hostname: bug fix for non-windows xgethostname and add test case

Cstr::from_bytes_with_nul needs input bytes null terminated. Current
version does not include the last null byte, hence
Cstr::from_bytes_with_nul will panic with error 'FromBytesWithNulError {
kind: NotNulTerminated }'

src/hostname/hostname.rs

@@ -157,13 +157,12 @@ fn xgethostname() -> io::Result<String> {
     };
 
     if err == 0 {
-        let mut last_char = name.iter().position(|byte| *byte == 0).unwrap_or(namelen);
-        if last_char == name.len() {
+        let null_pos = name.iter().position(|byte| *byte == 0).unwrap_or(namelen);
+        if null_pos == namelen {
             name.push(0);
-            last_char += 1;
         }
 
-        Ok(CStr::from_bytes_with_nul(&name[..last_char])
+        Ok(CStr::from_bytes_with_nul(&name[..null_pos + 1])
             .unwrap()
             .to_string_lossy()
             .into_owned())

tests/test_hostname.rs

@@ -0,0 +1,12 @@
+use common::util::*;
+
+#[test]
+fn test_hostname() {
+    let ls_default_res = new_ucmd!().succeeds();
+    let ls_short_res = new_ucmd!().arg("-s").succeeds();
+    let ls_domain_res = new_ucmd!().arg("-d").succeeds();
+
+    assert!(ls_default_res.stdout.len() >= ls_short_res.stdout.len());
+    assert!(ls_default_res.stdout.len() >= ls_domain_res.stdout.len());
+}
+

tests/tests.rs

@@ -91,6 +91,7 @@ generic! {
     "tsort", test_tsort;
     "unexpand", test_unexpand;
     "uniq", test_uniq;
+    "wc", test_wc;
     // Be aware of the trailing semicolon after the last item
-    "wc", test_wc
+    "hostname", test_hostname
 }