Summary

cc: #1088

This PR enhances H3's validation capabilities with comprehensive type-safe validation for routes and handlers:

• Route params validation: Added support for validating route parameters (e.g., /users/:id) with full type inference
• Response validation: Server-side response validation to ensure handlers return correctly shaped data
• Enhanced defineValidatedHandler: Now supports params and response schemas in addition to existing body, headers, and query validation
• Enhanced defineRoute: Full type-safe validation with proper TypeScript overloads for better DX
• New utilities: Exported syncValidate for synchronous validation and validateResponse for response validation
• Comprehensive tests: Added full test coverage including integration tests demonstrating complete validation workflows

Key Features

1. Params Validation

const handler = defineValidatedHandler({
  validate: {
    params: z.object({ id: z.string().uuid() })
  },
  handler: (event) => {
    // event.context.params is typed as { id: string }
    const id = event.context.params.id;
    return { userId: id };
  }
});

2. Response Validation

const route = defineRoute({
  method: 'POST',
  route: '/api/users',
  validate: {
    response: z.object({ id: z.string(), name: z.string() })
  },
  handler: async (event) => {
    // Return type is validated and type-checked
    return { id: '123', name: 'John' };
  }
});

3. Complete Validation

defineRoute({
  method: 'POST',
  route: '/api/users/:id',
  validate: {
    params: z.object({ id: z.string().uuid() }),
    query: z.object({ include: z.string().optional() }),
    body: z.object({ name: z.string(), email: z.string().email() }),
    response: z.object({ id: z.string(), name: z.string(), email: z.string() })
  },
  handler: async (event) => {
    // All types are inferred: params, query, body, and return type
    const { id } = event.context.params;
    const body = await event.req.json();
    return { id, name: body.name, email: body.email };
  }
});

Test Plan

• Unit tests for params validation in defineValidatedHandler
• Unit tests for response validation in defineValidatedHandler
• Integration tests for defineRoute with all validation schemas
• Error handling tests for invalid params, query, body, headers, and response
• Type inference tests demonstrating full type safety
• Existing tests continue to pass

🤖 Generated with Claude Code