feat(cmd-api-server): add Socket.IO as transport #297

[petermetz]

Dependencies

Depends on #896
Depends on #899
Depends on #902
Depends on #903

Commit to review

Author: Peter Somogyvari peter.somogyvari@accenture.com
Author Date: 2021-05-03 09:20:49 -0700
Committer: Peter Somogyvari peter.somogyvari@accenture.com
Committer Date: 2021-05-03 09:39:40 -0700

feat(cmd-api-server): add Socket.IO as transport #297

Primary changes:

1. The API server now has a SocketIO server running on the same port
   as the HTTP REST API.

2. The API server now has an ApiServerApiClient class which is an
   extension of the DefaultApi class that we generate from the OpenAPI
   specifications. The reason why this extension was necessary (something
   that we try to avoid like the plague normally) is because OpenAPI is
   strictly for defining HTTP/REST based APIs and not async/streaming
   ones such as WebSocket/SocketIO based ones and therefore the OpenAPI
   generator does not support these types of transports at all meaning
   that we have to manually write the client code for async endpoints
   which is why the class extension here is not something that we can
   get around.

3. The idea is that all async endpoints would declare their event
   names as constants in the OpenAPI specification so as to make it
   easier at least to some degree to implement solutions on top even
   if we cannot support async endpoints with the OpenAPI code
   generator to the same extend we do for HTTP RESTful endpoints.
   The five default events are Subscribe, Next, Unsubscribe, Error and
   Complete. These are defined in order to match what the client can
   do on the RxJS Observable object returned by the API client object's
   method that invokes the async endpoints.
   The difference between Unsubscribe and complete is subtle, but it definitely
   exists. The unsubscribe event is used by the client to tell the backend
   that it no longer requires updates, regardless of the streaming of data
   having been completed or not.
   The complete event on the other hand is for the backend to signal that
   the streaming of data is in fact completed. The complete event is only
   applicable for endpoints that do have an ending which is not the case
   for some endpoints that are usually time-series related and therefore
   a lot of times just stream endlessly until stopped.

Secondary change(s):

1. Added an async endpoint powered by the just now added SocketIO
   integration that streams the health check response every one second
   which is mainly added to that we can test the functionality but at
   could also be used for monitoring purposes by someone who'd rather
   implement something from scratch than use Prometheus for example.

To-do:

1. Socket provider singleton on client side for connection multiplexing

Fixes #297

Signed-off-by: Peter Somogyvari peter.somogyvari@accenture.com

[github-actions]

🎉 Great news! Looks like all the dependencies have been resolved:

• build: webpack ts-loader transpileOnly set to true #896
• feat: expose besu test ledger web socket API port #899
• feat(core-api): add SocketIoConnectionPathV1 constant to OpenAPI specs #902
• refactor(core-api): register web service method to accept socket io srv #903

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