Update serialization logic (#226)

Author: samchungy

README.md

@@ -223,6 +223,16 @@ const customSerializerCompiler = createSerializerCompiler({
 });
 ```
 
+By default, this library assumes that if a response schema provided is not a Zod Schema, it is a JSON Schema and will naively pass it straight into `fast-json-stringify`. This will not work in conjunction with Fastify's schema registration.
+
+If you have other routes with response schemas which are not Zod Schemas, you can supply a `fallbackSerializer` to `createSerializerCompiler`.
+
+```ts
+const customSerializerCompiler = createSerializerCompiler({
+  fallbackSerializer: ({ schema, url, method }) => customSerializer(schema),
+});
+```
+
 Please note: the `responses`, `parameters` components do not appear to be supported by the `@fastify/swagger` library.
 
 ### Create Document Options

package.json

@@ -61,6 +61,7 @@
     "@crackle/cli": "0.15.5",
     "@fastify/swagger": "9.4.2",
     "@fastify/swagger-ui": "5.2.1",
+    "@fastify/under-pressure": "9.0.3",
     "@types/node": "22.10.7",
     "eslint-plugin-zod-openapi": "1.0.0",
     "fastify": "5.2.1",

pnpm-lock.yaml

@@ -1,4 +1,6 @@
 import 'zod-openapi/extend';
+
+import UnderPressure from '@fastify/under-pressure';
 import fastify from 'fastify';
 import { z } from 'zod';
 import type { ZodOpenApiResponsesObject } from 'zod-openapi';
@@ -74,6 +76,72 @@ describe('serializerCompiler', () => {
     expect(result.json()).toEqual({ jobId: '60002023' });
   });
 
+  it('should handle a route with a JSON schema', async () => {
+    const app = fastify();
+
+    app.setSerializerCompiler(serializerCompiler);
+    app.post(
+      '/',
+      {
+        schema: {
+          response: {
+            200: {
+              type: 'object',
+              properties: {
+                jobId: { type: 'string' },
+              },
+            },
+          },
+        },
+      },
+      async (_req, res) =>
+        res.send({
+          jobId: '60002023',
+        }),
+    );
+
+    await app.ready();
+
+    const result = await app.inject().post('/');
+
+    expect(result.json()).toEqual({ jobId: '60002023' });
+  });
+
+  it('should work with under pressure', async () => {
+    const app = fastify();
+
+    app.register(UnderPressure, {
+      exposeStatusRoute: '/status/health-check',
+      healthCheck: () => Promise.resolve(true),
+    });
+    app.setSerializerCompiler(serializerCompiler);
+    app.post(
+      '/',
+      {
+        schema: {
+          response: {
+            200: {
+              type: 'object',
+              properties: {
+                jobId: { type: 'string' },
+              },
+            },
+          },
+        },
+      },
+      async (_req, res) =>
+        res.send({
+          jobId: '60002023',
+        }),
+    );
+
+    await app.ready();
+
+    const result = await app.inject().get('/status/health-check');
+
+    expect(result.json()).toEqual({ status: 'ok' });
+  });
+
   it('should fail an invalid response', async () => {
     const app = fastify();
 

src/serializerCompiler.test.ts

@@ -6,16 +6,25 @@ import type { FastifySerializerCompiler } from 'fastify/types/schema';
 import type { ZodType, ZodTypeAny } from 'zod';
 import { createSchema } from 'zod-openapi';
 
+import { isZodType } from './transformer';
 import { ResponseSerializationError } from './validationError';
 
 export interface SerializerOptions {
   components?: Record<string, ZodTypeAny>;
   stringify?: (value: unknown) => string;
+  fallbackSerializer?: FastifySerializerCompiler<ZodType>;
 }
 
 export const createSerializerCompiler =
   (opts?: SerializerOptions): FastifySerializerCompiler<ZodType> =>
-  ({ schema, method, url }) => {
+  (routeSchema) => {
+    const { schema, url, method } = routeSchema;
+    if (!isZodType(schema)) {
+      return opts?.fallbackSerializer
+        ? opts.fallbackSerializer(routeSchema)
+        : fastJsonStringify(schema);
+    }
+
     let stringify = opts?.stringify;
     if (!stringify) {
       const { schema: jsonSchema, components } = createSchema(schema, {