Chrome Installer for Mac -- the repository!

This Mac app installs Chrome on the machine it‘s run on. It’s meant to be the Mac app the user first downloads when they click ‘Download Chrome’ on a Mac machine. After the user runs the app, Chrome would launch directly after installation completes successfully.

The 10,000 Foot View

The installer breaks down its task into the following steps:

1. OmahaCommunication: Ask Omaha for a URL of the most recent compatible copy of the Google Chrome disk image in Google's servers.
2. Downloader: Download the disk image, via URL from OmahaCommunication.
3. Unpacker: Mount the disk image and extract the Chrome app bundle.
4. AuthorizedInstall: With privilege escalation if able, move the Chrome app into the Applications folder, set permissions, and hand ownership of the Chrome app to root.
5. Launch Chrome & close.

Each of the above modules are designed to carry one action before returning via delegate method. All of these main steps occur on a primary working thread (non-UI), with the exception of AuthorizedInstall, which makes use of an authorized-if-able subprocess. If the user does not provide permission to escalate privileges, AuthorizedInstall still does its job, but opts for the User's Applications folder instead of the system Applications folder.

The OmahaXML* classes and SystemInfo class are simply classes to help OmahaCommunication do its work.

The app's UI is made of a single window that has a determinate progress bar during download, which turns into an indeterminate one during installation. The options to set Chrome as a default browser and opt in for user metrics are made available to the user before they launch Chrome. Once Chrome is ready to launch, a Launch button will now be pressable -- this button will trigger Chrome to open and the installer app to close its remaining window. In the background, the app will take care of any tear-down tasks before exiting naturally.

We initialize the AuthorizedInstall class early in the life of the installer so the user can immediately choose to authorize the installer for root installation. The script consumes the authorization token (which expires in five minutes by default) immediately, then waits until the installer has progressed to step 4 (above).

The Class Breakdown

The Future

Here lies a list of hopes and dreams:

• Implement resumable downloads.
• Add in adequate testing using a local test server.
• Include basic error recovery attempts -- say, if during a download a URL does not provide a valid disk image, the installer can try re-downloading the disk image from another URL.
• Manage potential conflicts, in the case that Google Chrome already exists in the Applications folder when the installer is run.
• Trash the installer application after it has completed running.

Diagram Appendix

Task Flow

 Exposed Errors                Main Logic

                 +--------------------------------------+
                 |                                      |
                 |  Request authentication from users   |
                 |                                      |
                 +------------------+-------------------+
                                    |
                 +------------------v-------------------+
                 |                                      |
        +--------+ Ask Omaha for appropriate Chrome app |
        v        |                                      |
                 +------------------+-------------------+
 Network Error                      |
                 +------------------v-------------------+
        ^        |                                      |
        +--------+    Parse the response from Omaha     |
                 |                                      |
                 +------------------+-------------------+
                                    |
                 +------------------v-------------------+
                 |                                      |
Download Error <-+    Download the Chrome disk image    |
                 |                                      |
                 +------------------+-------------------+
                                    |
                 +------------------v-------------------+
                 |                                      |
        +--------+         Mount the disk image         |
        v        |                                      |
                 +------------------+-------------------+
 Install Error                      |
                 +------------------v-------------------+
        ^        |                                      |
        +--------+    Install & Configure Chrome app    |
                 |                                      |
                 +------------------+-------------------+
                                    |
                 +------------------v-------------------+
                 |                                      |
                 |          Unmount disk image          +-> If unmount fails, system
                 |                                      |   restart can resolve this.
                 +------------------+-------------------+
                                    |
                 +------------------v-------------------+
                 |                                      |
  Launch Error <-+            Launch Chrome             |
                 |                                      |
                 +--------------------------------------+

Class Heirarchy

                                 Users

                                ^     +
                                |     |
                                |     |
+-------------------------------+-----v--------------------------------+
|                                                                      |
|                       InstallerWindowController                      |
|                                                                      |
+-------+------^------------+---^--------+----^---------+---------^----+
        |      |            |   |        |    |         |         |
        |      |            |   |        |    |         |         |
        |      |            |   |        |    |         |         |
+-------v------+------------v---+--------v----+---------v---------+----+
|                                                                      |
|                              AppDelegate                             |
|                                                                      |
+-------+------^------------+---^--------+----^---------+---------^----+
        |      |            |   |        |    |         |         |
        |      |            |   |        |    |         |         |
        |      |            |   |        |    |         |         |
+-------v------+-----+ +----v---+---+ +--v----+--+ +----v---------+----+
|                    | |            | |          | |                   |
| OmahaCommunication | | Downloader | | Unpacker | | AuthorizedInstall |
|                    | |            | |          | |                   |
+-------^------^-----+ +------------+ +----------+ +---------^---------+
        |      |                                             |
        |      +------------+                                |
        |                   |                                |
+-------+---------+ +-------+--------+              +--------+--------+
|                 | |                |              |                 |
| OmahaXMLRequest | | OmahaXMLParser |              | copy_to_disk.sh |
|                 | |                |              |                 |
+-------^---------+ +----------------+              +-----------------+
        |
        |
        |
  +-----+------+
  |            |
  | SystemInfo |
  |            |
  +------------+