feat: Add eth_subscribe and eth_unsubscribe support to IPC service

[MqllR]

Add eth_subscribe and eth_unsubscribe support to IPC service

Description

This PR adds subscription support (eth_subscribe and eth_unsubscribe) to the IPC service, enabling applications to subscribe to blockchain events over Unix domain sockets without requiring WebSocket connections.

Motivation

Currently, subscription methods are only available through the WebSocket service. Applications using IPC sockets cannot subscribe to events like new block headers, logs, pending transactions, or syncing status. This limitation forces applications to maintain both IPC and WebSocket connections when they prefer IPC for security and performance reasons.

Changes

Core Implementation

JsonRpcIpcService.java:

• Added optional SubscriptionManager parameter (backward compatible)
• Generate unique connection IDs for each IPC socket connection
• Register Vert.x event bus consumers to receive subscription notifications
• Convert JsonRpcRequest to WebSocketRpcRequest with connection ID for single requests
• Send subscription notifications back through the IPC socket
• Clean up subscriptions when socket closes
• Note: Batch requests intentionally don't support subscriptions (they remain stateless)

RunnerBuilder.java:

• Centralized subscription service registration for both WebSocket and IPC
• Add subscription methods (eth_subscribe, eth_unsubscribe) to IPC using WebSocketMethodsFactory
• Pass SubscriptionManager to IPC service when enabled
• Added null check for jsonRpcIpcConfiguration

Testing

JsonRpcIpcServiceTest.java:

• Added test for successful eth_subscribe requests
• Added test for successful eth_unsubscribe requests
• Added test verifying batch requests don't support subscriptions
• All existing tests continue to pass

Usage Example

# Subscribe to new block headers
echo '{"jsonrpc":"2.0","method":"eth_subscribe","params":["newHeads"],"id":1}' | nc -U /path/to/besu.ipc
# Response: {"jsonrpc":"2.0","id":1,"result":"0x1"}

# Notifications will be sent automatically:
# {"jsonrpc":"2.0","method":"eth_subscription","params":{"subscription":"0x1","result":{...}}}

# Unsubscribe
echo '{"jsonrpc":"2.0","method":"eth_unsubscribe","params":["0x1"],"id":2}' | nc -U /path/to/besu.ipc
# Response: {"jsonrpc":"2.0","id":2,"result":true}

Benefits

• ✅ Applications using IPC can subscribe to blockchain events
• ✅ Maintains consistency between IPC and WebSocket APIs
• ✅ No breaking changes to existing functionality
• ✅ Backward compatible (optional parameter)
• ✅ Reuses existing subscription infrastructure

Testing

• All unit tests pass
• Added comprehensive tests for IPC subscription functionality
• Verified backward compatibility with existing IPC tests

Related Issues

Closes #9503

[macfarla]

@MqllR Thanks for the PR - can you add a changelog entry please, think this is worth including in the release notes

[macfarla]

is this change necessary?

[MqllR]

Tried without, but it turns out that this is what:

• enables the 2 methods for the service https://github.com/hyperledger/besu/blob/main/ethereum/api/src/main/java/org/hyperledger/besu/ethereum/api/jsonrpc/websocket/methods/WebSocketMethodsFactory.java#L36
• bind the subscription manager with the methods.

So unless we want to manage it in another way, I'd answer yes, it's necessary !

[jflo]

tagging this as #techdebt for later investigation, you've found a code smell: reactive methods are bound to a transport type, which is excessive coupling.