Roomserver perform join (#1001)

* Add PerformJoin template

* Try roomserver perform join

* Send correct server name to FS API

* Pass through content, try to handle multiple server names

* Fix local server checks

* Don't refer to non-existent error

* Add directory lookups of aliases

* Remove unneeded parameters

* Don't repeat join events into the roomserver

* Unmarshal the content, that would help

* Check if the user is already in the room in the fedeationapi too

* Return incompatible room version error

* Use Membership, don't try more servers than needed

* Review comments, make FS API take list of servernames, dedupe them, break out of loop properly on success

* Tweaks

4 files changed, 277 insertions, 0 deletions

diff --git a/roomserver/api/api.go b/roomserver/api/api.go
index c12dbddd..ae4beab2 100644
--- a/roomserver/api/api.go
+++ b/roomserver/api/api.go
@@ -18,6 +18,12 @@ type RoomserverInternalAPI interface {
 		response *InputRoomEventsResponse,
 	) error
 
+	PerformJoin(
+		ctx context.Context,
+		req *PerformJoinRequest,
+		res *PerformJoinResponse,
+	) error
+
 	// Query the latest events and state for a room from the room server.
 	QueryLatestEventsAndState(
 		ctx context.Context,
diff --git a/roomserver/api/perform.go b/roomserver/api/perform.go
new file mode 100644
index 00000000..e60c078b
--- /dev/null
+++ b/roomserver/api/perform.go
@@ -0,0 +1,59 @@
+package api
+
+import (
+	"context"
+
+	commonHTTP "github.com/matrix-org/dendrite/common/http"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/opentracing/opentracing-go"
+)
+
+const (
+	// RoomserverPerformJoinPath is the HTTP path for the PerformJoin API.
+	RoomserverPerformJoinPath = "/api/roomserver/performJoin"
+
+	// RoomserverPerformLeavePath is the HTTP path for the PerformLeave API.
+	RoomserverPerformLeavePath = "/api/roomserver/performLeave"
+)
+
+type PerformJoinRequest struct {
+	RoomIDOrAlias string                         `json:"room_id_or_alias"`
+	UserID        string                         `json:"user_id"`
+	Content       map[string]interface{}         `json:"content"`
+	ServerNames   []gomatrixserverlib.ServerName `json:"server_names"`
+}
+
+type PerformJoinResponse struct {
+}
+
+func (h *httpRoomserverInternalAPI) PerformJoin(
+	ctx context.Context,
+	request *PerformJoinRequest,
+	response *PerformJoinResponse,
+) error {
+	span, ctx := opentracing.StartSpanFromContext(ctx, "PerformJoin")
+	defer span.Finish()
+
+	apiURL := h.roomserverURL + RoomserverPerformJoinPath
+	return commonHTTP.PostJSON(ctx, span, h.httpClient, apiURL, request, response)
+}
+
+type PerformLeaveRequest struct {
+	RoomID string `json:"room_id"`
+	UserID string `json:"user_id"`
+}
+
+type PerformLeaveResponse struct {
+}
+
+func (h *httpRoomserverInternalAPI) PerformLeave(
+	ctx context.Context,
+	request *PerformLeaveRequest,
+	response *PerformLeaveResponse,
+) error {
+	span, ctx := opentracing.StartSpanFromContext(ctx, "PerformLeave")
+	defer span.Finish()
+
+	apiURL := h.roomserverURL + RoomserverPerformLeavePath
+	return commonHTTP.PostJSON(ctx, span, h.httpClient, apiURL, request, response)
+}
diff --git a/roomserver/internal/api.go b/roomserver/internal/api.go
index d1c443f2..1dc985ef 100644
--- a/roomserver/internal/api.go
+++ b/roomserver/internal/api.go
@@ -46,6 +46,19 @@ func (r *RoomserverInternalAPI) SetupHTTP(servMux *http.ServeMux) {
 			return util.JSONResponse{Code: http.StatusOK, JSON: &response}
 		}),
 	)
+	servMux.Handle(api.RoomserverPerformJoinPath,
+		common.MakeInternalAPI("performJoin", func(req *http.Request) util.JSONResponse {
+			var request api.PerformJoinRequest
+			var response api.PerformJoinResponse
+			if err := json.NewDecoder(req.Body).Decode(&request); err != nil {
+				return util.MessageResponse(http.StatusBadRequest, err.Error())
+			}
+			if err := r.PerformJoin(req.Context(), &request, &response); err != nil {
+				return util.ErrorResponse(err)
+			}
+			return util.JSONResponse{Code: http.StatusOK, JSON: &response}
+		}),
+	)
 	servMux.Handle(
 		api.RoomserverQueryLatestEventsAndStatePath,
 		common.MakeInternalAPI("queryLatestEventsAndState", func(req *http.Request) util.JSONResponse {
diff --git a/roomserver/internal/perform_join.go b/roomserver/internal/perform_join.go
new file mode 100644
index 00000000..3dfa118f
--- /dev/null
+++ b/roomserver/internal/perform_join.go
@@ -0,0 +1,199 @@
+package internal
+
+import (
+	"context"
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/matrix-org/dendrite/common"
+	fsAPI "github.com/matrix-org/dendrite/federationsender/api"
+	"github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/sirupsen/logrus"
+)
+
+// WriteOutputEvents implements OutputRoomEventWriter
+func (r *RoomserverInternalAPI) PerformJoin(
+	ctx context.Context,
+	req *api.PerformJoinRequest,
+	res *api.PerformJoinResponse,
+) error {
+	_, domain, err := gomatrixserverlib.SplitID('@', req.UserID)
+	if err != nil {
+		return fmt.Errorf("Supplied user ID %q in incorrect format", req.UserID)
+	}
+	if domain != r.Cfg.Matrix.ServerName {
+		return fmt.Errorf("User %q does not belong to this homeserver", req.UserID)
+	}
+	if strings.HasPrefix(req.RoomIDOrAlias, "!") {
+		return r.performJoinRoomByID(ctx, req, res)
+	}
+	if strings.HasPrefix(req.RoomIDOrAlias, "#") {
+		return r.performJoinRoomByAlias(ctx, req, res)
+	}
+	return fmt.Errorf("Room ID or alias %q is invalid", req.RoomIDOrAlias)
+}
+
+func (r *RoomserverInternalAPI) performJoinRoomByAlias(
+	ctx context.Context,
+	req *api.PerformJoinRequest,
+	res *api.PerformJoinResponse,
+) error {
+	// Get the domain part of the room alias.
+	_, domain, err := gomatrixserverlib.SplitID('#', req.RoomIDOrAlias)
+	if err != nil {
+		return fmt.Errorf("Alias %q is not in the correct format", req.RoomIDOrAlias)
+	}
+	req.ServerNames = append(req.ServerNames, domain)
+
+	// Check if this alias matches our own server configuration. If it
+	// doesn't then we'll need to try a federated join.
+	var roomID string
+	if domain != r.Cfg.Matrix.ServerName {
+		// The alias isn't owned by us, so we will need to try joining using
+		// a remote server.
+		dirReq := fsAPI.PerformDirectoryLookupRequest{
+			RoomAlias:  req.RoomIDOrAlias, // the room alias to lookup
+			ServerName: domain,            // the server to ask
+		}
+		dirRes := fsAPI.PerformDirectoryLookupResponse{}
+		err = r.fsAPI.PerformDirectoryLookup(ctx, &dirReq, &dirRes)
+		if err != nil {
+			logrus.WithError(err).Errorf("error looking up alias %q", req.RoomIDOrAlias)
+			return fmt.Errorf("Looking up alias %q over federation failed: %w", req.RoomIDOrAlias, err)
+		}
+		roomID = dirRes.RoomID
+		req.ServerNames = append(req.ServerNames, dirRes.ServerNames...)
+	} else {
+		// Otherwise, look up if we know this room alias locally.
+		roomID, err = r.DB.GetRoomIDForAlias(ctx, req.RoomIDOrAlias)
+		if err != nil {
+			return fmt.Errorf("Lookup room alias %q failed: %w", req.RoomIDOrAlias, err)
+		}
+	}
+
+	// If the room ID is empty then we failed to look up the alias.
+	if roomID == "" {
+		return fmt.Errorf("Alias %q not found", req.RoomIDOrAlias)
+	}
+
+	// If we do, then pluck out the room ID and continue the join.
+	req.RoomIDOrAlias = roomID
+	return r.performJoinRoomByID(ctx, req, res)
+}
+
+// TODO: Break this function up a bit
+// nolint:gocyclo
+func (r *RoomserverInternalAPI) performJoinRoomByID(
+	ctx context.Context,
+	req *api.PerformJoinRequest,
+	res *api.PerformJoinResponse, // nolint:unparam
+) error {
+	// Get the domain part of the room ID.
+	_, domain, err := gomatrixserverlib.SplitID('!', req.RoomIDOrAlias)
+	if err != nil {
+		return fmt.Errorf("Room ID %q is invalid", req.RoomIDOrAlias)
+	}
+	req.ServerNames = append(req.ServerNames, domain)
+
+	// Prepare the template for the join event.
+	userID := req.UserID
+	eb := gomatrixserverlib.EventBuilder{
+		Type:     gomatrixserverlib.MRoomMember,
+		Sender:   userID,
+		StateKey: &userID,
+		RoomID:   req.RoomIDOrAlias,
+		Redacts:  "",
+	}
+	if err = eb.SetUnsigned(struct{}{}); err != nil {
+		return fmt.Errorf("eb.SetUnsigned: %w", err)
+	}
+
+	// It is possible for the request to include some "content" for the
+	// event. We'll always overwrite the "membership" key, but the rest,
+	// like "display_name" or "avatar_url", will be kept if supplied.
+	if req.Content == nil {
+		req.Content = map[string]interface{}{}
+	}
+	req.Content["membership"] = "join"
+	if err = eb.SetContent(req.Content); err != nil {
+		return fmt.Errorf("eb.SetContent: %w", err)
+	}
+
+	// Try to construct an actual join event from the template.
+	// If this succeeds then it is a sign that the room already exists
+	// locally on the homeserver.
+	// TODO: Check what happens if the room exists on the server
+	// but everyone has since left. I suspect it does the wrong thing.
+	buildRes := api.QueryLatestEventsAndStateResponse{}
+	event, err := common.BuildEvent(
+		ctx,        // the request context
+		&eb,        // the template join event
+		r.Cfg,      // the server configuration
+		time.Now(), // the event timestamp to use
+		r,          // the roomserver API to use
+		&buildRes,  // the query response
+	)
+
+	switch err {
+	case nil:
+		// The room join is local. Send the new join event into the
+		// roomserver. First of all check that the user isn't already
+		// a member of the room.
+		alreadyJoined := false
+		for _, se := range buildRes.StateEvents {
+			if membership, merr := se.Membership(); merr == nil {
+				if se.StateKey() != nil && *se.StateKey() == *event.StateKey() {
+					alreadyJoined = (membership == "join")
+					break
+				}
+			}
+		}
+
+		// If we haven't already joined the room then send an event
+		// into the room changing our membership status.
+		if !alreadyJoined {
+			inputReq := api.InputRoomEventsRequest{
+				InputRoomEvents: []api.InputRoomEvent{
+					api.InputRoomEvent{
+						Kind:         api.KindNew,
+						Event:        event.Headered(buildRes.RoomVersion),
+						AuthEventIDs: event.AuthEventIDs(),
+						SendAsServer: string(r.Cfg.Matrix.ServerName),
+					},
+				},
+			}
+			inputRes := api.InputRoomEventsResponse{}
+			if err = r.InputRoomEvents(ctx, &inputReq, &inputRes); err != nil {
+				return fmt.Errorf("r.InputRoomEvents: %w", err)
+			}
+		}
+
+	case common.ErrRoomNoExists:
+		// The room doesn't exist. First of all check if the room is a local
+		// room. If it is then there's nothing more to do - the room just
+		// hasn't been created yet.
+		if domain == r.Cfg.Matrix.ServerName {
+			return fmt.Errorf("Room ID %q does not exist", req.RoomIDOrAlias)
+		}
+
+		// Try joining by all of the supplied server names.
+		fedReq := fsAPI.PerformJoinRequest{
+			RoomID:      req.RoomIDOrAlias, // the room ID to try and join
+			UserID:      req.UserID,        // the user ID joining the room
+			ServerNames: req.ServerNames,   // the server to try joining with
+			Content:     req.Content,       // the membership event content
+		}
+		fedRes := fsAPI.PerformJoinResponse{}
+		err = r.fsAPI.PerformJoin(ctx, &fedReq, &fedRes)
+		if err != nil {
+			return fmt.Errorf("Error joining federated room: %q", err)
+		}
+
+	default:
+		return fmt.Errorf("Error joining room %q: %w", req.RoomIDOrAlias, err)
+	}
+
+	return nil
+}