Auto merge of #15783 - ferjm:issue15756-parse-hosts, r=avadacatavra

Replace manual host parsing code with parse-host crate

This patch is replacing the code to parse the hosts file with the [parse-hosts](https://crates.io/crates/parse-hosts) crate. This crate has a [CC0 1.0 Universal License](https://creativecommons.org/publicdomain/zero/1.0/deed.en).

I could have used [HostsFile::load()](https://clarcharr.github.io/parse-hosts/parse_hosts/struct.HostsFile.html#method.load) directly, but this method loads `/etc/hosts` by default and does not allow to override the default path (for example with [env::var("HOST_FILE")](https://dxr.mozilla.org/servo/source/components/net_traits/hosts.rs#19)), so I kept the existing code to open and read the content of `env::var("HOST_FILE")` and also kept the [parse_hostsfile](https://dxr.mozilla.org/servo/source/components/net_traits/hosts.rs#42) method (used by the unit tests), but I modified it to use [HostsFile::read_buffered](https://clarcharr.github.io/parse-hosts/parse_hosts/struct.HostsFile.html#method.read_buffered), which is doing the actual hosts parsing for a given string buffer.

- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #15756 .
- [X] There are tests for these changes (tests/unit/net/resource_thread.rs and tests/unit/net/http_loader.rs)

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components/net_traits/Cargo.toml

@@ -21,6 +21,7 @@ lazy_static = "0.2"
 log = "0.3.5"
 msg = {path = "../msg"}
 num-traits = "0.1.32"
+parse-hosts = "0.3.0"
 serde = "0.9"
 serde_derive = "0.9"
 servo_config = {path = "../config", features = ["servo"]}

components/net_traits/hosts.rs

@@ -2,6 +2,7 @@
  * 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 servo_url::ServoUrl;
 use std::collections::HashMap;
 use std::env;
@@ -32,7 +33,7 @@ fn create_host_table() -> Option<HashMap<String, IpAddr>> {
         Err(_) => return None,
     };
 
-    return Some(parse_hostsfile(&lines));
+    Some(parse_hostsfile(&lines))
 }
 
 pub fn replace_host_table(table: HashMap<String, IpAddr>) {
@@ -41,19 +42,17 @@ pub fn replace_host_table(table: HashMap<String, IpAddr>) {
 
 pub fn parse_hostsfile(hostsfile_content: &str) -> HashMap<String, IpAddr> {
     let mut host_table = HashMap::new();
-    for line in hostsfile_content.split('\n') {
-        let mut ip_host = line.trim().split(|c: char| c == ' ' || c == '\t');
-        if let Some(ip) = ip_host.next() {
-            if let Ok(address) = ip.parse::<IpAddr>() {
-                for token in ip_host {
-                    if token.as_bytes()[0] == b'#' {
-                        break;
-                    }
-                    host_table.insert((*token).to_owned(), address);
+
+    for line in HostsFile::read_buffered(hostsfile_content.as_bytes()).lines() {
+        if let Ok(ref line) = line {
+            for host in line.hosts() {
+                if let Some(ip) = line.ip() {
+                    host_table.insert(host.to_owned(), ip);
                 }
             }
         }
     }
+
     host_table
 }
 

components/net_traits/lib.rs

@@ -22,6 +22,7 @@ extern crate lazy_static;
 extern crate log;
 extern crate msg;
 extern crate num_traits;
+extern crate parse_hosts;
 extern crate serde;
 #[macro_use]
 extern crate serde_derive;