make compatible with flutter web

[TimWhiting]

What kind of change does this PR introduce?

This change introduces an indirection in creating the default websocket to allow for web compatibility

What is the current behavior?

Web doesn't work unless you create a realtime client directly with the HtmlWebSocketChannel. Web support is missing on pub.dev in both supabase and realtime_client
Example error:
Socket error: Unsupported operation: Platform._version

What is the new behavior?

No new behavior except for the web

Additional context

• Dart has conditional imports to separate implementations of web / non-web behavior
  https://dart.dev/guides/libraries/create-library-packages#conditionally-importing-and-exporting-library-files

[TimWhiting]

Probably should test this with a real app before making the claim of web compatibility, but I'm just getting started with supabase and don't have an app to test it on yet. I've made a similar change in another library using websocket_channel so I'm fairly confident it will work though.

Edit:
Just tested it on a basic app using the sample Countries database. Seems to work better than before. (I'm getting feedback from the RealtimeClient.onMessage callback). However, I'm not getting anything from a SupabaseQueryBuilder.on method, but that is the same behavior on MacOS and web.

[phamhieu]

Hi @TimWhiting I pushed a fix related to channel subscription. Can you merge with the main branch and test again.

Thanks for the websocket update 👍

[TimWhiting]

@phamhieu
Merged with main branch.

[TimWhiting]

Also tested it. Thanks for the new realtime example code in the supabase package. I noticed however that the olds field in the SupabaseRealtimePayload always has null for all columns in the table except the id on a DELETE. Is that expected?

[phamhieu]

I noticed however that the olds field in the SupabaseRealtimePayload always has null for all columns in the table except the id on a DELETE. Is that expected?

yes, that's right. Only record ID is available for a delete event.

[phamhieu]

The code looks good to me 👍

I will merge this PR after you fix the conflicts. Thank you.

[TimWhiting]

@phamhieu
Fixed the conflict