From 2132f45fcb2ad6dc95a6c4721edde6787bc625fd Mon Sep 17 00:00:00 2001
From: Samuel Collins <samuel.collins@pexip.com>
Date: Mon, 28 Apr 2025 15:04:55 +0100
Subject: [PATCH] add support for padding string and char arguments

---
 src/format.rs            | 46 ++++++++++++++++++++++++++++++++++++++--
 tests/compare_to_libc.rs |  6 ++++++
 2 files changed, 50 insertions(+), 2 deletions(-)

diff --git a/src/format.rs b/src/format.rs
index dec4b40..de5cbfe 100644
--- a/src/format.rs
+++ b/src/format.rs
@@ -472,7 +472,29 @@ impl Printf for f32 {
 impl Printf for &str {
     fn format(&self, spec: &ConversionSpecifier) -> Result<String> {
         if spec.conversion_type == ConversionType::String {
-            Ok((*self).to_owned())
+            let mut s = String::new();
+
+            let width: usize = match spec.width {
+                NumericParam::Literal(w) => w,
+                _ => {
+                    return Err(PrintfError::Unknown); // should not happen at this point!!
+                }
+            }
+            .try_into()
+            .unwrap_or_default();
+
+            if spec.left_adj {
+                s.push_str(self);
+                while s.len() < width {
+                    s.push(' ');
+                }
+            } else {
+                while s.len() + self.len() < width {
+                    s.push(' ');
+                }
+                s.push_str(self);
+            }
+            Ok(s)
         } else {
             Err(PrintfError::WrongType)
         }
@@ -486,7 +508,27 @@ impl Printf for char {
     fn format(&self, spec: &ConversionSpecifier) -> Result<String> {
         if spec.conversion_type == ConversionType::Char {
             let mut s = String::new();
-            s.push(*self);
+
+            let width: usize = match spec.width {
+                NumericParam::Literal(w) => w,
+                _ => {
+                    return Err(PrintfError::Unknown); // should not happen at this point!!
+                }
+            }
+            .try_into()
+            .unwrap_or_default();
+
+            if spec.left_adj {
+                s.push(*self);
+                while s.len() < width {
+                    s.push(' ');
+                }
+            } else {
+                while s.len() + self.len_utf8() < width {
+                    s.push(' ');
+                }
+                s.push(*self);
+            }
             Ok(s)
         } else {
             Err(PrintfError::WrongType)
diff --git a/tests/compare_to_libc.rs b/tests/compare_to_libc.rs
index 74f0a9d..a76c8fd 100644
--- a/tests/compare_to_libc.rs
+++ b/tests/compare_to_libc.rs
@@ -116,6 +116,10 @@ fn test_str() {
     let c_string = CString::new("test").unwrap();
     check_fmt("%s", c_string.as_c_str());
     check_fmt("%s", c_string);
+    check_fmt_s("%4s", "A");
+    check_fmt_s("%4s", "𒀀"); // multi-byte character test (4 bytes)
+    check_fmt_s("%-4sX", "A");
+    check_fmt_s("%-4sX", "𒀀"); // multi-byte character test (4 bytes)
 }
 
 #[test]
@@ -125,6 +129,8 @@ fn test_char() {
     check_fmt("%c", b'x' as c_char);
     check_fmt("%c", u16::try_from('x').unwrap());
     check_fmt("%c", u32::try_from('x').unwrap());
+    check_fmt("%4c", 'A');
+    check_fmt("%-4cX", 'A');
 }
 
 #[test]