alnyan/yggdrasil: LookupHost from hosts file

library/std/src/sys/yggdrasil/net/dns.rs

@@ -2,14 +2,19 @@ use yggdrasil_rt::net::dns::{
     self, DnsClass, DnsMessage, DnsRecordData, DnsReplyCode, DnsType, UdpRequester,
 };
 
-use crate::io;
+use crate::fs::File;
+use crate::io::{self, BufRead, BufReader};
 use crate::net::{IpAddr, Ipv4Addr, SocketAddr, UdpSocket};
 use crate::os::{
     fd::AsRawFd,
     yggdrasil::io::{poll::PollChannel, timer::TimerFd},
 };
+use crate::str::FromStr;
 use crate::time::Duration;
 
+const NAMESERVER: SocketAddr = SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 53);
+const HOSTS_PATH: &str = "/etc/hosts";
+
 pub struct LookupHost {
     addresses: Vec<IpAddr>,
     port: u16,
@@ -24,8 +29,6 @@ struct DnsRequester {
     socket: UdpSocket,
 }
 
-const NAMESERVER: SocketAddr = SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 53);
-
 impl DnsRequester {
     pub fn new(nameserver: SocketAddr) -> io::Result<Self> {
         let mut poll = PollChannel::new()?;
@@ -111,12 +114,44 @@ impl<'a> TryFrom<(&'a str, u16)> for LookupHost {
     type Error = io::Error;
 
     fn try_from((hostname, port): (&'a str, u16)) -> io::Result<Self> {
+        if let Ok(addresses) = get_addresses_from_hosts(hostname) {
+            if !addresses.is_empty() {
+                return Ok(Self { addresses, port });
+            }
+        }
+
         let addresses = get_addresses_from_dns(hostname)?;
 
         Ok(Self { addresses, port })
     }
 }
 
+fn get_addresses_from_hosts(hostname: &str) -> io::Result<Vec<IpAddr>> {
+    let mut reader = BufReader::new(File::open(HOSTS_PATH)?);
+    let mut addresses = vec![];
+    for line in reader.lines() {
+        let line = line?;
+        let line = line.trim();
+        if line.starts_with('#') {
+            continue;
+        }
+        let Some((address, host)) = line.split_once(' ') else {
+            continue;
+        };
+        let address = address.trim();
+        let host = host.trim();
+        let Ok(address) = IpAddr::from_str(address) else {
+            continue;
+        };
+
+        if host == hostname {
+            addresses.push(address);
+        }
+    }
+
+    Ok(addresses)
+}
+
 fn get_addresses_from_dns(hostname: &str) -> io::Result<Vec<IpAddr>> {
     // TODO randomize xid/cookie
     let mut addresses = vec![];