Add canonical alias support (#2236)

* Add canonical support

* Add test

* Check that the send event is actually an m.room.canonical_alias
Check that we got an event from the database

* Update to get correct required events

* Add flakey test to blacklist

3 files changed, 140 insertions, 2 deletions

diff --git a/roomserver/api/alias.go b/roomserver/api/alias.go
index df69e5b4..be37333b 100644
--- a/roomserver/api/alias.go
+++ b/roomserver/api/alias.go
@@ -14,6 +14,8 @@
 
 package api
 
+import "regexp"
+
 // SetRoomAliasRequest is a request to SetRoomAlias
 type SetRoomAliasRequest struct {
 	// ID of the user setting the alias
@@ -84,3 +86,20 @@ type RemoveRoomAliasResponse struct {
 	// Did we remove it?
 	Removed bool `json:"removed"`
 }
+
+type AliasEvent struct {
+	Alias      string   `json:"alias"`
+	AltAliases []string `json:"alt_aliases"`
+}
+
+var validateAliasRegex = regexp.MustCompile("^#.*:.+$")
+
+func (a AliasEvent) Valid() bool {
+	for _, alias := range a.AltAliases {
+		if !validateAliasRegex.MatchString(alias) {
+			return false
+		}
+	}
+	return a.Alias == "" || validateAliasRegex.MatchString(a.Alias)
+}
+
diff --git a/roomserver/api/alias_test.go b/roomserver/api/alias_test.go
new file mode 100644
index 00000000..680493b7
--- /dev/null
+++ b/roomserver/api/alias_test.go
@@ -0,0 +1,62 @@
+package api
+
+import "testing"
+
+func TestAliasEvent_Valid(t *testing.T) {
+	type fields struct {
+		Alias      string
+		AltAliases []string
+	}
+	tests := []struct {
+		name   string
+		fields fields
+		want   bool
+	}{
+		{
+			name: "empty alias",
+			fields: fields{
+				Alias: "",
+			},
+			want: true,
+		},
+		{
+			name: "empty alias, invalid alt aliases",
+			fields: fields{
+				Alias: "",
+				AltAliases: []string{ "%not:valid.local"},
+			},
+		},
+		{
+			name: "valid alias, invalid alt aliases",
+			fields: fields{
+				Alias: "#valid:test.local",
+				AltAliases: []string{ "%not:valid.local"},
+			},
+		},
+		{
+			name: "empty alias, invalid alt aliases",
+			fields: fields{
+				Alias: "",
+				AltAliases: []string{ "%not:valid.local"},
+			},
+		},
+		{
+			name: "invalid alias",
+			fields: fields{
+				Alias: "%not:valid.local",
+				AltAliases: []string{ },
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			a := AliasEvent{
+				Alias:      tt.fields.Alias,
+				AltAliases: tt.fields.AltAliases,
+			}
+			if got := a.Valid(); got != tt.want {
+				t.Errorf("Valid() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
diff --git a/roomserver/internal/alias.go b/roomserver/internal/alias.go
index 7995279d..5c1c04f0 100644
--- a/roomserver/internal/alias.go
+++ b/roomserver/internal/alias.go
@@ -16,12 +16,18 @@ package internal
 
 import (
 	"context"
+	"database/sql"
+	"errors"
 	"fmt"
+	"time"
 
+	asAPI "github.com/matrix-org/dendrite/appservice/api"
+	"github.com/matrix-org/dendrite/internal/eventutil"
 	"github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/dendrite/roomserver/internal/helpers"
 	"github.com/matrix-org/gomatrixserverlib"
-
-	asAPI "github.com/matrix-org/dendrite/appservice/api"
+	"github.com/tidwall/gjson"
+	"github.com/tidwall/sjson"
 )
 
 // RoomserverInternalAPIDatabase has the storage APIs needed to implement the alias API.
@@ -183,6 +189,57 @@ func (r *RoomserverInternalAPI) RemoveRoomAlias(
 		}
 	}
 
+	ev, err := r.DB.GetStateEvent(ctx, roomID, gomatrixserverlib.MRoomCanonicalAlias, "")
+	if err != nil && err != sql.ErrNoRows {
+		return err
+	} else if ev != nil {
+		stateAlias := gjson.GetBytes(ev.Content(), "alias").Str
+		// the alias to remove is currently set as the canonical alias, remove it
+		if stateAlias == request.Alias {
+			res, err := sjson.DeleteBytes(ev.Content(), "alias")
+			if err != nil {
+				return err
+			}
+
+			sender := request.UserID
+			if request.UserID != ev.Sender() {
+				sender = ev.Sender()
+			}
+
+			builder := &gomatrixserverlib.EventBuilder{
+				Sender:   sender,
+				RoomID:   ev.RoomID(),
+				Type:     ev.Type(),
+				StateKey: ev.StateKey(),
+				Content:  res,
+			}
+
+			eventsNeeded, err := gomatrixserverlib.StateNeededForEventBuilder(builder)
+			if err != nil {
+				return fmt.Errorf("gomatrixserverlib.StateNeededForEventBuilder: %w", err)
+			}
+			if len(eventsNeeded.Tuples()) == 0 {
+				return errors.New("expecting state tuples for event builder, got none")
+			}
+
+			stateRes := &api.QueryLatestEventsAndStateResponse{}
+			if err := helpers.QueryLatestEventsAndState(ctx, r.DB, &api.QueryLatestEventsAndStateRequest{RoomID: roomID, StateToFetch: eventsNeeded.Tuples()}, stateRes); err != nil {
+				return err
+			}
+
+			newEvent, err := eventutil.BuildEvent(ctx, builder, r.Cfg.Matrix, time.Now(), &eventsNeeded, stateRes)
+			if err != nil {
+				return err
+			}
+
+			err = api.SendEvents(ctx, r.RSAPI, api.KindNew, []*gomatrixserverlib.HeaderedEvent{newEvent}, r.ServerName, r.ServerName, nil, false)
+			if err != nil {
+				return err
+			}
+
+		}
+	}
+
 	// Remove the alias from the database
 	if err := r.DB.RemoveRoomAlias(ctx, request.Alias); err != nil {
 		return err