Shitty grep implementation

grep.rs

use std::env;
use std::fs;
use std::io;
use std::path::Path;
use std::str;

fn main() -> io::Result<()> {
    let args: Vec<String> = env::args().collect();
    let pattern = &args[1];
    let path = &args[2];

    grep(Path::new(&path), pattern)?;
    Ok(())
}

pub fn grep(dir: &Path, pattern: &str) -> Result<(), io::Error> {
    if !dir.is_dir() {
        return Ok(());
    }

    let entries = fs::read_dir(dir)?;
    for entry in entries {
        let entry = entry?;
        let path = entry.path();

        match path.file_name() {
            Some(filename) => {
                let contents = fs::read_to_string(&path)?;
                println!("got the contents");

                let filename = filename.to_str().expect("invalid filename");
                if let Some(index) = contents.find(pattern) {
                    print_match(filename, &contents.as_bytes(), pattern, index);
                }
            }
            None => {
                grep(&path, pattern)?;
            }
        }
    }

    Ok(())
}

const NEWLINE_BYTE: u8 = 0xA;

fn print_match<'a>(filename: &str, contents: &[u8], _pattern: &str, index: usize) {
    let mut line_start = 0;
    let mut current = index;
    while current > 0 {
        current -= 1;
        if contents[current] == NEWLINE_BYTE {
            line_start = current;
            break;
        }
    }

    let mut line_end = contents.len();
    current = index;
    while current < contents.len() {
        current += 1;
        if contents[current] == NEWLINE_BYTE {
            line_end = current;
            break;
        }
    }

    if let Ok(line) = String::from_utf8(contents[line_start..line_end].to_vec()) {
        println!("{}:{}", filename, line);
    }
}