Sourcegraph extension architecture

The Sourcegraph extension API allows extension of Sourcegraph functionality through specific extension points. The Sourcegraph extension architecture refers to the system which allows Sourcegraph client applications, such as the web application or browser extension, to communicate with Sourcegraph extensions.

Glossary

Term	Definition
Client application	Platform (e.g. web application)
Platform context	Platform-specific data and methods
Extension host	Worker thread in which extensions run
Extensions controller	Object which handles all communication between the client application and extensions
Extension	JavaScript file that imports "sourcegraph" and exports an activate function

Extension host bootstrapping

The following diagram depicts the process by which the extension host is initialized. You can click on a function signature to view its definition on Sourcegraph.

Note that the extension host execution context varies depending on the client application:

Client application	Extension host execution context
Sourcegraph web application	Web Worker
Browser extensions	A Web Worker spawned in the browser extension's background page for each content script instance. Messages are forwarded from the content script to its corresponding worker.
Native Integration	Web Worker spawned in an <iframe/>. Messages are forwarded from the content script to the worker.

Inter-process communication

The client application runs on the main thread, while the extension host runs in a Web Worker, in a seperate global execution context. Under the hood, the client application and extension host communicate through messages, but the we rely on comlink, a proxy-based RPC library, in order to manage complexity and simplify implementation of new functionality.