Global Error Handler

Creating a .NET 𝗴𝗹𝗼𝗯𝗮𝗹 𝗲𝗿𝗿𝗼𝗿 𝗵𝗮𝗻𝗱𝗹𝗲r to catch unhandled exceptions that occur anywhere in an application.

Before .NET 8 you had to implement custom middleware to do this, but starting with ASP.NET Core 8 there’s a new IExceptionHandler interface that makes this much easier.

The idea behind is to map exceptions to the correct HTTP status code and log the appropriate exception details.

Problem details

Let's apply the standard error responses RFC 7807 that defines a common format for HTTP APIs to communicate errors. By using that standard, API consumers will get a much more useful response.

Technically speaking:

• AddProblemDetails() registers the Problem Details middleware. This middleware is responsible for handling exceptions and generating standardized problem details responses.
• UseStatusCodePages() integrates middleware into the request pipeline that generates Problem Details responses for common HTTP status codes. This middleware intercepts responses with certain status codes (like 404, 500) and returns a structured error response with details about the error.
• UseExceptionHandler() adds middleware that catches unhandled exceptions during request processing. When an unhandled exception occurs, this middleware generates a Problem Details response, detailing the error in a structured format without exposing internal server details.

Global exception handler

Instead of adding a try/catch block to each endpoint, which would result in a lot of duplicated code, we can create a global exception handler. This handler will:

• Catch all unhandled exceptions and return a problem details response.
• Map each exception to the appropriate problem details response.
• Log the exception details to our logging provider.

The new IExceptionHandler interface available with .NET 8, implementing this global exception handler is straightforward.

Here is an example of the returned result by using the GlobalExceptionHandler:

//500 internal server error
{
    "type": "https://tools.ietf.org/html/rfc9110#section-15.6.1",
    "title": "Internal Error Server: We are on it!",
    "status": 500,
    "detail": "The database connection is closed!"
}

//400 bad request
{
    "type": "https://tools.ietf.org/html/rfc9110#section-15.5.1",
    "title": "Bad request",
    "status": 400,
    "detail": "The id must be greater than 0! (Parameter 'id')"
}