WebTransport stats support

[jesup]

No description provided.

[Copilot]

Pull request overview

This PR adds richer transport-level byte/RTT/congestion statistics to neqo-transport and introduces WebTransport session-level statistics plumbing + APIs in neqo-http3, along with new tests to exercise the new fields.

Changes:

• Extend neqo-transport::Stats with byte counters (bytes_tx/rx/lost/acked) and additional path metrics (min_rtt, cwnd, bytes_in_flight), and populate these from connection/recovery paths.
• Add WebTransport session statistics (WebTransportSessionStats) with recording hooks for datagrams/bytes/streams, expose a client API to read stats, and return stats on session close.
• Add/expand HTTP/3 tests for WebTransport session stats and transport stats.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
neqo-transport/src/stats.rs	Adds new transport stats fields and prints them in Debug output (plus updates the debug snapshot test).
neqo-transport/src/sender.rs	Exposes bytes_in_flight() from congestion controller for stats reporting.
neqo-transport/src/recovery/mod.rs	Accumulates bytes_lost when packets are declared lost.
neqo-transport/src/connection/mod.rs	Records bytes TX/RX/ACKed and snapshots min_rtt, cwnd, bytes_in_flight.
neqo-http3/src/features/extended_connect/stats.rs	Introduces WebTransportSessionStats struct.
neqo-http3/src/features/extended_connect/webtransport_session.rs	Stores and updates per-session WebTransport stats and exposes them via the protocol trait.
neqo-http3/src/features/extended_connect/session.rs	Records datagram send/recv bytes and counts; adds session stats accessor; makes datagram() mutable to record stats.
neqo-http3/src/connection.rs	Returns session stats on webtransport_close_session and adds internal stats accessor.
neqo-http3/src/connection_client.rs	Changes close-session return type to stats and adds a public webtransport_session_stats() API.
neqo-http3/src/connection_server.rs	Changes close-session return type to stats.
neqo-http3/src/server_events.rs	Adapts request close API by discarding returned stats.
neqo-http3/tests/webtransport.rs	Adds new integration tests covering session stats and the new transport stats fields.
neqo-http3/src/features/extended_connect/tests/webtransport/sessions.rs	Adds unit tests for initial/session stats evolution.
neqo-http3/src/features/extended_connect/mod.rs	Exports the new stats module.

Comments suppressed due to low confidence (2)

neqo-http3/src/connection_server.rs:217

• This changes the public webtransport_close_session API to return WebTransportSessionStats instead of (), which is a breaking signature change for downstream callers. If compatibility matters, consider adding a new API that returns stats while keeping the existing signature, and update the rustdoc to describe the return value.

    pub fn webtransport_close_session(
        &mut self,
        conn: &mut Connection,
        session_id: StreamId,
        error: u32,
        message: &str,
        now: Instant,
    ) -> Res<crate::features::extended_connect::stats::WebTransportSessionStats> {
        self.needs_processing = true;
        self.base_handler
            .webtransport_close_session(conn, session_id, error, message, now)
    }

neqo-http3/src/connection_client.rs:781

• This changes the public webtransport_close_session API to return WebTransportSessionStats instead of (), which is a breaking signature change for downstream callers. If the intent is additive, consider introducing a new method (or an alternate *_with_stats variant) and keeping the existing signature, or ensure the docs clearly describe the returned stats and that any semver/compat expectations are addressed.

    pub fn webtransport_close_session(
        &mut self,
        session_id: StreamId,
        error: u32,
        message: &str,
        now: Instant,
    ) -> Res<crate::features::extended_connect::stats::WebTransportSessionStats> {
        self.base_handler.webtransport_close_session(
            &mut self.conn,
            session_id,
            error,
            message,
            now,
        )
    }

[mxinden]

If we want to merge these, can you add some basic tests?

[jesup]

This PR is part of a stack of 13 bookmarks:

1. trunk()
2. users/jesup/exportkey
3. users/jesup/draining
4. users/jesup/sub_protocol
5. users/jesup/sendGroup
6. users/jesup/stats ← this PR
7. users/jesup/highwatermarks
8. users/jesup/sendgroup_sendorder_tracking
9. users/jesup/stats_overhead
10. users/jesup/avoid_PMTUD
11. users/jesup/anticipated_streams
12. users/jesup/waitUntilAvailable
13. users/jesup/atomicWrite
14. users/jesup/WT_DRAIN_SESSION

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Created with jj-stack

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