error-handling.mdx

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Error Handling with Attributes

The erratt package provides an error type with structured key-value attributes, designed for use with slog and the EventHandler.Warn method.

Creating Errors

// Simple error
err := erratt.New("something went wrong")

// Error with attributes
err := erratt.New("error opening file", "filename", filename)
err := erratt.New("authentication failed", "username", user, "password", pass)

Wrapping Errors

Wrap existing Go errors while preserving attributes:

err := callFunction()
wrapped := erratt.Errorf("unexpected error: %w", err)

Adding Attributes

Chain With() to add context:

err := connectToServer(url, user, pass)
wrapped := erratt.Errorf("cannot connect: %w", err).
    With("url", url, "username", user)

Full Example

func auth() erratt.Error {
    return erratt.New("authentication failure",
        "username", "test-user",
        "password", "test-password",
    )
}

func connect() erratt.Error {
    err := auth()
    if err != nil {
        return erratt.Errorf("connect failed: %w", err).
            With("url", "https://example.com")
    }
    return nil
}

Output via slog:

ERRO connect failed: authentication failure url=https://example.com username=test-user password=test-password

Integration with EventHandler

The Warn method handles erratt.Error values, preserving structured attributes in the log output:

events.Warn(erratt.New("resource skipped", "kind", kind, "name", name))