capped string uppercase conversion

enumscribe/src/internal/capped_string.rs

@@ -1,42 +1,100 @@
 //! Module for the [`CappedString`](CappedString) type, which is a string type which always stores
 //! its data inline.
 
-use core::{str, convert::TryFrom, ops::Deref, borrow::Borrow, fmt};
+use core::{str, ops::Deref, borrow::Borrow, fmt};
 
 /// TODO: documentation
 pub struct CappedString<const N: usize> {
-    /// The string data. It is an invariant that this must always be valid UTF-8.
+    /// The string data. It is an invariant that the first `len` bytes must be valid UTF-8.
     buf: [u8; N],
+    // The length of the string data in the buffer. It is an invariant that `len <= N`.
+    len: usize,
 }
 
 impl<const N: usize> CappedString<N> {
     /// TODO: documentation
     #[inline]
     #[must_use]
-    pub fn new(s: &str) -> Option<Self> {
+    pub fn from_str(s: &str) -> Option<Self> {
         unsafe { Self::from_utf8_unchecked(s.as_bytes()) }
     }
 
     /// TODO: documentation
+    /// 
+    /// # Safety
+    /// - `bs` must be valid UTF-8.
     #[inline]
     #[must_use]
     pub unsafe fn from_utf8_unchecked(bs: &[u8]) -> Option<Self> {
-        let buf =  <[u8; N]>::try_from(bs).ok()?;
-        Some(Self { buf })
+        let mut buf = [0u8; N];
+        buf.get_mut(..bs.len())?.copy_from_slice(bs);
+        
+        // SAFETY:
+        // - `bs.len() <= N` has already been checked by the `get_mut` call, which will return
+        //   `None` and cause us to return early if the condition does not hold.
+        // 
+        unsafe { Some(Self::from_raw_parts(buf, bs.len())) }
+    }
+
+    /// TODO: documentation
+    /// 
+    /// # Safety
+    /// - `len <= N` must hold.
+    /// - The first `len` bytes of `buf` must be valid UTF-8.
+    #[inline]
+    #[must_use]
+    pub unsafe fn from_raw_parts(buf: [u8; N], len: usize) -> Self {
+        Self { buf, len }
+    }
+
+
+    /// TODO: documentation
+    #[inline]
+    #[must_use]
+    pub fn into_raw_parts(self) -> ([u8; N], usize) {
+        (self.buf, self.len)
     }
 
     /// TODO: documentation
     #[inline]
     #[must_use]
     pub fn as_str(&self) -> &str {
-        unsafe { str::from_utf8_unchecked(&self.buf) }
+        // SAFETY:
+        // - It is an invariant of `CappedString<N>` that `len <= N`.
+        // - It is an invariant of `CappedString<N>` that the first `len` bytes of `buf` are valid
+        //   UTF-8.
+        unsafe {
+            let buf_occupied_prefix = self.buf.get_unchecked(..self.len);
+            str::from_utf8_unchecked(buf_occupied_prefix)
+        }
     }
 
     /// TODO: documentation
     #[inline]
     #[must_use]
     pub fn to_uppercase<const M: usize>(&self) -> Option<CappedString<M>> {
-        todo!()
+        let mut buf = [0u8; M];
+        let mut cursor = 0usize;
+
+        for c_orig in self.as_str().chars() {
+            for c_upper in c_orig.to_uppercase() {
+                let encode_buf = cursor
+                    .checked_add(c_upper.len_utf8())
+                    .and_then(|encode_buf_end| buf.get_mut(cursor..encode_buf_end))?;
+
+                // FIXME: avoid the panic asm that gets generated for this encode (can never panic,
+                // as we always have at least `c_upper.len_utf8()` buffer space).
+                let encoded = c_upper.encode_utf8(encode_buf);
+                cursor = cursor.checked_add(encoded.len())?;
+            }
+        }
+
+        let filled_buf = buf.get(..cursor)?;
+
+        // SAFETY:
+        // `filled_buf` has been filled with a sequence of bytes obtained from `char::encode_utf8`,
+        // so it is valid UTF-8.
+        unsafe { CappedString::from_utf8_unchecked(filled_buf) }
     }
 }
 
@@ -86,7 +144,7 @@ impl<'de, const N: usize> serde::de::Visitor<'de> for CappedStringVisitor<N> {
     where
         E: serde::de::Error,
     {
-        CappedString::new(v)
+        CappedString::from_str(v)
             .ok_or_else(|| E::invalid_length(v.len(), &self))
     }
 
@@ -96,7 +154,50 @@ impl<'de, const N: usize> serde::de::Visitor<'de> for CappedStringVisitor<N> {
     {
         str::from_utf8(v)
             .map_err(|_| E::invalid_value(serde::de::Unexpected::Bytes(v), &self))
-            .and_then(|v| CappedString::new(v)
+            .and_then(|v| CappedString::from_str(v)
                 .ok_or_else(|| E::invalid_length(v.len(), &self)))
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::CappedString;
+
+    #[test]
+    fn test_capped_string_uppercase() {
+        {
+            let s1 = CappedString::<5>::from_str("hello").unwrap();
+            let s2 = s1.to_uppercase::<5>().unwrap();
+            assert_eq!(s2.as_str(), "HELLO");
+        }
+        {
+            let s1 = CappedString::<20>::from_str("hello").unwrap();
+            let s2 = s1.to_uppercase::<20>().unwrap();
+            assert_eq!(s2.as_str(), "HELLO");
+        }
+        {
+            let s1 = CappedString::<5>::from_str("hElLo").unwrap();
+            let s2 = s1.to_uppercase::<5>().unwrap();
+            assert_eq!(s2.as_str(), "HELLO");
+        }
+        {
+            let s1 = CappedString::<5>::from_str("hello").unwrap();
+            assert!(s1.to_uppercase::<4>().is_none());
+        }
+        {
+            let s1 = CappedString::<5>::from_str("groß").unwrap();
+            let s2 = s1.to_uppercase::<5>().unwrap();
+            assert_eq!(s2.as_str(), "GROSS");
+        }
+        {
+            let s1 = CappedString::<1>::from_str("").unwrap();
+            let s2 = s1.to_uppercase::<1>().unwrap();
+            assert_eq!(s2.as_str(), "");
+        }
+        {
+            let s1 = CappedString::<0>::from_str("").unwrap();
+            let s2 = s1.to_uppercase::<0>().unwrap();
+            assert_eq!(s2.as_str(), "");
+        }
+    }
+}