string: implement API to access raw string data

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 - Add `PyList::get_item_unchecked()` and `PyTuple::get_item_unchecked()` to get items without bounds checks. [#1733](https://github.com/PyO3/pyo3/pull/1733)
 - Add `PyAny::py()` as a convenience for `PyNativeType::py()`. [#1751](https://github.com/PyO3/pyo3/pull/1751)
+- Implement `PyString.data()` to access the raw bytes storing a Python string. [#1794](https://github.com/PyO3/pyo3/issues/1794)
 
 ### Changed
 

src/types/mod.rs

@@ -23,6 +23,8 @@ pub use self::num::PyLong as PyInt;
 pub use self::sequence::PySequence;
 pub use self::set::{PyFrozenSet, PySet};
 pub use self::slice::{PySlice, PySliceIndices};
+#[cfg(not(Py_LIMITED_API))]
+pub use self::string::PyStringData;
 pub use self::string::{PyString, PyString as PyUnicode};
 pub use self::tuple::PyTuple;
 pub use self::typeobject::PyType;

src/types/string.rs

@@ -1,14 +1,133 @@
 // Copyright (c) 2017-present PyO3 Project and Contributors
 
+#[cfg(not(Py_LIMITED_API))]
+use crate::exceptions::PyUnicodeDecodeError;
 use crate::types::PyBytes;
 use crate::{
  ffi, AsPyPointer, FromPyObject, IntoPy, PyAny, PyObject, PyResult, PyTryFrom, Python,
  ToPyObject,
 };
 use std::borrow::Cow;
+#[cfg(not(Py_LIMITED_API))]
+use std::ffi::CStr;
 use std::os::raw::c_char;
 use std::str;
 
+/// Represents raw data backing a Python `str`.
+///
+/// Python internally stores strings in various representations. This enumeration
+/// represents those variations.
+#[cfg(not(Py_LIMITED_API))]
+#[cfg_attr(docsrs, doc(cfg(not(Py_LIMITED_API))))]
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum PyStringData<'a> {
+ /// UCS1 representation.
+ Ucs1(&'a [u8]),
+
+ /// UCS2 representation.
+ Ucs2(&'a [u16]),
+
+ /// UCS4 representation.
+ Ucs4(&'a [u32]),
+}
+
+#[cfg(not(Py_LIMITED_API))]
+impl<'a> PyStringData<'a> {
+ /// Obtain the raw bytes backing this instance as a [u8] slice.
+ pub fn as_bytes(&self) -> &[u8] {
+ match self {
+ Self::Ucs1(s) => s,
+ Self::Ucs2(s) => unsafe {
+ std::slice::from_raw_parts(
+ s.as_ptr() as *const u8,
+ s.len() * self.value_width_bytes(),
+ )
+ },
+ Self::Ucs4(s) => unsafe {
+ std::slice::from_raw_parts(
+ s.as_ptr() as *const u8,
+ s.len() * self.value_width_bytes(),
+ )
+ },
+ }
+ }
+
+ /// Size in bytes of each value/item in the underlying slice.
+ #[inline]
+ pub fn value_width_bytes(&self) -> usize {
+ match self {
+ Self::Ucs1(_) => 1,
+ Self::Ucs2(_) => 2,
+ Self::Ucs4(_) => 4,
+ }
+ }
+
+ /// Convert the raw data to a Rust string.
+ ///
+ /// For UCS-1 / UTF-8, returns a borrow into the original slice. For UCS-2 and UCS-4,
+ /// returns an owned string.
+ ///
+ /// Returns [PyUnicodeDecodeError] if the string data isn't valid in its purported
+ /// storage format. This should only occur for strings that were created via Python
+ /// C APIs that skip input validation (like `PyUnicode_FromKindAndData`) and should
+ /// never occur for strings that were created from Python code.
+ pub fn to_string(self, py: Python) -> PyResult<Cow<'a, str>> {
+ match self {
+ Self::Ucs1(data) => match str::from_utf8(data) {
+ Ok(s) => Ok(Cow::Borrowed(s)),
+ Err(e) => Err(crate::PyErr::from_instance(PyUnicodeDecodeError::new_utf8(
+ py, data, e,
+ )?)),
+ },
+ Self::Ucs2(data) => match String::from_utf16(data) {
+ Ok(s) => Ok(Cow::Owned(s)),
+ Err(e) => {
+ let mut message = e.to_string().as_bytes().to_vec();
+ message.push(0);
+
+ Err(crate::PyErr::from_instance(PyUnicodeDecodeError::new(
+ py,
+ CStr::from_bytes_with_nul(b"utf-16\0").unwrap(),
+ self.as_bytes(),
+ 0..self.as_bytes().len(),
+ CStr::from_bytes_with_nul(&message).unwrap(),
+ )?))
+ }
+ },
+ Self::Ucs4(data) => match data.iter().map(|&c| std::char::from_u32(c)).collect() {
+ Some(s) => Ok(Cow::Owned(s)),
+ None => Err(crate::PyErr::from_instance(PyUnicodeDecodeError::new(
+ py,
+ CStr::from_bytes_with_nul(b"utf-32\0").unwrap(),
+ self.as_bytes(),
+ 0..self.as_bytes().len(),
+ CStr::from_bytes_with_nul(b"error converting utf-32\0").unwrap(),
+ )?)),
+ },
+ }
+ }
+
+ /// Convert the raw data to a Rust string, possibly with data loss.
+ ///
+ /// Invalid code points will be replaced with `U+FFFD REPLACEMENT CHARACTER`.
+ ///
+ /// Returns a borrow into original data, when possible, or owned data otherwise.
+ ///
+ /// The return value of this function should only disagree with [Self::to_string]
+ /// when that method would error.
+ pub fn to_string_lossy(self) -> Cow<'a, str> {
+ match self {
+ Self::Ucs1(data) => String::from_utf8_lossy(data),
+ Self::Ucs2(data) => Cow::Owned(String::from_utf16_lossy(data)),
+ Self::Ucs4(data) => Cow::Owned(
+ data.iter()
+ .map(|&c| std::char::from_u32(c).unwrap_or('\u{FFFD}'))
+ .collect(),
+ ),
+ }
+ }
+}
+
 /// Represents a Python `string` (a Unicode string object).
 ///
 /// This type is immutable.
@@ -89,6 +208,45 @@ impl PyString {
  }
  }
  }
+
+ /// Obtains the raw data backing the Python string.
+ ///
+ /// If the Python string object was created through legacy APIs, its internal
+ /// storage format will be canonicalized before data is returned.
+ #[cfg(not(Py_LIMITED_API))]
+ #[cfg_attr(docsrs, doc(cfg(not(Py_LIMITED_API))))]
+ pub fn data(&self) -> PyResult<PyStringData<'_>> {
+ let ptr = self.as_ptr();
+
+ if cfg!(not(Py_3_12)) {
+ #[allow(deprecated)]
+ let ready = unsafe { ffi::PyUnicode_READY(ptr) };
+ if ready != 0 {
+ // Exception was created on failure.
+ return Err(crate::PyErr::api_call_failed(self.py()));
+ }
+ }
+
+ // The string should be in its canonical form after calling `PyUnicode_READY()`.
+ // And non-canonical form not possible after Python 3.12. So it should be safe
+ // to call these APIs.
+ let length = unsafe { ffi::PyUnicode_GET_LENGTH(ptr) } as usize;
+ let raw_data = unsafe { ffi::PyUnicode_DATA(ptr) };
+ let kind = unsafe { ffi::PyUnicode_KIND(ptr) };
+
+ match kind {
+ ffi::PyUnicode_1BYTE_KIND => Ok(PyStringData::Ucs1(unsafe {
+ std::slice::from_raw_parts(raw_data as *const u8, length)
+ })),
+ ffi::PyUnicode_2BYTE_KIND => Ok(PyStringData::Ucs2(unsafe {
+ std::slice::from_raw_parts(raw_data as *const u16, length)
+ })),
+ ffi::PyUnicode_4BYTE_KIND => Ok(PyStringData::Ucs4(unsafe {
+ std::slice::from_raw_parts(raw_data as *const u32, length)
+ })),
+ _ => unreachable!(),
+ }
+ }
 }
 
 /// Converts a Rust `str` to a Python object.
@@ -193,8 +351,16 @@ impl FromPyObject<'_> for char {
 #[cfg(test)]
 mod tests {
  use super::PyString;
+ #[cfg(not(Py_LIMITED_API))]
+ use super::PyStringData;
+ #[cfg(not(Py_LIMITED_API))]
+ use crate::exceptions::PyUnicodeDecodeError;
+ #[cfg(not(Py_LIMITED_API))]
+ use crate::type_object::PyTypeObject;
  use crate::Python;
  use crate::{FromPyObject, PyObject, PyTryFrom, ToPyObject};
+ #[cfg(not(Py_LIMITED_API))]
+ use std::borrow::Cow;
 
  #[test]
  fn test_non_bmp() {
@@ -297,4 +463,124 @@ mod tests {
  assert_eq!(format!("{}", s), "Hello\n");
  })
  }
+
+ #[test]
+ #[cfg(not(Py_LIMITED_API))]
+ fn test_string_data_ucs1() {
+ Python::with_gil(|py| {
+ let s = PyString::new(py, "hello, world");
+ let data = s.data().unwrap();
+
+ assert_eq!(data, PyStringData::Ucs1(b"hello, world"));
+ assert_eq!(data.to_string(py).unwrap(), Cow::Borrowed("hello, world"));
+ assert_eq!(data.to_string_lossy(), Cow::Borrowed("hello, world"));
+ })
+ }
+
+ #[test]
+ #[cfg(not(Py_LIMITED_API))]
+ fn test_string_data_ucs1_invalid() {
+ Python::with_gil(|py| {
+ // 0xfe is not allowed in UTF-8.
+ let buffer = b"f\xfe\0";
+ let ptr = unsafe {
+ crate::ffi::PyUnicode_FromKindAndData(
+ crate::ffi::PyUnicode_1BYTE_KIND as _,
+ buffer.as_ptr() as *const _,
+ 2,
+ )
+ };
+ assert!(!ptr.is_null());
+ let s: &PyString = unsafe { py.from_owned_ptr(ptr) };
+ let data = s.data().unwrap();
+ assert_eq!(data, PyStringData::Ucs1(b"f\xfe"));
+ let err = data.to_string(py).unwrap_err();
+ assert_eq!(err.ptype(py), PyUnicodeDecodeError::type_object(py));
+ assert!(err
+ .to_string()
+ .contains("'utf-8' codec can't decode byte 0xfe in position 1"));
+ assert_eq!(data.to_string_lossy(), Cow::Borrowed("f�"));
+ });
+ }
+
+ #[test]
+ #[cfg(not(Py_LIMITED_API))]
+ fn test_string_data_ucs2() {
+ Python::with_gil(|py| {
+ let s = py.eval("'foo\\ud800'", None, None).unwrap();
+ let py_string = s.cast_as::<PyString>().unwrap();
+ let data = py_string.data().unwrap();
+
+ assert_eq!(data, PyStringData::Ucs2(&[102, 111, 111, 0xd800]));
+ assert_eq!(
+ data.to_string_lossy(),
+ Cow::Owned::<str>("foo�".to_string())
+ );
+ })
+ }
+
+ #[test]
+ #[cfg(not(Py_LIMITED_API))]
+ fn test_string_data_ucs2_invalid() {
+ Python::with_gil(|py| {
+ // U+FF22 (valid) & U+d800 (never valid)
+ let buffer = b"\x22\xff\x00\xd8\x00\x00";
+ let ptr = unsafe {
+ crate::ffi::PyUnicode_FromKindAndData(
+ crate::ffi::PyUnicode_2BYTE_KIND as _,
+ buffer.as_ptr() as *const _,
+ 2,
+ )
+ };
+ assert!(!ptr.is_null());
+ let s: &PyString = unsafe { py.from_owned_ptr(ptr) };
+ let data = s.data().unwrap();
+ assert_eq!(data, PyStringData::Ucs2(&[0xff22, 0xd800]));
+ let err = data.to_string(py).unwrap_err();
+ assert_eq!(err.ptype(py), PyUnicodeDecodeError::type_object(py));
+ assert!(err
+ .to_string()
+ .contains("'utf-16' codec can't decode bytes in position 0-3"));
+ assert_eq!(data.to_string_lossy(), Cow::Owned::<str>("Ｂ�".into()));
+ });
+ }
+
+ #[test]
+ #[cfg(not(Py_LIMITED_API))]
+ fn test_string_data_ucs4() {
+ Python::with_gil(|py| {
+ let s = "哈哈🐈";
+ let py_string = PyString::new(py, s);
+ let data = py_string.data().unwrap();
+
+ assert_eq!(data, PyStringData::Ucs4(&[21704, 21704, 128008]));
+ assert_eq!(data.to_string_lossy(), Cow::Owned::<str>(s.to_string()));
+ })
+ }
+
+ #[test]
+ #[cfg(not(Py_LIMITED_API))]
+ fn test_string_data_ucs4_invalid() {
+ Python::with_gil(|py| {
+ // U+20000 (valid) & U+d800 (never valid)
+ let buffer = b"\x00\x00\x02\x00\x00\xd8\x00\x00\x00\x00\x00\x00";
+ let ptr = unsafe {
+ crate::ffi::PyUnicode_FromKindAndData(
+ crate::ffi::PyUnicode_4BYTE_KIND as _,
+ buffer.as_ptr() as *const _,
+ 2,
+ )
+ };
+ assert!(!ptr.is_null());
+ let s: &PyString = unsafe { py.from_owned_ptr(ptr) };
+ let data = s.data().unwrap();
+ assert_eq!(data, PyStringData::Ucs4(&[0x20000, 0xd800]));
+ let err = data.to_string(py).unwrap_err();
+ assert_eq!(err.ptype(py), PyUnicodeDecodeError::type_object(py));
+ assert!(err
+ .to_string()
+ .contains("'utf-32' codec can't decode bytes in position 0-7"));
+ assert_eq!(data.to_string_lossy(), Cow::Owned::<str>("𠀀�".into()));
+ });
+ }
 }