Add a metric for the total number of proxied connections

It should allow us to tell apart SSL and non-SSL connections.

node/instrumentation.go

@@ -37,6 +37,13 @@ var (
 		},
 		[]string{"stream", "upstream"},
 	)
+	proxyConnections = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "proxy_connections_total",
+			Help: "Proxy connections.",
+		},
+		[]string{"proto"},
+	)
 
 	// Node metrics.
 	icecastUpdateFailed = prometheus.NewGauge(

node/proxy.go

@@ -107,12 +107,14 @@ func doIcecastProxy(rw http.ResponseWriter, req *http.Request, target *url.URL,
 	// httputil.ReverseProxy (not fully functional for sources, but
 	// meh).
 	if req.TLS != nil {
+		proxyConnections.WithLabelValues("https").Inc()
 		u := *outreq.URL
 		u.Path = "/"
 		rp := httputil.NewSingleHostReverseProxy(&u)
 		rp.ServeHTTP(rw, outreq)
 		return
 	}
+	proxyConnections.WithLabelValues("http").Inc()
 
 	// Create the upstream connection and write the HTTP request
 	// to it.