Crafting Custom Errors in Go

In Go, errors are a fundamental part of handling unexpected situations. While Go provides built-in error types, creating custom error types allows for more structured and informative error handling. This challenge will guide you in defining and using your own custom error types to represent specific failure scenarios in a program.

Problem Description

Your task is to implement a simple user registration system that validates user input. You need to define custom error types to clearly indicate different validation failures. Specifically, you will create two custom error types:

1. InvalidEmailError: To be returned when an email address is not in a valid format.
2. PasswordTooShortError: To be returned when a password is shorter than the minimum required length.

You will then implement a RegisterUser function that takes a username, email, and password. This function should perform the following validations:

• The email must contain an "@" symbol.
• The password must be at least 8 characters long.

If any validation fails, the function should return the appropriate custom error. If all validations pass, it should return nil for the error.

Key Requirements

• Define a custom error type InvalidEmailError that implements the error interface.
• Define a custom error type PasswordTooShortError that implements the error interface.
• Implement the RegisterUser function which takes username, email, and password (all strings).
• The RegisterUser function should return an error.
• Inside RegisterUser, check for email validity (presence of "@"). If invalid, return InvalidEmailError.
• Inside RegisterUser, check for password length (minimum 8 characters). If too short, return PasswordTooShortError.
• If both validations pass, RegisterUser should return nil.

Expected Behavior

When RegisterUser is called with invalid input, it should return the corresponding custom error. When called with valid input, it should return nil. The caller of RegisterUser should be able to distinguish between the different custom errors using type assertions.

Important Edge Cases

• Empty strings for email and password.
• Emails with multiple "@" symbols (though for this challenge, just the presence of one is sufficient).

Examples

Example 1:

Input:
username: "john_doe"
email: "john.doe@example.com"
password: "securepassword123"

Output:
nil
Explanation: The email is valid (contains "@") and the password is long enough (17 characters > 8).

Example 2:

Input:
username: "jane_doe"
email: "janedoeexample.com"
password: "short"

Output:
InvalidEmailError
Explanation: The email "janedoeexample.com" is missing the "@" symbol, triggering an `InvalidEmailError`.

Example 3:

Input:
username: "peter_pan"
email: "peter@neverland.com"
password: "weak"

Output:
PasswordTooShortError
Explanation: The email "peter@neverland.com" is valid, but the password "weak" is only 4 characters long, which is less than the required 8, triggering a `PasswordTooShortError`.

Example 4:

Input:
username: "alice"
email: ""
password: ""

Output:
InvalidEmailError
Explanation: An empty email string does not contain "@", triggering an `InvalidEmailError`. The password is also too short, but the email validation fails first.

Constraints

• Input strings for username, email, and password will not be nil.
• The minimum password length is strictly 8 characters.
• The focus of this challenge is on error definition and handling, not on complex email or password pattern matching.

Notes

• Remember to define your custom error types as structs.
• Implement the Error() method for each custom error type to satisfy the error interface. This method should return a descriptive string.
• When handling errors returned by RegisterUser, you can use type assertions (e.g., if err, ok := err.(InvalidEmailError); ok { ... }) to check for specific custom error types.
• Consider how your custom error messages can provide useful context to the user or developer.