Add matching rust implementation for Go HashMessage.

src/bin/mailparse.rs

@@ -1,12 +1,6 @@
-use std::env;
-use std::error::Error;
-use std::fs::File;
-use std::io::prelude::*;
-use std::process::exit;
-use std::slice::Iter;
+use std::{env, error::Error, fs::File, io::prelude::*, process::exit, slice::Iter};
 
-use mailparse::dateparse;
-use mailparse::MailHeaderMap;
+use mailparse::{dateparse, MailHeaderMap};
 
 fn newline(b: &u8) -> bool {
     *b == b'\n'
@@ -57,15 +51,15 @@ fn parse_mbox(mbox_bytes: &Vec<u8>) -> Result<(), Box<dyn Error>> {
         let mail = mailparse::parse_mail(mail_bytes).unwrap();
         println!(
             "{:?} {:?} from {:?}",
-            match mail.headers.get_first_value("Date")? {
+            match mail.headers.get_first_value("Date") {
                 Some(date) => date,
                 None => "NO DATE".to_string(),
             },
-            match mail.headers.get_first_value("Subject")? {
+            match mail.headers.get_first_value("Subject") {
                 Some(subject) => subject,
                 None => "NO SUBJECT".to_string(),
             },
-            match mail.headers.get_first_value("From")? {
+            match mail.headers.get_first_value("From") {
                 Some(from) => from,
                 None => "NO FROM".to_string(),
             },