2021-03-29 17:22:14 +00:00
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use std::{
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collections::HashMap,
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fmt,
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2021-04-07 08:00:52 +00:00
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fs::{self, File, OpenOptions},
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2021-03-29 17:22:14 +00:00
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io::{BufRead, BufReader, Write},
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net::IpAddr,
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path::{Path, PathBuf},
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result,
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};
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pub type Result<T> = result::Result<T, Box<dyn std::error::Error>>;
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/// A custom error struct for this crate.
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#[derive(Debug, Clone)]
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pub struct Error(String);
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impl fmt::Display for Error {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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write!(f, "{}", self.0)
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}
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}
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impl std::error::Error for Error {
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fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
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None
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}
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}
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/// `HostsBuilder` manages a section of /etc/hosts file that contains a list of IP to hostname
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/// mappings. A hosts file can have multiple sections that are distinguished by tag names.
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///
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/// # Examples
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///
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/// ```no_run
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/// use hostsfile::{HostsBuilder, Result};
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/// # fn main() -> Result<()> {
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/// let mut hosts = HostsBuilder::new("dns");
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/// hosts.add_hostname("8.8.8.8".parse().unwrap(), "google-dns1");
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/// hosts.add_hostname("8.8.4.4".parse().unwrap(), "google-dns2");
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/// hosts.write_to("/tmp/hosts")?;
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/// # Ok(())
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/// # }
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/// ```
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///
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/// `/tmp/hosts` will have a section:
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///
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/// ```text
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/// # DO NOT EDIT dns BEGIN
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/// 8.8.8.8 google-dns1
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/// 8.8.4.4 google-dns2
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/// # DO NOT EDIT dns END
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/// ```
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///
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/// Another run of `HostsBuilder` with the same tag name overrides the section.
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///
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/// ```no_run
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/// use hostsfile::{HostsBuilder, Result};
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/// # fn main() -> Result<()> {
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/// let mut hosts = HostsBuilder::new("dns");
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/// hosts.add_hostnames("1.1.1.1".parse().unwrap(), &["cloudflare-dns", "apnic-dns"]);
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/// hosts.write_to("/tmp/hosts")?;
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/// # Ok(())
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/// # }
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/// ```
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///
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/// `/tmp/hosts` will have a section:
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///
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/// ```text
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/// # DO NOT EDIT dns BEGIN
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/// 1.1.1.1 cloudflare-dns apnic-dns
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/// # DO NOT EDIT dns END
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/// ```
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pub struct HostsBuilder {
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tag: String,
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hostname_map: HashMap<IpAddr, Vec<String>>,
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}
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impl HostsBuilder {
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/// Creates a new `HostsBuilder` with the given tag name. It corresponds to a section in the
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/// hosts file containing a list of IP to hostname mappings.
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pub fn new<S: Into<String>>(tag: S) -> Self {
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Self {
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tag: tag.into(),
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hostname_map: HashMap::new(),
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}
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}
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/// Adds a mapping of `ip` to `hostname`. If there hostnames associated with the IP already,
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/// the hostname will be appended to the list.
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pub fn add_hostname<S: ToString>(&mut self, ip: IpAddr, hostname: S) {
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let hostnames_dest = self.hostname_map.entry(ip.into()).or_insert(Vec::new());
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hostnames_dest.push(hostname.to_string());
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}
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/// Adds a mapping of `ip` to a list of `hostname`s. If there hostnames associated with the IP
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/// already, the new hostnames will be appended to the list.
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pub fn add_hostnames<I: IntoIterator<Item = impl ToString>>(
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&mut self,
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ip: IpAddr,
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hostnames: I,
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) {
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let hostnames_dest = self.hostname_map.entry(ip.into()).or_insert(Vec::new());
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for hostname in hostnames.into_iter() {
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hostnames_dest.push(hostname.to_string());
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}
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}
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/// Inserts a new section to the system's default hosts file. If there is a section with the
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/// same tag name already, it will be replaced with the new list instead. Only Unix systems are
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/// supported now.
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pub fn write(&self) -> Result<()> {
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let hosts_file = if cfg!(unix) {
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PathBuf::from("/etc/hosts")
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} else {
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return Err(Box::new(Error("unsupported operating system.".to_owned())));
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};
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if !hosts_file.exists() {
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return Err(Box::new(Error(format!(
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"hosts file {:?} missing",
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&hosts_file
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))));
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}
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self.write_to(&hosts_file)
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}
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/// Inserts a new section to the specified hosts file. If there is a section with the same tag
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/// name already, it will be replaced with the new list instead.
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pub fn write_to<P: AsRef<Path>>(&self, hosts_path: P) -> Result<()> {
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let hosts_path = hosts_path.as_ref();
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let begin_marker = format!("# DO NOT EDIT {} BEGIN", &self.tag);
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let end_marker = format!("# DO NOT EDIT {} END", &self.tag);
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2021-04-07 08:00:52 +00:00
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let hosts_file = OpenOptions::new()
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.create(true)
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.read(true)
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.write(true)
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.open(hosts_path)?;
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let mut lines = BufReader::new(hosts_file)
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.lines()
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.map(|line| line.unwrap())
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.collect::<Vec<_>>();
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let begin = lines.iter().position(|line| line.trim() == begin_marker);
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let end = lines.iter().position(|line| line.trim() == end_marker);
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let insert = match (begin, end) {
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(Some(begin), Some(end)) => {
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lines.drain(begin..end + 1);
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begin
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},
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(None, None) => {
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// Insert a blank line before a new section.
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if let Some(last_line) = lines.iter().last() {
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if last_line != "" {
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lines.push("".to_string());
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}
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}
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lines.len()
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},
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_ => {
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return Err(Box::new(Error(format!(
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"start or end marker missing in {:?}",
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&hosts_path
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))));
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},
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};
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// The tempfile should be in the same filesystem as the hosts file.
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let hosts_dir = hosts_path
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.parent()
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.expect("hosts file must be an absolute file path");
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let temp_dir = tempfile::Builder::new().tempdir_in(hosts_dir)?;
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let temp_path = temp_dir.path().join("hosts");
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// Copy the existing hosts file to preserve permissions.
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fs::copy(&hosts_path, &temp_path)?;
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let mut file = File::create(&temp_path)?;
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for line in &lines[..insert] {
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writeln!(&mut file, "{}", line)?;
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}
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if !self.hostname_map.is_empty() {
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writeln!(&mut file, "{}", begin_marker)?;
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for (ip, hostnames) in &self.hostname_map {
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writeln!(&mut file, "{} {}", ip, hostnames.join(" "))?;
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}
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writeln!(&mut file, "{}", end_marker)?;
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}
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for line in &lines[insert..] {
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writeln!(&mut file, "{}", line)?;
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}
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// Move the file atomically to avoid a partial state.
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fs::rename(&temp_path, &hosts_path)?;
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Ok(())
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}
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}
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