[LingJueYa～ (LingJueYa)]

What

Fix connection attempts that can get stuck during the NATS handshake and prevent automatic reconnection from continuing.

• Create per-attempt promises before asynchronous setup starts, so an early server error or disconnect is retained and completes the attempt.
• Add a five-second handshake deadline after TCP connects, covering transport negotiation, INFO, credential loading, and CONNECT/PING/PONG. The existing TCP timeout remains separate.
• Complete the NATS handshake only on PONG, not on unrelated protocol messages.
• Cancel and drain failed attempts before retrying. Keep connection state and task ownership together so close, suspend, and reconnect cannot leave an attempt running or wait on itself.
• Add regression tests for these failure paths and for successful reconnection with subscription restoration.

Why

Previously, receiving INFO completed one continuation, but the continuation for connection establishment was registered only after credentials had been loaded and the nonce signed.

A server -ERR arriving in that gap could emit error events without completing either continuation. Since the handshake had no deadline, the connection attempt could remain suspended indefinitely and the reconnect loop could not start another attempt. A silent peer could cause a similar indefinite wait.

Before: INFO -> load credentials -> early error has no waiter -> reconnect stalls
After:  attempt owns its result from the start -> error or timeout -> cleanup -> retry

This fixes the failure at the client handshake boundary rather than relying on process restarts or a longer server authentication timeout. Changes to normal PING/RTT handling and connected-state error reporting are outside this PR.

Validation

• Reproduced the credential-loading failure on an unmodified upstream checkout: the same regression test failed because the handshake did not finish after a server error or disconnect. It passes with this patch.
• Added 10 regression tests covering early errors, silent handshakes, WebSocket upgrade timeout, cancellation, close/suspend, retry exhaustion, reconnect handoff, heartbeat counter reset, and subscription restoration.
• Ran the complete test suite locally: 76 Nats tests + 43 JetStream tests = 119 passing tests, including the 10 new tests.
• Strict formatting checks for changed files and git diff --check pass.

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Summary by CodeRabbit

• Bug Fixes
  • Improved connection and reconnection handling, including when a connection is cancelled, suspended, or closed during setup.
  • Improved recovery from handshake failures and timeouts, credential-loading failures, and heartbeat failures.
  • Connection setup now allows separate five-second periods for the TCP connection and handshake.
  • Improved cleanup of failed connection attempts and handling of connection events, helping prevent stale connections from interfering with recovery.

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📝 Walkthrough

ConnectionHandler now manages connection state, active tasks, retries, and shutdown. Each connection attempt uses handshake promises for INFO, transport upgrade, and establishment. New integration tests cover handshake failures, reconnects, cancellation, and shutdown.

Changes: Connection Flow

Layer / File(s)	Summary
Lifecycle and retry orchestration Sources/Nats/NatsClient/NatsClient.swift, Sources/Nats/NatsConnection.swift, Tests/NatsTests/Integration/HandshakeTests.swift	Client operations delegate to ConnectionHandler. The handler manages lifecycle state, connection tasks, shutdown, and retries. Integration tests cover reconnect behavior, lifecycle events, and retry-limit exhaustion.
Handshake and transport setup Sources/Nats/NatsConnection.swift, Tests/NatsTests/Integration/HandshakeTests.swift	Connection attempts use per-attempt promises for INFO, transport upgrade, and establishment. Transport setup handles TCP, TLS, and WebSocket connections. Integration tests cover handshake failures, timeouts, cancellation, and the loopback peer fixture.

Priority: ⬇️ Low

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant NatsClient
  participant ConnectionHandler
  participant connectToServer
  participant NATS_peer
  NatsClient->>ConnectionHandler: Delegate connect request
  ConnectionHandler->>connectToServer: Start connection attempt
  connectToServer->>NATS_peer: Configure transport and await INFO
  NATS_peer-->>connectToServer: Return INFO
  connectToServer->>NATS_peer: Send CONNECT and PING
  NATS_peer-->>connectToServer: Return PONG
  connectToServer-->>ConnectionHandler: Return established channel

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Merge Risk: ⚪ Minimal · up to 41b6d

The change makes connection attempts fail or time out cleanly instead of hanging, so automatic reconnection can proceed after authentication timeouts. It also adds regression tests for the failure and reconnect paths. No unresolved merge-blocking risk was identified.

Pre-merge checks · 4 · 1

Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 13.04% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 46 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks (4 passed)

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main change: preventing reconnect hangs after authentication timeouts.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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_{I’m a rabbit; I hop by the shore,
While handshakes complete and channels restore.
INFO arrives, then PONG rings clear,
Retries take shape when a link disappears.
I twitch my nose as the tests draw near.}

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Actionable comments posted: 1

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Inline comments:
Review comments at @Sources/Nats/NatsConnection.swift:
- Around line 212-219: Update the handshake interception in the
operation-processing loop to intercept operations only while
`handshake.established` is pending. Once it is fulfilled, allow subsequent
`.info` and `.error` operations to continue through normal server-info and error
handling.

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📚 Code guidelines (1)

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📓 Path-based instructions (2)

Start `NatsServer` explicitly for server-backed tests and stop it in `tearDown`; close clients and explicitly owned subscriptions or tasks as part of test cleanup.

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Files:

• Tests/NatsTests/Integration/HandshakeTests.swift

Keep Swift formatting consistent with `.swift-format`; CI runs its strict recursive lint over `Sources` and `Tests`.

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Files:

• Sources/Nats/NatsClient/NatsClient.swift
• Tests/NatsTests/Integration/HandshakeTests.swift
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🔇 Additional comments (3)

Sources/Nats/NatsClient/NatsClient.swift (1)

91-96: LGTM!

Also applies to: 107-107

Sources/Nats/NatsConnection.swift (1)

326-355: LGTM!

Also applies to: 755-781, 864-954

Tests/NatsTests/Integration/HandshakeTests.swift (1)

1-550: LGTM!

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