Confirm to trust certificate when there is error

For #26

src/browser/index.jsx

@@ -221,6 +221,10 @@ var MattermostView = React.createClass({
 
     webview.addEventListener('did-fail-load', function(e) {
       console.log(thisObj.props.name, 'webview did-fail-load', e);
+      if (e.errorCode === -3) { // An operation was aborted (due to user action).
+        return;
+      }
+
       // should use permanent way to indicate
       var did_fail_load_notification = new Notification(`Failed to load "${thisObj.props.name}"`, {
         body: `ErrorCode: ${e.errorCode}`,

src/main.js

@@ -10,6 +10,7 @@ const fs = require('fs');
 const path = require('path');
 
 var settings = require('./common/settings');
+var certificateStore = require('./main/certificateStore').load(path.resolve(app.getPath('userData'), 'certificate.json'));
 var appMenu = require('./main/menus/app');
 
 var argv = require('yargs').argv;
@@ -80,6 +81,38 @@ app.on('before-quit', function() {
   willAppQuit = true;
 });
 
+app.on('certificate-error', function(event, webContents, url, error, certificate, callback) {
+  if (certificateStore.isTrusted(url, certificate)) {
+    event.preventDefault();
+    callback(true);
+  }
+  else {
+    var detail = `URL: ${url}\nError: ${error}`;
+    if (certificateStore.isExisting(url)) {
+      detail = `Certificate is different from previous one.\n\n` + detail;
+    }
+
+    electron.dialog.showMessageBox(mainWindow, {
+      title: 'Certificate error',
+      message: `Do you trust certificate from "${certificate.issuerName}"?`,
+      detail: detail,
+      type: 'warning',
+      buttons: [
+        'Yes',
+        'No'
+      ],
+      cancelId: 1
+    }, function(response) {
+      if (response === 0) {
+        certificateStore.add(url, certificate);
+        certificateStore.save();
+        webContents.loadURL(url);
+      }
+    });
+    callback(false);
+  }
+});
+
 // This method will be called when Electron has finished
 // initialization and is ready to create browser windows.
 app.on('ready', function() {

src/main/certificateStore.js

@@ -0,0 +1,62 @@
+'use strict';
+
+const fs = require('fs');
+const url = require('url');
+
+function comparableCertificate(certificate) {
+  return {
+    data: certificate.data.toString(),
+    issuerName: certificate.issuerName
+  };
+}
+
+function areEqual(certificate0, certificate1) {
+  if (certificate0.data !== certificate1.data) {
+    return false;
+  }
+  if (certificate0.issuerName !== certificate1.issuerName) {
+    return false;
+  }
+  return true;
+}
+
+function getHost(targetURL) {
+  return url.parse(targetURL).host;
+}
+
+var CertificateStore = function(storeFile) {
+  this.storeFile = storeFile
+  try {
+    this.data = JSON.parse(fs.readFileSync(storeFile, 'utf-8'));
+  }
+  catch (e) {
+    console.log(e);
+    this.data = {};
+  }
+};
+
+CertificateStore.prototype.save = function() {
+  fs.writeFileSync(this.storeFile, JSON.stringify(this.data, null, '  '));
+};
+
+CertificateStore.prototype.add = function(targetURL, certificate) {
+  this.data[getHost(targetURL)] = comparableCertificate(certificate);
+};
+
+CertificateStore.prototype.isExisting = function(targetURL) {
+  return this.data.hasOwnProperty(getHost(targetURL));
+};
+
+CertificateStore.prototype.isTrusted = function(targetURL, certificate) {
+  var host = getHost(targetURL);
+  if (!this.isExisting(targetURL)) {
+    return false;
+  }
+  return areEqual(this.data[host], comparableCertificate(certificate));
+};
+
+module.exports = {
+  load: function(storeFile) {
+    return new CertificateStore(storeFile);
+  }
+};