Replace parse-hosts crate with 10 lines of code.

This removes 3927 lines of Rust code in 6 crates from the dependency graph:
parse-hosts, multistr, bow, extra-default, len-trait, and push-trait.

One of these crates doesn’t build in today’s Nightly:
rust-lang/rust#46328

components/net/Cargo.toml

@@ -28,7 +28,6 @@ mime_guess = "1.8.0"
 msg = {path = "../msg"}
 net_traits = {path = "../net_traits"}
 openssl = "0.9"
-parse-hosts = "0.5.0"
 profile_traits = {path = "../profile_traits"}
 serde = "1.0"
 serde_json = "1.0"

components/net/hosts.rs

@@ -2,13 +2,12 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use parse_hosts::HostsFile;
 use std::borrow::Cow;
 use std::collections::HashMap;
 use std::env;
 use std::fs::File;
 use std::io::{BufReader, Read};
-use std::net::IpAddr;
+use std::net::{IpAddr, Ipv4Addr};
 use std::sync::Mutex;
 
 lazy_static! {
@@ -32,10 +31,17 @@ pub fn replace_host_table(table: HashMap<String, IpAddr>) {
 }
 
 pub fn parse_hostsfile(hostsfile_content: &str) -> HashMap<String, IpAddr> {
-    HostsFile::read_buffered(hostsfile_content.as_bytes())
-        .pairs()
-        .filter_map(Result::ok)
-        .collect()
+    hostsfile_content.lines().filter_map(|line| {
+        let mut iter = line.split('#').next().unwrap().split_whitespace();
+        Some((iter.next()?.parse().ok()?, iter))
+    }).flat_map(|(ip, hosts)| {
+        hosts.filter(|host| {
+            let invalid = ['\0', '\t', '\n', '\r', ' ', '#', '%', '/', ':', '?', '@', '[', '\\', ']'];
+            host.parse::<Ipv4Addr>().is_err() && !host.contains(&invalid[..])
+        }).map(move |host| {
+            (host.to_owned(), ip)
+        })
+    }).collect()
 }
 
 pub fn replace_host(host: &str) -> Cow<str> {

components/net/lib.rs

@@ -24,7 +24,6 @@ extern crate mime_guess;
 extern crate msg;
 extern crate net_traits;
 extern crate openssl;
-extern crate parse_hosts;
 extern crate profile_traits;
 #[macro_use] extern crate serde;
 extern crate serde_json;