|Status note||Product Management needs to flesh out the feature page so that development can be unblocked.|
|Product manager||Jennifer Arguello|
|Directly Responsible Individual||Jennifer Arguello|
|Lead engineer||Gregory Szorc|
|Security lead||Yvan Boily|
|Localization lead||Axel Hecht|
|QA lead||Tracy Walker|
|UX lead||Alex Faaborg|
|Product marketing lead||Jaclyn Fu|
|Additional members||Ibai Garcia (SUMO)|
Stage 1: Definition
1. Feature overview
Add-ons are synchronized between Sync clients. Sync will ensure that add-ons are installed, uninstalled, updated, and enabled as they are changed on each client.
2. Users & use cases
- Install propagation
- User installs an add-on on one browser. When a sync occurs, this add-on record is uploaded to the Sync server. When another browser in the Sync profile connects, the add-on is installed automatically.
- Uninstall propagation
- This is the same as install propagation except for uninstalls. An uninstall on one client will trigger an uninstall on another.
- User enabled state propagation
- User opens add-on manager and disables an add-on. Sync will propagate this change to other clients. Ditto for enabling. Sync should not propagate the enabled state if it is due to application compatibility (e.g. version upgrades causing incompatibilities). Only the user's explicit enabling and disabling of an add-on should be propagated.
- Update propagation
- User updates an add-on on one machine. Sync notices the update and schedules other clients to look for an update.
- Sync GUID added to XPI Provider
- Sync requires non-deterministic IDs to be affiliated with synchronized records. XPI add-ons currently don't have a suitable ID so once will need to be created.
- Non-impact on add-on manager metrics
- The presence of Sync should not skew the metrics in the add-on manager and addons.mozilla.org. Currently, some APIs on the AddonManager upload metrics.
Sync will not synchronize non-XPI add-ons such as plugins, lightweight themes, and search engines. Sync will also not synchronize add-ons installed outside of the currently running profile.
Stage 2: Design
5. Functional specification
The Addon Manager maintainers would like to see Sync support all add-on providers so as to not introduce 1st and 2nd class providers.
The solution to this problem will consist of the following:
- Optional properties on add-on objects that describe the add-on for purposes of use in Sync
- Functions on AddonManager that take above properties and perform actions
For add-on objects, providers wishing to opt in to Sync will expose the following read-only, optional properties:
- a string that describes data necessary to synchronize the add-on between clients. The format of the string is opaque to Sync code. From the perspective of add-on providers, it should be a JSON object with a *type* field that is used to route it to the proper provider.
- a GUID used to identify this add-on across Sync client instances. The GUID should be generated using Utils.makeGUID() from the Sync code. It is basically a Base64-encoded representation of 9 random bytes.
(These properties will need to be documented at https://developer.mozilla.org/en/Addons/Add-on_Manager/Addon)
The AddonManager will support the following APIs:
- getAddonBySyncGUID(syncGUID, callback)
- Obtain an add-on from its Sync GUID. Calls the supplied function when that add-on is retrieved. The callback receives null on unknown add-on or the add-on object (generated from the underlying provider) on success. This API technically isn't required, but it makes the Sync code smaller by pushing out logic and possibly caching.
- applyRecords(records, callbackObj)
- This applies an array of records that contain add-on metadata and makes the current state of the world agree with that data as much as possible.
The callbackObj is an object containing the following optional keys:
- onSuccess - Invoked when an individual record is processed successfully. Arguments are the record itself.
- onFailure - Invoked when an individual record could not be processed successfully. Arguments are the record itself.
- onFinished - Invoked when all records have finished processing.
Each record is an object containing the following keys:
- syncGUID (required) - The Sync GUID for this record
- syncData (optional) - The .syncData field from an add-on
- deleted (optional) - If evaluates to true, indicates that the record was deleted. Application of this record should involve trying to delete this add-on if present or no-op if not present.
The implementation of applyRecords() will resemble the following pseudocode:
foreach record in records: if record.deleted: found = this.getAddonBySyncGUID(record.syncGUID) if found: this.deleteAddon(found) # else nothing to do since record not found callbackObj.onSuccess(record) continue existing = this.getExistingAddonBySyncData(record.syncData) result = null if existing: # ensure the Sync GUIDs agree. incoming records always win fight if existing.syncGUID != record.syncGUID: existing.syncGUID = record.syncGUID # TODO this probably requires additional API formalization. Each # provider likely has its own semantics. But, common operations would # likely include updating common add-on fields (like source and install # URLs) and upgrading the add-on version. result = existing.updateFromSyncData(record.syncData) else: result = this.installAddonFromSyncData(syncGUID, syncData) result ? callbackObj.onSuccess(record) : callbackObj.onFailure(record) callbackObj.onFinished()
TODO: we should formalize how the Sync engine gets informed of whether a restart is required to finish the record application. Do we catch this in the tracker observers or install observers local to the sync method of the engine?
The add-ons Sync engine will discover the set of add-ons that can be synced via the following procedure:
- Query AddonManager.getAllAddons()
- Filter the returned list by items that have the *syncData* and *syncGUID* properties and are installed in the profile add-on scope (addon.scope == AddonManager.SCOPE_PROFILE)
- Open Issue: Should the AddonManager do this filtering? Should the add-on providers only expose syncData on add-ons installed in the proper location?
The engine will process incoming records by converting them to the API accepted by AddonManager.applyRecords() and will invoke that function with them. This is similar to how the history engine works.
The Sync add-on tracker will install add-on listeners in the AddonManager and will listen for the following events:
When these are observed, the tracker will:
- Verify the changed add-on is in the set of Sync-able add-ons (using same heuristics as add-on discovery documented above, if needed)
- Mark the GUID as changed
- This will result in a new record for that GUID being created automagically. The createRecord() procedure will in turn create the necessary record by querying AddonManager which will be queued for upload to the Sync server.
On start-up, the add-on engine will query AddonManager.getStartupChanges() for changes applied on application start-up. These are not observed by Sync because they occur before Sync is registered and running. Even if Sync does catch them in its tracker, it should be safe to mark records as changed. The only side-effect will be a slightly different modified time.
AddonManager.getStartupChanges() will be queried for the following change types:
TODO: Sync should catch all startup change types (the constants above) and react to them. We may need an API or some kind of verification/test to ensure newly-introduced startup changes/constants aren't missed by Sync. (This is all because getStartupChanges() requires a type as a parameter.)
There are some interesting implications for the design proposed above. AddonManager and providers - not Sync - would be responsible for the format of the records containing add-on metadata and this means the onus of ensuring forwards and backwards compatibility (since e.g. a version 9 client could receive a Sync record from a version 14 client and vice-versa) reside in the AddonManager and providers. This might be new territory for AddonManager and providers. Unfortunately, the alternative means lots of AddonManager-specific code in Sync (at best) or giving up provider agnostic add-on sync (at worst).
6. User experience design
Stage 3: Planning
7. Implementation plan
Quality Assurance review
Stage 4: Development
Stage 5: Release
10. Landing criteria
|Theme / Goal||Experience|
Team status notes
Discussion notes from 2011-08-16:
- add 'guid' column to 'addon' table in extensions.sqlite
- add GUID support to AddonsManager (have it automatically generated, 12 chars base64url)
- findings addons shouldn't count as daily update pings, or if they do, is it a problem?
- generate one record per app per addon, silently drop records from other apps and unknown addons (unknown to AMO)
- add option to locally disable enabled state sync (the "web developer case") in about:config