feat(event streaming): implement push-only streaming channels and SSE

[onur-ozkan]

This implements streaming channels using mpsc(underlying part of SSE) and SSE for sending data to clients continiously. Currently, only NETWORK event is implemented, further events will be added after the collaboration with the GUI team.

Supported platforms: all other than WASM(Simply because we can't serve a server on browser. I have a solution idea to this, but it's too early to talk about).

Enabling Event Streaming:

1. To enable event streaming, add the event_stream_configuration property to the mm2 configuration. Use the following sample values:

{
	"gui": "core_readme",
	"netid": 7777,
	// ... other parts
	"event_stream_configuration": {
		"access_control_allow_origin": "*",
		"active_events": {
			"NETWORK": { "stream_interval_seconds": 0.5 }
		}
	}
}

2- Start mm2 and wait for the initialization log message similar to: mm2_net::network_event:54] INFO NETWORK event is activated with 0.5 seconds interval.

3- Open examples/sse/index.html in your browser; events should start appearing on the screen.

Client-Side Filtering:

By default, clients listen to all events activated on the mm2 side. If you're interested in specific events, you can filter incoming events (using the filter query string parameter) to reduce network overhead.

For instance, open examples/sse/index.html with a text editor and append ?filter=TEST,DEMO,BALANCES to the EventSource url. After that, you will no longer receive NETWORK events. (Note that currently we only stream NETWORK events on mm2 side. Filtering out the NETWORK event will result in no events being received.)

Helps to #1901

[onur-ozkan]

These notes are not related with this work. They don't seem right in general. Having TODOs will help us tracking them later.

[onur-ozkan]

☝️

[onur-ozkan]

☝️

[shamardy]

Great Work! First review iteration!

[shamardy]

Re-approve

[shamardy]

@KomodoPlatform/qa: Refer to this comment #1945 (comment) to see how you can test this new event streaming feature. The above comment is also a starting point for documenting this feature, if you wish to begin documentation at this early stage. If you have any questions, please direct them to @onur-ozkan

[smk762]

Open examples/sse/index.html

I assume this means http://127.0.0.1:7783/examples/sse/index.html?
Response is {"error":"EOF while parsing a value at line 1 column 0"}

and in mm2.log 22 07:03:25, mm2_main::mm2::rpc:286] ERROR RPC error response: EOF while parsing a value at line 1 column 0

[onur-ozkan]

I assume this means http://127.0.0.1:7783/examples/sse/index.html?

No, it's independent HTML page(for testing SSE connection), you just need to open it in browser. You can serve using any web server like using python SimpleHTTPServer(see https://github.com/KomodoPlatform/komodo-defi-framework/blob/push-only-streaming-channels/examples/sse/README.md#listening-event-stream-from-komodo-defi-framework)
), nodejs http-server, nginx. Or you can open it using the filesystem directly like:

[smk762]

Confirm that event steam appears in browser from examples/sse/index.html, and modifying index.html to add a filter works.

Is there a plan to allow the filter to be applied via browser url in future? E.g. examples/sse/index.html?filter=BALANCES instead of editing index.html

[onur-ozkan]

Confirm that event steam appears in browser from examples/sse/index.html, and modifying index.html to add a filter works.

Is there a plan to allow the filter to be applied via browser url in future? E.g. examples/sse/index.html?filter=BALANCES instead of editing index.html

GUI can already achieve that by using URL parameters(e.g., https://developer.mozilla.org/en-US/docs/Web/API/Window/location) in the SSE connection string. mm2 can't know what page it's being used for.

[kivqa]

Approved.
Event steam displayed for following places :
http://localhost:7783/event-stream
komodo-defi-framework/examples/sse/index.html
http://127.0.0.1:8000/

Filter works as expected: for ?filter=NETWORK events are displayed, for other values of filter event stream is empty.