From a205bbb1d286d78efbb325dac1d465c6908e0026 Mon Sep 17 00:00:00 2001
From: Matthias Schiffer <mschiffer@universe-factory.net>
Date: Fri, 1 May 2020 22:21:17 +0200
Subject: Use extern type for CStr

---
 safe_libc/src/boxed.rs  | 78 +++++++++++++++++++++++++++++++++++++++++++++++++
 safe_libc/src/lib.rs    |  3 +-
 safe_libc/src/string.rs | 36 +++++++++++++----------
 src/main.rs             |  5 ++++
 4 files changed, 105 insertions(+), 17 deletions(-)
 create mode 100644 safe_libc/src/boxed.rs

diff --git a/safe_libc/src/boxed.rs b/safe_libc/src/boxed.rs
new file mode 100644
index 0000000..a0bbfb4
--- /dev/null
+++ b/safe_libc/src/boxed.rs
@@ -0,0 +1,78 @@
+use core::{marker, mem, ptr};
+use core::ops::{Deref, DerefMut};
+
+pub trait Dealloc<T: ?Sized> {
+	unsafe fn dealloc(p: *mut T);
+}
+
+#[repr(transparent)]
+pub struct BoxLike<T: ?Sized, D: Dealloc<T>> {
+	inner: ptr::NonNull<T>,
+	_phantom: marker::PhantomData<T>,
+	_dropper: marker::PhantomData<D>,
+}
+
+impl<T: ?Sized, D: Dealloc<T>> BoxLike<T, D> {
+	#[inline]
+	pub unsafe fn from_raw_unchecked(p: *mut T) -> Self {
+		BoxLike {
+			inner: ptr::NonNull::new_unchecked(p),
+			_phantom: marker::PhantomData,
+			_dropper: marker::PhantomData,
+		}
+	}
+
+	#[inline]
+	pub unsafe fn from_raw(p: *mut T) -> Option<Self> {
+		if p.is_null() {
+			None
+		} else {
+			Some(Self::from_raw_unchecked(p))
+		}
+	}
+
+	#[inline]
+	pub fn into_raw(self) -> *mut T {
+		let p = self.inner.as_ptr();
+		mem::forget(self);
+		p
+	}
+}
+
+impl<T: ?Sized, D: Dealloc<T>> Drop for BoxLike<T, D> {
+	#[inline]
+	fn drop(&mut self) {
+		let p = self.inner.as_ptr();
+		unsafe {
+			ptr::drop_in_place(p);
+			D::dealloc(p);
+		}
+	}
+}
+
+impl<T: ?Sized, D: Dealloc<T>> Deref for BoxLike<T, D> {
+	type Target = T;
+
+	#[inline]
+	fn deref(&self) -> &T {
+		unsafe { self.inner.as_ref() }
+	}
+}
+
+impl<T: ?Sized, D: Dealloc<T>> DerefMut for BoxLike<T, D> {
+	#[inline]
+	fn deref_mut(&mut self) -> &mut T {
+		unsafe { self.inner.as_mut() }
+	}
+}
+
+pub struct DeallocFree;
+
+impl<T: ?Sized> Dealloc<T> for DeallocFree {
+	#[inline]
+	unsafe fn dealloc(p: *mut T) {
+		libc::free(p as _);
+	}
+}
+
+pub type CBox<T> = BoxLike<T, DeallocFree>;
diff --git a/safe_libc/src/lib.rs b/safe_libc/src/lib.rs
index 6d9baf2..2e39b8d 100644
--- a/safe_libc/src/lib.rs
+++ b/safe_libc/src/lib.rs
@@ -1,6 +1,6 @@
 #![no_std]
+#![feature(extern_types)]
 #![feature(slice_ptr_len)]
-#![feature(min_specialization)]
 // #![feature(ffi_const)]
 
 extern crate alloc;
@@ -9,6 +9,7 @@ pub use libc::*;
 
 mod util;
 
+pub mod boxed;
 pub mod errno;
 pub mod stdio;
 pub mod string;
diff --git a/safe_libc/src/string.rs b/safe_libc/src/string.rs
index 6a8308a..5483e08 100644
--- a/safe_libc/src/string.rs
+++ b/safe_libc/src/string.rs
@@ -1,24 +1,26 @@
-use crate::{self as libc, util};
+use crate::{self as libc, boxed::CBox, util};
 
-use alloc::boxed::Box;
-use core::{ops::{Deref, DerefMut}, slice};
+use core::{mem, slice};
+use core::ops::{Deref, DerefMut};
 
 //pub struct FromBytesWithNulError {}
 
-#[repr(transparent)]
-pub struct CStr {
-	inner: libc::c_char,
+extern "C" {
+	type RawCStr;
 }
 
+#[repr(transparent)]
+pub struct CStr(RawCStr);
+
 impl CStr {
 	#[inline]
 	pub unsafe fn from_ptr<'a>(p: *const libc::c_char) -> &'a CStr {
-		&*p.cast()
+		&*(p as *const CStr)
 	}
 
 	#[inline]
 	pub unsafe fn from_mut_ptr<'a>(p: *mut libc::c_char) -> &'a mut CStr {
-		&mut *p.cast()
+		&mut *(p as *mut CStr)
 	}
 
 	#[inline]
@@ -37,12 +39,12 @@ impl CStr {
 
 	#[inline]
 	pub const fn as_ptr(&self) -> *const libc::c_char {
-		&self.inner
+		(self as *const CStr).cast()
 	}
 
 	#[inline]
 	pub fn as_mut_ptr(&mut self) -> *mut libc::c_char {
-		&mut self.inner
+		(self as *mut CStr).cast()
 	}
 
 	#[inline]
@@ -79,20 +81,22 @@ macro_rules! cstr {
 }
 
 pub struct CString {
-	inner: Box<libc::c_char>,
+	inner: CBox<CStr>,
 }
 
 impl CString {
 	#[inline]
 	pub unsafe fn from_raw(p: *mut libc::c_char) -> CString {
 		CString {
-			inner: Box::from_raw(p),
+			inner: CBox::from_raw_unchecked(p as *mut CStr)
 		}
 	}
 
 	#[inline]
-	pub fn into_raw(self) -> *mut libc::c_char {
-		Box::into_raw(self.inner)
+	pub fn into_raw(mut self) -> *mut libc::c_char {
+		let p = self.as_mut_ptr();
+		mem::forget(self);
+		p
 	}
 }
 
@@ -101,14 +105,14 @@ impl Deref for CString {
 
 	#[inline]
 	fn deref(&self) -> &CStr {
-		unsafe { CStr::from_ptr(&*self.inner) }
+		&*self.inner
 	}
 }
 
 impl DerefMut for CString {
 	#[inline]
 	fn deref_mut(&mut self) -> &mut CStr {
-		unsafe { CStr::from_mut_ptr(&mut *self.inner) }
+		&mut *self.inner
 	}
 }
 
diff --git a/src/main.rs b/src/main.rs
index fe151fe..c6ec961 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -27,6 +27,11 @@ pub extern "C" fn main(_nargs: libc::c_int, _args: *const *const libc::c_char) -
 		let _ = writeln!(stdout, "Foo: {} {} {}", z[0], z[1], z[2]);
 	}
 
+	{
+		let x = libc::string::CString::from("bar");
+		let _ = stdout.puts(&x);
+	}
+
 	{
 		let b = alloc::boxed::Box::new(42);
 		let _ = writeln!(stdout, "Bar: {}", b);
-- 
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