Environment Variable Configuration in Rust

This challenge focuses on reading and utilizing environment variables within a Rust program. Environment variables are a common way to configure applications without modifying the code itself, allowing for flexibility across different deployments. Your task is to create a Rust program that reads specific environment variables and uses their values to configure its behavior.

Problem Description

You need to write a Rust program that reads three environment variables: API_KEY, LOG_LEVEL, and PORT. The program should then print these values to the console in a formatted way. If any of the environment variables are not set, the program should print a helpful error message indicating which variable is missing and exit with a non-zero exit code. The LOG_LEVEL variable should be treated as an enum, with possible values "DEBUG", "INFO", and "ERROR". If the LOG_LEVEL is not one of these values, print an error and exit. The PORT variable should be parsed as an unsigned 16-bit integer. If parsing fails, print an error and exit.

Key Requirements:

• Error Handling: Gracefully handle missing environment variables and invalid LOG_LEVEL values.
• Type Safety: Parse the PORT variable as an u16.
• Formatted Output: Print the retrieved values in a clear and readable format.
• Exit Codes: Use a non-zero exit code (e.g., 1) to indicate an error.
• Enum Usage: Use an enum to represent the LOG_LEVEL.

Expected Behavior:

1. The program should attempt to read the API_KEY, LOG_LEVEL, and PORT environment variables.
2. If all variables are found and valid, the program should print a message like: "API Key: <value>, Log Level: <value>, Port: <value>".
3. If any variable is missing, the program should print an error message like: "Error: Missing environment variable API_KEY" and exit with code 1.
4. If the LOG_LEVEL is invalid, the program should print an error message like: "Error: Invalid log level. Must be DEBUG, INFO, or ERROR" and exit with code 1.
5. If the PORT cannot be parsed as a u16, the program should print an error message like: "Error: Invalid port number" and exit with code 1.

Examples

Example 1:

Input:
API_KEY=my_secret_key
LOG_LEVEL=INFO
PORT=8080

Output:

API Key: my_secret_key, Log Level: INFO, Port: 8080

Explanation: All environment variables are set correctly.

Example 2:

Input:
LOG_LEVEL=DEBUG
PORT=8080

Output:

Error: Missing environment variable API_KEY

Explanation: The API_KEY environment variable is not set.

Example 3:

Input:
API_KEY=my_secret_key
LOG_LEVEL=WARNING
PORT=8080

Output:

Error: Invalid log level. Must be DEBUG, INFO, or ERROR

Explanation: The LOG_LEVEL is not a valid value.

Example 4:

Input:
API_KEY=my_secret_key
LOG_LEVEL=INFO
PORT=abc

Output:

Error: Invalid port number

Explanation: The PORT cannot be parsed as a u16.

Constraints

• The program must compile and run without external dependencies beyond the Rust standard library.
• The program should handle potential errors gracefully and provide informative error messages.
• The PORT must be parsed as an u16.
• The LOG_LEVEL must be one of the following values: "DEBUG", "INFO", or "ERROR".
• The program should exit with a non-zero exit code (1) upon encountering an error.

Notes

• Consider using the std::env module to access environment variables.
• Use Result to handle potential errors during parsing and variable retrieval.
• An enum is a good way to represent the different possible values for LOG_LEVEL.
• Remember to handle the unwrap() or expect() calls carefully to avoid panics. Use match or if let for safer error handling.
• Think about how to best format the output for readability.