feat: add runtime-gated QUIC connection diagnostic logging

[iamvamsikrishnad]

Summary

Adds detailed tracing-based logging across the QUIC connection lifecycle to help diagnose connection drops. All logging is gated behind a runtime toggle so library consumers opt in explicitly.

Motivation

QUIC connections can drop for many reasons (idle timeouts, transport errors, stateless resets, version mismatches, peer closures) but the library previously provided no diagnostic visibility into these events. Handshake failures were silently swallowed with .ok().

Changes

New module: \snocat::quic_logging\

Runtime toggle backed by \AtomicBool\ — zero overhead when disabled:
\
ust
snocat::quic_logging::enable(); // opt in
snocat::quic_logging::disable(); // opt out
snocat::quic_logging::is_enabled(); // check
\\

Logging coverage (all gated behind the toggle)

Area	File	What's logged
Error conversion	\quinn_tunnel.rs\	Each \quinn::ConnectionError\ variant logged with distinct message, structured fields (error codes, reasons)
Tunnel creation	\quinn_tunnel.rs\	Tunnel ID, remote address, side, stable ID
Incoming stream failures	\quinn_tunnel.rs\	\�ccept_bi()\ errors with per-variant messages
Outgoing stream failures	\quinn_tunnel.rs\	\open_bi()\ errors with per-variant messages
Tunnel close	\quinn_tunnel.rs\	Close reason, tunnel ID, remote address
Endpoint lifecycle	\ unnel_source/mod.rs\	Bind success, handshake initiation, termination
Handshake failures	\server.rs\	Previously swallowed with .ok(), now logged
Client connection	\client.rs\	Connection initiation to server

Severity levels

• \�rror\ — transport errors (protocol violations)
• \warn\ — version mismatch, stateless reset, idle timeout, peer close failures
• \info\ — connection creation, graceful peer/app close, tunnel close
• \debug\ — local close, endpoint polling

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Contribution License Agreement

This Contribution License Agreement (“Agreement”) is agreed to by the party signing below (“You”),
and conveys certain license rights to Microsoft Corporation and its affiliates (“Microsoft”) for Your
contributions to Microsoft open source projects. This Agreement is effective as of the latest signature
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[Copilot]

Pull request overview

Adds runtime-gated tracing diagnostics for QUIC connection lifecycle events in the snocat library (plus a couple of CLI-side connection/handshake logs) to improve visibility into connection drops and failures.

Changes:

• Introduces snocat::quic_logging with a global AtomicBool runtime toggle (enable/disable/is_enabled).
• Adds toggle-gated QUIC lifecycle logs in the library (endpoint bind/accept lifecycle, tunnel creation/close, stream open/accept failures, connection error conversion).
• Replaces a swallowed handshake failure (.ok()) with explicit logging in snocat-cli, and logs client connection initiation.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
snocat/src/quic_logging.rs	New runtime toggle module for enabling/disabling QUIC diagnostic logs.
snocat/src/lib.rs	Exposes the new quic_logging module publicly.
snocat/src/common/tunnel_source/mod.rs	Adds gated endpoint bind/accept/termination tracing.
snocat/src/common/protocol/tunnel/quinn_tunnel.rs	Adds gated tunnel/stream lifecycle tracing and detailed ConnectionError logging.
snocat-cli/src/server.rs	Logs successful/failed incoming QUIC handshakes (previously swallowed).
snocat-cli/src/client.rs	Logs QUIC client connection initiation.

Comments suppressed due to low confidence (1)

snocat/src/common/protocol/tunnel/quinn_tunnel.rs:169

• In the incoming stream inspect_err handler, the close reason is always stored as TunnelError::ConnectionClosed regardless of the actual tunnel_error (ApplicationClosed/TimedOut/TransportError/LocallyClosed). This can make on_closed() and other close-reason reporting inaccurate; store the actual error (clone of tunnel_error) instead of hard-coding ConnectionClosed.

        let close_reason = TunnelCloseReason::Error(TunnelError::ConnectionClosed);
        {
          let close_reason_store = &close_reason_store;
          close_reason_store.store(Arc::new(close_reason));
        };

---

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[Copilot]

reason = %e.reason likely won’t compile because quinn::TransportError::reason is a byte buffer type (e.g., bytes::Bytes) that does not implement Display. Use ?e.reason (Debug) or convert to a lossy/hex string before emitting it as a % field.

Suggested change

	reason = %e.reason,
	reason = %String::from_utf8_lossy(&e.reason),

[Copilot]

PR description says transport errors should be logged at error severity, but quinn::ConnectionError::TransportError is currently emitted with tracing::warn!. Either bump this to error! (to match the stated severity and the other TransportError logs in this file) or update the PR description to reflect the intended level.