Move all login error string generation into view

This makes all the various hits done by login report the same
useful error messages and gets rid of the broken ones like printing
the http status code even if it was undefined. Also add text for
the case of overzealous browser extensions because lots of people
get bitten by it.

src/components/structures/login/Login.js

@@ -87,7 +87,24 @@ module.exports = React.createClass({
         ).then((data) => {
             this.props.onLoggedIn(data);
         }, (error) => {
-            this._setStateFromError(error, true);
+            let errorText;
+
+            // Some error strings only apply for logging in
+            const usingEmail = username.indexOf("@");
+            if (error.httpStatus == 400 && usingEmail) {
+                errorText = _t('This Home Server does not support login using email address.');
+            } else if (error.httpStatus == 401 || error.httpStatus === 403) {
+                errorText = _t('Incorrect username and/or password.');
+            } else {
+                // other errors, not specific to doing a password login
+                errorText = this._errorTextFromError(error);
+            }
+
+            this.setState({
+                errorText: errorText,
+                // https://matrix.org/jira/browse/SYN-744
+                loginIncorrect: error.httpStatus == 401 || error.httpStatus == 403
+            });
         }).finally(() => {
             this.setState({
                 busy: false
@@ -110,7 +127,16 @@ module.exports = React.createClass({
         this._loginLogic.loginAsGuest().then(function(data) {
             self.props.onLoggedIn(data);
         }, function(error) {
-            self._setStateFromError(error, true);
+            let errorText;
+            if (error.httpStatus === 403) {
+                errorText = _t("Guest access is disabled on this Home Server.");
+            } else {
+                errorText = self._errorTextFromError(error);
+            }
+            self.setState({
+                errorText: errorText,
+                loginIncorrect: false,
+            });
         }).finally(function() {
             self.setState({
                 busy: false
@@ -183,31 +209,22 @@ module.exports = React.createClass({
                 currentFlow: self._getCurrentFlowStep(),
             });
         }, function(err) {
-            self._setStateFromError(err, false);
+            self.setState({
+                errorText: self._errorTextFromError(err),
+                loginIncorrect: false,
+            });
         }).finally(function() {
             self.setState({
                 busy: false,
             });
-        });
+        }).done();
     },
 
     _getCurrentFlowStep: function() {
         return this._loginLogic ? this._loginLogic.getCurrentFlowStep() : null;
     },
 
-    _setStateFromError: function(err, isLoginAttempt) {
-        this.setState({
-            errorText: this._errorTextFromError(err),
-            // https://matrix.org/jira/browse/SYN-744
-            loginIncorrect: isLoginAttempt && (err.httpStatus == 401 || err.httpStatus == 403)
-        });
-    },
-
     _errorTextFromError(err) {
-        if (err.friendlyText) {
-            return err.friendlyText;
-        }
-
         let errCode = err.errcode;
         if (!errCode && err.httpStatus) {
             errCode = "HTTP " + err.httpStatus;
@@ -230,7 +247,7 @@ module.exports = React.createClass({
                 </span>;
             } else {
                 errorText = <span>
-                    { _tJsx("Can't connect to homeserver - please check your connectivity and ensure your <a>homeserver's SSL certificate</a> is trusted.",
+                    { _tJsx("Can't connect to homeserver - please check your connectivity and ensure your <a>homeserver's SSL certificate</a> is trusted and that a browser extension is not blocking requests.",
                       /<a>(.*?)<\/a>/,
                       (sub) => { return <a href={this.state.enteredHomeserverUrl}>{ sub }</a>; }
                     )}