Add /heads page (#3410)

beacon-chain/blockchain/BUILD.bazel

@@ -4,6 +4,7 @@ go_library(
     name = "go_default_library",
     srcs = [
         "chain_info.go",
+        "info.go",
         "log.go",
         "metrics.go",
         "receive_attestation.go",

beacon-chain/blockchain/info.go

@@ -0,0 +1,57 @@
+package blockchain
+
+import (
+	"bytes"
+	"encoding/hex"
+	"fmt"
+	"net/http"
+	"sort"
+
+	"github.com/prysmaticlabs/prysm/shared/bytesutil"
+	"github.com/sirupsen/logrus"
+)
+
+const latestSlotCount = 10
+
+// HeadsHandler is a handler to serve /heads page in metrics.
+func (c *ChainService) HeadsHandler(w http.ResponseWriter, _ *http.Request) {
+	buf := new(bytes.Buffer)
+
+	if _, err := fmt.Fprintf(w, "\n %s\t%s\t", "Head slot", "Head root"); err != nil {
+		logrus.WithError(err).Error("Failed to render chain heads page")
+		return
+	}
+
+	if _, err := fmt.Fprintf(w, "\n %s\t%s\t", "---------", "---------"); err != nil {
+		logrus.WithError(err).Error("Failed to render chain heads page")
+		return
+	}
+
+	slots := c.latestHeadSlots()
+	for _, s := range slots {
+		r := hex.EncodeToString(bytesutil.Trunc(c.canonicalRoots[uint64(s)]))
+		if _, err := fmt.Fprintf(w, "\n %d\t\t%s\t", s, r); err != nil {
+			logrus.WithError(err).Error("Failed to render chain heads page")
+			return
+		}
+	}
+
+	w.WriteHeader(http.StatusOK)
+	if _, err := w.Write(buf.Bytes()); err != nil {
+		log.WithError(err).Error("Failed to render chain heads page")
+	}
+
+}
+
+// This returns the latest head slots in a slice and up to latestSlotCount
+func (c *ChainService) latestHeadSlots() []int {
+	s := make([]int, 0, len(c.canonicalRoots))
+	for k := range c.canonicalRoots {
+		s = append(s, int(k))
+	}
+	sort.Ints(s)
+	if (len(s)) > latestSlotCount {
+		return s[len(s)-latestSlotCount:]
+	}
+	return s
+}

beacon-chain/node/node.go

@@ -414,9 +414,14 @@ func (b *BeaconNode) registerPrometheusService(ctx *cli.Context) error {
 	if err := b.services.FetchService(&p); err != nil {
 		panic(err)
 	}
-
 	additionalHandlers = append(additionalHandlers, prometheus.Handler{Path: "/p2p", Handler: p.InfoHandler})
 
+	var c *blockchain.ChainService
+	if err := b.services.FetchService(&c); err != nil {
+		panic(err)
+	}
+	additionalHandlers = append(additionalHandlers, prometheus.Handler{Path: "/heads", Handler: c.HeadsHandler})
+
 	service := prometheus.NewPrometheusService(
 		fmt.Sprintf(":%d", ctx.GlobalInt64(cmd.MonitoringPortFlag.Name)),
 		b.services,