Offline builds of Android applications that use Glean

The Glean Kotlin SDK has basic support for building Android applications that use Glean in offline mode.

The Glean Kotlin SDK uses a Python script, glean_parser to generate code for metrics from the metrics.yaml and pings.yaml files when Glean-using applications are built. When online, the pieces necessary to run this script are installed automatically.

For offline builds, the Python environment, and packages of glean_parser and its dependencies must be provided prior to building the Glean-using application.

To build a Glean-using application in offline mode, you can either:

Provide an externally-managed virtualenv

Set ext.gleanPythonEnvDir to your existing virtualenv before applying the plugin, see gleanPythonEnvDir.

Provide a Python interpreter and the required wheels

In this mode Glean will setup its own virtualenv in $gradleUserHomeDir/glean, controlled by the GLEAN_PYTHON and GLEAN_PYTHON_WHEELS_DIR environment variables.

  • Install Python 3.8 or later and ensure it's on the PATH.

    • On Linux, installing Python from your Linux distribution's package manager is usually sufficient.

    • On macOS, installing Python from homebrew is known to work, but other package managers may also work.

    • On Windows, we recommend installing one of the official Python installers from python.org.

  • Determine the version of glean_parser required.

    • It can be really difficult to manually determine the version of glean_parser that is required for a given application, since it needs to be tracked through android-components, to glean-core and finally to glean_parser. The required version of glean_parser can be determined by running the following at the top-level of the Glean-using application:

      $ ./gradlew | grep "Requires glean_parser"
Requires glean_parser==1.28.1

  • Download packages for glean_parser and its dependencies:

    • In the root directory of the Glean-using project, create a directory called glean-wheels and cd into it.

    • Download packages for glean_parser and its dependencies, replacing X.Y.Z with the correct version of glean_parser:

      $ python3 -m pip download glean_parser==X.Y.Z

  • Build the Glean-using project using ./gradlew, but passing in the --offline flag.

There are a couple of environment variables that control offline building:

  • To override the location of the Python interpreter to use, set the GLEAN_PYTHON environment variable. If unset, the first Python interpreter on the PATH will be used.

  • To override the location of the downloaded Python wheels, set the GLEAN_PYTHON_WHEELS_DIR environment variable. If unset ${projectDir}/glean-wheels will be used.