perf(standard-server): reduce payload size for batch responses (#354)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Refactor**
- Enhanced batch response processing to ensure a consistent structure
and improved asynchronous handling, including proper cleanup.

- **Tests**
- Updated validation criteria for response items to align with the
refined response format.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: unnoq

packages/standard-server/src/batch/response.test.ts

@@ -3,8 +3,8 @@ import { isAsyncIteratorObject } from '@orpc/shared'
 import { parseBatchResponse, toBatchResponse } from './response'
 
 describe('toBatchResponse & parseBatchResponse', () => {
-  const r1: BatchResponseBodyItem = { index: 0, status: 200, headers: { 'x-custom': 'value1' }, body: 'test1' }
-  const r2: BatchResponseBodyItem = { index: 1, status: 205, headers: { 'x-custom': 'value2' }, body: 'test2' }
+  const r1: BatchResponseBodyItem = { index: 0, status: 200, headers: { }, body: 'test1' }
+  const r2: BatchResponseBodyItem = { index: 1, status: 207, headers: { 'x-custom': 'value2' }, body: 'test2' }
 
   it('success', async () => {
     const response = toBatchResponse({
@@ -45,7 +45,7 @@ describe('parseBatchResponse', () => {
       status: 207,
       headers: { 'x-custom': 'value' },
       body: (async function*() {
-        yield 'invalid' as any
+        yield { headers: {} } as any
       })(),
     }))
 

packages/standard-server/src/batch/response.ts

@@ -1,4 +1,4 @@
-import type { StandardResponse } from '../types'
+import type { StandardHeaders, StandardResponse } from '../types'
 import { isAsyncIteratorObject, isObject } from '@orpc/shared'
 
 export interface BatchResponseBodyItem extends StandardResponse {
@@ -10,7 +10,24 @@ export interface ToBatchResponseOptions extends StandardResponse {
 }
 
 export function toBatchResponse(options: ToBatchResponseOptions): StandardResponse {
-  return options
+  return {
+    ...options,
+    body: (async function* () {
+      try {
+        for await (const item of options.body) {
+          yield {
+            index: item.index,
+            status: item.status === options.status ? undefined : item.status,
+            headers: Object.keys(item.headers).length ? item.headers : undefined,
+            body: item.body,
+          } satisfies Partial<BatchResponseBodyItem>
+        }
+      }
+      finally {
+        options.body.return?.()
+      }
+    })(),
+  }
 }
 
 export function parseBatchResponse(response: StandardResponse): AsyncGenerator<BatchResponseBodyItem> {
@@ -25,13 +42,18 @@ export function parseBatchResponse(response: StandardResponse): AsyncGenerator<B
   return (async function* () {
     try {
       for await (const item of body) {
-        if (!isObject(item) || !('index' in item) || !('status' in item) || !('headers' in item)) {
+        if (!isObject(item) || !('index' in item) || typeof item.index !== 'number') {
           throw new TypeError('Invalid batch response', {
             cause: item,
           })
         }
 
-        yield item as unknown as BatchResponseBodyItem
+        yield {
+          index: item.index as number,
+          status: item.status as undefined | number ?? response.status,
+          headers: item.headers as undefined | StandardHeaders ?? {},
+          body: item.body,
+        } satisfies BatchResponseBodyItem
       }
     }
     finally {