feat(image-stream): Make invalid images user errors (#1369)

This displays a user error if the reading the image causes an error,
instead of letting it fall through and get reported.
This is to avoid reporting errors that are not due to malfunction of the software,
but due to malformatted images.

Change-Type: minor
Changelog-Entry: Display nicer error dialog when reading an invalid image

lib/image-stream/handlers.js

@@ -27,6 +27,8 @@ const udif = Bluebird.promisifyAll(require('udif'));
 const archive = require('./archive');
 const zipArchiveHooks = require('./archive-hooks/zip');
 const fileExtensions = require('../shared/file-extensions');
+const path = require('path');
+const errors = require('../shared/errors');
 
 /**
  * @summary Image handlers
@@ -161,6 +163,16 @@ module.exports = {
         },
         transform: new PassThroughStream()
       };
+    }).catch((error) => {
+      if (/invalid footer/i.test(error.message)) {
+        throw errors.createUserError({
+          title: 'Invalid image',
+          description: `There was an error reading "${path.basename(file)}". `
+            + 'The image does not appear to be a valid Apple Disk Image (dmg), or may have the wrong filename extension.\n\n'
+            + `Error: ${error.description || error.message}`
+        });
+      }
+      throw error;
     });
   },
 

tests/image-stream/dmg.spec.js

@@ -105,4 +105,14 @@ describe('ImageStream: DMG', function() {
 
   });
 
+  context('invalid', function() {
+
+    describe('given an invalid dmg file', function() {
+      tester.expectError(
+        path.join(DATA_PATH, 'unrecognized', 'invalid.dmg'),
+        'Invalid image', 'Invalid footer');
+    });
+
+  });
+
 });

tests/image-stream/tester.js

@@ -43,11 +43,14 @@ const deleteIfExists = (file) => {
   });
 };
 
-exports.expectError = function(file, errorMessage) {
+exports.expectError = function(file, errorMessage, errorDetail) {
   it('should be rejected with an error', function() {
     return imageStream.getFromFilePath(file).catch((error) => {
       m.chai.expect(error).to.be.an.instanceof(Error);
       m.chai.expect(error.message).to.equal(errorMessage);
+      if (errorDetail) {
+        m.chai.expect(error.description).to.contain(errorDetail);
+      }
       m.chai.expect(error.description).to.be.a.string;
       m.chai.expect(error.description.length > 0).to.be.true;
     });