gh-132162: Add tests for Py_UniversalNewlineFgets() (#132164)

Author: alex-semenyuk

Lib/test/test_capi/test_file.py

@@ -294,7 +294,28 @@ def test_py_fopen(self):
         # CRASHES py_fopen(NULL, 'rb')
         # CRASHES py_fopen(__file__, NULL)
 
-    # TODO: Test Py_UniversalNewlineFgets()
+    def test_py_universalnewlinefgets(self):
+        py_universalnewlinefgets = _testcapi.py_universalnewlinefgets
+        filename = os_helper.TESTFN
+        self.addCleanup(os_helper.unlink, filename)
+
+        with open(filename, "wb") as fp:
+            fp.write(b"line1\nline2")
+
+        line = py_universalnewlinefgets(filename, 1000)
+        self.assertEqual(line, b"line1\n")
+
+        with open(filename, "wb") as fp:
+            fp.write(b"line2\r\nline3")
+
+        line = py_universalnewlinefgets(filename, 1000)
+        self.assertEqual(line, b"line2\n")
+
+        with open(filename, "wb") as fp:
+            fp.write(b"line3\rline4")
+
+        line = py_universalnewlinefgets(filename, 1000)
+        self.assertEqual(line, b"line3\n")
 
     # PyFile_SetOpenCodeHook() and PyFile_OpenCode() are tested by
     # test_embed.test_open_code_hook()

Modules/_testcapi/clinic/file.c.h

@@ -57,9 +57,50 @@ _testcapi_py_fopen_impl(PyObject *module, PyObject *path, const char *mode,
 }
 
 
+/*[clinic input]
+_testcapi.py_universalnewlinefgets
+
+    file: object
+    size: int
+    /
+
+Read a line from a file using Py_UniversalNewlineFgets.
+[clinic start generated code]*/
+
+static PyObject *
+_testcapi_py_universalnewlinefgets_impl(PyObject *module, PyObject *file,
+                                        int size)
+/*[clinic end generated code: output=2ce1bc76c9dc871c input=02c236049d18569a]*/
+{
+    FILE *fp = Py_fopen(file, "rb");
+    if (fp == NULL) {
+        return NULL;
+    }
+
+    char *buf = (char *)PyMem_Malloc(size);
+    if (buf == NULL) {
+        Py_fclose(fp);
+        return PyErr_NoMemory();
+    }
+
+    char *result = Py_UniversalNewlineFgets(buf, size, fp, NULL);
+    if (result == NULL) {
+        PyMem_Free(buf);
+        Py_fclose(fp);
+        Py_RETURN_NONE;
+    }
+
+    PyObject *line = PyBytes_FromString(result);
+    PyMem_Free(buf);
+    Py_fclose(fp);
+
+    return line;
+}
+
 static PyMethodDef test_methods[] = {
     _TESTCAPI_PYFILE_NEWSTDPRINTER_METHODDEF
     _TESTCAPI_PY_FOPEN_METHODDEF
+    _TESTCAPI_PY_UNIVERSALNEWLINEFGETS_METHODDEF
     {NULL},
 };