websockets client / wrapper

[jakemcdermott]

This is for adding a basic ws module to the client:

• global subscriptions / global states
• view-specific / per-job subscriptions

[jakemcdermott]

some notes:

when we launch a job in AWX, the following things happen sequentially:

1. client makes an http request to /api/v2/item/n/launch
2. api responds with a job id
3. client uses job id to subscribe to a channel with the shared socket service, which delivers the job-specific ws events over that channel.

Ideally we want to eliminate the possibility for race conditions and missed job events between steps 2 and 3.

[jakemcdermott]

more notes:

• The implementation should be framework-agnostic and testable in isolation. For example, it should be straightforward to write a functional test or debugging script that imports this module by itself to test important behavior (connect / disconnect, subscribing, unsubscribing, etc.) with a real or mocked backend.

• The api design encourages clients to be idempotent with subscription state, which is favorable for a variety of reasons. We should:

  • keep the client-side representation of the subscription state as close to the API version as possible, ideally identical. In current AWX, we maintain a separate data structure and convert it to the one the API expects whenever subscriptions are changed. This is fragile and difficult to debug.

  • expose asynchronous parts of the connect, disconnect, and (re)subscribe cycle as promises or something chainable. For example, someone developing a new page or feature should, if necessary, be able to ensure that a newly requested subscription state is ready before something else happens.

[jakemcdermott]

Potentially useful for any presentational components that are driven by job statuses (status icons, etc.): https://reactjs.org/docs/hooks-custom.html

[wenottingham]

tangentially: #1611

[wenottingham]

Also tangentially: as part of this we should revisit moving to a daphne/channels version from this century

[jakemcdermott]

Mike and I are breaking this work up into smaller issues:

#5883
#5885
#5886