Support routing matrix.to links to joinable rooms

karma.conf.js

@@ -199,12 +199,25 @@ module.exports = function (config) {
 
                     'matrix-react-sdk': path.resolve('test/skinned-sdk.js'),
                     'sinon': 'sinon/pkg/sinon.js',
+
+                    // To make webpack happy
+                    // Related: https://github.com/request/request/issues/1529
+                    // (there's no mock available for fs, so we fake a mock by using
+                    // an in-memory version of fs)
+                    "fs": "memfs",
                 },
                 modules: [
                     path.resolve('./test'),
                     "node_modules"
                 ],
             },
+            node: {
+                // Because webpack is made of fail
+                // https://github.com/request/request/issues/1529
+                // Note: 'mock' is the new 'empty'
+                net: 'mock',
+                tls: 'mock'
+            },
             devtool: 'inline-source-map',
             externals: {
                 // Don't try to bundle electron: leave it as a commonjs dependency

package.json

@@ -76,6 +76,7 @@
     "lodash": "^4.13.1",
     "lolex": "2.3.2",
     "matrix-js-sdk": "matrix-org/matrix-js-sdk#develop",
+    "memfs": "^2.10.1",
     "optimist": "^0.6.1",
     "pako": "^1.0.5",
     "prop-types": "^15.5.8",

src/components/structures/LoggedInView.js

@@ -64,6 +64,9 @@ const LoggedInView = React.createClass({
 
         teamToken: PropTypes.string,
 
+        // Used by the RoomView to handle joining rooms
+        viaServers: PropTypes.arrayOf(PropTypes.string),
+
         // and lots and lots of other stuff.
     },
 
@@ -389,6 +392,7 @@ const LoggedInView = React.createClass({
                         onRegistered={this.props.onRegistered}
                         thirdPartyInvite={this.props.thirdPartyInvite}
                         oobData={this.props.roomOobData}
+                        viaServers={this.props.viaServers}
                         eventPixelOffset={this.props.initialEventPixelOffset}
                         key={this.props.currentRoomId || 'roomview'}
                         disabled={this.props.middleDisabled}

src/components/structures/MatrixChat.js

@@ -840,6 +840,7 @@ export default React.createClass({
             page_type: PageTypes.RoomView,
             thirdPartyInvite: roomInfo.third_party_invite,
             roomOobData: roomInfo.oob_data,
+            viaServers: roomInfo.via_servers,
         };
 
         if (roomInfo.room_alias) {
@@ -1489,9 +1490,21 @@ export default React.createClass({
                 inviterName: params.inviter_name,
             };
 
+            // on our URLs there might be a ?via=matrix.org or similar to help
+            // joins to the room succeed. We'll pass these through as an array
+            // to other levels. If there's just one ?via= then params.via is a
+            // single string. If someone does something like ?via=one.com&via=two.com
+            // then params.via is an array of strings.
+            let via = [];
+            if (params.via) {
+                if (typeof(params.via) === 'string') via = [params.via];
+                else via = params.via;
+            }
+
             const payload = {
                 action: 'view_room',
                 event_id: eventId,
+                via_servers: via,
                 // If an event ID is given in the URL hash, notify RoomViewStore to mark
                 // it as highlighted, which will propagate to RoomView and highlight the
                 // associated EventTile.

src/components/structures/RoomView.js

@@ -88,6 +88,9 @@ module.exports = React.createClass({
 
         // is the RightPanel collapsed?
         collapsedRhs: PropTypes.bool,
+
+        // Servers the RoomView can use to try and assist joins
+        viaServers: PropTypes.arrayOf(PropTypes.string),
     },
 
     getInitialState: function() {
@@ -833,7 +836,7 @@ module.exports = React.createClass({
                 action: 'do_after_sync_prepared',
                 deferred_action: {
                     action: 'join_room',
-                    opts: { inviteSignUrl: signUrl },
+                    opts: { inviteSignUrl: signUrl, viaServers: this.props.viaServers },
                 },
             });
 
@@ -875,7 +878,7 @@ module.exports = React.createClass({
                 this.props.thirdPartyInvite.inviteSignUrl : undefined;
             dis.dispatch({
                 action: 'join_room',
-                opts: { inviteSignUrl: signUrl },
+                opts: { inviteSignUrl: signUrl, viaServers: this.props.viaServers },
             });
             return Promise.resolve();
         });

src/components/structures/UserSettings.js

@@ -1298,7 +1298,7 @@ module.exports = React.createClass({
         // If the olmVersion is not defined then either crypto is disabled, or
         // we are using a version old version of olm. We assume the former.
         let olmVersionString = "<not-enabled>";
-        if (olmVersion !== undefined) {
+        if (olmVersion) {
             olmVersionString = `${olmVersion[0]}.${olmVersion[1]}.${olmVersion[2]}`;
         }
 

src/matrix-to.js

@@ -14,21 +14,104 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+import MatrixClientPeg from "./MatrixClientPeg";
+
 export const host = "matrix.to";
 export const baseUrl = `https://${host}`;
 
 export function makeEventPermalink(roomId, eventId) {
-    return `${baseUrl}/#/${roomId}/${eventId}`;
+    const serverCandidates = pickServerCandidates(roomId);
+    return `${baseUrl}/#/${roomId}/${eventId}?${encodeServerCandidates(serverCandidates)}`;
 }
 
 export function makeUserPermalink(userId) {
     return `${baseUrl}/#/${userId}`;
 }
 
 export function makeRoomPermalink(roomId) {
-    return `${baseUrl}/#/${roomId}`;
+    const serverCandidates = pickServerCandidates(roomId);
+    return `${baseUrl}/#/${roomId}?${encodeServerCandidates(serverCandidates)}`;
 }
 
 export function makeGroupPermalink(groupId) {
     return `${baseUrl}/#/${groupId}`;
 }
+
+export function encodeServerCandidates(candidates) {
+    if (!candidates) return '';
+    return `via=${candidates.map(c => encodeURIComponent(c)).join("&via=")}`
+}
+
+export function pickServerCandidates(roomId) {
+    const client = MatrixClientPeg.get();
+    const room = client.getRoom(roomId);
+    if (!room) return [];
+
+    // Permalinks can have servers appended to them so that the user
+    // receiving them can have a fighting chance at joining the room.
+    // These servers are called "candidates" at this point because
+    // it is unclear whether they are going to be useful to actually
+    // join in the future.
+    //
+    // We pick 3 servers based on the following criteria:
+    //
+    //   Server 1: The highest power level user in the room, provided
+    //   they are at least PL 50. We don't calculate "what is a moderator"
+    //   here because it is less relevant for the vast majority of rooms.
+    //   We also want to ensure that we get an admin or high-ranking mod
+    //   as they are less likely to leave the room. If no user happens
+    //   to meet this criteria, we'll pick the most popular server in the
+    //   room.
+    //
+    //   Server 2: The next most popular server in the room (in user
+    //   distribution). This will probably be matrix.org in most cases
+    //   although it is certainly possible to be some other server. This
+    //   cannot be the same as Server 1. If no other servers are available
+    //   then we'll only return Server 1.
+    //
+    //   Server 3: The next most popular server by user distribution. This
+    //   has the same rules as Server 2, with the added exception that it
+    //   must be unique from Server 1 and 2.
+
+    // Rationale for popular servers: It's hard to get rid of people when
+    // they keep flocking in from a particular server. Sure, the server could
+    // be ACL'd in the future or for some reason be evicted from the room
+    // however an event like that is unlikely the larger the room gets.
+
+    // Note: Users receiving permalinks that happen to have all 3 potential
+    // servers fail them (in terms of joining) are somewhat expected to hunt
+    // down the person who gave them the link to ask for a participating server.
+    // The receiving user can then manually append the known-good server to
+    // the list and magically have the link work.
+
+    const populationMap: {[server:string]:number} = {};
+    const highestPlUser = {userId:null, powerLevel: 0, serverName: null};
+
+    for (const member of room.getJoinedMembers()) {
+        const serverName = member.userId.split(":").splice(1).join(":");
+        if (member.powerLevel > highestPlUser.powerLevel) {
+            highestPlUser.userId = member.userId;
+            highestPlUser.powerLevel = member.powerLevel;
+            highestPlUser.serverName = serverName;
+        }
+
+        if (!populationMap[serverName]) populationMap[serverName] = 0;
+        populationMap[serverName]++;
+    }
+
+    const candidates = [];
+    if (highestPlUser.powerLevel >= 50) candidates.push(highestPlUser.serverName);
+
+    const beforePopulation = candidates.length;
+    const maxCandidates = 3;
+    const serversByPopulation = Object.keys(populationMap)
+        .sort((a, b) => populationMap[b] - populationMap[a])
+        .filter(a => !candidates.includes(a));
+    for (let i = beforePopulation; i <= maxCandidates; i++) {
+        const idx = i - beforePopulation;
+        if (idx >= serversByPopulation.length) break;
+        candidates.push(serversByPopulation[idx]);
+    }
+
+    return candidates;
+}