send bad request if Accept value doesn't include type/html with `grap…

…hiql: true`

examples/oak.ts

@@ -11,20 +11,22 @@ const typeDefs = gql`
 
 const resolvers = {
   Query: {
-    hello: () => `Hello World!`
+    hello: (_root: any, _args: any, ctx: { request: ServerRequest }) => {
+      return `Hello World! from ${ctx.request.url}`
+    }
   }
 }
 
 const schema = makeExecutableSchema({ resolvers, typeDefs })
 
 const app = new Application()
 
-app.use((ctx) =>
-  GraphQLHTTP<ServerRequest>({
+app.use(async (ctx) => {
+  return await GraphQLHTTP<ServerRequest>({
     schema,
     graphiql: true
   })(ctx.request.originalRequest as ServerRequest)
-)
+})
 
 console.log(`☁  Started on http://localhost:3000`)
 

http.ts

@@ -19,16 +19,23 @@ export function GraphQLHTTP<Req extends Request = Request, Ctx extends { request
   options: GraphQLOptions<Ctx, Req>
 ) {
   return async (request: Req) => {
-    if (options.graphiql && request.method === 'GET' && request.headers.get('Accept')?.includes('text/html')) {
-      const { renderPlaygroundPage } = await import('./graphiql/render.ts')
-      const playground = renderPlaygroundPage({ endpoint: '/graphql' })
+    if (options.graphiql && request.method === 'GET') {
+      if (request.headers.get('Accept')?.includes('text/html')) {
+        const { renderPlaygroundPage } = await import('./graphiql/render.ts')
+        const playground = renderPlaygroundPage({ endpoint: '/graphql' })
 
-      await request.respond({
-        headers: new Headers({
-          'Content-Type': 'text/html'
-        }),
-        body: playground
-      })
+        await request.respond({
+          headers: new Headers({
+            'Content-Type': 'text/html'
+          }),
+          body: playground
+        })
+      } else {
+        request.respond({
+          status: 400,
+          body: '"Accept" header value must include text/html'
+        })
+      }
     } else {
       if (!['PUT', 'POST', 'PATCH'].includes(request.method)) {
         return await request.respond({