🔧 chore: preserve toResponse() status before mapping, let toResponse() decide the final status and resolve Async toResponse() still collapsing to 500

Author: MarcelOlsen

src/adapter/bun/handler.ts

@@ -530,7 +530,19 @@ export const errorToResponse = (error: Error, set?: Context['set']) => {
 	// @ts-expect-error
 	if (typeof error?.toResponse === 'function') {
 		// @ts-expect-error
-		return mapResponse(error.toResponse(), set ?? { headers: {}, status: 200, redirect: '' })
+		const raw = error.toResponse()
+		const targetSet =
+			set ?? ({ headers: {}, status: 200, redirect: '' } as Context['set'])
+		const apply = (resolved: unknown) => {
+			if (resolved instanceof Response) targetSet.status = resolved.status
+			return mapResponse(resolved, targetSet)
+		}
+
+		// @ts-expect-error
+		return typeof raw?.then === 'function'
+			? // @ts-expect-error
+			  raw.then(apply)
+			: apply(raw)
 	}
 
 	return new Response(

src/adapter/web-standard/handler.ts

@@ -563,7 +563,19 @@ export const errorToResponse = (error: Error, set?: Context['set']) => {
 	// @ts-expect-error
 	if (typeof error?.toResponse === 'function') {
 		// @ts-expect-error
-		return mapResponse(error.toResponse(), set ?? { headers: {}, status: 200, redirect: '' })
+		const raw = error.toResponse()
+		const targetSet =
+			set ?? ({ headers: {}, status: 200, redirect: '' } as Context['set'])
+		const apply = (resolved: unknown) => {
+			if (resolved instanceof Response) targetSet.status = resolved.status
+			return mapResponse(resolved, targetSet)
+		}
+
+		// @ts-expect-error
+		return typeof raw?.then === 'function'
+			? // @ts-expect-error
+			  raw.then(apply)
+			: apply(raw)
 	}
 
 	return new Response(

src/compose.ts

@@ -2603,10 +2603,14 @@ export const composeErrorHandler = (app: AnyElysia) => {
 	// BUT exclude ValidationError and TransformDecodeError to allow proper validation error handling
 	fnLiteral +=
 		`if(typeof error?.toResponse==='function'&&error.constructor.name!=="ValidationError"&&error.constructor.name!=="TransformDecodeError"){` +
-		`const errorResponse=error.toResponse()\n` +
-		`if(errorResponse instanceof Response)set.status=errorResponse.status\n` +
+		`const raw=error.toResponse()\n` +
+		`const apply=(resolved)=>{` +
+		`if(resolved instanceof Response)set.status=resolved.status\n` +
 		afterResponse() +
-		`return context.response=context.responseValue=mapResponse(${saveResponse}errorResponse,set${adapter.mapResponseContext})\n` +
+		`return context.response=context.responseValue=mapResponse(${saveResponse}resolved,set${adapter.mapResponseContext})\n` +
+		`}\n` +
+		`if(typeof raw?.then==='function')return raw.then(apply)\n` +
+		`return apply(raw)\n` +
 		`}\n`
 
 	if (app.event.error)

test/core/handle-error.test.ts

@@ -432,4 +432,87 @@ describe('Handle Error', () => {
 		expect(res.status).toBe(418)
 		expect(res.headers.get('X-Custom-Header')).toBe('custom-value')
 	})
+
+	it('handle async toResponse() when thrown', async () => {
+		class AsyncError extends Error {
+			async toResponse() {
+				// Simulate async operation
+				await new Promise(resolve => setTimeout(resolve, 10))
+				return Response.json({ error: 'async error' }, { status: 418 })
+			}
+		}
+
+		const app = new Elysia().get('/', () => {
+			throw new AsyncError()
+		})
+
+		const res = await app.handle(req('/'))
+
+		expect(await res.json()).toEqual({ error: 'async error' })
+		expect(res.status).toBe(418)
+	})
+
+	it('handle async toResponse() when returned', async () => {
+		class AsyncError extends Error {
+			async toResponse() {
+				// Simulate async operation
+				await new Promise(resolve => setTimeout(resolve, 10))
+				return Response.json({ error: 'async error' }, { status: 418 })
+			}
+		}
+
+		const app = new Elysia().get('/', () => {
+			return new AsyncError()
+		})
+
+		const res = await app.handle(req('/'))
+
+		expect(await res.json()).toEqual({ error: 'async error' })
+		expect(res.status).toBe(418)
+	})
+
+	it('handle async toResponse() with custom headers', async () => {
+		class AsyncErrorWithHeaders extends Error {
+			async toResponse() {
+				await new Promise(resolve => setTimeout(resolve, 10))
+				return Response.json(
+					{ error: 'async with headers' },
+					{
+						status: 419,
+						headers: {
+							'X-Async-Header': 'async-value'
+						}
+					}
+				)
+			}
+		}
+
+		const app = new Elysia().get('/', () => {
+			throw new AsyncErrorWithHeaders()
+		})
+
+		const res = await app.handle(req('/'))
+
+		expect(await res.json()).toEqual({ error: 'async with headers' })
+		expect(res.status).toBe(419)
+		expect(res.headers.get('X-Async-Header')).toBe('async-value')
+	})
+
+	it('handle non-Error with async toResponse()', async () => {
+		class AsyncNonError {
+			async toResponse() {
+				await new Promise(resolve => setTimeout(resolve, 10))
+				return Response.json({ error: 'non-error async' }, { status: 418 })
+			}
+		}
+
+		const app = new Elysia().get('/', () => {
+			throw new AsyncNonError()
+		})
+
+		const res = await app.handle(req('/'))
+
+		expect(await res.json()).toEqual({ error: 'non-error async' })
+		expect(res.status).toBe(418)
+	})
 })