firefox/toolkit/components/glean/docs/dev/code_organization.md

FOG code organization

The diagram shows the different modules of Project FOG.

FOG control

This module is the glue between Firefox and Glean.

• The code lives in toolkit/components/glean/src.
• It is written in Rust.
• The crate is named fog_control.
• It is not published to crates.io.
• It is not consumed by other Rust crates inside mozilla-central.

This module is responsible for

• collecting and assembling the client information
• configuring the Glean SDK via the Rust Language Binding
• watching the Firefox Telemetry data upload preference (datareporting.healthreport.uploadEnabled)
• scheduling builtin pings
• controling ping upload workers
• passing IPC buffers

It calls into glean (the Glean SDK Rust Language Binding) to:

• configure and initialize Glean
• toggle upload_enabled
• get upload tasks

It calls into fog to:

• pass IPC buffers
• record to its own metrics

FOG API

This module provides the user-facing API for Glean inside mozilla-central.

• The code lives in toolkit/components/glean/api.
• It is written in Rust.
• The crate is named fog.
• It is not published to crates.io.
• It can be consumed by other Rust crates inside mozilla-central for their Glean usage.

This module is responsible for

• exposing a specific metric API in Rust
• wrapping metric implementations for handling IPC
• exposing FFI functionality to implement other language APIs on top. See also Adding a New Metric Type.

It calls into glean (the Glean SDK Rust Language Binding) for:

• metric types (including pings)