feat(server-utils): Restore caller context for callback tracing channels#21863
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`bindTracingChannelToSpan` only bound the span store on `start`, which covers the synchronous frame but not a callback the library dispatches from a detached async context (e.g. a socket data handler or a `setImmediate` drain). There, native async-context propagation no longer reaches the caller, so work issued inside the callback lost its parent. Stash the caller's store at `start` and re-bind it on `asyncStart`, so callback-style channels run their continuation in the caller's context — the same way a promise's `.then` does natively. It's inert for promise channels, which `publish` `asyncStart` rather than `runStores` it. Migrate the lru-memoizer subscriber onto the helper (`getSpan` returns `undefined`, so no span is created — it only needs the context rebind), dropping its hand-rolled callback re-wrapping.
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… caller context The asyncStart producer used `data._sentryCallerStore ?? asyncLocalStorage.getStore()`. When the caller had no active store, `_sentryCallerStore` is `undefined` and the fallback bound whatever was ambient at callback time — for a callback dispatched from a pooled socket handler, that can be another request's store. `start` always runs first and sets `_sentryCallerStore`, so return it verbatim (no fallback), matching the synchronous path: no caller context restores to none, not a foreign one.
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Works, and makes the mysql integration work. Will update pg PR once these two land.
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bindTracingChannelToSpanbound the span store onstartonly. That covers the synchronous frames and traces run throughtracePromise. In general it covers start wrapped continuations.We noticed that this doesn't work well for some callback-based traced calls, where
asyncStartcan run in a detached context. The main difference between promise-based traced calls and callback-based is callback continuations are run outside thestartrunStores callback. So adding a context rebind for asyncStart would fix that, and would be a safe change overall.I used
lru-memoizeras a POC to test this out. It creates no span, all it wants is the context rebind which is what the helper does anyways but was missing theasyncStartfor that case specifically. With these changes we can drop the hand rolled logic.