Guard against PyUnicode_AsUTF8AndSize returning null

src/types/string.rs

@@ -7,8 +7,8 @@ use crate::instance::PyNativeType;
 use crate::object::PyObject;
 use crate::types::PyAny;
 use crate::AsPyPointer;
+use crate::IntoPy;
 use crate::Python;
-use crate::{exceptions, IntoPy};
 use crate::{ffi, FromPy};
 use std::borrow::Cow;
 use std::ops::Index;
@@ -59,29 +59,27 @@ impl PyString {
     }
 
     /// Get the Python string as a byte slice.
+    ///
+    /// Returns a `UnicodeEncodeError` if the input is not valid unicode
+    /// (containing unpaired surrogates).
     #[inline]
-    pub fn as_bytes(&self) -> &[u8] {
+    pub fn as_bytes(&self) -> PyResult<&[u8]> {
         unsafe {
             let mut size: ffi::Py_ssize_t = 0;
             let data = ffi::PyUnicode_AsUTF8AndSize(self.0.as_ptr(), &mut size) as *const u8;
-            // PyUnicode_AsUTF8AndSize would return null if the pointer did not reference a valid
-            // unicode object, but because we have a valid PyString, assume success
-            debug_assert!(!data.is_null());
-            std::slice::from_raw_parts(data, size as usize)
+            if data.is_null() {
+                Err(PyErr::fetch(self.py()))
+            } else {
+                Ok(std::slice::from_raw_parts(data, size as usize))
+            }
         }
     }
 
     /// Convert the `PyString` into a Rust string.
-    ///
-    /// Returns a `UnicodeDecodeError` if the input is not valid unicode
-    /// (containing unpaired surrogates).
     pub fn to_string(&self) -> PyResult<Cow<str>> {
-        match std::str::from_utf8(self.as_bytes()) {
-            Ok(s) => Ok(Cow::Borrowed(s)),
-            Err(e) => Err(PyErr::from_instance(
-                exceptions::UnicodeDecodeError::new_utf8(self.py(), self.as_bytes(), e)?,
-            )),
-        }
+        let bytes = self.as_bytes()?;
+        let string = std::str::from_utf8(bytes)?;
+        Ok(Cow::Borrowed(string))
     }
 
     /// Convert the `PyString` into a Rust string.
@@ -89,7 +87,10 @@ impl PyString {
     /// Unpaired surrogates invalid UTF-8 sequences are
     /// replaced with U+FFFD REPLACEMENT CHARACTER.
     pub fn to_string_lossy(&self) -> Cow<str> {
-        String::from_utf8_lossy(self.as_bytes())
+        // TODO: Handle error of `as_bytes`
+        // see https://github.com/PyO3/pyo3/pull/634
+        let bytes = self.as_bytes().unwrap();
+        String::from_utf8_lossy(bytes)
     }
 }
 
@@ -273,7 +274,16 @@ mod test {
         let s = "ascii 🐈";
         let obj: PyObject = PyString::new(py, s).into();
         let py_string = <PyString as PyTryFrom>::try_from(obj.as_ref(py)).unwrap();
-        assert_eq!(s.as_bytes(), py_string.as_bytes());
+        assert_eq!(s.as_bytes(), py_string.as_bytes().unwrap());
+    }
+
+    #[test]
+    fn test_as_bytes_surrogate() {
+        let gil = Python::acquire_gil();
+        let py = gil.python();
+        let obj: PyObject = py.eval(r#"'\ud800'"#, None, None).unwrap().into();
+        let py_string = <PyString as PyTryFrom>::try_from(obj.as_ref(py)).unwrap();
+        assert!(py_string.as_bytes().is_err());
     }
 
     #[test]

tests/test_string.rs

@@ -0,0 +1,29 @@
+use pyo3::prelude::*;
+use pyo3::py_run;
+use pyo3::wrap_pyfunction;
+
+mod common;
+
+#[pyfunction]
+fn take_str(_s: &str) -> PyResult<()> {
+    Ok(())
+}
+
+#[test]
+fn test_unicode_encode_error() {
+    let gil = Python::acquire_gil();
+    let py = gil.python();
+
+    let take_str = wrap_pyfunction!(take_str)(py);
+    py_run!(
+        py,
+        take_str,
+        r#"
+        try:
+            take_str('\ud800')
+        except UnicodeEncodeError as e:
+            error_msg = "'utf-8' codec can't encode character '\\ud800' in position 0: surrogates not allowed"
+            assert str(e) == error_msg
+        "#
+    );
+}