innernet/hostsfile/src/lib.rs

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