Removes Display implementation on EfiStr and EfiString

Author: ultimaweapon

README.md

@@ -204,6 +204,7 @@ Keep in mind that you need to put everything your test needed in the same functi
 - `SystemTable::current()` was replaced with `zfi::system_table()`.
 - `Image::current()` was replaced with `zfi::current_image()`.
 - All getters on `SystemTable` no longer return a static lifetime.
+- `EfiStr` and `EfiString` to longer implement `Display`. Use `EfiStr::display()` instead.
 
 ## License
 

src/string.rs

@@ -1,8 +1,7 @@
 use alloc::borrow::ToOwned;
-use alloc::string::String;
 use alloc::vec::Vec;
 use core::borrow::Borrow;
-use core::fmt::{Display, Formatter};
+use core::fmt::{Formatter, Write};
 use core::mem::transmute;
 use core::slice::{from_raw_parts, IterMut};
 use core::str::FromStr;
@@ -15,6 +14,7 @@ use core::str::FromStr;
 pub struct EfiStr([u16]);
 
 impl EfiStr {
+    /// An empty string with only NUL character.
     pub const EMPTY: &'static Self = unsafe { Self::new_unchecked(&[0]) };
 
     /// # Safety
@@ -40,17 +40,26 @@ impl EfiStr {
         Self::new_unchecked(from_raw_parts(ptr, len + 1))
     }
 
+    /// Returnes a pointer to the first character.
     pub const fn as_ptr(&self) -> *const u16 {
         self.0.as_ptr()
     }
 
+    /// Returnes length of this string without NUL, in character.
     pub const fn len(&self) -> usize {
         self.0.len() - 1
     }
 
+    /// Returns `true` if this string contains only NUL character.
     pub const fn is_empty(&self) -> bool {
         self.len() == 0
     }
+
+    /// Returns object that implement [`core::fmt::Display`] for safely printing string that may
+    /// contain non-Unicode data.
+    pub const fn display(&self) -> impl core::fmt::Display + '_ {
+        Display(self)
+    }
 }
 
 impl AsRef<EfiStr> for EfiStr {
@@ -83,12 +92,24 @@ impl ToOwned for EfiStr {
     }
 }
 
-impl Display for EfiStr {
+/// Provides [`core::fmt::Display`] to display [`EfiStr`] lossy.
+struct Display<'a>(&'a EfiStr);
+
+impl<'a> core::fmt::Display for Display<'a> {
     fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
-        let d = &self.0[..(self.0.len() - 1)]; // Exclude NUL.
-        let s = String::from_utf16(d).unwrap();
+        // SAFETY: EfiStr guarantee to have NUL at the end.
+        let mut ptr = self.0.as_ptr();
+
+        while unsafe { *ptr != 0 } {
+            let c = unsafe { *ptr };
+            let c = char::from_u32(c.into()).unwrap_or(char::REPLACEMENT_CHARACTER);
+
+            f.write_char(c)?;
+
+            unsafe { ptr = ptr.add(1) };
+        }
 
-        f.write_str(&s)
+        Ok(())
     }
 }
 
@@ -166,12 +187,6 @@ impl Borrow<EfiStr> for EfiString {
     }
 }
 
-impl Display for EfiString {
-    fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
-        self.as_ref().fmt(f)
-    }
-}
-
 /// A non-NUL character in the EFI string.
 #[repr(transparent)]
 pub struct EfiChar(u16);