Write short form hostname

src/cli/multi.rs

@@ -21,8 +21,11 @@ pub struct CliMulti {
     #[arg(long)]
     check_in: bool,
     /// The file into which the hostname should be written
-    #[arg(long = "hostname", value_name = "path")]
+    #[arg(group = "hostname", long = "hostname", value_name = "path")]
     hostname_file: Option<String>,
+    /// Parse the hostname retrieved from metadata as a short hostname
+    #[arg(long = "short", requires = "hostname")]
+    short_hostname: bool,
     /// The directory into which network units are written
     #[arg(long = "network-units", value_name = "path")]
     network_units_dir: Option<String>,
@@ -64,7 +67,7 @@ impl CliMulti {
 
         // write hostname if configured to do so
         self.hostname_file
-            .map_or(Ok(()), |x| metadata.write_hostname(x))
+            .map_or(Ok(()), |x| metadata.write_hostname(x, self.short_hostname))
             .context("writing hostname")?;
 
         // write network units if configured to do so

src/providers/mod.rs

@@ -238,9 +238,21 @@ pub trait MetadataProvider {
         Ok(())
     }
 
-    fn write_hostname(&self, hostname_file_path: String) -> Result<()> {
+    fn write_hostname(&self, hostname_file_path: String, short: bool) -> Result<()> {
         if let Some(mut hostname) = self.hostname()? {
             if let Some(maxlen) = max_hostname_len()? {
+                if short {
+                    // Get the short form hostname (i.e. without the domain name).
+                    // The domain name is usually set as a search domain via DHCP, and
+                    // it can optionally be added as a canonical hostname to /etc/hosts
+                    // as well, as the first value after the local IP address.
+                    //
+                    // Example:
+                    // 127.0.0.1  example.local example
+                    if let Some(idx) = hostname.find('.') {
+                        hostname.truncate(idx);
+                    }
+                }
                 if hostname.len() > maxlen {
                     // Value exceeds the system's maximum hostname length.
                     // Truncate hostname to the first dot, or to the maximum
@@ -309,11 +321,11 @@ mod tests {
     }
 
     // write specified hostname to a file, then read it back
-    fn try_write_hostname(hostname: &str) -> String {
+    fn try_write_hostname(hostname: &str, short: bool) -> String {
         let mut temp = NamedTempFile::new().unwrap();
         let provider = HostnameMock(hostname.into());
         provider
-            .write_hostname(temp.path().to_str().unwrap().into())
+            .write_hostname(temp.path().to_str().unwrap().into(), short)
             .unwrap();
         let mut ret = String::new();
         temp.read_to_string(&mut ret).unwrap();
@@ -330,30 +342,35 @@ mod tests {
             .take(maxlen * 2)
             .collect::<String>();
         // simple hostname
-        assert_eq!(try_write_hostname("hostname7"), "hostname7");
+        assert_eq!(try_write_hostname("hostname7", false), "hostname7");
         // simple FQDN
         assert_eq!(
-            try_write_hostname("hostname7.example.com"),
+            try_write_hostname("hostname7.example.com", false),
             "hostname7.example.com"
         );
+        // short form hostname
+        assert_eq!(
+            try_write_hostname("hostname7.example.com", true),
+            "hostname7"
+        );
         // truncated simple hostname
         assert_eq!(
-            try_write_hostname(&long_string[0..maxlen + 10]),
+            try_write_hostname(&long_string[0..maxlen + 10], false),
             long_string[0..maxlen]
         );
         // truncated FQDN
         assert_eq!(
-            try_write_hostname(&format!("{}.example.com", &long_string[0..maxlen + 5])),
+            try_write_hostname(&format!("{}.example.com", &long_string[0..maxlen + 5]), false),
             long_string[0..maxlen]
         );
         // truncate to first dot
         assert_eq!(
-            try_write_hostname(&format!("{}.example.com", &long_string[0..maxlen - 5])),
+            try_write_hostname(&format!("{}.example.com", &long_string[0..maxlen - 5]), false),
             long_string[0..maxlen - 5]
         );
         // truncate to first dot even if we could truncate to second dot
         assert_eq!(
-            try_write_hostname(&format!("{}.example.com", &long_string[0..maxlen - 10])),
+            try_write_hostname(&format!("{}.example.com", &long_string[0..maxlen - 10]), false),
             long_string[0..maxlen - 10]
         );
     }