Merge pull request #1431 from nyurik/as_c_str

feat: add `CxxString::as_c_str() -> &CStr`

src/cxx.cc

@@ -19,6 +19,10 @@ const char *cxxbridge1$cxx_string$data(const std::string &s) noexcept {
   return s.data();
 }
 
+const char *cxxbridge1$cxx_string$c_str(const std::string &s) noexcept {
+  return s.c_str();
+}
+
 std::size_t cxxbridge1$cxx_string$length(const std::string &s) noexcept {
   return s.length();
 }

src/cxx_string.rs

@@ -5,6 +5,7 @@ use alloc::borrow::Cow;
 #[cfg(feature = "alloc")]
 use alloc::string::String;
 use core::cmp::Ordering;
+use core::ffi::c_char;
 use core::fmt::{self, Debug, Display};
 use core::hash::{Hash, Hasher};
 use core::marker::{PhantomData, PhantomPinned};
@@ -20,6 +21,8 @@ extern "C" {
     fn string_destroy(this: &mut MaybeUninit<CxxString>);
     #[link_name = "cxxbridge1$cxx_string$data"]
     fn string_data(this: &CxxString) -> *const u8;
+    #[link_name = "cxxbridge1$cxx_string$c_str"]
+    fn string_c_str(this: &CxxString) -> *const c_char;
     #[link_name = "cxxbridge1$cxx_string$length"]
     fn string_length(this: &CxxString) -> usize;
     #[link_name = "cxxbridge1$cxx_string$clear"]
@@ -141,6 +144,11 @@ impl CxxString {
         str::from_utf8(self.as_bytes())
     }
 
+    /// Produces a `&CStr` view of the string without additional allocations.
+    pub fn as_c_str(&self) -> &std::ffi::CStr {
+        unsafe { std::ffi::CStr::from_ptr(string_c_str(self)) }
+    }
+
     /// If the contents of the C++ string are valid UTF-8, this function returns
     /// a view as a Cow::Borrowed &amp;str. Otherwise replaces any invalid UTF-8
     /// sequences with the U+FFFD [replacement character] and returns a

tests/test.rs

@@ -12,7 +12,7 @@ use cxx::{SharedPtr, UniquePtr};
 use cxx_test_suite::module::ffi2;
 use cxx_test_suite::{cast, ffi, R};
 use std::cell::Cell;
-use std::ffi::CStr;
+use std::ffi::{CStr, CString};
 use std::panic::{self, RefUnwindSafe, UnwindSafe};
 
 thread_local! {
@@ -54,6 +54,8 @@ fn test_c_return() {
     assert_eq!("2020", ffi::c_return_rust_string());
     assert_eq!("Hello \u{fffd}World", ffi::c_return_rust_string_lossy());
     assert_eq!("2020", ffi::c_return_unique_ptr_string().to_str().unwrap());
+    // TODO: Use C-string literal c"2020" once MSRV is v1.77+
+    assert_eq!(CString::new("2020").unwrap().as_c_str(), ffi::c_return_unique_ptr_string().as_c_str());
     assert_eq!(4, ffi::c_return_unique_ptr_vector_u8().len());
     assert_eq!(
         200_u8,