[MM-55268] Implement ServeMetrics plugins hook (#24249)

* Implement ServeMetrics plugins hook

* Update error id

* Simplify

* Revert "Simplify"

This reverts commit c9dc5d5eac6c933ff69e158cf3e34d0973bd3bcd.

* Add comment and error handler

* Wrap error

* Update translation file

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/app/platform/metrics.go

@@ -9,7 +9,9 @@ import (
 	"net"
 	"net/http"
 	"net/http/pprof"
+	"path"
 	"runtime"
+	"strings"
 	"sync"
 	"text/template"
 	"time"
@@ -19,7 +21,9 @@ import (
 	"github.com/pkg/errors"
 
 	"github.com/mattermost/mattermost/server/public/model"
+	"github.com/mattermost/mattermost/server/public/plugin"
 	"github.com/mattermost/mattermost/server/public/shared/mlog"
+	"github.com/mattermost/mattermost/server/v8/channels/utils"
 	"github.com/mattermost/mattermost/server/v8/einterfaces"
 )
 
@@ -35,6 +39,8 @@ type platformMetrics struct {
 
 	cfgFn      func() *model.Config
 	listenAddr string
+
+	getPluginsEnv func() *plugin.Environment
 }
 
 // resetMetrics resets the metrics server. Clears the metrics if the metrics are disabled by the config.
@@ -56,6 +62,12 @@ func (ps *PlatformService) resetMetrics() error {
 		cfgFn:       ps.Config,
 		metricsImpl: ps.metricsIFace,
 		logger:      ps.logger,
+		getPluginsEnv: func() *plugin.Environment {
+			if ps.pluginEnv == nil {
+				return nil
+			}
+			return ps.pluginEnv.GetPluginsEnvironment()
+		},
 	}
 
 	if err := ps.metrics.initMetricsRouter(); err != nil {
@@ -166,9 +178,56 @@ func (pm *platformMetrics) initMetricsRouter() error {
 	pm.router.Handle("/debug/pprof/threadcreate", pprof.Handler("threadcreate"))
 	pm.router.Handle("/debug/pprof/block", pprof.Handler("block"))
 
+	// Plugins metrics route
+	pluginsMetricsRoute := pm.router.PathPrefix("/plugins/{plugin_id:[A-Za-z0-9\\_\\-\\.]+}/metrics").Subrouter()
+	pluginsMetricsRoute.HandleFunc("", pm.servePluginMetricsRequest)
+	pluginsMetricsRoute.HandleFunc("/{anything:.*}", pm.servePluginMetricsRequest)
+
 	return nil
 }
 
+func (pm *platformMetrics) servePluginMetricsRequest(w http.ResponseWriter, r *http.Request) {
+	pluginID := mux.Vars(r)["plugin_id"]
+
+	pluginsEnvironment := pm.getPluginsEnv()
+	if pluginsEnvironment == nil {
+		appErr := model.NewAppError("ServePluginMetricsRequest", "app.plugin.disabled.app_error",
+			nil, "Enable plugins to serve plugin metric requests", http.StatusNotImplemented)
+		mlog.Error(appErr.Error())
+		w.WriteHeader(appErr.StatusCode)
+		w.Header().Set("Content-Type", "application/json")
+		w.Write([]byte(appErr.ToJSON()))
+		return
+	}
+
+	hooks, err := pluginsEnvironment.HooksForPlugin(pluginID)
+	if err != nil {
+		mlog.Debug("Access to route for non-existent plugin",
+			mlog.String("missing_plugin_id", pluginID),
+			mlog.String("url", r.URL.String()),
+			mlog.Err(err))
+		http.NotFound(w, r)
+		return
+	}
+
+	subpath, err := utils.GetSubpathFromConfig(pm.cfgFn())
+	if err != nil {
+		appErr := model.NewAppError("ServePluginMetricsRequest", "app.plugin.subpath_parse.app_error",
+			nil, "Failed to parse SiteURL subpath", http.StatusInternalServerError).Wrap(err)
+		mlog.Error(appErr.Error())
+		w.WriteHeader(appErr.StatusCode)
+		w.Header().Set("Content-Type", "application/json")
+		w.Write([]byte(appErr.ToJSON()))
+		return
+	}
+
+	r.URL.Path = strings.TrimPrefix(r.URL.Path, path.Join(subpath, "plugins", pluginID, "metrics"))
+
+	// Passing an empty plugin context for the time being. To be decided whether we
+	// should support forms of authentication in the future.
+	hooks.ServeMetrics(&plugin.Context{}, w, r)
+}
+
 func (ps *PlatformService) HandleMetrics(route string, h http.Handler) {
 	if ps.metrics != nil {
 		ps.metrics.router.Handle(route, h)

server/channels/app/plugin_api_test.go

@@ -2305,3 +2305,63 @@ func TestSendPushNotification(t *testing.T) {
 	}
 	assert.Equal(t, 6, numMessages)
 }
+
+func TestPluginServeMetrics(t *testing.T) {
+	th := Setup(t, StartMetrics)
+	defer th.TearDown()
+
+	var prevEnable *bool
+	var prevAddress *string
+	th.App.UpdateConfig(func(cfg *model.Config) {
+		prevEnable = cfg.MetricsSettings.Enable
+		prevAddress = cfg.MetricsSettings.ListenAddress
+		cfg.MetricsSettings.Enable = model.NewBool(true)
+		cfg.MetricsSettings.ListenAddress = model.NewString(":30067")
+	})
+	defer th.App.UpdateConfig(func(cfg *model.Config) {
+		cfg.MetricsSettings.Enable = prevEnable
+		cfg.MetricsSettings.ListenAddress = prevAddress
+	})
+
+	testFolder, found := fileutils.FindDir("channels/app/plugin_api_tests")
+	require.True(t, found, "Cannot find tests folder")
+	fullPath := path.Join(testFolder, "manual.test_serve_metrics_plugin", "main.go")
+
+	pluginCode, err := os.ReadFile(fullPath)
+	require.NoError(t, err)
+	require.NotEmpty(t, pluginCode)
+
+	tearDown, ids, errors := SetAppEnvironmentWithPlugins(t, []string{string(pluginCode)}, th.App, th.NewPluginAPI)
+	defer tearDown()
+	require.NoError(t, errors[0])
+	require.Len(t, ids, 1)
+
+	pluginID := ids[0]
+	require.NotEmpty(t, pluginID)
+
+	reqURL := fmt.Sprintf("http://localhost%s/plugins/%s/metrics", *th.App.Config().MetricsSettings.ListenAddress, pluginID)
+	req, err := http.NewRequest("GET", reqURL, nil)
+	require.NoError(t, err)
+
+	client := &http.Client{}
+	resp, err := client.Do(req)
+	require.NoError(t, err)
+
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(resp.Body)
+	require.NoError(t, err)
+	require.Equal(t, "METRICS", string(body))
+
+	reqURL = fmt.Sprintf("http://localhost%s/plugins/%s/metrics/subpath", *th.App.Config().MetricsSettings.ListenAddress, pluginID)
+	req, err = http.NewRequest("GET", reqURL, nil)
+	require.NoError(t, err)
+
+	resp, err = client.Do(req)
+	require.NoError(t, err)
+	defer resp.Body.Close()
+
+	body, err = io.ReadAll(resp.Body)
+	require.NoError(t, err)
+	require.Equal(t, "METRICS SUBPATH", string(body))
+}

server/channels/app/plugin_api_tests/manual.test_serve_metrics_plugin/main.go

@@ -0,0 +1,27 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package main
+
+import (
+	"net/http"
+
+	"github.com/mattermost/mattermost/server/public/plugin"
+)
+
+type Plugin struct {
+	plugin.MattermostPlugin
+}
+
+func (p *Plugin) ServeMetrics(_ *plugin.Context, w http.ResponseWriter, r *http.Request) {
+	if r.URL.Path == "/subpath" {
+		w.Write([]byte("METRICS SUBPATH"))
+		return
+	}
+
+	w.Write([]byte("METRICS"))
+}
+
+func main() {
+	plugin.ClientMain(&Plugin{})
+}