Respect Accept headers in a more strict way

.changeset/more-accept-headers.md

@@ -0,0 +1,5 @@
+---
+'graphql-yoga': major
+---
+
+Now it is possible to decide the returned `Content-Type` by specifying the `Accept` header. So if `Accept` header has `text/event-stream` without `application/json`, Yoga respects that returns `text/event-stream` instead of `application/json`.

e2e/utils.ts

@@ -111,7 +111,7 @@ export async function assertQuery(
   const response = await fetch(endpoint, {
     method: 'POST',
     headers: {
-      accept: 'applications/json',
+      accept: 'application/json',
       'content-type': 'application/json',
     },
     body: JSON.stringify({

packages/graphql-yoga/__tests__/node.spec.ts

@@ -621,6 +621,7 @@ describe('Incremental Delivery', () => {
       body: formData,
     })
 
+    expect(response.status).toBe(200)
     const body = await response.json()
 
     expect(body.errors).toBeUndefined()
@@ -1481,3 +1482,58 @@ describe('404 Handling', () => {
     expect(body).toEqual('Do you really like em?')
   })
 })
+
+describe('Respect Accept headers', () => {
+  const yoga = createYoga({
+    schema,
+  })
+  const server = createServer(yoga)
+  let port: number
+  let url: string
+  beforeAll((done) => {
+    port = Math.floor(Math.random() * 100) + 4000
+    url = `http://localhost:${port}/graphql`
+    server.listen(port, done)
+  })
+  afterAll(() => {
+    server.close()
+  })
+  it('should force the server return event stream even if the result is not', async () => {
+    const response = await fetch(`${url}?query=query{ping}`, {
+      headers: {
+        Accept: 'text/event-stream',
+      },
+    })
+    expect(response.headers.get('content-type')).toEqual('text/event-stream')
+    const iterator = response.body![Symbol.asyncIterator]()
+    const { value } = await iterator.next()
+    const valueStr = Buffer.from(value).toString('utf-8')
+    expect(valueStr).toContain(
+      `data: ${JSON.stringify({ data: { ping: 'pong' } })}`,
+    )
+  })
+  it('should force the server return multipart even if the result is not', async () => {
+    const response = await fetch(`${url}?query=query{ping}`, {
+      headers: {
+        Accept: 'multipart/mixed',
+      },
+    })
+    expect(response.headers.get('content-type')).toEqual(
+      'multipart/mixed; boundary="-"',
+    )
+    const iterator = response.body![Symbol.asyncIterator]()
+    const { value } = await iterator.next()
+    const valueStr = Buffer.from(value).toString('utf-8')
+    expect(valueStr).toContain(`Content-Type: application/json; charset=utf-8`)
+    expect(valueStr).toContain(`Content-Length: 24`)
+    expect(valueStr).toContain(`${JSON.stringify({ data: { ping: 'pong' } })}`)
+  })
+  it('should not allow to return if the result is an async iterable and accept is just json', async () => {
+    const response = await fetch(`${url}?query=subscription{counter}`, {
+      headers: {
+        Accept: 'application/json',
+      },
+    })
+    expect(response.status).toEqual(406)
+  })
+})

packages/graphql-yoga/src/plugins/resultProcessor/multipart.ts

@@ -1,20 +1,15 @@
 import { isAsyncIterable } from '@envelop/core'
 import { ExecutionResult } from 'graphql'
-import { ExecutionPatchResult, FetchAPI } from '../../types.js'
+import { FetchAPI } from '../../types.js'
 import { ResultProcessorInput } from '../types.js'
 
-export function isMultipartResult(
-  request: Request,
-  result: ResultProcessorInput,
-): result is AsyncIterable<ExecutionPatchResult> {
-  return (
-    isAsyncIterable(result) &&
-    !!request.headers.get('accept')?.includes('multipart/mixed')
-  )
+export function isMultipartResult(request: Request): boolean {
+  // There should be an explicit accept header for this result type
+  return !!request.headers.get('accept')?.includes('multipart/mixed')
 }
 
 export function processMultipartResult(
-  executionPatchResultIterable: AsyncIterable<ExecutionPatchResult>,
+  result: ResultProcessorInput,
   fetchAPI: FetchAPI,
 ): Response {
   const headersInit: HeadersInit = {
@@ -33,7 +28,20 @@ export function processMultipartResult(
 
   const readableStream = new fetchAPI.ReadableStream({
     start(controller) {
-      iterator = executionPatchResultIterable[Symbol.asyncIterator]()
+      if (isAsyncIterable(result)) {
+        iterator = result[Symbol.asyncIterator]()
+      } else {
+        let finished = false
+        iterator = {
+          next: () => {
+            if (finished) {
+              return Promise.resolve({ done: true, value: null })
+            }
+            finished = true
+            return Promise.resolve({ done: false, value: result })
+          },
+        }
+      }
       controller.enqueue(textEncoder.encode(`---`))
     },
     async pull(controller) {

packages/graphql-yoga/src/plugins/resultProcessor/push.ts

@@ -3,18 +3,13 @@ import { ExecutionResult } from 'graphql'
 import { FetchAPI } from '../../types.js'
 import { ResultProcessorInput } from '../types.js'
 
-export function isPushResult(
-  request: Request,
-  result: ResultProcessorInput,
-): result is AsyncIterable<ExecutionResult> {
-  return (
-    isAsyncIterable(result) &&
-    !!request.headers.get('accept')?.includes('text/event-stream')
-  )
+export function isPushResult(request: Request): boolean {
+  // There should be an explicit accept header for this result type
+  return !!request.headers.get('accept')?.includes('text/event-stream')
 }
 
 export function processPushResult(
-  result: AsyncIterable<ExecutionResult>,
+  result: ResultProcessorInput,
   fetchAPI: FetchAPI,
 ): Response {
   const headersInit: HeadersInit = {
@@ -33,7 +28,20 @@ export function processPushResult(
   const textEncoder = new fetchAPI.TextEncoder()
   const readableStream = new fetchAPI.ReadableStream({
     start() {
-      iterator = result[Symbol.asyncIterator]()
+      if (isAsyncIterable(result)) {
+        iterator = result[Symbol.asyncIterator]()
+      } else {
+        let finished = false
+        iterator = {
+          next: () => {
+            if (finished) {
+              return Promise.resolve({ done: true, value: null })
+            }
+            finished = true
+            return Promise.resolve({ done: false, value: result })
+          },
+        }
+      }
     },
     async pull(controller) {
       const { done, value } = await iterator.next()

packages/graphql-yoga/src/plugins/resultProcessor/regular.ts

@@ -1,24 +1,45 @@
 import { isAsyncIterable } from '@graphql-tools/utils'
-import { ExecutionResult } from 'graphql'
 import { FetchAPI } from '../../types.js'
 import { ResultProcessorInput } from '../types.js'
 
+const acceptHeaderByResult = new WeakMap<ResultProcessorInput, string>()
+
 export function isRegularResult(
   request: Request,
   result: ResultProcessorInput,
-): result is ExecutionResult {
-  return !isAsyncIterable(result)
+): boolean {
+  if (!isAsyncIterable(result)) {
+    const acceptHeader = request.headers.get('accept')
+    if (acceptHeader && !acceptHeader.includes('*/*')) {
+      if (acceptHeader.includes('application/json')) {
+        acceptHeaderByResult.set(result, 'application/json')
+        return true
+      }
+      if (acceptHeader.includes('application/graphql+json')) {
+        acceptHeaderByResult.set(result, 'application/graphql+json')
+        return true
+      }
+      // If there is an accept header but this processer doesn't support, reject
+      return false
+    }
+    // If there is no header, assume it's a regular result per spec
+    acceptHeaderByResult.set(result, 'application/json')
+    return true
+  }
+  // If it is not an async iterable, it's not a regular result
+  return false
 }
 
 export function processRegularResult(
-  executionResult: ExecutionResult,
+  executionResult: ResultProcessorInput,
   fetchAPI: FetchAPI,
 ): Response {
   const textEncoder = new fetchAPI.TextEncoder()
   const responseBody = JSON.stringify(executionResult)
   const decodedString = textEncoder.encode(responseBody)
+  const contentType = acceptHeaderByResult.get(executionResult)
   const headersInit: HeadersInit = {
-    'Content-Type': 'application/json',
+    'Content-Type': contentType || 'application/json',
     'Content-Length': decodedString.byteLength.toString(),
   }
   const responseInit: ResponseInit = {

packages/graphql-yoga/src/plugins/types.ts

@@ -70,21 +70,21 @@ export type OnResultProcess = (
   payload: OnResultProcessEventPayload,
 ) => PromiseOrValue<void>
 
-export type ResultProcessorInput = PromiseOrValue<
-  ExecutionResult | AsyncIterable<ExecutionResult | ExecutionPatchResult>
->
+export type ResultProcessorInput =
+  | ExecutionResult
+  | AsyncIterable<ExecutionResult>
+  | AsyncIterable<ExecutionPatchResult>
 
-export type ResultProcessor<
-  TResult extends ResultProcessorInput = ResultProcessorInput,
-> = (result: TResult, fetchAPI: FetchAPI) => PromiseOrValue<Response>
+export type ResultProcessor = (
+  result: ResultProcessorInput,
+  fetchAPI: FetchAPI,
+) => PromiseOrValue<Response>
 
 export interface OnResultProcessEventPayload {
   request: Request
   result: ResultProcessorInput
   resultProcessor?: ResultProcessor
-  setResultProcessor<TResult extends ResultProcessorInput>(
-    resultProcessor: ResultProcessor<TResult>,
-  ): void
+  setResultProcessor(resultProcessor: ResultProcessor): void
 }
 
 export type OnResponseHook<TServerContext> = (

packages/graphql-yoga/src/plugins/useResultProcessor.ts

@@ -1,15 +1,13 @@
 import { Plugin, ResultProcessor, ResultProcessorInput } from './types.js'
 
-export interface ResultProcessorPluginOptions<
-  TResult extends ResultProcessorInput,
-> {
-  processResult: ResultProcessor<TResult>
-  match?(request: Request, result: ResultProcessorInput): result is TResult
+export interface ResultProcessorPluginOptions {
+  processResult: ResultProcessor
+  match?(request: Request, result: ResultProcessorInput): boolean
 }
 
-export function useResultProcessor<
-  TResult extends ResultProcessorInput = ResultProcessorInput,
->(options: ResultProcessorPluginOptions<TResult>): Plugin {
+export function useResultProcessor(
+  options: ResultProcessorPluginOptions,
+): Plugin {
   const matchFn = options.match || (() => true)
   return {
     onResultProcess({ request, result, setResultProcessor }) {

packages/graphql-yoga/src/processRequest.ts

@@ -21,7 +21,7 @@ export async function processResult({
    */
   onResultProcessHooks: OnResultProcess[]
 }) {
-  let resultProcessor: ResultProcessor<any> | undefined
+  let resultProcessor: ResultProcessor | undefined
 
   for (const onResultProcessHook of onResultProcessHooks) {
     await onResultProcessHook({
@@ -79,7 +79,5 @@ export async function processRequest<TContext>({
       : enveloped.execute
 
   // Get the result to be processed
-  const result = await executeFn(executionArgs)
-
-  return result
+  return executeFn(executionArgs)
 }

packages/graphql-yoga/src/server.ts

@@ -387,16 +387,16 @@ export class YogaServer<
       }),
       // Middlewares after the GraphQL execution
       useResultProcessor({
-        match: isRegularResult,
-        processResult: processRegularResult,
+        match: isMultipartResult,
+        processResult: processMultipartResult,
       }),
       useResultProcessor({
         match: isPushResult,
         processResult: processPushResult,
       }),
       useResultProcessor({
-        match: isMultipartResult,
-        processResult: processMultipartResult,
+        match: isRegularResult,
+        processResult: processRegularResult,
       }),
       ...(options?.plugins ?? []),