In the legacy connection path, `nsSocketTransport::RecoverFromError` re-resolves the host with TRR disabled (`DISABLE_TRR | BYPASS_CACHE | REFRESH_CACHE`) and retries once all TRR-resolved addresses have failed to connect, except in `TRR_ONLY` mode. Happy Eyeballs, by contrast, resolves once through the engine and then hands each connection a single pre-resolved address, so that fallback never runs — the engine simply reports `Output::Failed` with no native re-resolution. As a result, a host whose TRR answer resolves but whose addresses do not connect, for example because of a stale or poisoned record, or an edge outage affecting only the TRR-provided answer, fails under HE in cases where the legacy path would previously recover.
Bug 2051614 Comment 0 Edit History
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In the legacy connection path, `nsSocketTransport::RecoverFromError` re-resolves the host with TRR disabled (`DISABLE_TRR | BYPASS_CACHE | REFRESH_CACHE`) and retries once all TRR-resolved addresses have failed to connect, except in `TRR_ONLY` mode. Happy Eyeballs, by contrast, resolves once through the engine and then hands each connection a single pre-resolved address, so that fallback never runs — the engine simply reports `Output::Failed` with no native re-resolution.