fix: use res.send instead of res.json

lib/internals/handler.ts

@@ -137,7 +137,7 @@ async function runMainLayer(
       res.send(returnValue.contents);
     }
   } else {
-    res.json(returnValue ?? null);
+    res.send(returnValue ?? null);
   }
 }
 

test/e2e-buffer.test.ts

@@ -0,0 +1,44 @@
+import 'reflect-metadata';
+import request from 'supertest';
+import { createHandler, Get, SetHeader } from '../lib';
+import { setupServer } from './setupServer';
+
+const nextJsLogo = Buffer.from(
+  'iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAYAAAAf8/9hAAAA6UlEQVQ4ja3TMUpDYRAE4K8wYCM2kljb2IidvU2apE1ErNQcQMFCjRohx/AUXkOPYERvYBUkihKLf5+8BM3LEwe2WXaGf2b35x+xiibaBdWM2Qlc4B0jvBTUCG/oZuQOhmhhYY6XVmJ2iAN4xGUZr4ErPMAn6ljBxhzEdawF5wPG2MaulMPxDHIHrzgJzjgvAHuSt1ss54iLuJECPIrejwKwGd6ecIZTDPCMrdzcrwKwhGvc4R79qRdNCGQhlsV3iAN/W2NPrPFQCq4tHUkRKtgJzn7W7ErnWeaUz6eVa2go/kwNVEtYnY0vxaFKHj8ZCrUAAAAASUVORK5CYII=',
+  'base64'
+);
+
+class TestHandler {
+  @Get()
+  @SetHeader('Content-Type', 'image/png')
+  public image() {
+    return nextJsLogo;
+  }
+}
+
+describe('E2E - Buffer', () => {
+  let server: ReturnType<typeof setupServer>;
+  beforeAll(() => {
+    server = setupServer(createHandler(TestHandler));
+  });
+
+  afterAll(() => {
+    if ('close' in server && typeof server.close === 'function') {
+      server.close();
+    }
+  });
+
+  it('Should return the image with the correct headers.', () =>
+    request(server)
+      .get('/')
+      .expect(200)
+      .then(res =>
+        expect(res).toMatchObject({
+          header: {
+            'content-type': 'image/png',
+            'content-length': nextJsLogo.length.toString()
+          },
+          body: nextJsLogo
+        })
+      ));
+});