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diff --git a/toolkit/mozapps/extensions/docs/SystemAddons.rst b/toolkit/mozapps/extensions/docs/SystemAddons.rst new file mode 100644 index 0000000000..a8524a44b6 --- /dev/null +++ b/toolkit/mozapps/extensions/docs/SystemAddons.rst @@ -0,0 +1,275 @@ +System Add-ons Overview +======================= + +System add-ons are a method for shipping extensions to Firefox that: + +* are hidden from the about:addons UI +* cannot be user disabled +* can be updated restartlessly based on criteria Mozilla sets + +Generally these are considered to be built-in features to Firefox, and the +fact that they are extensions and can be updated restartlessly are implementation +details as far as users are concerned. + +If you'd like to ship an add-on with Firefox or as an update (either to an existing +feature or as a "hotfix" to patch critical problems in the wild) please contact the +GoFaster team: https://mail.mozilla.org/listinfo/gofaster + +The add-ons themselves are either legacy Firefox add-ons or WebExtensions. +They must be: + +* restartless +* multi-process compatible + +Other than these restrictions there is nothing special or different about +the extensions themselves. + +It is possible to override an installed system add-on by installing a different add-on +with the same ID into a higher priority location. + +Available locations, starting from the highest priority include: + +1) temporary install (about:debugging) +2) normal user install into profile (about:addons or AMO/TestPilot/etc.) +3) system add-on updates +4) built-in system add-ons + +This makes it possible for a developer or user to override a system add-on +by installing an add-on with the same ID from AMO or TestPilot or as a temporary +add-on. + +Default, built-in system add-ons +-------------------------------- + +The set of **default** system add-ons are checked into `mozilla-central` under +`./browser/extensions`. These get placed into the `features` directory of the +application directory at build time. + +System add-on updates +--------------------- + +System add-on **updates** are served via Mozilla's Automatic Update Service +(AUS, aka `Balrog`_). These are installed into the users profile under the `features` +directory. + +Updates must be specifically signed by Mozilla - the signature that addons.mozilla.org +uses will not work for system add-ons. + +As noted above, these updates may override a built-in system add-on, or they may +be a new install. Updates are always served as a set - if any add-on in the set +fails to install or upgrade, then the whole set fails. This is to leave Firefox +in a consistent state. + +System add-on updates are removed when the Firefox application version changes, +to avoid compatibility problems - for instance a user downgrading to an earlier +version of Firefox than the update supports will end up with a disabled update +rather than falling back to the built-in version. + +Firefox System Add-on Update Protocol +===================================== +This section describes the protocol that Firefox uses when retrieving updates +from AUS, and the expected behavior of Firefox based on the updater service's response. + +.. _Balrog: https://wiki.mozilla.org/Balrog + +Update Request +-------------- +To determine what updates to install, Firefox makes an HTTP **GET** request to +AUS once a day via a URL of the form:: + + https://aus5.mozilla.org/update/3/SystemAddons/%VERSION%/%BUILD_ID%/%BUILD_TARGET%/%LOCALE%/%CHANNEL%/%OS_VERSION%/%DISTRIBUTION%/%DISTRIBUTION_VERSION%/update.xml + +The path segments surrounded by ``%`` symbols are variable fields that Firefox +fills in with information about itself and the environment it's running in: + +``VERSION`` + Firefox version number +``BUILD_ID`` + Build ID +``BUILD_TARGET`` + Build target +``LOCALE`` + Build locale +``CHANNEL`` + Update channel +``OS_VERSION`` + OS Version +``DISTRIBUTION`` + Firefox Distribution +``DISTRIBUTION_VERSION`` + Firefox Distribution version + +Update Response +--------------- +AUS should respond with an XML document that looks something like this: + +.. code-block:: xml + + <?xml version="1.0"?> + <updates> + <addons> + <addon id="flyweb@mozilla.org" URL="https://ftp.mozilla.org/pub/system-addons/flyweb/flyweb@mozilla.org-1.0.xpi" hashFunction="sha512" hashValue="abcdef123" size="1234" version="1.0"/> + <addon id="pocket@mozilla.org" URL="https://ftp.mozilla.org/pub/system-addons/pocket/pocket@mozilla.org-1.0.xpi" hashFunction="sha512" hashValue="abcdef123" size="1234" version="1.0"/> + </addons> + </updates> + +* The root element is ``<updates>``, used for all updater responses. +* The only child of ``<updates>`` is ``<addons>``, which represents a list of + system add-ons to update. +* Within ``<addons>`` are several ``<addon>`` tags, each one corresponding to a + system add-on to update. + +``<addon>`` tags **must** have the following attributes: + +``id`` + The extension ID +``URL`` + URL to a signed XPI of the specified add-on version to download +``hashFunction`` + Identifier of the hash function used to generate the hashValue attribute. +``hashValue`` + Hash of the XPI file linked from the URL attribute, calculated using the function specified in the hashValue attribute. +``size`` + Size (in bytes) of the XPI file linked from the URL attribute. +``version`` + Version number of the add-on + +Update Behavior +--------------- +After receiving the update response, Firefox modifies the **update** add-ons +according to the following algorithm: + +1. If the ``<addons>`` tag is empty (``<addons></addons>``) in the response, + **remove all system add-on updates**. +2. If no add-ons were specified in the response (i.e. the ``<addons>`` tag + is not present), do nothing and finish. +3. If the **update** add-on set is equal to the set of add-ons specified in the + update response, do nothing and finish. +4. If the set of **default** add-ons is equal to the set of add-ons specified in + the update response, remove all the **update** add-ons and finish. +5. Download each add-on specified in the update response and store them in the + "downloaded add-on set". A failed download **must** abort the entire system + add-on update. +6. Validate the downloaded add-ons. The following **must** be true for all + downloaded add-ons, or the update process is aborted: + + a. The ID and version of the downloaded add-on must match the specified ID or + version in the update response. + b. The hash provided in the update response must match the downloaded add-on + file. + c. The downloaded add-on file size must match the size given in the update + response. + d. The add-on must be compatible with Firefox (i.e. it must not be for a + different application, such as Thunderbird). + e. The add-on must be packed (i.e. be an XPI file). + f. The add-on must be restartless. + g. The add-on must be signed by the system add-on root certificate. + +6. Once all downloaded add-ons are validated, install them into the profile + directory as part of the **update** set. + +Notes on the update process: + +* Add-ons are considered "equal" if they have the same ID and version number. + +Examples +-------- +The follow section describes common situations that we have or expect to run +into and how the protocol described above handles them. + +For simplicity, unless otherwise specified, all examples assume that there are +two system add-ons in existence: **FlyWeb** and **Pocket**. + +Basic +~~~~~ +A user has Firefox 45, which shipped with FlyWeb 1.0 and Pocket 1.0. We want to +update users to FlyWeb 2.0. AUS sends out the following update response: + +.. code-block:: xml + + <updates> + <addons> + <addon id="flyweb@mozilla.org" URL="https://ftp.mozilla.org/pub/system-addons/flyweb/flyweb@mozilla.org-2.0.xpi" hashFunction="sha512" hashValue="abcdef123" size="1234" version="2.0"/> + <addon id="pocket@mozilla.org" URL="https://ftp.mozilla.org/pub/system-addons/pocket/pocket@mozilla.org-1.0.xpi" hashFunction="sha512" hashValue="abcdef123" size="1234" version="1.0"/> + </addons> + </updates> + +Firefox will download FlyWeb 2.0 and Pocket 1.0 and store them in the profile directory. + +Missing Add-on +~~~~~~~~~~~~~~ +A user has Firefox 45, which shipped with FlyWeb 1.0 and Pocket 1.0. We want to +update users to FlyWeb 2.0, but accidentally forget to specify Pocket in the +update response. AUS sends out the following: + +.. code-block:: xml + + <updates> + <addons> + <addon id="flyweb@mozilla.org" URL="https://ftp.mozilla.org/pub/system-addons/flyweb/flyweb@mozilla.org-2.0.xpi" hashFunction="sha512" hashValue="abcdef123" size="1234" version="2.0"/> + </addons> + </updates> + +Firefox will download FlyWeb 2.0 and store it in the profile directory. Pocket +1.0 from the **default** location will be used. + +Remove all system add-on updates +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +A response from AUS with an empty add-on set will *remove all system add-on +updates*: + +.. code-block:: xml + + <updates> + <addons></addons> + </updates> + +Rollout +~~~~~~~ +A user has Firefox 45, which shipped with FlyWeb 1.0 and Pocket 1.0. We want to +rollout FlyWeb 2.0 at a 10% sample rate. 10% of the time, AUS sends out: + +.. code-block:: xml + + <updates> + <addons> + <addon id="flyweb@mozilla.org" URL="https://ftp.mozilla.org/pub/system-addons/flyweb/flyweb@mozilla.org-2.0.xpi" hashFunction="sha512" hashValue="abcdef123" size="1234" version="2.0"/> + <addon id="pocket@mozilla.org" URL="https://ftp.mozilla.org/pub/system-addons/pocket/pocket@mozilla.org-1.0.xpi" hashFunction="sha512" hashValue="abcdef123" size="1234" version="1.0"/> + </addons> + </updates> + +With this response, Firefox will download Pocket 1.0 and FlyWeb 2.0 and install +them into the profile directory. + +The other 90% of the time, AUS sends out an empty response: + +.. code-block:: xml + + <updates></updates> + +With the empty response, Firefox will not make any changes. This means users who +haven’t seen the 10% update response will stay on FlyWeb 1.0, and users who have +seen it will stay on FlyWeb 2.0. + +Once we’re happy with the rollout and want to switch to 100%, AUS will send the +10% update response to 100% of users, upgrading everyone to FlyWeb 2.0. + +Rollback +~~~~~~~~ +This example continues from the “Rollout” example. If, during the 10% rollout, +we find a major issue with FlyWeb 2.0, we want to roll all users back to FlyWeb 1.0. +AUS sends out the following: + +.. code-block:: xml + + <updates> + <addons> + <addon id="flyweb@mozilla.org" URL="https://ftp.mozilla.org/pub/system-addons/flyweb/flyweb@mozilla.org-1.0.xpi" hashFunction="sha512" hashValue="abcdef123" size="1234" version="1.0"/> + <addon id="pocket@mozilla.org" URL="https://ftp.mozilla.org/pub/system-addons/pocket/pocket@mozilla.org-1.0.xpi" hashFunction="sha512" hashValue="abcdef123" size="1234" version="1.0"/> + </addons> + </updates> + +For users who have updated, Firefox will download FlyWeb 1.0 and Pocket 1.0 and +install them into the profile directory. For users that haven’t yet updated, +Firefox will see that the **default** add-on set matches the set in the update +ping and clear the **update** add-on set. |