network/utils: add resolvconf helpers

src/network/mod.rs

@@ -25,6 +25,7 @@ use std::string::String;
 use std::string::ToString;
 
 mod ip_cli;
+pub mod utils;
 
 pub const BONDING_MODE_BALANCE_RR: u32 = 0;
 pub const BONDING_MODE_ACTIVE_BACKUP: u32 = 1;

src/network/utils.rs

@@ -0,0 +1,35 @@
+/// Misc network-related helpers.
+use crate::errors::*;
+use std::io::Write;
+use std::net::IpAddr;
+
+/// Write nameservers in `resolv.conf` format.
+pub(crate) fn write_resolvconf<T>(writer: &mut T, nameservers: &[IpAddr]) -> Result<()>
+where
+    T: Write,
+{
+    slog_scope::trace!("writing {} nameservers", nameservers.len());
+
+    for ns in nameservers {
+        let entry = format!("nameserver {}\n", ns);
+        writer.write_all(&entry.as_bytes())?;
+        writer.flush()?;
+    }
+
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_write_resolvconf() {
+        let nameservers = vec![IpAddr::from([4, 4, 4, 4]), IpAddr::from([8, 8, 8, 8])];
+        let expected = "nameserver 4.4.4.4\nnameserver 8.8.8.8\n";
+        let mut buf = vec![];
+
+        write_resolvconf(&mut buf, &nameservers).unwrap();
+        assert_eq!(buf, expected.as_bytes());
+    }
+}