Error Propagation in File Handling

Error propagation is a core concept in Rust that allows you to handle errors in a clean and structured way. Instead of having to handle each error manually on every step, you can easily use the ? operator to propagate errors to a higher level so that they can be handled in a single place.

In this challenge, you’ll use io::Error to represent potential issues when working with file I/O. This approach leverages Rust’s standard library for concise and idiomatic error handling.

Your Task

Your task is to implement a function that reads integers from a file, computes their sum, and gracefully propagates any errors using the ? operator.

Implement the function sum_integers_from_file:

  • Takes the file path as a parameter.
  • Reads the file line by line, assuming each line contains a single integer or invalid data.
  • Computes and returns the sum of all integers as a Result<i32, io::Error>.
  • Handles the following:
    • If the file cannot be opened, propagate the io::Error.
    • If a line cannot be parsed as an integer, propagate a custom io::Error with a meaningful message.

Requirements
  1. Handle errors cleanly and propagate them using the ? operator.
  2. For invalid lines, create an io::Error with io::ErrorKind::InvalidData.

Hints

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

Click here to reveal hints
  • Use std::fs::File::open to open a file.
  • Use io::BufReader::new to read lines from the file.
  • Convert strings to integers with the str::parse method.
  • The io::Error::new function can create custom errors.
  • To create the error type we want for invalid numbers, you can do the following: 
    let error = io::Error::new(io::ErrorKind::InvalidData, "Invalid number");
  • To propagate an error, use the ? operator. e.g. 
    let file = File::open(file_path)?;
  • You can transform an error type to another error type by using the map_err method. e.g. 
    let num = num_str.parse::<i32>().map_err(|_| io::Error::new(io::ErrorKind::InvalidData, "Invalid number"))?;