Add functionality and tests

Signed-off-by: Malhar Vora <mlvora.2010@gmail.com>

Author: vbmade2000

src/uu/lsns/src/lsns.rs

@@ -102,7 +102,7 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
 
     read_namespaces(&mut lsns)?;
 
-    display_namespaces(&lsns)?;
+    display_namespaces(&lsns, noheadings)?;
 
     Ok(())
 }
@@ -491,7 +491,7 @@ impl NamespaceType {
 
 /// Display namespaces in default format using smartcols
 #[cfg(target_os = "linux")]
-fn display_namespaces(lsns: &Lsns) -> Result<(), LsnsError> {
+fn display_namespaces(lsns: &Lsns, noheadings: bool) -> Result<(), LsnsError> {
     use smartcols_sys::{SCOLS_FL_RIGHT, SCOLS_FL_TRUNC};
 
     // Initialize smartcols
@@ -500,6 +500,11 @@ fn display_namespaces(lsns: &Lsns) -> Result<(), LsnsError> {
     // Create table
     let mut table = Table::new()?;
 
+    // Enable or disable headings based on flag
+    if noheadings {
+        table.enable_headings(false)?;
+    }
+
     // NS: width_hint=10, right-aligned
     table.new_column(c"NS", 10.0, SCOLS_FL_RIGHT)?;
     // TYPE: width_hint=5, left-aligned
@@ -567,7 +572,7 @@ fn display_namespaces(lsns: &Lsns) -> Result<(), LsnsError> {
 }
 
 #[cfg(not(target_os = "linux"))]
-fn display_namespaces(_lsns: &Lsns) -> Result<(), LsnsError> {
+fn display_namespaces(_lsns: &Lsns, _noheadings: bool) -> Result<(), LsnsError> {
     Err(LsnsError::UnsupportedPlatform)
 }
 

src/uu/lsns/src/smartcols.rs

@@ -9,8 +9,8 @@ use std::{io, ptr};
 
 use smartcols_sys::{
     libscols_column, libscols_line, libscols_table, scols_init_debug, scols_line_set_data,
-    scols_new_table, scols_print_table, scols_table_new_column, scols_table_new_line,
-    scols_unref_table,
+    scols_new_table, scols_print_table, scols_table_enable_noheadings, scols_table_new_column,
+    scols_table_new_line, scols_unref_table,
 };
 
 use crate::errors::LsnsError;
@@ -45,6 +45,12 @@ impl Drop for Table {
 pub(crate) trait TableOperations: Sized {
     fn as_ptr(&self) -> *mut libscols_table;
 
+    fn enable_headings(&mut self, enable: bool) -> Result<(), LsnsError> {
+        let no_headings = c_int::from(!enable);
+        let r = unsafe { scols_table_enable_noheadings(self.as_ptr(), no_headings) };
+        LsnsError::io_from_neg_errno("scols_table_enable_noheadings", r).map(|_| ())
+    }
+
     fn new_column(
         &mut self,
         name: &CStr,

tests/by-util/test_lsns.rs

@@ -94,6 +94,20 @@ fn test_output_format() {
     }
 }
 
+#[test]
+#[cfg(target_os = "linux")]
+fn test_noheadings() {
+    let res = new_ucmd!().arg("-n").succeeds();
+    let stdout = res.no_stderr().stdout_str();
+
+    let headers = ["NS", "TYPE", "NPROCS", "PID", "USER", "COMMAND"];
+
+    for header in headers {
+        let msg = format!("{} header should not be present when -n is used", header);
+        assert!(!stdout.contains(header), "{}", msg);
+    }
+}
+
 #[test]
 #[cfg(target_os = "linux")]
 fn test_namespace_ids_are_numeric() {