Add support for /hierarchy API and fall back to /spaces API if needed

src/@types/spaces.ts

@@ -15,26 +15,46 @@ limitations under the License.
 */
 
 import { IPublicRoomsChunkRoom } from "../client";
+import { RoomType } from "./event";
+import { IStrippedState } from "../sync-accumulator";
 
 // Types relating to Rooms of type `m.space` and related APIs
 
 /* eslint-disable camelcase */
+/** @deprecated Use hierarchy instead where possible. */
 export interface ISpaceSummaryRoom extends IPublicRoomsChunkRoom {
     num_refs: number;
     room_type: string;
 }
 
+/** @deprecated Use hierarchy instead where possible. */
 export interface ISpaceSummaryEvent {
     room_id: string;
     event_id: string;
     origin_server_ts: number;
     type: string;
     state_key: string;
+    sender: string;
     content: {
         order?: string;
         suggested?: boolean;
         auto_join?: boolean;
         via?: string[];
     };
 }
+
+export interface IHierarchyRelation extends IStrippedState {
+    room_id: string;
+    origin_server_ts: number;
+    content: {
+        order?: string;
+        suggested?: boolean;
+        via?: string[];
+    };
+}
+
+export interface IHierarchyRoom extends IPublicRoomsChunkRoom {
+    room_type?: RoomType | string;
+    children_state: IHierarchyRelation[];
+}
 /* eslint-enable camelcase */

src/client.ts

@@ -140,7 +140,7 @@ import {
     SearchOrderBy,
 } from "./@types/search";
 import { ISynapseAdminDeactivateResponse, ISynapseAdminWhoisResponse } from "./@types/synapse";
-import { ISpaceSummaryEvent, ISpaceSummaryRoom } from "./@types/spaces";
+import { IHierarchyRoom, ISpaceSummaryEvent, ISpaceSummaryRoom } from "./@types/spaces";
 import { IPusher, IPusherRequest, IPushRules, PushRuleAction, PushRuleKind, RuleId } from "./@types/PushRules";
 import { IThreepid } from "./@types/threepids";
 import { CryptoStore } from "./crypto/store/base";
@@ -7973,14 +7973,15 @@ export class MatrixClient extends EventEmitter {
     }
 
     /**
-     * Fetches or paginates a summary of a space as defined by MSC2946
+     * Fetches or paginates a summary of a space as defined by an initial version of MSC2946
      * @param {string} roomId The ID of the space-room to use as the root of the summary.
      * @param {number?} maxRoomsPerSpace The maximum number of rooms to return per subspace.
      * @param {boolean?} suggestedOnly Whether to only return rooms with suggested=true.
      * @param {boolean?} autoJoinOnly Whether to only return rooms with auto_join=true.
      * @param {number?} limit The maximum number of rooms to return in total.
      * @param {string?} batch The opaque token to paginate a previous summary request.
-     * @returns {Promise} the response, with next_batch, rooms, events fields.
+     * @returns {Promise} the response, with next_token, rooms fields.
+     * @deprecated in favour of `getRoomHierarchy` due to the MSC changing paths.
      */
     public getSpaceSummary(
         roomId: string,
@@ -8008,6 +8009,60 @@ export class MatrixClient extends EventEmitter {
         });
     }
 
+    /**
+     * Fetches or paginates a room hierarchy as defined by MSC2946.
+     * Falls back gracefully to sourcing its data from `getSpaceSummary` if this API is not yet supported by the server.
+     * @param {string} roomId The ID of the space-room to use as the root of the summary.
+     * @param {number?} limit The maximum number of rooms to return per page.
+     * @param {number?} maxDepth The maximum depth in the tree from the root room to return.
+     * @param {boolean?} suggestedOnly Whether to only return rooms with suggested=true.
+     * @param {string?} fromToken The opaque token to paginate a previous request.
+     * @returns {Promise} the response, with next_batch & rooms fields.
+     */
+    public getRoomHierarchy(
+        roomId: string,
+        limit?: number,
+        maxDepth?: number,
+        suggestedOnly = false,
+        fromToken?: string,
+    ): Promise<{
+        rooms: IHierarchyRoom[];
+        next_batch?: string; // eslint-disable-line camelcase
+    }> {
+        const path = utils.encodeUri("/rooms/$roomId/hierarchy", {
+            $roomId: roomId,
+        });
+
+        return this.http.authedRequest(undefined, "GET", path, {
+            suggested_only: suggestedOnly,
+            max_depth: maxDepth,
+            from: fromToken,
+            limit,
+        }, undefined, {
+            prefix: "/_matrix/client/unstable/org.matrix.msc2946",
+        }).catch(e => {
+            if (e.errcode === "M_UNRECOGNIZED") {
+                // fall back to the older space summary API as it exposes the same data just in a different shape.
+                return this.getSpaceSummary(roomId, undefined, suggestedOnly, undefined, limit)
+                    .then(({ rooms, events }) => {
+                        // Translate response from `/spaces` to that we expect in this API.
+                        const roomMap = new Map(rooms.map(r => {
+                            return [r.room_id, <IHierarchyRoom>{ ...r, children_state: [] }];
+                        }));
+                        events.forEach(e => {
+                            roomMap.get(e.room_id)?.children_state.push(e);
+                        });
+
+                        return {
+                            rooms: Array.from(roomMap.values()),
+                        };
+                    });
+            }
+
+            throw e;
+        });
+    }
+
     /**
      * Creates a new file tree space with the given name. The client will pick
      * defaults for how it expects to be able to support the remaining API offered

src/room-hierarchy.ts

@@ -0,0 +1,149 @@
+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+/**
+ * @module room-hierarchy
+ */
+
+import { Room } from "./models/room";
+import { IHierarchyRoom, IHierarchyRelation } from "./@types/spaces";
+import { MatrixClient } from "./client";
+import { EventType } from "./@types/event";
+
+export class RoomHierarchy {
+    // Map from room id to list of servers which are listed as a via somewhere in the loaded hierarchy
+    public readonly viaMap = new Map<string, Set<string>>();
+    // Map from room id to list of rooms which claim this room as their child
+    public readonly backRefs = new Map<string, string[]>();
+    // Map from room id to object
+    public readonly roomMap = new Map<string, IHierarchyRoom>();
+    private loadRequest: ReturnType<MatrixClient["getRoomHierarchy"]>;
+    private nextBatch?: string;
+    private _rooms?: IHierarchyRoom[];
+    private serverSupportError?: Error;
+
+    /**
+     * Construct a new RoomHierarchy
+     *
+     * A RoomHierarchy instance allows you to easily make use of the /hierarchy API and paginate it.
+     *
+     * @param {Room} root the root of this hierarchy
+     * @param {number} pageSize the maximum number of rooms to return per page, can be overridden per load request.
+     * @param {number} maxDepth the maximum depth to traverse the hierarchy to
+     * @param {boolean} suggestedOnly whether to only return rooms with suggested=true.
+     * @constructor
+     */
+    constructor(
+        private readonly root: Room,
+        private readonly pageSize?: number,
+        private readonly maxDepth?: number,
+        private readonly suggestedOnly = false,
+    ) {}
+
+    public get noSupport(): boolean {
+        return !!this.serverSupportError;
+    }
+
+    public get canLoadMore(): boolean {
+        return !!this.serverSupportError || !!this.nextBatch || !this._rooms;
+    }
+
+    public get rooms(): IHierarchyRoom[] {
+        return this._rooms;
+    }
+
+    public async load(pageSize = this.pageSize): Promise<IHierarchyRoom[]> {
+        if (this.loadRequest) return this.loadRequest.then(r => r.rooms);
+
+        this.loadRequest = this.root.client.getRoomHierarchy(
+            this.root.roomId,
+            pageSize,
+            this.maxDepth,
+            this.suggestedOnly,
+            this.nextBatch,
+        );
+
+        let rooms: IHierarchyRoom[];
+        try {
+            ({ rooms, next_batch: this.nextBatch } = await this.loadRequest);
+        } catch (e) {
+            if (e.errcode === "M_UNRECOGNIZED") {
+                this.serverSupportError = e;
+            } else {
+                throw e;
+            }
+
+            return [];
+        } finally {
+            this.loadRequest = null;
+        }
+
+        if (this._rooms) {
+            this._rooms = this._rooms.concat(rooms);
+        } else {
+            this._rooms = rooms;
+        }
+
+        rooms.forEach(room => {
+            this.roomMap.set(room.room_id, room);
+
+            room.children_state.forEach(ev => {
+                if (ev.type !== EventType.SpaceChild) return;
+                const childRoomId = ev.state_key;
+
+                // track backrefs for quicker hierarchy navigation
+                if (!this.backRefs.has(childRoomId)) {
+                    this.backRefs.set(childRoomId, []);
+                }
+                this.backRefs.get(childRoomId).push(ev.room_id);
+
+                // fill viaMap
+                if (Array.isArray(ev.content.via)) {
+                    if (!this.viaMap.has(childRoomId)) {
+                        this.viaMap.set(childRoomId, new Set());
+                    }
+                    const vias = this.viaMap.get(childRoomId);
+                    ev.content.via.forEach(via => vias.add(via));
+                }
+            });
+        });
+
+        return rooms;
+    }
+
+    public getRelation(parentId: string, childId: string): IHierarchyRelation {
+        return this.roomMap.get(parentId)?.children_state.find(e => e.state_key === childId);
+    }
+
+    public isSuggested(parentId: string, childId: string): boolean {
+        return this.getRelation(parentId, childId)?.content.suggested;
+    }
+
+    // locally remove a relation as a form of local echo
+    public removeRelation(parentId: string, childId: string): void {
+        const backRefs = this.backRefs.get(childId);
+        if (backRefs?.length === 1) {
+            this.backRefs.delete(childId);
+        } else if (backRefs?.length) {
+            this.backRefs.set(childId, backRefs.filter(ref => ref !== parentId));
+        }
+
+        const room = this.roomMap.get(parentId);
+        if (room) {
+            room.children_state = room.children_state.filter(ev => ev.state_key !== childId);
+        }
+    }
+}