Add UnwrapRpcResponse<T> + splitSolanaRpcResponse() to @solana/rpc-types#1678
Add UnwrapRpcResponse<T> + splitSolanaRpcResponse() to @solana/rpc-types#1678mcintyre94 wants to merge 1 commit into
UnwrapRpcResponse<T> + splitSolanaRpcResponse() to @solana/rpc-types#1678Conversation
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…pc-types`
Adds a co-located type-level and runtime decomposition for the `SolanaRpcResponse<T>` envelope, so callers can handle notifications that may or may not be wrapped without re-implementing the duck-type check.
`UnwrapRpcResponse<T>` is a conditional type that unwraps `SolanaRpcResponse<U>` → `U` and passes through other shapes unchanged. `splitSolanaRpcResponse()` runtime-detects the envelope via duck-type (`'context' in x && 'value' in x`) and decomposes into the inner value and the lifted slot. Raw notifications pass through with `slot: undefined`; `undefined` input returns both halves as `undefined`. Four overloads narrow the return type to match the input: `SolanaRpcResponse<T>` → `{ slot: Slot; value: T }`; `undefined` → `{ slot: undefined; value: undefined }`; `SolanaRpcResponse<T> | undefined` → `{ slot: Slot | undefined; value: T | undefined }`; raw `T` → `{ slot: undefined; value: T }`. The third overload lets callers pipe a possibly-undefined source straight through without an external null-check.
T is intentionally unconstrained — the runtime check handles arbitrary shapes, and the overloads surface precise return types per call site. Tests cover the envelope path, raw passthrough, `undefined`/`null` inputs, malformed shapes (missing `context` or `value`), primitives, and envelopes whose `value` itself is `undefined` / `null`.
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Summary
Adds two helpers to @solana/rpc-types:
UnwrapRpcResponse<T>— conditional type that unwrapsSolanaRpcResponse<U>toU, passes other types through.splitSolanaRpcResponse()— runtime helper that duck-types the envelope shape ('context' in x && 'value' in x) and decomposes into{ value, slot }. Raw inputs pass through withslot: undefined;undefinedreturns both halves asundefined.
Four overloads cover the envelope, undefined, SolanaRpcResponse<T> | undefined, and raw T cases. Comes with a thorough unit test file and a small type test, plus a minor changeset.
Things to watch out for / notes for subsequent reviewers
1. Missing README update. The package's README.md documents every existing public type and function but isn't updated here. Per the repo's TypeScript READMEs skill ("When adding a new public API, add or update the package's README"), this PR should add UnwrapRpcResponse under "Types" and splitSolanaRpcResponse under "Functions". The JSDoc is solid, but the README is the user-facing entry point.
2. Type-level gap for genuinely mixed unions. The PR description says these helpers handle "an input that may or may not be a SolanaRpcResponse". The overloads cover SolanaRpcResponse<T>, undefined, SolanaRpcResponse<T> | undefined, and raw T — but not SolanaRpcResponse<T> | T (i.e. the case where the call site genuinely doesn't know which it has). With a union like SolanaRpcResponse<X> | RawX, none of overloads 1–3 match (each arm fails them), so it falls through to overload 4 (notification: T) and you get { slot: undefined; value: SolanaRpcResponse<X> | RawX } — slot is statically undefined even though at runtime the envelope arm would produce a real slot.
For the React-hook use case (a single subscription whose envelope-ness is statically known) this is fine. But if the intent is broader, consider adding an overload before overload 4 along the lines of:
export function splitSolanaRpcResponse<TRaw>(
notification: SolanaRpcResponse<TRaw> | TRaw
): { slot: Slot | undefined; value: TRaw };A matching type-test case would also be worth adding so the resolution doesn't silently regress.
3. Overload ordering is correct, but fragile. Overload 4 (<T>(notification: T)) is broad enough to swallow envelope inputs if TS ever picked it. It works today because earlier overloads come first and TS picks the first matching signature, but it's worth a comment explaining the ordering so a future contributor doesn't reorder them. Adding the union overload above would push overload 4 even further down — also fine, just keep it as the final fallback.
4. Minor: null handling is implicit. The runtime guard (notification != null) accepts null, but the public overloads don't list it; the test for null casts via as unknown as undefined. Either extend the undefined overload to null | undefined and add a real null overload, or have the test cover only what the type contract promises. The current state is slightly misleading.
5. Naming. splitSolanaRpcResponse is descriptive, but the function also unwraps — unwrapSolanaRpcResponse would arguably read better as a callsite verb (const { value, slot } = unwrapSolanaRpcResponse(...)). Subjective, not blocking.
Nothing here is a correctness issue — the runtime behaviour and tests are tight. Main asks are the README update and a decision on whether the mixed-union case is in scope.
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Summary of Changes
This PR adds a new type
UnwrapRpcResponsewhich unwrapsSolanaRpcResponse<T>toTand leaves any other type unchanged. In practice this allows extracting the inner value type from an input that may or may not be aSolanaRpcResponse.Alongside this it adds a new function
splitSolanaRpcResponsewhich takes an input that may be aSolanaRpcResponseand unwraps it to{value, slot: Slot}. If the input is notSolanaRpcResponsethen it is returned asvaluewithslot: undefined. The input can be undefined to allow bridging from a store with optional data.These helpers are intended for processing RPC subscriptions in a react hook, but they apply to RPC requests with the
SolanaRpcResponsewrapper too.