docs: spell out that a cancelled request surfaces as .transport, not CancellationError - #1344
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…orage and Functions Auth, PostgREST, Storage and Functions now retry through a single middleware driven by a `RetryPolicy` value: full-jitter capped exponential backoff, `Retry-After` honoured up to the cap, idempotent methods only unless an `Idempotency-Key` header is present, stop on cancellation. The retry rule is per target. PostgREST keeps its fixed postgrest-js rule (GET/HEAD, 503/520, 4 attempts) and only its on/off switch is public; its private loop is deleted. Storage and Functions gain retries for the first time, with a public, configurable `retryPolicy`. Auth keeps retrying POST so token refreshes are replayed. The Realtime reconnect delay carries the same full jitter. BREAKING CHANGE: retry timing changes for every module (jitter instead of a fixed schedule; Auth makes 3 attempts instead of 2), Storage and Functions start retrying transient failures by default, and only `URLError` counts as a retryable transport failure. See V3_MIGRATION.md. Fixes SDK-1791 Co-Authored-By: Claude <noreply@anthropic.com>
`URLSession`'s async APIs report a cancelled `Task` as `URLError(.cancelled)`, not `CancellationError`, so a cancelled request is wrapped as the module error with kind `.transport` like any other `URLError`. The V3 migration guide only promised that `CancellationError` propagates as itself, which left a caller to assume `catch is CancellationError` would match a cancellation. It does not. Keep the wrapping and document it: the guide now shows the before/after for checking the code on `underlyingError`, and says the break compiles silently. Add one Storage test pinning the decision next to `cancellationIsNotWrapped`, so the contrast between the two forms is visible at the point of confusion. Retries already handle this: `RetryRequestInterceptor` skips a cancellation in either form (SDK-1791), so nothing was needed there. Fixes SDK-1849
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In `@Tests/StorageTests/StorageFileAPITests.swift`:
- Around line 117-128: Add a separate URLSessionTransport cancellation test that
starts a URLSession-backed request, cancels its URLSessionTask, and verifies the
resulting StorageError has kind .transport with an underlying URLError whose
code is .cancelled. Keep cancelledURLErrorIsWrapped() unchanged as the
ClosureTransport wrapping test, and use the existing test helpers and
URLSession-backed storage setup.
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`cancelledURLErrorIsWrapped()` stubs the transport, so it asserts the wrapping but assumes the premise it rests on: that cancelling a `Task` makes `URLSession` fail with `URLError(.cancelled)`. Nothing checked that, in Storage or in `URLSessionTransportTests`. Add an end-to-end test that runs a `URLSessionTransport`-backed request against a delayed mock, cancels the enclosing `Task` once `MockingURLProtocol` reports the request in flight, and asserts the caller sees `StorageError(.transport)` with `URLError(.cancelled)` in `underlyingError`. The request callback runs before the delay is scheduled, so the cancel always lands mid-flight and the delay is never waited out — the test completes in ~12ms and passed 10/10 consecutive runs.
2 participants
Stacked on #1341 — review and merge that first.
URLSession's async APIs report a cancelledTaskasURLError(.cancelled),not
CancellationError. Every module wraps aURLErroras its module errorwith kind
.transport, so a cancelled request surfaces asStorageError(transport),PostgrestError(transport), and so on. The V3migration guide only promised that
CancellationErrorpropagates as itself,which reads as "cancelling gives you a
CancellationError" — it does not, so acaller guarding an error banner with
error is CancellationErrorshows thebanner for a request the user cancelled.
The decision here is to keep the wrapping and document it. Rethrowing the
URLErrorunchanged and converting it toCancellationErrorwere bothconsidered and rejected: the latter misreports a
URLError(.cancelled)thatdid not come from
Taskcancellation (URLSession.invalidateAndCancel()) andloses the original error.
So this is a docs change plus one test:
V3_MIGRATION.md, in the existing "Network and decoding failures are wrappedin the module error" section: a before/after showing the
underlyingErrorcheck, and an explicit note that the break compiles silently.
cancelledURLErrorIsWrapped()inTests/StorageTests/StorageFileAPITests.swift,placed directly after
cancellationIsNotWrapped()so the two forms arecontrasted where the confusion is. One test, not one per module: each module
already has a
transportFailureIsWrappedtest provingURLError→.transport, and.cancelledis deliberately not special.SDK-1849 also asked for
shouldRetryto stop retrying a cancelled request.#1341 already does that — it deletes PostgREST's legacy
shouldRetryand routesevery module through
RetryRequestInterceptor, which returnserror.code != .cancelledand is covered bydoesNotRetryCancelledURLError().Nothing was needed here.
Testing
Per-target, all green:
swift-format lint --recursive --strict Sources Testsand./scripts/spell-check.shboth clean.Risks
Documentation and one test; no source change, so no runtime risk.
Unrelated, but worth a separate look: whole-package
swift testsegfaults onthis base (signal 11, before any test completes). It reproduces with this
commit reverted, so it predates the branch — but CI only runs the per-platform
jobs, which pass, so nothing currently catches it.
Fixes SDK-1849