WebSocket subscription updates silently dropped when frame fails to deserialize

[hwildwood]

Summary

In starknet-rust-tokio-tungstenite, inbound subscription notifications that fail to deserialize into StreamUpdateOrResponse are silently discarded.

This is a serious DX issue: subscription.recv() never yields, never errors, and no log is emitted, so callers see a healthy WebSocket that appears to hang indefinitely.

Repro context

• Crate rev: 7caedfe
• Server: pathfinder, JSON-RPC 0.8.x
• Call: stream.subscribe_new_heads(ConfirmedBlockId::Latest)
• Handshake succeeds and subscribe ack is received
• Server sends starknet_subscriptionNewHeads notifications
• Client reads frames from the socket, but subscription.recv() never yields

Root cause

In [stream/read.rs](https://github.com/software-mansion/starknet-rust/blob/7caedfe/starknet-rust-tokio-tungstenite/src/stream/read.rs), handle_message returns HandleMessageResult::MalformedMessage when this fails:

serde_json::from_str::<StreamUpdateOrResponse>(text)

The run loop then drops it silently:

HandleMessageResult::Success | HandleMessageResult::MalformedMessage => {}

In our case this was caused by a spec mismatch from hitting the wrong RPC endpoint, but the silent drop made it very difficult to diagnose.

Suggested fix

At minimum, log the deserialization error and a truncated copy of the raw frame:

log::warn!("malformed websocket message: {err}; raw={truncated_text}");

Optionally, propagate this through Subscription::recv() as a non-fatal warning/error so callers can decide whether to reconnect.

This would make client/server spec drift visible instead of presenting as an indefinite hang.

[revastas]

Summary

In starknet-rust-tokio-tungstenite, inbound subscription notifications that fail to deserialize into StreamUpdateOrResponse are silently discarded.

This is a serious DX issue: subscription.recv() never yields, never errors, and no log is emitted, so callers see a healthy WebSocket that appears to hang indefinitely.

Repro context

• Crate rev: 7caedfe
• Server: pathfinder, JSON-RPC 0.8.x
• Call: stream.subscribe_new_heads(ConfirmedBlockId::Latest)
• Handshake succeeds and subscribe ack is received
• Server sends starknet_subscriptionNewHeads notifications
• Client reads frames from the socket, but subscription.recv() never yields

Root cause

In [stream/read.rs](https://github.com/software-mansion/starknet-rust/blob/7caedfe/starknet-rust-tokio-tungstenite/src/stream/read.rs), handle_message returns HandleMessageResult::MalformedMessage when this fails:

serde_json::from_str::(text)
The run loop then drops it silently:

HandleMessageResult::Success | HandleMessageResult::MalformedMessage => {}
In our case this was caused by a spec mismatch from hitting the wrong RPC endpoint, but the silent drop made it very difficult to diagnose.

Suggested fix

At minimum, log the deserialization error and a truncated copy of the raw frame:

log::warn!("malformed websocket message: {err}; raw={truncated_text}");
Optionally, propagate this through Subscription::recv() as a non-fatal warning/error so callers can decide whether to reconnect.

This would make client/server spec drift visible instead of presenting as an indefinite hang.