gh-127350: Add Py_fopen() and Py_fclose() functions (#127821)

Author: vstinner

Doc/c-api/sys.rst

@@ -216,6 +216,38 @@ Operating System Utilities
       The function now uses the UTF-8 encoding on Windows if
       :c:member:`PyPreConfig.legacy_windows_fs_encoding` is zero.
 
+.. c:function:: FILE* Py_fopen(PyObject *path, const char *mode)
+
+   Similar to :c:func:`!fopen`, but *path* is a Python object and
+   an exception is set on error.
+
+   *path* must be a :class:`str` object, a :class:`bytes` object,
+   or a :term:`path-like object`.
+
+   On success, return the new file pointer.
+   On error, set an exception and return ``NULL``.
+
+   The file must be closed by :c:func:`Py_fclose` rather than calling directly
+   :c:func:`!fclose`.
+
+   The file descriptor is created non-inheritable (:pep:`446`).
+
+   The caller must hold the GIL.
+
+   .. versionadded:: next
+
+
+.. c:function:: int Py_fclose(FILE *file)
+
+   Close a file that was opened by :c:func:`Py_fopen`.
+
+   On success, return ``0``.
+   On error, return ``EOF`` and ``errno`` is set to indicate the error.
+   In either case, any further access (including another call to
+   :c:func:`Py_fclose`) to the stream results in undefined behavior.
+
+   .. versionadded:: next
+
 
 .. _systemfunctions:
 

Doc/whatsnew/3.14.rst

@@ -1237,6 +1237,12 @@ New features
   :monitoring-event:`BRANCH_LEFT` and :monitoring-event:`BRANCH_RIGHT`
   events, respectively.
 
+* Add :c:func:`Py_fopen` function to open a file. Similar to the
+  :c:func:`!fopen` function, but the *path* parameter is a Python object and an
+  exception is set on error. Add also :c:func:`Py_fclose` function to close a
+  file.
+  (Contributed by Victor Stinner in :gh:`127350`.)
+
 
 Porting to Python 3.14
 ----------------------

Include/cpython/fileutils.h

@@ -2,7 +2,13 @@
 #  error "this header file must not be included directly"
 #endif
 
-// Used by _testcapi which must not use the internal C API
-PyAPI_FUNC(FILE*) _Py_fopen_obj(
+PyAPI_FUNC(FILE*) Py_fopen(
     PyObject *path,
     const char *mode);
+
+// Deprecated alias to Py_fopen() kept for backward compatibility
+Py_DEPRECATED(3.14) PyAPI_FUNC(FILE*) _Py_fopen_obj(
+    PyObject *path,
+    const char *mode);
+
+PyAPI_FUNC(int) Py_fclose(FILE *file);

Lib/test/test_capi/test_file.py

@@ -0,0 +1,67 @@
+import os
+import unittest
+from test import support
+from test.support import import_helper, os_helper
+
+_testcapi = import_helper.import_module('_testcapi')
+
+
+class CAPIFileTest(unittest.TestCase):
+    def test_py_fopen(self):
+        # Test Py_fopen() and Py_fclose()
+
+        with open(__file__, "rb") as fp:
+            source = fp.read()
+
+        for filename in (__file__, os.fsencode(__file__)):
+            with self.subTest(filename=filename):
+                data = _testcapi.py_fopen(filename, "rb")
+                self.assertEqual(data, source[:256])
+
+                data = _testcapi.py_fopen(os_helper.FakePath(filename), "rb")
+                self.assertEqual(data, source[:256])
+
+        filenames = [
+            os_helper.TESTFN,
+            os.fsencode(os_helper.TESTFN),
+        ]
+        # TESTFN_UNDECODABLE cannot be used to create a file on macOS/WASI.
+        if os_helper.TESTFN_UNENCODABLE is not None:
+            filenames.append(os_helper.TESTFN_UNENCODABLE)
+        for filename in filenames:
+            with self.subTest(filename=filename):
+                try:
+                    with open(filename, "wb") as fp:
+                        fp.write(source)
+
+                    data = _testcapi.py_fopen(filename, "rb")
+                    self.assertEqual(data, source[:256])
+                finally:
+                    os_helper.unlink(filename)
+
+        # embedded null character/byte in the filename
+        with self.assertRaises(ValueError):
+            _testcapi.py_fopen("a\x00b", "rb")
+        with self.assertRaises(ValueError):
+            _testcapi.py_fopen(b"a\x00b", "rb")
+
+        # non-ASCII mode failing with "Invalid argument"
+        with self.assertRaises(OSError):
+            _testcapi.py_fopen(__file__, "\xe9")
+
+        # invalid filename type
+        for invalid_type in (123, object()):
+            with self.subTest(filename=invalid_type):
+                with self.assertRaises(TypeError):
+                    _testcapi.py_fopen(invalid_type, "rb")
+
+        if support.MS_WINDOWS:
+            with self.assertRaises(OSError):
+                # On Windows, the file mode is limited to 10 characters
+                _testcapi.py_fopen(__file__, "rt+, ccs=UTF-8")
+
+        # CRASHES py_fopen(__file__, None)
+
+
+if __name__ == "__main__":
+    unittest.main()

Lib/test/test_ssl.py

@@ -1325,8 +1325,7 @@ def test_load_verify_cadata(self):
     def test_load_dh_params(self):
         ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
         ctx.load_dh_params(DHFILE)
-        if os.name != 'nt':
-            ctx.load_dh_params(BYTES_DHFILE)
+        ctx.load_dh_params(BYTES_DHFILE)
         self.assertRaises(TypeError, ctx.load_dh_params)
         self.assertRaises(TypeError, ctx.load_dh_params, None)
         with self.assertRaises(FileNotFoundError) as cm:

Misc/NEWS.d/next/C_API/2024-12-11-13-01-26.gh-issue-127350.uEBZZ4.rst

@@ -0,0 +1,5 @@
+Add :c:func:`Py_fopen` function to open a file. Similar to the :c:func:`!fopen`
+function, but the *path* parameter is a Python object and an exception is set
+on error. Add also :c:func:`Py_fclose` function to close a file, function
+needed for Windows support.
+Patch by Victor Stinner.

Modules/_ssl.c

@@ -4377,7 +4377,7 @@ _ssl__SSLContext_load_dh_params_impl(PySSLContext *self, PyObject *filepath)
     FILE *f;
     DH *dh;
 
-    f = _Py_fopen_obj(filepath, "rb");
+    f = Py_fopen(filepath, "rb");
     if (f == NULL)
         return NULL;
 

Modules/_ssl/debughelpers.c

@@ -180,8 +180,8 @@ _PySSLContext_set_keylog_filename(PySSLContext *self, PyObject *arg, void *c) {
         return 0;
     }
 
-    /* _Py_fopen_obj() also checks that arg is of proper type. */
-    fp = _Py_fopen_obj(arg, "a" PY_STDIOTEXTMODE);
+    /* Py_fopen() also checks that arg is of proper type. */
+    fp = Py_fopen(arg, "a" PY_STDIOTEXTMODE);
     if (fp == NULL)
         return -1;
 

Modules/_testcapi/clinic/file.c.h

@@ -1,8 +1,43 @@
+// clinic/file.c.h uses internal pycore_modsupport.h API
+#define PYTESTCAPI_NEED_INTERNAL_API
+
 #include "parts.h"
 #include "util.h"
+#include "clinic/file.c.h"
+
+/*[clinic input]
+module _testcapi
+[clinic start generated code]*/
+/*[clinic end generated code: output=da39a3ee5e6b4b0d input=6361033e795369fc]*/
+
+/*[clinic input]
+_testcapi.py_fopen
+
+    path: object
+    mode: str
+    /
+
+Call Py_fopen(), fread(256) and Py_fclose(). Return read bytes.
+[clinic start generated code]*/
 
+static PyObject *
+_testcapi_py_fopen_impl(PyObject *module, PyObject *path, const char *mode)
+/*[clinic end generated code: output=5a900af000f759de input=d7e7b8f0fd151953]*/
+{
+    FILE *fp = Py_fopen(path, mode);
+    if (fp == NULL) {
+        return NULL;
+    }
+
+    char buffer[256];
+    size_t size = fread(buffer, 1, Py_ARRAY_LENGTH(buffer), fp);
+    Py_fclose(fp);
+
+    return PyBytes_FromStringAndSize(buffer, size);
+}
 
 static PyMethodDef test_methods[] = {
+    _TESTCAPI_PY_FOPEN_METHODDEF
     {NULL},
 };