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What we covered in the previous challenges were recoverable errors, meaning they can be handled during runtime. However, in Rust we have unrecoverable errors that are so severe that the program cannot safely continue and it will shut down completely.

You can trigger an unrecoverable error using the panic! macro, for example: panic!("This is an unrecoverable error!").

In this challenge, you will write a function that retrieves the value of an environment variable named DATABASE_URL if the environment variable is not set, you will exit the program using panic!, it makes sense to use panic! instead of Result<T, E> because the program will not be able to run database queries if this value isn't available.

Just to make it more interesting, there is another requirement, your function must validate that the value starts with postgresql://, this is not a full proof validation for real life applications, but we'll keep it simple for this challenge.

Your Task

Write a function, get_database_url, that retrieves the value of the DATABASE_URL environment variable and validates it. The function should behave as follows:

  1. If the DATABASE_URL variable is set and starts with postgresql://, return its value as a String.
  2. If the DATABASE_URL variable is not set, the function should terminate the program by calling panic! with the exact message "DATABASE_URL environment variable is not set.".
  3. If the DATABASE_URL variable is set but does not start with postgresql://, the function should terminate the program by calling panic! with the message "DATABASE_URL must start with 'postgresql://'".

Hints

If you're stuck, here are some hints to help you solve the challenge:

<details> <summary>Click here to reveal hints</summary>
  • Use the std::env::var() function to retrieve the value of an environment variable. e.g. std::env::var("DATABASE_URL").
  • Use the starts_with method to check if a string starts with a specific prefix. e.g. my_string.starts_with("prefix").
</details>
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pub fn get_database_url() -> String {
    // Your code here...
}


/// Example usage
pub fn main() {
    std::env::set_var("DATABASE_URL", "postgresql://localhost");


    let db_url = get_database_url();
    println!("Database URL: {}", db_url);


    std::env::remove_var("DATABASE_URL"); // Missing variable scenario
    get_database_url();


    std::env::set_var("DATABASE_URL", "mysql://localhost"); // Invalid prefix scenario
    get_database_url();
}