From 7d3529f60041a08de1033a36848f49e2ce7f7898 Mon Sep 17 00:00:00 2001
From: Johann150 <johann.galle@protonmail.com>
Date: Wed, 19 May 2021 17:23:56 +0200
Subject: [PATCH] hostsfile: support Windows (#79)

Windows has some peculiarities for example it only allows one hostname per line
and the file's location depends on an environment variable. Although in most
cases just using C:\Windows\ for %WinDir% would probably work.

Note that editing the hosts file on Windows will require running with elevated
privileges ("Run as Administrator") and in some cases also antivirus may block
access to the file.
---
 hostsfile/src/lib.rs | 33 ++++++++++++++++++++++++++++++---
 1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/hostsfile/src/lib.rs b/hostsfile/src/lib.rs
index 437867b..da1bc94 100644
--- a/hostsfile/src/lib.rs
+++ b/hostsfile/src/lib.rs
@@ -70,6 +70,14 @@ impl std::error::Error for Error {
 /// 1.1.1.1 cloudflare-dns apnic-dns
 /// # DO NOT EDIT dns END
 /// ```
+///
+/// On Windows the host file format is slightly different in this case:
+/// ```text
+/// # DO NOT EDIT dns BEGIN
+/// 1.1.1.1 cloudflare-dns
+/// 1.1.1.1 apnic-dns
+/// # DO NOT EDIT dns END
+/// ```
 pub struct HostsBuilder {
     tag: String,
     hostname_map: HashMap<IpAddr, Vec<String>>,
@@ -106,11 +114,19 @@ impl HostsBuilder {
     }
 
     /// Inserts a new section to the system's default hosts file.  If there is a section with the
-    /// same tag name already, it will be replaced with the new list instead. Only Unix systems are
-    /// supported now.
+    /// same tag name already, it will be replaced with the new list instead.
     pub fn write(&self) -> Result<()> {
         let hosts_file = if cfg!(unix) {
             PathBuf::from("/etc/hosts")
+        } else if cfg!(windows) {
+            PathBuf::from(
+                // according to https://support.microsoft.com/en-us/topic/how-to-reset-the-hosts-file-back-to-the-default-c2a43f9d-e176-c6f3-e4ef-3500277a6dae
+                // the location depends on the environment variable %WinDir%.
+                format!(
+                    "{}\\System32\\Drivers\\Etc\\hosts",
+                    std::env::var("WinDir")?
+                ),
+            )
         } else {
             return Err(Box::new(Error("unsupported operating system.".to_owned())));
         };
@@ -127,6 +143,9 @@ impl HostsBuilder {
 
     /// Inserts a new section to the specified hosts file.  If there is a section with the same tag
     /// name already, it will be replaced with the new list instead.
+    ///
+    /// On Windows, the format of one hostname per line will be used, all other systems will use
+    /// the same format as Unix and Unix-like systems (i.e. allow multiple hostnames per line).
     pub fn write_to<P: AsRef<Path>>(&self, hosts_path: P) -> Result<()> {
         let hosts_path = hosts_path.as_ref();
         let begin_marker = format!("# DO NOT EDIT {} BEGIN", &self.tag);
@@ -185,7 +204,15 @@ impl HostsBuilder {
         if !self.hostname_map.is_empty() {
             writeln!(&mut file, "{}", begin_marker)?;
             for (ip, hostnames) in &self.hostname_map {
-                writeln!(&mut file, "{} {}", ip, hostnames.join(" "))?;
+                if cfg!(windows) {
+                    // windows only allows one hostname per line
+                    for hostname in hostnames {
+                        writeln!(&mut file, "{} {}", ip, hostname)?;
+                    }
+                } else {
+                    // assume the same format as Unix
+                    writeln!(&mut file, "{} {}", ip, hostnames.join(" "))?;
+                }
             }
             writeln!(&mut file, "{}", end_marker)?;
         }