Move decryptFile into a utility function so that it can be shared between different components

Conflicts:
	src/components/views/messages/MImageBody.js

src/components/views/messages/MImageBody.js

@@ -18,12 +18,12 @@ limitations under the License.
 
 var React = require('react');
 var filesize = require('filesize');
-
 var MatrixClientPeg = require('../../../MatrixClientPeg');
 var ImageUtils = require('../../../ImageUtils');
 var Modal = require('../../../Modal');
 var sdk = require('../../../index');
 var dis = require("../../../dispatcher");
+var DecryptFile = require('../../../utils/DecryptFile');
 
 module.exports = React.createClass({
     displayName: 'MImageBody',
@@ -110,34 +110,18 @@ module.exports = React.createClass({
         var self = this;
         if (content.file !== undefined && this.state.decryptedUrl === null) {
             // TODO: hook up an error handler to the promise.
-            this.decryptFile(content.file).catch(function (err) {
+            DecryptFile.decryptFile(content.file).then(function(blob) {
-                console.warn("Unable to decrypt attachment: ", err)
-                // Set a placeholder image when we can't decrypt the image.
-                self.refs.image.src = "img/warning.svg";
-            });
-        }
-    },
-
-    decryptFile: function(file) {
-        var url = MatrixClientPeg.get().mxcUrlToHttp(file.url);
-        var self = this;
-        // Download the encrypted file as an array buffer.
-        return fetch(url).then(function (response) {
-            return response.arrayBuffer();
-        }).then(function (responseData) {
-            // Decrypt the array buffer using the information taken from
-            // the event content.
-            return encrypt.decryptAttachment(responseData, file);
-        }).then(function(dataArray) {
-            // Turn the array into a Blob and use createObjectUrl to make
-            // a url that we can use as an img src.
-            var blob = new Blob([dataArray], {type: file.mimetype});
                 if (!self._unmounted) {
                     self.setState({
                         decryptedUrl: window.URL.createObjectURL(blob),
                     });
                 }
+            }).catch(function (err) {
+                console.warn("Unable to decrypt attachment: ", err)
+                // Set a placeholder image when we can't decrypt the image.
+                self.refs.image.src = "img/warning.svg";
             });
+        }
     },
 
     componentWillUnmount: function() {

src/utils/DecryptFile.js

@@ -0,0 +1,42 @@
+/*
+Copyright 2016 OpenMarket Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+'use struct';
+
+// Pull in the encryption lib so that we can decrypt attachments.
+var encrypt = require("browser-encrypt-attachment");
+// Pull in a fetch polyfill so we can download encrypted attachments.
+require("isomorphic-fetch");
+// Grab the client so that we can turn mxc:// URLs into https:// URLS.
+var MatrixClientPeg = require('../MatrixClientPeg');
+
+
+export function decryptFile(file) {
+    var url = MatrixClientPeg.get().mxcUrlToHttp(file.url);
+    var self = this;
+    // Download the encrypted file as an array buffer.
+    return fetch(url).then(function (response) {
+        return response.arrayBuffer();
+    }).then(function (responseData) {
+        // Decrypt the array buffer using the information taken from
+        // the event content.
+        return encrypt.decryptAttachment(responseData, file);
+    }).then(function(dataArray) {
+        // Turn the array into a Blob and give it the correct MIME-type.
+        var blob = new Blob([dataArray], {type: file.mimetype});
+        return blob;
+    });
+}