsRegisterDbStats() {
 	if f := store.Store.DbStats(); f != nil {
+		if expvar.Get("DbStats") != nil {
+			return
+		}
 		expvar.Publish("DbStats", expvar.Func(f))
 	}
 }
 
 // Register integer variable. Don't check for initialization.
 func statsRegisterInt(name string) {
+	if expvar.Get(name) != nil {
+		return
+	}
 	expvar.Publish(name, new(expvar.Int))
 }
 
 // Register histogram variable. `bounds` specifies histogram buckets/bins
 // (see comment next to the `histogram` struct definition).
 func statsRegisterHistogram(name string, bounds []float64) {
+	if expvar.Get(name) != nil {
+		return
+	}
 	numBuckets := len(bounds) + 1
 	expvar.Publish(name, &histogram{
 		CountPerBucket: make([]int64, numBuckets),