Add revision to version string (element-hq#3147)

Since the removal of `build.sh`, we don't include any information about
the revision Dendrite was build from. Since go1.18, the revision a
binary was build from is automatically included, so we can try to get
that instead.

This also adds a `dendrite_up` metric showing the current version
(`dendrite_up{version="0.13.1+c796f20"} 1`)

Closes element-hq#2993

.dockerignore

@@ -1,3 +1,2 @@
 bin
-*.wasm
-.git
+*.wasm

Dockerfile

@@ -4,7 +4,7 @@
 # base installs required dependencies and runs go mod download to cache dependencies
 #
 FROM --platform=${BUILDPLATFORM} docker.io/golang:1.20-alpine AS base
-RUN apk --update --no-cache add bash build-base curl
+RUN apk --update --no-cache add bash build-base curl git
 
 #
 # build creates all needed binaries

cmd/dendrite/main.go

@@ -26,6 +26,7 @@ import (
 	"github.com/matrix-org/dendrite/setup/jetstream"
 	"github.com/matrix-org/dendrite/setup/process"
 	"github.com/matrix-org/gomatrixserverlib/fclient"
+	"github.com/prometheus/client_golang/prometheus"
 	"github.com/sirupsen/logrus"
 
 	"github.com/matrix-org/dendrite/appservice"
@@ -187,6 +188,16 @@ func main() {
 		}
 	}
 
+	upCounter := prometheus.NewCounter(prometheus.CounterOpts{
+		Namespace: "dendrite",
+		Name:      "up",
+		ConstLabels: map[string]string{
+			"version": internal.VersionString(),
+		},
+	})
+	upCounter.Add(1)
+	prometheus.MustRegister(upCounter)
+
 	// Expose the matrix APIs directly rather than putting them under a /api path.
 	go func() {
 		basepkg.SetupAndServeHTTP(processCtx, cfg, routers, httpAddr, nil, nil)

internal/version.go

@@ -2,6 +2,7 @@ package internal
 
 import (
 	"fmt"
+	"runtime/debug"
 	"strings"
 )
 
@@ -19,6 +20,8 @@ const (
 	VersionMinor = 13
 	VersionPatch = 1
 	VersionTag   = "" // example: "rc1"
+
+	gitRevLen = 7 // 7 matches the displayed characters on github.com
 )
 
 func VersionString() string {
@@ -37,7 +40,30 @@ func init() {
 	if branch != "" {
 		parts = append(parts, branch)
 	}
-	if len(parts) > 0 {
-		version += "+" + strings.Join(parts, ".")
+
+	defer func() {
+		if len(parts) > 0 {
+			version += "+" + strings.Join(parts, ".")
+		}
+	}()
+
+	// Try to get the revision Dendrite was build from.
+	// If we can't, e.g. Dendrite wasn't built (go run) or no VCS version is present,
+	// we just use the provided version above.
+	info, ok := debug.ReadBuildInfo()
+	if !ok {
+		return
+	}
+
+	for _, setting := range info.Settings {
+		if setting.Key == "vcs.revision" {
+			revLen := len(setting.Value)
+			if revLen >= gitRevLen {
+				parts = append(parts, setting.Value[:gitRevLen])
+			} else {
+				parts = append(parts, setting.Value[:revLen])
+			}
+			break
+		}
 	}
 }