Add running chain hashes handler on http server (#908)

* add running chain hashes handler
* add test for running chains on http relay

http/server.go

@@ -97,6 +97,7 @@ func New(ctx context.Context, c client.Client, version string, logger log.Logger
 	mux.HandleFunc("/public/{"+roundParamKey+"}", withCommonHeaders(version, handler.PublicRand))
 	mux.HandleFunc("/info", withCommonHeaders(version, handler.ChainInfo))
 	mux.HandleFunc("/health", withCommonHeaders(version, handler.Health))
+	mux.HandleFunc("/chains", withCommonHeaders(version, handler.ChainHashes))
 
 	handler.httpHandler = promhttp.InstrumentHandlerCounter(
 		metrics.HTTPCallCounter,
@@ -529,6 +530,22 @@ func (h *DrandHandler) Health(w http.ResponseWriter, r *http.Request) {
 	_, _ = w.Write(b)
 }
 
+func (h *DrandHandler) ChainHashes(w http.ResponseWriter, r *http.Request) {
+	chainHashes := make([]string, 0)
+	for chainHash := range h.beacons {
+		if chainHash != common.DefaultChainHash {
+			chainHashes = append(chainHashes, chainHash)
+		}
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	w.Header().Set("Cache-Control", "max-age=300")
+
+	w.WriteHeader(http.StatusOK)
+	b, _ := json.Marshal(chainHashes)
+	_, _ = w.Write(b)
+}
+
 func readChainHash(r *http.Request) ([]byte, error) {
 	var err error
 	chainHashHex := make([]byte, 0)

http/server_test.go

@@ -33,6 +33,7 @@ func withClient(t *testing.T) (c client.Client, emit func(bool)) {
 	return c, s.(mock.MockService).EmitRand
 }
 
+//nolint:funlen
 func TestHTTPRelay(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
@@ -64,8 +65,27 @@ func TestHTTPRelay(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	getChains := fmt.Sprintf("http://%s/chains", listener.Addr().String())
+	resp, err := http.Get(getChains)
+	require.NoError(t, err)
+
+	if resp.StatusCode != 200 {
+		t.Error("expected http status code 200")
+	}
+
+	var chains []string
+	require.NoError(t, json.NewDecoder(resp.Body).Decode(&chains))
+	require.NoError(t, resp.Body.Close())
+
+	if len(chains) != 1 {
+		t.Error("expected chain hash qty not valid")
+	}
+	if chains[0] != info.HashString() {
+		t.Error("expected chain hash not valid")
+	}
+
 	getChain := fmt.Sprintf("http://%s/%s/info", listener.Addr().String(), info.HashString())
-	resp, err := http.Get(getChain)
+	resp, err = http.Get(getChain)
 	require.NoError(t, err)
 	cip := new(drand.ChainInfoPacket)
 	require.NoError(t, json.NewDecoder(resp.Body).Decode(cip))