Preserve own properties of Error instances across serialization/deserialization#166
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aron-cf wants to merge 1 commit intocloudflare:mainfrom
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Preserve own properties of Error instances across serialization/deserialization#166aron-cf wants to merge 1 commit intocloudflare:mainfrom
aron-cf wants to merge 1 commit intocloudflare:mainfrom
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This commit ensures that own properties are sent across the RPC boundary and reconstructed on the Error instance on the other side. The `cause` field and, in the case of `errors` for `AggregateError` are also copied over.
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aron-cf
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Apr 30, 2026
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| Property values that cannot be represented over the wire (capabilities without a session, cycles, unsupported types) are silently dropped from the error's property bag; the error itself always reaches the receiver. Use `onSendError` to scrub fields explicitly if you need control over what gets sent. | ||
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| The wire format change is backwards-compatible: errors with no extras are still emitted in the legacy 3- or 4-element form, and older peers that only understand that form will simply ignore the new trailing element. |
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Happy to make this shorter if we want terser changelog entries.
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| // supported type round-trips. If a property's value can't be serialized (a capability | ||
| // without a session, a cycle, an Object.create(null), …) we silently drop it: the | ||
| // error itself must always make it through. Use `onSendError` to scrub heavy or | ||
| // sensitive fields explicitly. |
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Would appreciate feedback on whether we just drop the entire property if it fails to serialize rather than making a best effort attempt.
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| When `props` is present, `stack` is normalised to `null` if absent so that positional indexing for `props` is unambiguous. When there are no extras, the legacy 3- or 4-element form is emitted unchanged. | ||
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| The `props` element is backwards-compatible: a peer that only understands the 4-element form ignores it and recovers the standard `name`/`message`/`stack`. A peer that understands `props` but receives the 3- or 4-element form simply sees no extras. |
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Happy to remove this if it's too much information but felt it might be useful to have documented.
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Closes #87.
Today the wire format for
Erroronly carriesname,message, and (optionally)stack. Anything a user attaches to the error —code,details, acause, the inner errors of anAggregateError— is lost the moment the error crosses an RPC boundary.This PR extends the
errorexpression with an optional fifth element,props. This uses the same serialization/deserialization as any other object.Error.causeandAggregateError.errorsare normally non-enumerable, so they are picked up explicitly by the encoder. On the receive side, the decoder constructs the error as before and then assigns each entry frompropsas an own enumerable property on the result.The wire format change is fully backwards-compatible.
Tests have been added to verify the serialization/deserialization of various different error cases and failure modes. There may be too many, happy to remove any if needed.
The
errorexpression in protocol.md now documents the optionalpropselement, the lossy-fallback semantics, and the backwards-compatibility rule.