read_u24_be.rs

use std::fmt;
use std::error::Error;

type Buffer = Vec<u8>;

pub trait ReadU24BE {
    fn read_u24_be(&self, pos: usize) -> Result<u32, OutOfRangeError>;
}

impl ReadU24BE for Buffer {
    fn read_u24_be(&self, offset: usize) -> Result<u32, OutOfRangeError> {
        let len = self.len();
        if len - offset < 3 {
            return Err(OutOfRangeError::new(len - 3, offset));
        }
        let mut sum: u32 = 0;
        sum |= u32::from(self[offset+0]) << 16;
        sum |= u32::from(self[offset+1]) <<  8;
        sum |= u32::from(self[offset+2]) <<  0;
        Ok(sum)
    }
}

#[derive(Debug)]
pub struct OutOfRangeError {
    max: usize,
    received: usize,
}

impl OutOfRangeError {
    pub fn new(max: usize, received: usize) -> Self {
        Self { max, received }
    }
}

impl fmt::Display for OutOfRangeError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "The offset is out of range. It must be <= {}. Received {}", self.max, self.received)
    }
}

impl Error for OutOfRangeError {}