feat: add Prometheus metrics (#439)

* feat: add Prometheus metrics

* setup metrics using Prometheus client under /metrics endpoint
* add configuration value for metrics
* configure Prometheus middleware for generic metrics
* provide metrics for totals of users, gists and SSH keys
* modify test request to optionally return the response
* provide integration test for Prometheus metrics
* update documentation

* chore: make fmt

internal/config/config.go

@@ -71,6 +71,8 @@ type config struct {
 	OIDCSecret       string `yaml:"oidc.secret" env:"OG_OIDC_SECRET"`
 	OIDCDiscoveryUrl string `yaml:"oidc.discovery-url" env:"OG_OIDC_DISCOVERY_URL"`
 
+	MetricsEnabled bool `yaml:"metrics.enabled" env:"OG_METRICS_ENABLED"`
+
 	CustomName    string       `yaml:"custom.name" env:"OG_CUSTOM_NAME"`
 	CustomLogo    string       `yaml:"custom.logo" env:"OG_CUSTOM_LOGO"`
 	CustomFavicon string       `yaml:"custom.favicon" env:"OG_CUSTOM_FAVICON"`
@@ -110,6 +112,8 @@ func configWithDefaults() (*config, error) {
 	c.GiteaUrl = "https://gitea.com"
 	c.GiteaName = "Gitea"
 
+	c.MetricsEnabled = false
+
 	return c, nil
 }
 

internal/web/handlers/health/metrics.go

@@ -1,9 +0,0 @@
-package health
-
-import "github.com/thomiceli/opengist/internal/web/context"
-
-// Metrics is a dummy handler to satisfy the /metrics endpoint (for Prometheus, Openmetrics, etc.)
-// until we have a proper metrics endpoint
-func Metrics(ctx *context.Context) error {
-	return ctx.String(200, "")
-}

internal/web/handlers/metrics/metrics.go

@@ -0,0 +1,101 @@
+package metrics
+
+import (
+	"github.com/labstack/echo-contrib/echoprometheus"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+	"github.com/thomiceli/opengist/internal/config"
+	"github.com/thomiceli/opengist/internal/db"
+	"github.com/thomiceli/opengist/internal/web/context"
+)
+
+var (
+	// Using promauto to automatically register metrics with the default registry
+	countUsersGauge   prometheus.Gauge
+	countGistsGauge   prometheus.Gauge
+	countSSHKeysGauge prometheus.Gauge
+
+	metricsInitialized bool = false
+)
+
+// initMetrics initializes metrics if they're not already initialized
+func initMetrics() {
+	if metricsInitialized {
+		return
+	}
+
+	// Only initialize metrics if they're enabled
+	if config.C.MetricsEnabled {
+		countUsersGauge = promauto.NewGauge(
+			prometheus.GaugeOpts{
+				Name: "opengist_users_total",
+				Help: "Total number of users",
+			},
+		)
+
+		countGistsGauge = promauto.NewGauge(
+			prometheus.GaugeOpts{
+				Name: "opengist_gists_total",
+				Help: "Total number of gists",
+			},
+		)
+
+		countSSHKeysGauge = promauto.NewGauge(
+			prometheus.GaugeOpts{
+				Name: "opengist_ssh_keys_total",
+				Help: "Total number of SSH keys",
+			},
+		)
+
+		metricsInitialized = true
+	}
+}
+
+// updateMetrics refreshes all metric values from the database
+func updateMetrics() {
+	// Only update metrics if they're enabled
+	if !config.C.MetricsEnabled || !metricsInitialized {
+		return
+	}
+
+	// Update users count
+	countUsers, err := db.CountAll(&db.User{})
+	if err == nil {
+		countUsersGauge.Set(float64(countUsers))
+	}
+
+	// Update gists count
+	countGists, err := db.CountAll(&db.Gist{})
+	if err == nil {
+		countGistsGauge.Set(float64(countGists))
+	}
+
+	// Update SSH keys count
+	countKeys, err := db.CountAll(&db.SSHKey{})
+	if err == nil {
+		countSSHKeysGauge.Set(float64(countKeys))
+	}
+}
+
+// Metrics handles prometheus metrics endpoint requests.
+func Metrics(ctx *context.Context) error {
+	// If metrics are disabled, return 404
+	if !config.C.MetricsEnabled {
+		return ctx.NotFound("Metrics endpoint is disabled")
+	}
+
+	// Initialize metrics if not already done
+	initMetrics()
+
+	// Update metrics
+	updateMetrics()
+
+	// Get the Echo context
+	echoCtx := ctx.Context
+
+	// Use the Prometheus metrics handler
+	handler := echoprometheus.NewHandler()
+
+	// Call the handler
+	return handler(echoCtx)
+}

internal/web/server/middlewares.go

@@ -3,6 +3,7 @@ package server
 import (
 	"errors"
 	"fmt"
+	"github.com/labstack/echo-contrib/echoprometheus"
 	"github.com/labstack/echo/v4"
 	"github.com/labstack/echo/v4/middleware"
 	"github.com/rs/zerolog/log"
@@ -34,6 +35,10 @@ func (s *Server) useCustomContext() {
 func (s *Server) registerMiddlewares() {
 	s.echo.Use(Middleware(dataInit).toEcho())
 	s.echo.Use(Middleware(locale).toEcho())
+	if config.C.MetricsEnabled {
+		p := echoprometheus.NewMiddleware("opengist")
+		s.echo.Use(p)
+	}
 
 	s.echo.Pre(middleware.MethodOverrideWithConfig(middleware.MethodOverrideConfig{
 		Getter: middleware.MethodFromForm("_method"),

internal/web/server/router.go

@@ -1,6 +1,13 @@
 package server
 
 import (
+	"net/http"
+	"os"
+	"path"
+	"path/filepath"
+	"strings"
+	"time"
+
 	"github.com/labstack/echo/v4"
 	"github.com/thomiceli/opengist/internal/config"
 	"github.com/thomiceli/opengist/internal/index"
@@ -10,14 +17,9 @@ import (
 	"github.com/thomiceli/opengist/internal/web/handlers/gist"
 	"github.com/thomiceli/opengist/internal/web/handlers/git"
 	"github.com/thomiceli/opengist/internal/web/handlers/health"
+	"github.com/thomiceli/opengist/internal/web/handlers/metrics"
 	"github.com/thomiceli/opengist/internal/web/handlers/settings"
 	"github.com/thomiceli/opengist/public"
-	"net/http"
-	"os"
-	"path"
-	"path/filepath"
-	"strings"
-	"time"
 )
 
 func (s *Server) registerRoutes() {
@@ -29,7 +31,10 @@ func (s *Server) registerRoutes() {
 		r.POST("/preview", gist.Preview, logged)
 
 		r.GET("/healthcheck", health.Healthcheck)
-		r.GET("/metrics", health.Metrics)
+
+		if config.C.MetricsEnabled {
+			r.GET("/metrics", metrics.Metrics)
+		}
 
 		r.GET("/register", auth.Register)
 		r.POST("/register", auth.ProcessRegister)

internal/web/test/metrics_test.go

@@ -0,0 +1,113 @@
+package test
+
+import (
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/thomiceli/opengist/internal/db"
+	"io"
+	"net/http"
+	"os"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+var (
+	SSHKey = db.SSHKeyDTO{
+		Title:   "Test SSH Key",
+		Content: `ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAklOUpkDHrfHY17SbrmTIpNLTGK9Tjom/BWDSUGPl+nafzlHDTYW7hdI4yZ5ew18JH4JW9jbhUFrviQzM7xlELEVf4h9lFX5QVkbPppSwg0cda3Pbv7kOdJ/MTyBlWXFCR+HAo3FXRitBqxiX1nKhXpHAZsMciLq8V6RjsNAQwdsdMFvSlVK/7XAt3FaoJoAsncM1Q9x5+3V0Ww68/eIFmb1zuUFljQJKprrX88XypNDvjYNby6vw/Pb0rwert/EnmZ+AW4OZPnTPI89ZPmVMLuayrD2cE86Z/il8b+gw3r3+1nKatmIkjn2so1d01QraTlMqVSsbxNrRFi9wrf+M7Q== admin@admin.local`,
+	}
+	AdminUser = db.UserDTO{
+		Username: "admin",
+		Password: "admin",
+	}
+
+	SimpleGist = db.GistDTO{
+		Title:       "Simple Test Gist",
+		Description: "A simple gist for testing",
+		VisibilityDTO: db.VisibilityDTO{
+			Private: 0,
+		},
+		Name:    []string{"file1.txt"},
+		Content: []string{"This is the content of file1"},
+		Topics:  "",
+	}
+)
+
+// TestMetrics tests the metrics endpoint functionality of the application.
+// It verifies that the metrics endpoint correctly reports counts for:
+// - Total number of users
+// - Total number of gists
+// - Total number of SSH keys
+//
+// The test follows these steps:
+// 1. Enables metrics via environment variable
+// 2. Sets up test environment
+// 3. Registers and logs in an admin user
+// 4. Creates a gist and adds an SSH key
+// 5. Queries the metrics endpoint
+// 6. Verifies the reported metrics match expected values
+//
+// Environment variables:
+//   - OG_METRICS_ENABLED: Set to "true" for this test
+func TestMetrics(t *testing.T) {
+	originalValue := os.Getenv("OG_METRICS_ENABLED")
+
+	os.Setenv("OG_METRICS_ENABLED", "true")
+
+	defer os.Setenv("OG_METRICS_ENABLED", originalValue)
+
+	s := Setup(t)
+	defer Teardown(t, s)
+
+	register(t, s, AdminUser)
+	login(t, s, AdminUser)
+
+	err := s.Request("GET", "/all", nil, 200)
+	require.NoError(t, err)
+
+	err = s.Request("POST", "/", SimpleGist, 302)
+	require.NoError(t, err)
+
+	err = s.Request("POST", "/settings/ssh-keys", SSHKey, 302)
+	require.NoError(t, err)
+
+	var metricsRes http.Response
+	err = s.Request("GET", "/metrics", nil, 200, &metricsRes)
+	require.NoError(t, err)
+
+	body, err := io.ReadAll(metricsRes.Body)
+	defer metricsRes.Body.Close()
+	require.NoError(t, err)
+
+	lines := strings.Split(string(body), "\n")
+	var usersTotal float64
+	var gistsTotal float64
+	var sshKeysTotal float64
+
+	for _, line := range lines {
+		if strings.HasPrefix(line, "opengist_users_total") {
+			parts := strings.Fields(line)
+			if len(parts) == 2 {
+				usersTotal, err = strconv.ParseFloat(parts[1], 64)
+				assert.NoError(t, err)
+			}
+		} else if strings.HasPrefix(line, "opengist_gists_total") {
+			parts := strings.Fields(line)
+			if len(parts) == 2 {
+				gistsTotal, err = strconv.ParseFloat(parts[1], 64)
+				assert.NoError(t, err)
+			}
+		} else if strings.HasPrefix(line, "opengist_ssh_keys_total") {
+			parts := strings.Fields(line)
+			if len(parts) == 2 {
+				sshKeysTotal, err = strconv.ParseFloat(parts[1], 64)
+				assert.NoError(t, err)
+			}
+		}
+	}
+
+	assert.Equal(t, 1.0, usersTotal, "opengist_users_total should be 1")
+	assert.Equal(t, 1.0, gistsTotal, "opengist_gists_total should be 1")
+	assert.Equal(t, 1.0, sshKeysTotal, "opengist_ssh_keys_total should be 1")
+}

internal/web/test/server.go

@@ -48,7 +48,7 @@ func (s *TestServer) stop() {
 	s.server.Stop()
 }
 
-func (s *TestServer) Request(method, uri string, data interface{}, expectedCode int) error {
+func (s *TestServer) Request(method, uri string, data interface{}, expectedCode int, responsePtr ...*http.Response) error {
 	var bodyReader io.Reader
 	if method == http.MethodPost || method == http.MethodPut {
 		values := structToURLValues(data)
@@ -92,6 +92,11 @@ func (s *TestServer) Request(method, uri string, data interface{}, expectedCode
 		}
 	}
 
+	// If a response pointer was provided, fill it with the response data
+	if len(responsePtr) > 0 && responsePtr[0] != nil {
+		*responsePtr[0] = *w.Result()
+	}
+
 	return nil
 }
 
@@ -157,7 +162,7 @@ func Setup(t *testing.T) *TestServer {
 	databaseType = os.Getenv("OPENGIST_TEST_DB")
 	switch databaseType {
 	case "sqlite":
-		databaseDsn = "file:" + filepath.Join(homePath, "tmp", "opengist.db")
+		databaseDsn = "file:" + filepath.Join(homePath, "tmp", "opengist_test.db")
 	case "postgres":
 		databaseDsn = "postgres://postgres:opengist@localhost:5432/opengist_test"
 	case "mysql":