std: Redesign c_str and c_vec

This commit is an implementation of [RFC 494][rfc] which removes the entire
`std::c_vec` module and redesigns the `std::c_str` module as `std::ffi`.

[rfc]: https://github.com/rust-lang/rfcs/blob/master/text/0494-c_str-and-c_vec-stability.md

The interface of the new `CString` is outlined in the linked RFC, the primary
changes being:

* The `ToCStr` trait is gone, meaning the `with_c_str` and `to_c_str` methods
  are now gone. These two methods are replaced with a `CString::from_slice`
  method.
* The `CString` type is now just a wrapper around `Vec<u8>` with a static
  guarantee that there is a trailing nul byte with no internal nul bytes. This
  means that `CString` now implements `Deref<Target = [c_char]>`, which is where
  it gains most of its methods from. A few helper methods are added to acquire a
  slice of `u8` instead of `c_char`, as well as including a slice with the
  trailing nul byte if necessary.
* All usage of non-owned `CString` values is now done via two functions inside
  of `std::ffi`, called `c_str_to_bytes` and `c_str_to_bytes_with_nul`. These
  functions are now the one method used to convert a `*const c_char` to a Rust
  slice of `u8`.

Many more details, including newly deprecated methods, can be found linked in
the RFC. This is a:

[breaking-change]
Closes #20444

2 files changed, 238 insertions, 0 deletions

diff --git a/src/libstd/ffi/c_str.rs b/src/libstd/ffi/c_str.rs
new file mode 100644
index 00000000000..bef2344d9e8
--- /dev/null
+++ b/src/libstd/ffi/c_str.rs
@@ -0,0 +1,218 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use fmt;
+use iter::IteratorExt;
+use libc;
+use mem;
+use ops::Deref;
+use slice::{self, SliceExt, AsSlice};
+use string::String;
+use vec::Vec;
+
+/// A type representing a C-compatible string
+///
+/// This type serves the primary purpose of being able to generate a
+/// C-compatible string from a Rust byte slice or vector. An instance of this
+/// type is a static guarantee that the underlying bytes contain no interior 0
+/// bytes and the final byte is 0.
+///
+/// A `CString` is created from either a byte slice or a byte vector. After
+/// being created, a `CString` predominately inherits all of its methods from
+/// the `Deref` implementation to `[libc::c_char]`. Note that the underlying
+/// array is represented as an array of `libc::c_char` as opposed to `u8`. A
+/// `u8` slice can be obtained with the `as_bytes` method.  Slices produced from
+/// a `CString` do *not* contain the trailing nul terminator unless otherwise
+/// specified.
+///
+/// # Example
+///
+/// ```no_run
+/// # extern crate libc;
+/// # fn main() {
+/// use std::ffi::CString;
+/// use libc;
+///
+/// extern {
+///     fn my_printer(s: *const libc::c_char);
+/// }
+///
+/// let to_print = "Hello, world!";
+/// let c_to_print = CString::from_slice(to_print.as_bytes());
+/// unsafe {
+///     my_printer(c_to_print.as_ptr());
+/// }
+/// # }
+/// ```
+#[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash)]
+pub struct CString {
+    inner: Vec<libc::c_char>,
+}
+
+impl CString {
+    /// Create a new C-compatible string from a byte slice.
+    ///
+    /// This method will copy the data of the slice provided into a new
+    /// allocation, ensuring that there is a trailing 0 byte.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if there are any 0 bytes already in the slice
+    /// provided.
+    pub fn from_slice(v: &[u8]) -> CString {
+        CString::from_vec(v.to_vec())
+    }
+
+    /// Create a C-compatible string from a byte vector.
+    ///
+    /// This method will consume ownership of the provided vector, appending a 0
+    /// byte to the end after verifying that there are no interior 0 bytes.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if there are any 0 bytes already in the vector
+    /// provided.
+    pub fn from_vec(v: Vec<u8>) -> CString {
+        assert!(!v.iter().any(|&x| x == 0));
+        unsafe { CString::from_vec_unchecked(v) }
+    }
+
+    /// Create a C-compatibel string from a byte vector without checking for
+    /// interior 0 bytes.
+    ///
+    /// This method is equivalent to `from_vec` except that no runtime assertion
+    /// is made that `v` contains no 0 bytes.
+    pub unsafe fn from_vec_unchecked(mut v: Vec<u8>) -> CString {
+        v.push(0);
+        CString { inner: mem::transmute(v) }
+    }
+
+    /// Create a view into this C string which includes the trailing nul
+    /// terminator at the end of the string.
+    pub fn as_slice_with_nul(&self) -> &[libc::c_char] { self.inner.as_slice() }
+
+    /// Similar to the `as_slice` method, but returns a `u8` slice instead of a
+    /// `libc::c_char` slice.
+    pub fn as_bytes(&self) -> &[u8] {
+        unsafe { mem::transmute(self.as_slice()) }
+    }
+
+    /// Equivalend to `as_slice_with_nul` except that the type returned is a
+    /// `u8` slice instead of a `libc::c_char` slice.
+    pub fn as_bytes_with_nul(&self) -> &[u8] {
+        unsafe { mem::transmute(self.as_slice_with_nul()) }
+    }
+}
+
+impl Deref for CString {
+    type Target = [libc::c_char];
+
+    fn deref(&self) -> &[libc::c_char] {
+        self.inner.slice_to(self.inner.len() - 1)
+    }
+}
+
+impl fmt::Show for CString {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        String::from_utf8_lossy(self.as_bytes()).fmt(f)
+    }
+}
+
+/// Interpret a C string as a byte slice.
+///
+/// This function will calculate the length of the C string provided, and it
+/// will then return a corresponding slice for the contents of the C string not
+/// including the nul terminator.
+///
+/// This function will tie the lifetime of the returned slice to the lifetime of
+/// the pointer provided. This is done to help prevent the slice from escaping
+/// the lifetime of the pointer itself. If a longer lifetime is needed, then
+/// `mem::copy_lifetime` should be used.
+///
+/// This function is unsafe because there is no guarantee of the validity of the
+/// pointer `raw` or a guarantee that a nul terminator will be found.
+///
+/// # Example
+///
+/// ```no_run
+/// # extern crate libc;
+/// # fn main() {
+/// use std::ffi;
+/// use std::str;
+/// use libc;
+///
+/// extern {
+///     fn my_string() -> *const libc::c_char;
+/// }
+///
+/// unsafe {
+///     let to_print = my_string();
+///     let slice = ffi::c_str_to_bytes(&to_print);
+///     println!("string returned: {}", str::from_utf8(slice).unwrap());
+/// }
+/// # }
+/// ```
+pub unsafe fn c_str_to_bytes<'a>(raw: &'a *const libc::c_char) -> &'a [u8] {
+    let len = libc::strlen(*raw);
+    slice::from_raw_buf(&*(raw as *const _ as *const *const u8), len as uint)
+}
+
+/// Interpret a C string as a byte slice with the nul terminator.
+///
+/// This function is identical to `from_raw_buf` except that the returned slice
+/// will include the nul terminator of the string.
+pub unsafe fn c_str_to_bytes_with_nul<'a>(raw: &'a *const libc::c_char) -> &'a [u8] {
+    let len = libc::strlen(*raw) + 1;
+    slice::from_raw_buf(&*(raw as *const _ as *const *const u8), len as uint)
+}
+
+#[cfg(test)]
+mod tests {
+    use prelude::v1::*;
+    use super::*;
+    use libc;
+    use mem;
+
+    #[test]
+    fn c_to_rust() {
+        let data = b"123\0";
+        let ptr = data.as_ptr() as *const libc::c_char;
+        unsafe {
+            assert_eq!(c_str_to_bytes(&ptr), b"123");
+            assert_eq!(c_str_to_bytes_with_nul(&ptr), b"123\0");
+        }
+    }
+
+    #[test]
+    fn simple() {
+        let s = CString::from_slice(b"1234");
+        assert_eq!(s.as_bytes(), b"1234");
+        assert_eq!(s.as_bytes_with_nul(), b"1234\0");
+        unsafe {
+            assert_eq!(s.as_slice(),
+                       mem::transmute::<_, &[libc::c_char]>(b"1234"));
+            assert_eq!(s.as_slice_with_nul(),
+                       mem::transmute::<_, &[libc::c_char]>(b"1234\0"));
+        }
+    }
+
+    #[should_fail] #[test]
+    fn build_with_zero1() { CString::from_slice(b"\0"); }
+    #[should_fail] #[test]
+    fn build_with_zero2() { CString::from_vec(vec![0]); }
+
+    #[test]
+    fn build_with_zero3() {
+        unsafe {
+            let s = CString::from_vec_unchecked(vec![0]);
+            assert_eq!(s.as_bytes(), b"\0");
+        }
+    }
+}
diff --git a/src/libstd/ffi/mod.rs b/src/libstd/ffi/mod.rs
new file mode 100644
index 00000000000..cc86f804e3e
--- /dev/null
+++ b/src/libstd/ffi/mod.rs
@@ -0,0 +1,20 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Utilities related to FFI bindings.
+
+#![unstable = "module just underwent fairly large reorganization and the dust \
+               still needs to settle"]
+
+pub use self::c_str::CString;
+pub use self::c_str::c_str_to_bytes;
+pub use self::c_str::c_str_to_bytes_with_nul;
+
+mod c_str;