git-repo/docs/smart-sync.md

repo Smart Syncing

Repo normally fetches & syncs manifests from the same URL specified during repo init, and that often fetches the latest revisions of all projects in the manifest. This flow works well for tracking and developing with the latest code, but often it's desirable to sync to other points. For example, to get a local build matching a specific release or build to reproduce bugs reported by other people.

Repo's sync subcommand has support for fetching manifests from a server over an XML-RPC connection. The local configuration and network API are defined by repo, but individual projects have to host their own server for the client to communicate with.

This process is called "smart syncing" -- instead of blindly fetching the latest revision of all projects and getting an unknown state to develop against, the client passes a request to the server and is given a matching manifest that typically specifies specific commits for every project to fetch a known source state.

[TOC]

Manifest Configuration

The manifest specifies the server to communicate with via the the <manifest-server> element element. This is how the client knows what service to talk to.

  <manifest-server url="https://example.com/your/manifest/server/url" />

If the URL starts with persistent-, then the git-remote-persistent-https helper is used to communicate with the server.

Credentials

Credentials may be specified directly in typical username:password URI syntax in the <manifest-server> element directly in the manifest.

If they are not specified, repo sync has --manifest-server-username=USERNAME and --manifest-server-password=PASSWORD options.

If those are not used, then repo will look up the host in your ~/.netrc database.

When making the connection, cookies matching the host are automatically loaded from the cookiejar specified in Git's http.cookiefile setting.

Manifest Server

Unfortunately, there are no public reference implementations. Google has an internal one for Android, but it is written using Google's internal systems, so wouldn't be that helpful as a reference.

That said, the XML-RPC API is pretty simple, so any standard XML-RPC server example would do. Google's internal server uses Python's xmlrpc.server.SimpleXMLRPCDispatcher.

Network API

The manifest server should implement the following RPC methods.

GetApprovedManifest

GetApprovedManifest(branch: str, target: Optional[str]) -> str

The meaning of branch and target is not strictly defined. The server may interpret them however it wants. The recommended interpretation is that the branch matches the manifest branch, and target is an identifier for your project that matches something users would build.

See the client section below for how repo typically generates these values.

The server will return a manifest or an error. If it's an error, repo will show the output directly to the user to provide a limited feedback channel.

If the user's request is ambiguous and could match multiple manifests, the server has to decide whether to pick one automatically (and silently such that the user won't know there were multiple matches), or return an error and force the user to be more specific.

GetManifest

GetManifest(tag: str) -> str

The meaning of tag is not strictly defined. Projects are encouraged to use a system where the tag matches a unique source state.

See the client section below for how repo typically generates these values.

The server will return a manifest or an error. If it's an error, repo will show the output directly to the user to provide a limited feedback channel.

If the user's request is ambiguous and could match multiple manifests, the server has to decide whether to pick one automatically (and silently such that the user won't know there were multiple matches), or return an error and force the user to be more specific.

Client Options

Once repo has successfully downloaded the manifest from the server, it saves a copy into .repo/manifests/smart_sync_override.xml so users can examine it. The next time repo sync is run, this file is automatically replaced or removed based on the current set of options.

--smart-sync

Repo will call GetApprovedManifest(branch[, target]).

The branch is determined by the current manifest branch as specified by --manifest-branch=BRANCH when running repo init.

The target is defined by environment variables in the order below. If none of them match, then target is omitted. These variables were decided as they match the settings Android build environments automatically setup.

1. ${SYNC_TARGET}: If defined, the value is used directly.
2. ${TARGET_PRODUCT}-${TARGET_RELEASE}-${TARGET_BUILD_VARIANT}: If these variables are all defined, then they are merged with - and used.
3. ${TARGET_PRODUCT}-${TARGET_BUILD_VARIANT}: If these variables are all defined, then they are merged with - and used.

--smart-tag=TAG

Repo will call GetManifest(TAG).