fix(use/fastify): Include middleware headers

Closes #91

src/use/fastify.ts

@@ -63,8 +63,8 @@ export function createHandler<Context extends OperationContext = undefined>(
       url: req.url,
       headers: {
         get(key) {
-          const header = req.headers[key];
-          return Array.isArray(header) ? header.join('\n') : header;
+          const header = reply.getHeader(key) ?? req.headers[key];
+          return Array.isArray(header) ? header.join('\n') : String(header);
         },
       },
       body: () =>
@@ -87,7 +87,16 @@ export function createHandler<Context extends OperationContext = undefined>(
       context: { reply },
     });
 
-    reply.raw.writeHead(init.status, init.statusText, init.headers);
+    const middlewareHeaders: Record<string, string> = {};
+    for (const [key, val] of Object.entries(reply.getHeaders())) {
+      middlewareHeaders[key] = Array.isArray(val)
+        ? val.join('\n')
+        : String(val);
+    }
+    reply.raw.writeHead(init.status, init.statusText, {
+      ...middlewareHeaders,
+      ...init.headers,
+    });
 
     if (!body || typeof body === 'string') {
       return new Promise<void>((resolve) =>

tests/use.test.ts

@@ -177,3 +177,38 @@ data: {"data":{"ping":"pong"}}
     // nothing should explode
   },
 );
+
+it("should include middleware headers with 'fastify' handler", async () => {
+  const fastify = Fastify();
+
+  fastify.addHook('onRequest', (_, reply, done) => {
+    reply.header('x-custom', 'cust');
+    done();
+  });
+  fastify.all(
+    '/',
+    createFastifyHandler({
+      schema,
+      onConnect(req) {
+        expect(req.headers.get('x-custom')).toBe('cust');
+      },
+    }),
+  );
+
+  const url = await fastify.listen({ port: 0 });
+  makeDisposeForServer(fastify.server);
+
+  const res = await fetch(url, {
+    method: 'POST',
+    headers: {
+      accept: 'text/event-stream',
+      'content-type': 'application/json',
+    },
+    body: JSON.stringify({
+      query: '{ getValue }',
+    }),
+  });
+
+  expect(res.ok).toBeTruthy();
+  expect(res.headers.get('x-custom')).toBe('cust');
+});