[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/public/plugin/client_rpc.go

@@ -953,3 +953,107 @@ func (s *apiRPCServer) UploadData(args *Z_UploadDataArgs, returns *Z_UploadDataR
 	returns.A, returns.B = hook.UploadData(args.A, pluginReader)
 	return nil
 }
+
+func init() {
+	hookNameToId["ServeMetrics"] = ServeMetricsID
+}
+
+type Z_ServeMetricsArgs struct {
+	ResponseWriterStream uint32
+	Request              *http.Request
+	Context              *Context
+	RequestBodyStream    uint32
+}
+
+func (g *hooksRPCClient) ServeMetrics(c *Context, w http.ResponseWriter, r *http.Request) {
+	if !g.implemented[ServeMetricsID] {
+		http.NotFound(w, r)
+		return
+	}
+
+	serveMetricsStreamId := g.muxBroker.NextId()
+	go func() {
+		connection, err := g.muxBroker.Accept(serveMetricsStreamId)
+		if err != nil {
+			g.log.Error("Plugin failed to ServeMetrics, muxBroker couldn't accept connection", mlog.Uint32("serve_http_stream_id", serveMetricsStreamId), mlog.Err(err))
+			return
+		}
+		defer connection.Close()
+
+		rpcServer := rpc.NewServer()
+		if err := rpcServer.RegisterName("Plugin", &httpResponseWriterRPCServer{w: w, log: g.log}); err != nil {
+			g.log.Error("Plugin failed to ServeMetrics, couldn't register RPC name", mlog.Err(err))
+			return
+		}
+		rpcServer.ServeConn(connection)
+	}()
+
+	requestBodyStreamId := uint32(0)
+	if r.Body != nil {
+		requestBodyStreamId = g.muxBroker.NextId()
+		go func() {
+			bodyConnection, err := g.muxBroker.Accept(requestBodyStreamId)
+			if err != nil {
+				g.log.Error("Plugin failed to ServeMetrics, muxBroker couldn't Accept request body connection", mlog.Err(err))
+				return
+			}
+			defer bodyConnection.Close()
+			serveIOReader(r.Body, bodyConnection)
+		}()
+	}
+
+	forwardedRequest := &http.Request{
+		Method:     r.Method,
+		URL:        r.URL,
+		Proto:      r.Proto,
+		ProtoMajor: r.ProtoMajor,
+		ProtoMinor: r.ProtoMinor,
+		Header:     r.Header,
+		Host:       r.Host,
+		RemoteAddr: r.RemoteAddr,
+		RequestURI: r.RequestURI,
+	}
+
+	if err := g.client.Call("Plugin.ServeMetrics", Z_ServeMetricsArgs{
+		Context:              c,
+		ResponseWriterStream: serveMetricsStreamId,
+		Request:              forwardedRequest,
+		RequestBodyStream:    requestBodyStreamId,
+	}, nil); err != nil {
+		g.log.Error("Plugin failed to ServeMetrics, RPC call failed", mlog.Err(err))
+		http.Error(w, "500 internal server error", http.StatusInternalServerError)
+	}
+}
+
+func (s *hooksRPCServer) ServeMetrics(args *Z_ServeMetricsArgs, returns *struct{}) error {
+	connection, err := s.muxBroker.Dial(args.ResponseWriterStream)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "[ERROR] Can't connect to remote response writer stream, error: %v", err.Error())
+		return err
+	}
+	w := connectHTTPResponseWriter(connection)
+	defer w.Close()
+
+	r := args.Request
+	if args.RequestBodyStream != 0 {
+		connection, err := s.muxBroker.Dial(args.RequestBodyStream)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "[ERROR] Can't connect to remote request body stream, error: %v", err.Error())
+			return err
+		}
+		r.Body = connectIOReader(connection)
+	} else {
+		r.Body = io.NopCloser(&bytes.Buffer{})
+	}
+	defer r.Body.Close()
+
+	if hook, ok := s.impl.(interface {
+		ServeMetrics(c *Context, w http.ResponseWriter, r *http.Request)
+	}); ok {
+		hook.ServeMetrics(args.Context, w, r)
+	} else {
+		http.NotFound(w, r)
+	}
+
+	return nil
+}

server/public/plugin/hooks.go

@@ -54,6 +54,7 @@ const (
 	UserHasBeenDeactivatedID                  = 36
 	MessageHasBeenDeletedID                   = 37
 	MessagesWillBeConsumedID                  = 38
+	ServeMetricsID                            = 39
 	TotalHooksID                              = iota
 )
 
@@ -322,4 +323,11 @@ type Hooks interface {
 	//
 	// Minimum server version: 9.1
 	UserHasBeenDeactivated(c *Context, user *model.User)
+
+	// ServeMetrics allows plugins to expose their own metrics endpoint through
+	// the server's metrics HTTP listener (e.g. "localhost:8067").
+	// Requests destined to the /plugins/{id}/metrics path will be routed to the plugin.
+	//
+	// Minimum server version: 9.2
+	ServeMetrics(c *Context, w http.ResponseWriter, r *http.Request)
 }

server/public/plugin/hooks_timer_layer_generated.go

@@ -244,3 +244,9 @@ func (hooks *hooksTimerLayer) UserHasBeenDeactivated(c *Context, user *model.Use
 	hooks.hooksImpl.UserHasBeenDeactivated(c, user)
 	hooks.recordTime(startTime, "UserHasBeenDeactivated", true)
 }
+
+func (hooks *hooksTimerLayer) ServeMetrics(c *Context, w http.ResponseWriter, r *http.Request) {
+	startTime := timePkg.Now()
+	hooks.hooksImpl.ServeMetrics(c, w, r)
+	hooks.recordTime(startTime, "ServeMetrics", true)
+}

server/public/plugin/interface_generator/main.go

@@ -37,6 +37,7 @@ var excludedPluginHooks = []string{
 	"PluginHTTP",
 	"ServeHTTP",
 	"UploadData",
+	"ServeMetrics",
 }
 
 var excludedProductHooks = []string{

server/public/plugin/plugintest/hooks.go

@@ -360,6 +360,11 @@ func (_m *Hooks) ServeHTTP(c *plugin.Context, w http.ResponseWriter, r *http.Req
 	_m.Called(c, w, r)
 }
 
+// ServeMetrics provides a mock function with given fields: c, w, r
+func (_m *Hooks) ServeMetrics(c *plugin.Context, w http.ResponseWriter, r *http.Request) {
+	_m.Called(c, w, r)
+}
+
 // UserHasBeenCreated provides a mock function with given fields: c, user
 func (_m *Hooks) UserHasBeenCreated(c *plugin.Context, user *model.User) {
 	_m.Called(c, user)

server/public/plugin/product_hooks_generated.go

@@ -9,6 +9,7 @@ package plugin
 import (
 	"errors"
 	"io"
+	"net/http"
 	"reflect"
 
 	"github.com/mattermost/mattermost/server/public/model"
@@ -134,6 +135,10 @@ type UserHasBeenDeactivatedIFace interface {
 	UserHasBeenDeactivated(c *Context, user *model.User)
 }
 
+type ServeMetricsIFace interface {
+	ServeMetrics(c *Context, w http.ResponseWriter, r *http.Request)
+}
+
 type HooksAdapter struct {
 	implemented  map[int]struct{}
 	productHooks any
@@ -417,6 +422,15 @@ func NewAdapter(productHooks any) (*HooksAdapter, error) {
 		return nil, errors.New("hook has UserHasBeenDeactivated method but does not implement plugin.UserHasBeenDeactivated interface")
 	}
 
+	// Assessing the type of the productHooks if it individually implements ServeMetrics interface.
+	tt = reflect.TypeOf((*ServeMetricsIFace)(nil)).Elem()
+
+	if ft.Implements(tt) {
+		a.implemented[ServeMetricsID] = struct{}{}
+	} else if _, ok := ft.MethodByName("ServeMetrics"); ok {
+		return nil, errors.New("hook has ServeMetrics method but does not implement plugin.ServeMetrics interface")
+	}
+
 	return a, nil
 }
 
@@ -689,3 +703,12 @@ func (a *HooksAdapter) UserHasBeenDeactivated(c *Context, user *model.User) {
 	a.productHooks.(UserHasBeenDeactivatedIFace).UserHasBeenDeactivated(c, user)
 
 }
+
+func (a *HooksAdapter) ServeMetrics(c *Context, w http.ResponseWriter, r *http.Request) {
+	if _, ok := a.implemented[ServeMetricsID]; !ok {
+		panic("product hooks must implement ServeMetrics")
+	}
+
+	a.productHooks.(ServeMetricsIFace).ServeMetrics(c, w, r)
+
+}