Add a fallback home server to log into

src/Signup.js

@@ -293,8 +293,9 @@ class Register extends Signup {
 
 
 class Login extends Signup {
-    constructor(hsUrl, isUrl) {
+    constructor(hsUrl, isUrl, fallbackHsUrl) {
         super(hsUrl, isUrl);
+        this._fallbackHsUrl = fallbackHsUrl;
         this._currentFlowIndex = 0;
         this._flows = [];
     }
@@ -359,6 +360,30 @@ class Login extends Signup {
                 error.friendlyText = (
                     'Incorrect username and/or password.'
                 );
+                if (self._fallbackHsUrl) {
+                    // as per elsewhere, it would be much nicer to not replace the global
+                    // client just to try an alternate HS
+                    MatrixClientPeg.replaceUsingUrls(
+                        self._fallbackHsUrl,
+                        self._isUrl
+                    );
+                    return MatrixClientPeg.get().login('m.login.password', loginParams).then(function(data) {
+                        return q({
+                            homeserverUrl: self._fallbackHsUrl,
+                            identityServerUrl: self._isUrl,
+                            userId: data.user_id,
+                            accessToken: data.access_token
+                        });
+                    }, function(fallback_error) {
+                        // We also have to put the default back again if it fails...
+                        MatrixClientPeg.replaceUsingUrls(
+                            this._hsUrl,
+                            this._isUrl
+                        );
+                        // throw the original error
+                        throw error;
+                    });
+                }
             }
             else {
                 error.friendlyText = (

src/components/structures/MatrixChat.js

@@ -103,6 +103,10 @@ module.exports = React.createClass({
         return "https://matrix.org";
     },
 
+    getFallbackHsUrl: function() {
+        return this.props.config.fallback_hs_url;
+    },
+
     getCurrentIsUrl: function() {
         if (this.state.register_is_url) {
             return this.state.register_is_url;
@@ -1183,6 +1187,7 @@ module.exports = React.createClass({
                     defaultIsUrl={this.props.config.default_is_url}
                     customHsUrl={this.getCurrentHsUrl()}
                     customIsUrl={this.getCurrentIsUrl()}
+                    fallbackHsUrl={this.getFallbackHsUrl()}
                     onForgotPasswordClick={this.onForgotPasswordClick}
                     onLoginAsGuestClick={this.props.enableGuest && this.props.config && this.props.config.default_hs_url ? this._registerAsGuest.bind(this, true) : undefined}
                     onCancelClick={ this.state.guestCreds ? this.onReturnToGuestClick : null }

src/components/structures/login/Login.js

@@ -35,6 +35,10 @@ module.exports = React.createClass({displayName: 'Login',
         customIsUrl: React.PropTypes.string,
         defaultHsUrl: React.PropTypes.string,
         defaultIsUrl: React.PropTypes.string,
+        // Secondary HS which we try to log into if the user is using
+        // the default HS but login fails. Useful for migrating to a
+        // different home server without confusing users.
+        fallbackHsUrl: React.PropTypes.string,
 
         // login shouldn't know or care how registration is done.
         onRegisterClick: React.PropTypes.func.isRequired,
@@ -105,7 +109,9 @@ module.exports = React.createClass({displayName: 'Login',
         hsUrl = hsUrl || this.state.enteredHomeserverUrl;
         isUrl = isUrl || this.state.enteredIdentityServerUrl;
 
-        var loginLogic = new Signup.Login(hsUrl, isUrl);
+        var fallbackHsUrl = hsUrl == this.props.defaultHsUrl ? this.props.fallbackHsUrl : null;
+
+        var loginLogic = new Signup.Login(hsUrl, isUrl, fallbackHsUrl);
         this._loginLogic = loginLogic;
 
         loginLogic.getFlows().then(function(flows) {