Migrating from 0.10 to 0.11

Version 0.11 makes runtime failures easier to diagnose. Transport send and receive errors keep the backend's original error instead of a flattened String, and misconfiguration is reported as a typed InvalidConfig error instead of wearing an I/O costume. This guide covers these two error-surface changes; the release's other breaking changes are listed at the end.

Structured transport error causes

SignalFishError::TransportSend and SignalFishError::TransportReceive now carry a boxed original error (Box<dyn Error + Send + Sync>) as their #[source] cause instead of a String:

Diff

-Err(SignalFishError::TransportSend(message)) => {
+Err(SignalFishError::TransportSend(cause)) => {
     eprintln!("Transport send failed: {cause}");
 }

Log lines need no change: Display is byte-identical to 0.10 because the boxed cause's own message replaces the old flattened text. Simple bindings like the one above keep compiling.

What breaks is code that relied on the payload being a String — for example message.as_str(), storing it in a Vec<String>, or matching on string content. For programmatic handling, walk the cause chain with Error::source(). The built-in native WebSocket boxes the backend's own tungstenite::Error, whose chain reaches the underlying std::io::Error when there is one:

Rust

use std::error::Error as _;

match client.send_game_data(payload) {
    Ok(()) => {}
    Err(err) => {
        eprintln!("send failed: {err}");
        // New in 0.11: reach the root cause for programmatic handling.
        let mut source = err.source();
        while let Some(cause) = source {
            if let Some(io) = cause.downcast_ref::<std::io::Error>() {
                eprintln!("root cause: {} ({:?})", io, io.kind());
            }
            source = cause.source();
        }
    }
}

Custom transports box whatever error they produce — an io::Error, a typed backend error, or a plain string detail. Constructing from a string keeps working through .into():

Rust

Err(SignalFishError::TransportSend(
    "this text-only loopback does not accept binary frames".into(),
))

When a backend error's own Debug would embed application payload bytes, box its Display text instead so ambient logs stay redacted.

Typed configuration errors

The new exhaustive variant SignalFishError::InvalidConfig { field, problem } reports caller-supplied values rejected before any network I/O. Exhaustive SignalFishError matches must add the arm:

Rust

match error {
    SignalFishError::InvalidConfig { field, problem } => {
        // The value itself is unusable; retrying without correcting it
        // keeps failing.
        eprintln!("invalid configuration: {field}: {problem}");
    }
    // ... remaining arms unchanged
}

Each rejected value in this table returns InvalidConfig where 0.11 development builds surfaced Io (with ErrorKind::InvalidInput or ErrorKind::Other); the zero-limit options themselves are also new in this release. Code matching Io around connect-time validation should match InvalidConfig instead:

Rejected value	Where
Zero max_inbound_message_size	Native WebSocketTransport options
Zero max_inbound_queue_bytes	Emscripten EmscriptenWebSocketConnectOptions
URL that cannot be parsed into a WebSocket request	Native transport (checked before I/O) and Godot adapter (ERR_INVALID_PARAMETER)
URL containing interior NUL bytes	Emscripten transport
wss:// URL without the opt-in tls feature	Native transport

Failures determined by the engine or the network keep the Io classification: Godot's ERR_UNAVAILABLE/FAILED engine faults, malformed server handshake responses, and HTTP upgrade rejections. The split is deliberate — InvalidConfig means "the value is wrong on its face", while Io still means "something outside your configuration failed".

Other 0.11 breaking changes

The 0.11 window deliberately bundles further breaking changes that have their own migration notes:

• Custom transports must implement abort explicitly; see Migrating custom transports for 0.11.
• supports_mesh() semantics and the new exhaustive ClientSnapshot fields; see the 0.11 capability-versus-active-plan migration.
• The remaining API additions — pre-authentication refusals, token-binding connect options, generation-bound driver signaling, and the new error variants behind exhaustive matches — are enumerated under CHANGELOG.md's [0.11.0] Breaking bullets and in the errors guide variant table.