feat: allow resolver to return a promise

Author: antfu

src/index.ts

@@ -3,8 +3,9 @@ export type ReturnType<T> = T extends (...args: any) => infer R ? R : never
 export type PromisifyFn<T> = ReturnType<T> extends Promise<any>
   ? T
   : (...args: ArgumentsType<T>) => Promise<Awaited<ReturnType<T>>>
+export type Thenable<T> = T | PromiseLike<T>
 
-export type BirpcResolver = (name: string, resolved: (...args: unknown[]) => unknown) => ((...args: unknown[]) => unknown) | undefined
+export type BirpcResolver = (name: string, resolved: (...args: unknown[]) => unknown) => Thenable<((...args: unknown[]) => unknown) | undefined>
 
 export interface ChannelOptions {
   /**
@@ -329,9 +330,9 @@ export function createBirpc<RemoteFunctions = Record<string, never>, LocalFuncti
     if (msg.t === TYPE_REQUEST) {
       const { m: method, a: args } = msg
       let result, error: any
-      const fn = resolver
+      const fn = await (resolver
         ? resolver(method, (functions as any)[method])
-        : (functions as any)[method]
+        : (functions as any)[method])
 
       if (!fn) {
         error = new Error(`[birpc] function "${method}" not found`)

test/resolver.test.ts

@@ -1,5 +1,6 @@
 import { MessageChannel } from 'node:worker_threads'
 import { expect, it } from 'vitest'
+import type { Thenable } from '../src';
 import { createBirpc } from '../src'
 import * as Alice from './alice'
 import * as Bob from './bob'
@@ -18,7 +19,7 @@ it('resolver', async () => {
     },
   )
 
-  let customResolverFn: ((...args: any[]) => any) | undefined
+  let customResolverFn: Thenable<((...args: any[]) => any) | undefined> | undefined
 
   const alice = createBirpc<BobFunctions, AliceFunctions>(
     { ...Alice },
@@ -46,7 +47,7 @@ it('resolver', async () => {
     .rejects
     .toThrow('[birpc] function "foo" not found')
 
-  customResolverFn = (a: string) => `Custom resolve function to ${a}`
+  customResolverFn = Promise.resolve((a: string) => `Custom resolve function to ${a}`)
 
   // @ts-expect-error `foo` is not defined
   expect(await bob.foo('Bob'))