Add conversion for &Cstr, Cstring and Cow<Cstr> (#5482)

* Add conversion for `&Cstr`, `Cstring` and `Cow<Cstr>`

* Add `Cow<Cstr>` roundtrip test

* fix test

* Cast to pystring before converting

* fix MSRV

* Safety comment

Author: bschoenmaeckers

newsfragments/5482.added.md

@@ -0,0 +1 @@
+Add conversion for `&Cstr`, `Cstring` and `Cow<Cstr>`

src/conversions/std/cstring.rs

@@ -0,0 +1,188 @@
+use crate::types::PyString;
+use crate::{Borrowed, Bound, FromPyObject, IntoPyObject, PyAny, PyErr, Python};
+use std::borrow::Cow;
+use std::ffi::{CStr, CString};
+use std::str::Utf8Error;
+#[cfg(any(Py_3_10, not(Py_LIMITED_API)))]
+use {
+    crate::{exceptions::PyValueError, ffi},
+    std::slice,
+};
+
+impl<'py> IntoPyObject<'py> for &CStr {
+    type Target = PyString;
+    type Output = Bound<'py, Self::Target>;
+    type Error = Utf8Error;
+
+    #[inline]
+    fn into_pyobject(self, py: Python<'py>) -> Result<Self::Output, Self::Error> {
+        self.to_str()?.into_pyobject(py).map_err(|err| match err {})
+    }
+}
+
+impl<'py> IntoPyObject<'py> for CString {
+    type Target = PyString;
+    type Output = Bound<'py, Self::Target>;
+    type Error = Utf8Error;
+
+    #[inline]
+    fn into_pyobject(self, py: Python<'py>) -> Result<Self::Output, Self::Error> {
+        (&*self).into_pyobject(py)
+    }
+}
+
+impl<'py> IntoPyObject<'py> for &CString {
+    type Target = PyString;
+    type Output = Bound<'py, Self::Target>;
+    type Error = Utf8Error;
+
+    #[inline]
+    fn into_pyobject(self, py: Python<'py>) -> Result<Self::Output, Self::Error> {
+        (&**self).into_pyobject(py)
+    }
+}
+
+impl<'py> IntoPyObject<'py> for Cow<'_, CStr> {
+    type Target = PyString;
+    type Output = Bound<'py, Self::Target>;
+    type Error = Utf8Error;
+
+    fn into_pyobject(self, py: Python<'py>) -> Result<Self::Output, Self::Error> {
+        (*self).into_pyobject(py)
+    }
+}
+
+impl<'py> IntoPyObject<'py> for &Cow<'_, CStr> {
+    type Target = PyString;
+    type Output = Bound<'py, Self::Target>;
+    type Error = Utf8Error;
+
+    fn into_pyobject(self, py: Python<'py>) -> Result<Self::Output, Self::Error> {
+        (&**self).into_pyobject(py)
+    }
+}
+
+#[cfg(any(Py_3_10, not(Py_LIMITED_API)))]
+impl<'a> FromPyObject<'a, '_> for &'a CStr {
+    type Error = PyErr;
+
+    fn extract(obj: Borrowed<'a, '_, PyAny>) -> Result<Self, Self::Error> {
+        let obj = obj.cast::<PyString>()?;
+        let mut size = 0;
+        // SAFETY: obj is a PyString so we can safely call PyUnicode_AsUTF8AndSize
+        let ptr = unsafe { ffi::PyUnicode_AsUTF8AndSize(obj.as_ptr(), &mut size) };
+
+        if ptr.is_null() {
+            return Err(PyErr::fetch(obj.py()));
+        }
+
+        // SAFETY: PyUnicode_AsUTF8AndSize always returns a NUL-terminated string but size does not
+        // include the NUL terminator. So we add 1 to the size to include it.
+        let slice = unsafe { slice::from_raw_parts(ptr.cast(), size as usize + 1) };
+
+        CStr::from_bytes_with_nul(slice).map_err(|err| PyValueError::new_err(err.to_string()))
+    }
+}
+
+impl<'a> FromPyObject<'a, '_> for Cow<'a, CStr> {
+    type Error = PyErr;
+
+    fn extract(obj: Borrowed<'a, '_, PyAny>) -> Result<Self, Self::Error> {
+        #[cfg(any(Py_3_10, not(Py_LIMITED_API)))]
+        {
+            Ok(Cow::Borrowed(obj.extract::<&CStr>()?))
+        }
+
+        #[cfg(not(any(Py_3_10, not(Py_LIMITED_API))))]
+        {
+            Ok(Cow::Owned(obj.extract::<CString>()?))
+        }
+    }
+}
+impl FromPyObject<'_, '_> for CString {
+    type Error = PyErr;
+
+    fn extract(obj: Borrowed<'_, '_, PyAny>) -> Result<Self, Self::Error> {
+        #[cfg(any(Py_3_10, not(Py_LIMITED_API)))]
+        {
+            Ok(obj.extract::<&CStr>()?.to_owned())
+        }
+
+        #[cfg(not(any(Py_3_10, not(Py_LIMITED_API))))]
+        {
+            CString::new(&*obj.cast::<PyString>()?.to_cow()?).map_err(Into::into)
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::types::string::PyStringMethods;
+    use crate::types::PyAnyMethods;
+    use crate::Python;
+
+    #[test]
+    fn test_into_pyobject() {
+        Python::attach(|py| {
+            let s = "Hello, Python!";
+            let cstr = CString::new(s).unwrap();
+
+            let py_string = cstr.as_c_str().into_pyobject(py).unwrap();
+            assert_eq!(py_string.to_cow().unwrap(), s);
+
+            let py_string = cstr.into_pyobject(py).unwrap();
+            assert_eq!(py_string.to_cow().unwrap(), s);
+        })
+    }
+
+    #[test]
+    fn test_extract_with_nul_error() {
+        Python::attach(|py| {
+            let s = "Hello\0Python";
+            let py_string = s.into_pyobject(py).unwrap();
+
+            #[cfg(any(Py_3_10, not(Py_LIMITED_API)))]
+            {
+                let err = py_string.extract::<&CStr>();
+                assert!(err.is_err());
+            }
+
+            let err = py_string.extract::<CString>();
+            assert!(err.is_err());
+        })
+    }
+
+    #[test]
+    fn test_extract_cstr_and_cstring() {
+        Python::attach(|py| {
+            let s = "Hello, world!";
+            let cstr = CString::new(s).unwrap();
+            let py_string = cstr.as_c_str().into_pyobject(py).unwrap();
+
+            #[cfg(any(Py_3_10, not(Py_LIMITED_API)))]
+            {
+                let extracted_cstr: &CStr = py_string.extract().unwrap();
+                assert_eq!(extracted_cstr.to_str().unwrap(), s);
+            }
+
+            let extracted_cstring: CString = py_string.extract().unwrap();
+            assert_eq!(extracted_cstring.to_str().unwrap(), s);
+        })
+    }
+
+    #[test]
+    fn test_cow_roundtrip() {
+        Python::attach(|py| {
+            let s = "Hello, world!";
+            let cstr = CString::new(s).unwrap();
+            let cow: Cow<'_, CStr> = Cow::Borrowed(cstr.as_c_str());
+
+            let py_string = cow.into_pyobject(py).unwrap();
+            assert_eq!(py_string.to_cow().unwrap(), s);
+
+            let roundtripped: Cow<'_, CStr> = py_string.extract().unwrap();
+            assert_eq!(roundtripped.as_ref(), cstr.as_c_str());
+        })
+    }
+}

src/conversions/std/mod.rs

@@ -1,5 +1,6 @@
 mod array;
 mod cell;
+mod cstring;
 mod ipaddr;
 mod map;
 mod num;