ask electron users to do captchas in a web browser.

This will happen anyway when they follow email verification links.
make captchas poll for success so if they are completed elsewhere, electron moves on

src/Signup.js

@@ -191,7 +191,7 @@ class Register extends Signup {
                     }
                 }
                 if (poll_for_success) {
-                    return q.delay(5000).then(function() {
+                    return q.delay(2000).then(function() {
                         return self._tryRegister(client, authDict, poll_for_success);
                     });
                 } else {

src/SignupStages.js

@@ -52,7 +52,13 @@ DummyStage.TYPE = "m.login.dummy";
 class RecaptchaStage extends Stage {
     constructor(matrixClient, signupInstance) {
         super(RecaptchaStage.TYPE, matrixClient, signupInstance);
-        this.defer = q.defer(); // resolved with the captcha response
+        this.authDict = {
+            auth: {
+                type: 'm.login.recaptcha',
+                // we'll add in the response param if we get one from the local user.
+            },
+            poll_for_success: true,
+        };
     }
 
     // called when the recaptcha has been completed.
@@ -60,16 +66,15 @@ class RecaptchaStage extends Stage {
         if (!data || !data.response) {
             return;
         }
-        this.defer.resolve({
-            auth: {
-                type: 'm.login.recaptcha',
-                response: data.response,
-            }
-        });
+        this.authDict.response = data.response;
     }
 
     complete() {
-        return this.defer.promise;
+        // we return the authDict with no response, telling Signup to keep polling
+        // the server in case the captcha is filled in on another window (e.g. by
+        // following a nextlink from an email signup).  If the user completes the
+        // captcha locally, then we return at the next poll.
+        return q(this.authDict);
     }
 }
 RecaptchaStage.TYPE = "m.login.recaptcha";

src/components/structures/login/Registration.js

@@ -273,6 +273,7 @@ module.exports = React.createClass({
                 if (serverParams && serverParams["m.login.recaptcha"]) {
                     publicKey = serverParams["m.login.recaptcha"].public_key;
                 }
+
                 registerStep = (
                     <CaptchaForm sitePublicKey={publicKey}
                         onCaptchaResponse={this.onCaptchaResponse}

src/components/views/login/CaptchaForm.js

@@ -52,13 +52,24 @@ module.exports = React.createClass({
             this._onCaptchaLoaded();
         } else {
             console.log("Loading recaptcha script...");
-            var scriptTag = document.createElement('script');
             window.mx_on_recaptcha_loaded = () => {this._onCaptchaLoaded()};
-            var protocol = global.location.protocol === "file:" ? "https:" : global.location.protocol;
-            scriptTag.setAttribute(
-                'src', protocol+"//www.google.com/recaptcha/api.js?onload=mx_on_recaptcha_loaded&render=explicit"
-            );
-            this.refs.recaptchaContainer.appendChild(scriptTag);
+            var protocol = global.location.protocol;
+            if (protocol === "file:") {
+                var warning = document.createElement('div');
+                // XXX: fix hardcoded app URL.  Better solutions include:
+                // * jumping straight to a hosted captcha page (but we don't support that yet)
+                // * embedding the captcha in an iframe (if that works)
+                // * using a better captcha lib
+                warning.innerHTML = "Robot check is currently unavailable on desktop - please sign up <a href='https://riot.im/app'>using a web browser</a>.";
+                this.refs.recaptchaContainer.appendChild(warning);
+            }
+            else {
+                var scriptTag = document.createElement('script');
+                scriptTag.setAttribute(
+                    'src', protocol+"//www.google.com/recaptcha/api.js?onload=mx_on_recaptcha_loaded&render=explicit"
+                );
+                this.refs.recaptchaContainer.appendChild(scriptTag);
+            }
         }
     },
 
@@ -107,6 +118,7 @@ module.exports = React.createClass({
         return (
             <div ref="recaptchaContainer">
                 This Home Server would like to make sure you are not a robot
+                <br/>
                 <div id={DIV_ID}></div>
                 {error}
             </div>