Add new RpcRequest, RpcResponse types and their transformer types

packages/rpc-spec/README.md

@@ -41,6 +41,32 @@ Calling the `send(options)` method on a `PendingRpcRequest` will trigger the req
 
 An object that exposes all of the functions described by `TRpcMethods`, and fulfils them using `TRpcTransport`. Calling each method returns a `PendingRpcRequest<TResponse>` where `TResponse` is that method's response type.
 
+### `RpcRequest`
+
+An object that describes the elements of a JSON RPC request. It consists of the following properties:
+
+-   `methodName`: The name of the JSON RPC method to be called.
+-   `params`: The parameters to be passed to the JSON RPC method.
+
+### `RpcRequestTransformer`
+
+A function that accepts an `RpcRequest` and returns another `RpcRequest`. This allows the `RpcApi` to transform the request before it is sent to the JSON RPC server.
+
+### `RpcResponse`
+
+An object that represents the response from a JSON RPC server. It contains two asynchronous methods that can be used to access the response data:
+
+-   `await response.json()`: Returns the data as a JSON object.
+-   `await response.text()`: Returns the data, unparsed, as a JSON string.
+
+This allows the `RpcApi` to decide whether they want the parsed JSON object or the raw JSON string. Ultimately, the `json` method will be used by the `Rpc` to provide the final response to the caller.
+
+### `RpcResponseTransformer`
+
+A function that accepts an `RpcResponse` and returns another `RpcResponse`. This allows the `RpcApi` to transform the response before it is returned to the caller.
+
+Note that a `RpcResponseTransformerFor<T>` generic function type is also available to ensure the response data returned by the transformer matches the expected type `T`.
+
 ### `RpcApi<TRpcMethods>`
 
 For each of `TRpcMethods` this object exposes a method with the same name that maps between its input arguments and a `RpcApiRequestPlan<TResponse>` that describes how to prepare a JSON RPC request to fetch `TResponse`.
@@ -51,7 +77,7 @@ This is a marker interface that all RPC method definitions must extend to be acc
 
 ### `RpcApiRequestPlan`
 
-This type describes how a particular request should be issued to the JSON RPC server. Given a function that was called on a `Rpc`, this object gives you the opportunity to:
+This type allows an `RpcApi` to describe how a particular request should be issued to the JSON RPC server. Given a function that was called on a `Rpc`, this object gives you the opportunity to:
 
 -   customize the JSON RPC method name in the case that it's different than the name of that function
 -   define the shape of the JSON RPC params in case they are different than the arguments provided to that function
@@ -116,3 +142,17 @@ A config object with the following properties:
 
 -   `parametersTransformer<T>(params: T, methodName): unknown`: An optional function that maps between the shape of the arguments an RPC method was called with and the shape of the params expected by the JSON RPC server.
 -   `responseTransformer<T>(response, methodName): T`: An optional function that maps between the shape of the JSON RPC server response for a given method and the shape of the response expected by the `RpcApi`.
+
+### `createJsonRpcResponseTransformer<T>(jsonTransformer)`
+
+Creates an `RpcResponseTransformerFor<T>` function from a function that transforms any JSON value to a value of type `T` by wrapping it in a `json` async function.
+
+```ts
+const getResultTransformer = createJsonRpcResponseTransformer((json: unknown) => {
+    return (json as { result: TResponse }).result;
+});
+```
+
+#### Arguments
+
+-   `jsonTransformer: (json: unknown, request: RpcRequest) => T`: A function that transforms an unknown JSON value to a value of type `T`.

packages/rpc-spec/src/__tests__/rpc-shared-test.ts

@@ -0,0 +1,56 @@
+import '@solana/test-matchers/toBeFrozenObject';
+
+import { createJsonRpcResponseTransformer, RpcRequest, RpcResponse } from '../rpc-shared';
+
+describe('createJsonRpcResponseTransformer', () => {
+    it('can alter the value of the json Promise', async () => {
+        expect.assertions(1);
+
+        // Given a request and a response that returns a number.
+        const request = { methodName: 'someMethod', params: [123] };
+        const response = {
+            json: () => Promise.resolve(123),
+            text: () => Promise.resolve('123'),
+        };
+
+        // When we create a JSON transformer that doubles the number.
+        const transformer = createJsonRpcResponseTransformer((json: unknown) => (json as number) * 2);
+
+        // Then the transformed response should return the doubled number.
+        const transformedResponse = transformer(response, request);
+        transformedResponse satisfies RpcResponse<number>;
+        await expect(transformedResponse.json()).resolves.toBe(246);
+    });
+
+    it('does not alter the value of the text Promise', async () => {
+        expect.assertions(1);
+
+        // Given a request and a response that returns a number.
+        const request = { methodName: 'someMethod', params: [123] };
+        const response = {
+            json: () => Promise.resolve(123),
+            text: () => Promise.resolve('123'),
+        };
+
+        // When we create a JSON transformer that doubles the number.
+        const transformer = createJsonRpcResponseTransformer((json: unknown) => (json as number) * 2);
+
+        // Then the text should function should return the original string.
+        const transformedResponse = transformer(response, request);
+        await expect(transformedResponse.text()).resolves.toBe('123');
+    });
+
+    it('returns a frozen object as the Reponse', () => {
+        // Given any response.
+        const response = {
+            json: () => Promise.resolve(123),
+            text: () => Promise.resolve('123'),
+        };
+
+        // When we pass it through a JSON transformer.
+        const transformedResponse = createJsonRpcResponseTransformer(x => x)(response, {} as RpcRequest);
+
+        // Then we expect the transformed response to be frozen.
+        expect(transformedResponse).toBeFrozenObject();
+    });
+});

packages/rpc-spec/src/index.ts

@@ -1,4 +1,5 @@
 export * from './rpc';
 export * from './rpc-api';
 export * from './rpc-request';
+export * from './rpc-shared';
 export * from './rpc-transport';

packages/rpc-spec/src/rpc-shared.ts

@@ -0,0 +1,35 @@
+export type RpcRequest<TParams = unknown> = {
+    readonly methodName: string;
+    readonly params: TParams;
+};
+
+export type RpcResponse<TResponse = unknown> = {
+    readonly json: () => Promise<TResponse>;
+    readonly text: () => Promise<string>;
+};
+
+export type RpcRequestTransformer = {
+    <TParams>(request: RpcRequest<unknown>): RpcRequest<TParams>;
+};
+
+export type RpcResponseTransformer = {
+    <TResponse>(response: RpcResponse<unknown>, request: RpcRequest<unknown>): RpcResponse<TResponse>;
+};
+
+export type RpcResponseTransformerFor<TResponse> = {
+    (response: RpcResponse<unknown>, request: RpcRequest<unknown>): RpcResponse<TResponse>;
+};
+
+export function createJsonRpcResponseTransformer<TResponse>(
+    jsonTransformer: (json: unknown, request: RpcRequest) => TResponse,
+): RpcResponseTransformerFor<TResponse> {
+    return function (response: RpcResponse, request: RpcRequest): RpcResponse<TResponse> {
+        return Object.freeze({
+            ...response,
+            json: async () => {
+                const json = await response.json();
+                return jsonTransformer(json, request);
+            },
+        });
+    };
+}