mail_header_imp.rs

use std::collections::HashMap;
use std::fs::File;
use std::io::{BufRead, BufReader, Result};

type MailHeader = HashMap<String, Vec<String>>;

fn proc_folding_line(line: String, prev_fname: &String, mail_header: &mut MailHeader) {
    if prev_fname == "" {
        eprintln!("prev-key error: line: {}", line);
    }
    else {
        match mail_header.get_mut(prev_fname) {
            Some(v) => match v.last_mut() {
                Some(last) => *last = format!("{} {}", last, line.trim_start()),
                None => eprintln!("vec error: prev_fname: {}, line: {}", prev_fname, line),
            },
            None => eprintln!("key error: prev_fname: {}, line: {}", prev_fname, line),
        }
    }
}

fn proc_header_line(line: String, mail_header: &mut MailHeader) -> String {
    let kv: Vec<&str> = line.splitn(2, ':').collect();

    let fname = kv[0].to_lowercase().to_string();
    let fvalue = kv[1].trim_start().to_string();

    match mail_header.get_mut(&fname) {
        Some(v) => v.push(fvalue),
        None => {
            mail_header.insert(fname.clone(), vec![fvalue]);
        },
    }

    fname
}

fn main() {
    let mut mail_header: MailHeader = HashMap::new();
    let file = File::open("data.txt").expect("IO error");
    let mut prev_fname = String::from("");

    for line in BufReader::new(file).lines().filter_map(Result::ok) {
        if line == "" { // \r\n\r\n
            break;
        }

        if line.starts_with(' ') || line.starts_with('\t') {
            proc_folding_line(line, &prev_fname, &mut mail_header);
        }
        else {
            prev_fname = proc_header_line(line, &mut mail_header);
        }
    }

    //println!("{:?}", mail_header);
    for (fname, fvalue) in mail_header {
        println!("{}: {:?}", fname, fvalue);
    }
}