Getting Started

Repository to demonstrate differences between error handler logic in fastify v3/v4, which was initially reported at https://github.com/fastify/help/issues/695

It contains two exact fastify applications, except for the setErrorHandler-logic in index.js (and a slightly different configuration logic for the fastify startup that is necessary for v4 migration).

The applications offers a testing endpoint GET /tests, that expects the mandatory header property "Client-Locale" (due to route schema configuration).

In fastify v3, the endpoint returns

HTTP/1.1 400 Bad Request
content-type: application/json; charset=utf-8
content-length: 106
Date: Fri, 17 Jun 2022 12:53:29 GMT
Connection: close

{
"statusCode": 400,
"error": "Bad Request",
"message": "headers should have required property 'client-locale'"
}

In fastify v4, the endpoint returns

HTTP/1.1 500 Internal Server Error
content-type: application/json; charset=utf-8
content-length: 82
Date: Fri, 17 Jun 2022 12:55:02 GMT
Connection: close

{
"message": "headers must have required property 'client-locale'",
"statusCode": 500
}

Issue: v4-application should return also with 400 and property "error", as it was before in v3-application.

Update

After more discussions in https://github.com/fastify/help/issues/695, an additional folder v4-2 was added to the repository to test possible solutions by changing the route handler implementation in routes.js

The previous /test-route was split up into two routes:

• GET /tests/option-1 -> async route handler with additional return statement
• GET /tests/option-2 -> route handler without async option and without return statement

Setup

You can install each application separately by switching to their respective folders and executing npm install

Each application can be started with npm run start

# Install v3
cd v3
npm install

# Install v4
cd v4
npm install

# Install v4-2
cd v4-2
npm install

# Run applications
npm run start