Switch websocket client to reactive Flux/Mono

[tcheeric]

Summary

• switch StandardWebSocketClient to return Flux instead of blocking
• update WebSocketClientHandler and NostrSpringWebSocketClient for reactive API
• adjust NostrIF and examples for new async behaviour
• add unit test for non-blocking StandardWebSocketClient
• update docs for reactive usage

Testing

• mvn -q verify (fails: Could not find a valid Docker environment for integration tests)

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https://chatgpt.com/codex/tasks/task_b_688be0122f6483318c314e7eeb8bf301

[Copilot]

Pull Request Overview

This PR modernizes the WebSocket client implementation by switching from blocking operations to reactive programming using Project Reactor's Flux/Mono. The change transforms synchronous message handling into asynchronous streams.

• Replaces blocking WebSocket client behavior with reactive Flux streams
• Updates all APIs to return Flux or Mono instead of List
• Adds block() calls throughout examples and tests to maintain compatibility

Reviewed Changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
StandardWebSocketClient.java	Core transformation from blocking to reactive using Sinks.Many for message emission
WebSocketClientIF.java	Interface updated to return Flux instead of List
NostrIF.java	Main API interface updated for reactive return types
EventNostr.java	Event handling converted to Mono with proper error handling
NostrApiExamples.java	All examples updated with block() calls to maintain synchronous behavior
Test files	Integration tests updated to use blockFirst() or collectList().block()
README.md	Documentation updated to reflect reactive API usage

Comments suppressed due to low confidence (1)

nostr-java-client/src/test/java/nostr/client/springwebsocket/StandardWebSocketClientTest.java:15

• The test uses reflection to bypass normal object construction, which doesn't test the actual initialization behavior. Consider adding a constructor or factory method for testing, or test the real initialization path.

    private static StandardWebSocketClient createClient() throws Exception {

[Copilot]

Using sun.misc.Unsafe is strongly discouraged as it's an internal API that may be removed in future Java versions. Consider using reflection with constructor.setAccessible(true) or dependency injection for testing instead.

Suggested change

	import sun.misc.Unsafe;
	class StandardWebSocketClientTest {
	private static StandardWebSocketClient createClient() throws Exception {
	Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
	theUnsafe.setAccessible(true);
	Unsafe unsafe = (Unsafe) theUnsafe.get(null);
	StandardWebSocketClient client = (StandardWebSocketClient) unsafe.allocateInstance(StandardWebSocketClient.class);
	class StandardWebSocketClientTest {
	private static StandardWebSocketClient createClient() throws Exception {
	var constructor = StandardWebSocketClient.class.getDeclaredConstructor();
	constructor.setAccessible(true);
	StandardWebSocketClient client = constructor.newInstance();

[Copilot]

Unsafe cast without type checking. The sign().send(relays) returns Mono but casting it as (Mono) could cause ClassCastException. Remove the cast since the return type is already correct.

Suggested change

	return (Mono<U>) sign().send(relays);
	return sign().send(relays);

[Copilot]

The method returns the same Flux instance for every call to send(), which means all callers will receive all messages from this sink, not just responses to their specific message. Consider creating a new Flux that only contains responses to this specific message.