fix(pubsub): avoid panics on Channel conflict and Ring empty subscribe

[VedantMadane]

Summary

Fixes #3761.

• PubSub.Channel / ChannelWithSubscriptions mutual-exclusion misuse no longer panics; returns a closed channel and logs a warning.
• Ring.Subscribe / PSubscribe / SSubscribe no longer panic on empty channels or shard lookup failure; return a PubSub with a sticky error (as the existing TODO suggested).

Test plan

• TestRingSubscribeEmptyChannelsNoPanic
• TestPubSubChannelMutualExclusionNoPanic

---

Note

Medium Risk
Changes error handling in PubSub and Ring subscribe paths; callers that relied on panics may see errors or empty channels instead, but behavior is more predictable for production code.

Overview
Fixes #3761 by replacing several PubSub panics with recoverable behavior.

Ring Subscribe / PSubscribe / SSubscribe no longer panic when channels are missing or shard routing fails. They return a normal *PubSub with a sticky error (failedPubSub); Receive and connection setup surface that error via conn().

Calling Channel after ChannelWithSubscriptions (or the reverse) no longer panics. The second call logs a warning and returns an already-closed Go channel so range/select can fail safely.

Tests cover empty Ring subscribe and the Channel API conflict.

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Let Close override the sticky error

When Ring.Subscribe, PSubscribe, or SSubscribe returns a failed PubSub and the caller uses either channel API, the receiver goroutine repeatedly gets stickyErr. After Close sets closed, this ordering still returns the sticky error instead of pool.ErrClosed, so initMsgChan/initAllChan never exits or closes the documented output channel; consumers can remain blocked and one goroutine leaks per failed subscription. Check closed before stickyErr, or otherwise make channels terminate for a permanently failed PubSub.

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[chatgpt-codex-connector]

Avoid reading the receiver command from the logging path

When the caller invokes the conflicting channel API after the first channel API returns, that first call has already started a receiver goroutine which initializes c.cmd in ReceiveTimeout; this new c.getContext() call reads the same field without synchronization and can therefore race with that initialization even though the two public calls were sequential. The symmetric logging path in ChannelWithSubscriptions has the same problem; log with a context that does not inspect receiver-owned state or synchronize access to that state.

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[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

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[cursor]

Sticky error blocks Channel close

High Severity

conn returns stickyErr before checking closed, so after Close on a failed PubSub (from Ring empty subscribe or shard lookup failure), Receive never yields pool.ErrClosed. initMsgChan / initAllChan only exit on that error, so calling Channel then Close leaves the receive goroutine running forever and for range on the channel hangs. That breaks the documented contract that the Go channel closes with the PubSub. The pool sticky pattern in SingleConnPool.Close overrides sticky with ErrClosed instead.

Additional Locations (2)

• pubsub.go#L219-L235
• pubsub.go#L777-L787

 

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