Service workers

This is Chromium's implementation of service workers. See the Service Worker specification.

Directory structure

• content/browser/service_worker: Browser process code, including stored registration data, the inception of starting a service worker, and controlling navigations. The browser process has host objects of most live renderer entities that deal with service workers, and the bulk of work is performed by these host objects.
• content/renderer/service_worker: Renderer process code. This should move to third_party/blink per Onion Soup.
• content/common/service_worker: Common process code.
• third_party/blink/common/service_worker: Common process code. Contains the implementation of third_party/blink/public/common/service_worker.
• third_party/blink/public/common/service_worker: Header files for common process code that can be used by both inside Blink and outside Blink.
• third_party/blink/public/mojom/service_worker: Mojom files for common process code that can be used by both Blink and content.
• third_party/blink/public/platform/modules/service_worker: Blink Public API header files. This should be removed per Onion Soup.
• third_party/blink/public/web/modules/service_worker: More Blink Public API header files. This should be removed per Onion Soup.
• third_party/blink/renderer/modules/service_worker: Renderer process code in Blink. This is the closest code to the web-exposed Service Worker API.

UseCounter integration

Blink has a UseCounter mechanism intended to measure the percentage of page loads on the web that used a given feature. Service workers complicate this measurement because a feature use in a service worker potentially affects many page loads, including ones in the future.

Therefore, service workers integrate with the UseCounter mechanism as follows:

• If a feature use occurs before the service worker finished installing, it is recorded in storage along with the service worker. Any page thereafter that the service worker controls is counted as using the feature.
• If a feature use occurs after the service worker finished installing, all currently controlled pages are counted as using the feature.

For more details and rationale, see Design of UseCounter for workers and crbug 376039.

Code pointers include:

• (Browser -> Page) ServiceWorkerContainer.SetController and ServiceWorkerContainer.CountFeature in service_worker_container.mojom.
• (Service worker -> Browser) EmbeddedWorkerInstanceHost.CountFeature in embedded_worker.mojom.
• (Persistence) ServiceWorkerDatabase::RegistrationData::used_features in service_worker_database.h.

Other documentation

• Service Worker Security FAQ