Improve fallback host resolution in connection logic

[ttypic]

Resolves #1238

Refinements made to the connection logic include:

• Ensuring checkFallback verifies internet connectivity via checkConnectivity and only resolves fallback hosts when a valid pending connection exists.
• Enhancing code readability by updating variable names and simplifying conditions related to fallback logic.

Summary by CodeRabbit

• Bug Fixes
  • Improved fallback connection checks by consistently verifying network connectivity, including when no connection attempt is pending.
  • Preserved fallback-host selection behavior for server errors and unavailable connections.

[coderabbitai]

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Reviewing files that changed from the base of the PR and between b92aa74 and cad7635.

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• lib/src/main/java/io/ably/lib/transport/ConnectionManager.java

Walkthrough

checkFallback now probes connectivity before checking for a pending connection. The fallback decision retains the existing status and connectivity conditions.

Changes

Connectivity fallback

Layer / File(s)	Summary
Update fallback evaluation lib/src/main/java/io/ably/lib/transport/ConnectionManager.java	checkFallback stores the pending connection locally, calls checkConnectivity() unconditionally, and evaluates the combined fallback condition.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Suggested reviewers: sacoo7

Merge Risk: 🔵 Low · up to b92aa

Connection-loss handling can incur an unnecessary network delay before completing recovery or suspension handling.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the main change: updates to fallback host resolution in the connection logic.

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_{A rabbit checks the signal bright
Before a pending hop takes flight
The fallback gate now tests with care
Connectivity everywhere
Ears up, the path is clear tonight}

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[coderabbitai]

Actionable comments posted: 1

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Inline comments:
In `@lib/src/main/java/io/ably/lib/transport/ConnectionManager.java`:
- Around line 1481-1488: Update checkFallback to verify pendingConnect is
non-null before invoking checkConnectivity(), so established-connection loss
paths avoid the unnecessary synchronous HTTP request; preserve the existing
fallback-host logic for pending connections.

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Configuration used: Organization UI

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📥 Commits

Reviewing files that changed from the base of the PR and between 243a08c and b92aa74.

📒 Files selected for processing (1)

• lib/src/main/java/io/ably/lib/transport/ConnectionManager.java

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[Copilot]

Pull request overview

Improves fallback host resolution and connectivity handling in ConnectionManager.

Changes:

• Refines fallback eligibility checks.
• Avoids unnecessary connectivity checks.
• Rechecks pending connection state during fallback resolution.

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 1 comment.

Suppressed comments (1)

lib/src/main/java/io/ably/lib/transport/ConnectionManager.java:1487

• pendingConnect is still read on both sides of the blocking connectivity call. While it blocks, the action thread can replace the field in connectImpl; this callback can then apply the old transport's failure to the new attempt, or clear that new attempt at line 1496. Snapshot the failed attempt before the call and, after the call, only select a fallback or clear the field if it still refers to that same attempt, using a visibility strategy that makes this cross-thread check reliable.

        boolean internetIsUp = shouldTryFallback(pendingConnect, reason) && checkConnectivity();
        TransportParams pendingConnectionParams = pendingConnect;

[sacOO7]

LGTM