gh-119182: Add PyUnicodeWriter_DecodeUTF8Stateful() (#120639)

Add PyUnicodeWriter_WriteWideChar() and
PyUnicodeWriter_DecodeUTF8Stateful() functions.

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

5 files changed, 332 insertions, 68 deletions

diff --git a/Doc/c-api/unicode.rst b/Doc/c-api/unicode.rst
index 02e696c..4ea20bd 100644
--- a/Doc/c-api/unicode.rst
+++ b/Doc/c-api/unicode.rst
@@ -1551,9 +1551,17 @@ object.
    On success, return ``0``.
    On error, set an exception, leave the writer unchanged, and return ``-1``.
 
-   To use a different error handler than ``strict``,
-   :c:func:`PyUnicode_DecodeUTF8` can be used with
-   :c:func:`PyUnicodeWriter_WriteStr`.
+   See also :c:func:`PyUnicodeWriter_DecodeUTF8Stateful`.
+
+.. c:function:: int PyUnicodeWriter_WriteWideChar(PyUnicodeWriter *writer, const wchar_t *str, Py_ssize_t size)
+
+   Writer the wide string *str* into *writer*.
+
+   *size* is a number of wide characters. If *size* is equal to ``-1``, call
+   ``wcslen(str)`` to get the string length.
+
+   On success, return ``0``.
+   On error, set an exception, leave the writer unchanged, and return ``-1``.
 
 .. c:function:: int PyUnicodeWriter_WriteStr(PyUnicodeWriter *writer, PyObject *obj)
 
@@ -1586,3 +1594,24 @@ object.
 
    On success, return ``0``.
    On error, set an exception, leave the writer unchanged, and return ``-1``.
+
+.. c:function:: int PyUnicodeWriter_DecodeUTF8Stateful(PyUnicodeWriter *writer, const char *string, Py_ssize_t length, const char *errors, Py_ssize_t *consumed)
+
+   Decode the string *str* from UTF-8 with *errors* error handler and write the
+   output into *writer*.
+
+   *size* is the string length in bytes. If *size* is equal to ``-1``, call
+   ``strlen(str)`` to get the string length.
+
+   *errors* is an error handler name, such as ``"replace"``. If *errors* is
+   ``NULL``, use the strict error handler.
+
+   If *consumed* is not ``NULL``, set *\*consumed* to the number of decoded
+   bytes on success.
+   If *consumed* is ``NULL``, treat trailing incomplete UTF-8 byte sequences
+   as an error.
+
+   On success, return ``0``.
+   On error, set an exception, leave the writer unchanged, and return ``-1``.
+
+   See also :c:func:`PyUnicodeWriter_WriteUTF8`.
diff --git a/Doc/whatsnew/3.14.rst b/Doc/whatsnew/3.14.rst
index 804d39a..2eefa23 100644
--- a/Doc/whatsnew/3.14.rst
+++ b/Doc/whatsnew/3.14.rst
@@ -291,10 +291,12 @@ New Features
   * :c:func:`PyUnicodeWriter_Finish`.
   * :c:func:`PyUnicodeWriter_WriteChar`.
   * :c:func:`PyUnicodeWriter_WriteUTF8`.
+  * :c:func:`PyUnicodeWriter_WriteWideChar`.
   * :c:func:`PyUnicodeWriter_WriteStr`.
   * :c:func:`PyUnicodeWriter_WriteRepr`.
   * :c:func:`PyUnicodeWriter_WriteSubstring`.
   * :c:func:`PyUnicodeWriter_Format`.
+  * :c:func:`PyUnicodeWriter_DecodeUTF8Stateful`.
 
   (Contributed by Victor Stinner in :gh:`119182`.)
 
diff --git a/Include/cpython/unicodeobject.h b/Include/cpython/unicodeobject.h
index e5e1b6b..059bec8 100644
--- a/Include/cpython/unicodeobject.h
+++ b/Include/cpython/unicodeobject.h
@@ -459,6 +459,10 @@ PyAPI_FUNC(int) PyUnicodeWriter_WriteUTF8(
     PyUnicodeWriter *writer,
     const char *str,
     Py_ssize_t size);
+PyAPI_FUNC(int) PyUnicodeWriter_WriteWideChar(
+    PyUnicodeWriter *writer,
+    const wchar_t *str,
+    Py_ssize_t size);
 
 PyAPI_FUNC(int) PyUnicodeWriter_WriteStr(
     PyUnicodeWriter *writer,
@@ -475,6 +479,12 @@ PyAPI_FUNC(int) PyUnicodeWriter_Format(
     PyUnicodeWriter *writer,
     const char *format,
     ...);
+PyAPI_FUNC(int) PyUnicodeWriter_DecodeUTF8Stateful(
+    PyUnicodeWriter *writer,
+    const char *string,         /* UTF-8 encoded string */
+    Py_ssize_t length,          /* size of string */
+    const char *errors,         /* error handling */
+    Py_ssize_t *consumed);      /* bytes consumed */
 
 
 /* --- Private _PyUnicodeWriter API --------------------------------------- */
diff --git a/Modules/_testcapi/unicode.c b/Modules/_testcapi/unicode.c
index 79f99c4..da658b4 100644
--- a/Modules/_testcapi/unicode.c
+++ b/Modules/_testcapi/unicode.c
@@ -375,6 +375,119 @@ test_unicodewriter_recover_error(PyObject *self, PyObject *Py_UNUSED(args))
 
 
 static PyObject *
+test_unicodewriter_decode_utf8(PyObject *self, PyObject *Py_UNUSED(args))
+{
+    // test PyUnicodeWriter_DecodeUTF8Stateful()
+    PyUnicodeWriter *writer = PyUnicodeWriter_Create(0);
+    if (writer == NULL) {
+        return NULL;
+    }
+    if (PyUnicodeWriter_DecodeUTF8Stateful(writer, "ign\xFFore", -1, "ignore", NULL) < 0) {
+        goto error;
+    }
+    if (PyUnicodeWriter_WriteChar(writer, '-') < 0) {
+        goto error;
+    }
+    if (PyUnicodeWriter_DecodeUTF8Stateful(writer, "replace\xFF", -1, "replace", NULL) < 0) {
+        goto error;
+    }
+    if (PyUnicodeWriter_WriteChar(writer, '-') < 0) {
+        goto error;
+    }
+
+    // incomplete trailing UTF-8 sequence
+    if (PyUnicodeWriter_DecodeUTF8Stateful(writer, "incomplete\xC3", -1, "replace", NULL) < 0) {
+        goto error;
+    }
+
+    PyObject *result = PyUnicodeWriter_Finish(writer);
+    if (result == NULL) {
+        return NULL;
+    }
+    assert(PyUnicode_EqualToUTF8(result,
+                                 "ignore-replace\xef\xbf\xbd"
+                                 "-incomplete\xef\xbf\xbd"));
+    Py_DECREF(result);
+
+    Py_RETURN_NONE;
+
+error:
+    PyUnicodeWriter_Discard(writer);
+    return NULL;
+}
+
+
+static PyObject *
+test_unicodewriter_decode_utf8_consumed(PyObject *self, PyObject *Py_UNUSED(args))
+{
+    // test PyUnicodeWriter_DecodeUTF8Stateful()
+    PyUnicodeWriter *writer = PyUnicodeWriter_Create(0);
+    if (writer == NULL) {
+        return NULL;
+    }
+    Py_ssize_t consumed;
+
+    // valid string
+    consumed = 12345;
+    if (PyUnicodeWriter_DecodeUTF8Stateful(writer, "text", -1, NULL, &consumed) < 0) {
+        goto error;
+    }
+    assert(consumed == 4);
+    if (PyUnicodeWriter_WriteChar(writer, '-') < 0) {
+        goto error;
+    }
+
+    // non-ASCII
+    consumed = 12345;
+    if (PyUnicodeWriter_DecodeUTF8Stateful(writer, "\xC3\xA9-\xE2\x82\xAC", 6, NULL, &consumed) < 0) {
+        goto error;
+    }
+    assert(consumed == 6);
+    if (PyUnicodeWriter_WriteChar(writer, '-') < 0) {
+        goto error;
+    }
+
+    // consumed is 0 if write fails
+    consumed = 12345;
+    assert(PyUnicodeWriter_DecodeUTF8Stateful(writer, "invalid\xFF", -1, NULL, &consumed) < 0);
+    PyErr_Clear();
+    assert(consumed == 0);
+
+    // ignore error handler
+    consumed = 12345;
+    if (PyUnicodeWriter_DecodeUTF8Stateful(writer, "more\xFF", -1, "ignore", &consumed) < 0) {
+        goto error;
+    }
+    assert(consumed == 5);
+    if (PyUnicodeWriter_WriteChar(writer, '-') < 0) {
+        goto error;
+    }
+
+    // incomplete trailing UTF-8 sequence
+    consumed = 12345;
+    if (PyUnicodeWriter_DecodeUTF8Stateful(writer, "incomplete\xC3", -1, "ignore", &consumed) < 0) {
+        goto error;
+    }
+    assert(consumed == 10);
+
+    PyObject *result = PyUnicodeWriter_Finish(writer);
+    if (result == NULL) {
+        return NULL;
+    }
+    assert(PyUnicode_EqualToUTF8(result,
+                                 "text-\xC3\xA9-\xE2\x82\xAC-"
+                                 "more-incomplete"));
+    Py_DECREF(result);
+
+    Py_RETURN_NONE;
+
+error:
+    PyUnicodeWriter_Discard(writer);
+    return NULL;
+}
+
+
+static PyObject *
 test_unicodewriter_format(PyObject *self, PyObject *Py_UNUSED(args))
 {
     PyUnicodeWriter *writer = PyUnicodeWriter_Create(0);
@@ -436,6 +549,42 @@ test_unicodewriter_format_recover_error(PyObject *self, PyObject *Py_UNUSED(args
 }
 
 
+static PyObject *
+test_unicodewriter_widechar(PyObject *self, PyObject *Py_UNUSED(args))
+{
+    PyUnicodeWriter *writer = PyUnicodeWriter_Create(0);
+    if (writer == NULL) {
+        return NULL;
+    }
+    if (PyUnicodeWriter_WriteWideChar(writer, L"latin1=\xE9 IGNORED", 8) < 0) {
+        goto error;
+    }
+    if (PyUnicodeWriter_WriteWideChar(writer, L"-", 1) < 0) {
+        goto error;
+    }
+    if (PyUnicodeWriter_WriteWideChar(writer, L"euro=\u20AC", -1) < 0) {
+        goto error;
+    }
+    if (PyUnicodeWriter_WriteChar(writer, '.') < 0) {
+        goto error;
+    }
+
+    PyObject *result = PyUnicodeWriter_Finish(writer);
+    if (result == NULL) {
+        return NULL;
+    }
+    assert(PyUnicode_EqualToUTF8(result,
+                                 "latin1=\xC3\xA9-euro=\xE2\x82\xAC."));
+    Py_DECREF(result);
+
+    Py_RETURN_NONE;
+
+error:
+    PyUnicodeWriter_Discard(writer);
+    return NULL;
+}
+
+
 static PyMethodDef TestMethods[] = {
     {"unicode_new",              unicode_new,                    METH_VARARGS},
     {"unicode_fill",             unicode_fill,                   METH_VARARGS},
@@ -448,8 +597,11 @@ static PyMethodDef TestMethods[] = {
     {"test_unicodewriter_utf8",  test_unicodewriter_utf8,        METH_NOARGS},
     {"test_unicodewriter_invalid_utf8", test_unicodewriter_invalid_utf8, METH_NOARGS},
     {"test_unicodewriter_recover_error", test_unicodewriter_recover_error, METH_NOARGS},
+    {"test_unicodewriter_decode_utf8", test_unicodewriter_decode_utf8, METH_NOARGS},
+    {"test_unicodewriter_decode_utf8_consumed", test_unicodewriter_decode_utf8_consumed, METH_NOARGS},
     {"test_unicodewriter_format", test_unicodewriter_format,     METH_NOARGS},
     {"test_unicodewriter_format_recover_error", test_unicodewriter_format_recover_error, METH_NOARGS},
+    {"test_unicodewriter_widechar", test_unicodewriter_widechar, METH_NOARGS},
     {NULL},
 };
 
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index bca2ab1..74a7438 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -1374,46 +1374,6 @@ PyUnicode_New(Py_ssize_t size, Py_UCS4 maxchar)
     return obj;
 }
 
-#if SIZEOF_WCHAR_T == 2
-/* Helper function to convert a 16-bits wchar_t representation to UCS4, this
-   will decode surrogate pairs, the other conversions are implemented as macros
-   for efficiency.
-
-   This function assumes that unicode can hold one more code point than wstr
-   characters for a terminating null character. */
-static void
-unicode_convert_wchar_to_ucs4(const wchar_t *begin, const wchar_t *end,
-                              PyObject *unicode)
-{
-    const wchar_t *iter;
-    Py_UCS4 *ucs4_out;
-
-    assert(unicode != NULL);
-    assert(_PyUnicode_CHECK(unicode));
-    assert(_PyUnicode_KIND(unicode) == PyUnicode_4BYTE_KIND);
-    ucs4_out = PyUnicode_4BYTE_DATA(unicode);
-
-    for (iter = begin; iter < end; ) {
-        assert(ucs4_out < (PyUnicode_4BYTE_DATA(unicode) +
-                           _PyUnicode_GET_LENGTH(unicode)));
-        if (Py_UNICODE_IS_HIGH_SURROGATE(iter[0])
-            && (iter+1) < end
-            && Py_UNICODE_IS_LOW_SURROGATE(iter[1]))
-        {
-            *ucs4_out++ = Py_UNICODE_JOIN_SURROGATES(iter[0], iter[1]);
-            iter += 2;
-        }
-        else {
-            *ucs4_out++ = *iter;
-            iter++;
-        }
-    }
-    assert(ucs4_out == (PyUnicode_4BYTE_DATA(unicode) +
-                        _PyUnicode_GET_LENGTH(unicode)));
-
-}
-#endif
-
 static int
 unicode_check_modifiable(PyObject *unicode)
 {
@@ -1937,6 +1897,62 @@ unicode_char(Py_UCS4 ch)
     return unicode;
 }
 
+
+static inline void
+unicode_write_widechar(int kind, void *data,
+                       const wchar_t *u, Py_ssize_t size,
+                       Py_ssize_t num_surrogates)
+{
+    switch (kind) {
+    case PyUnicode_1BYTE_KIND:
+        _PyUnicode_CONVERT_BYTES(wchar_t, unsigned char, u, u + size, data);
+        break;
+
+    case PyUnicode_2BYTE_KIND:
+#if SIZEOF_WCHAR_T == 2
+        memcpy(data, u, size * 2);
+#else
+        _PyUnicode_CONVERT_BYTES(wchar_t, Py_UCS2, u, u + size, data);
+#endif
+        break;
+
+    case PyUnicode_4BYTE_KIND:
+    {
+#if SIZEOF_WCHAR_T == 2
+        // Convert a 16-bits wchar_t representation to UCS4, this will decode
+        // surrogate pairs.
+        const wchar_t *end = u + size;
+        Py_UCS4 *ucs4_out = (Py_UCS4*)data;
+#  ifndef NDEBUG
+        Py_UCS4 *ucs4_end = (Py_UCS4*)data + (size - num_surrogates);
+#  endif
+        for (const wchar_t *iter = u; iter < end; ) {
+            assert(ucs4_out < ucs4_end);
+            if (Py_UNICODE_IS_HIGH_SURROGATE(iter[0])
+                && (iter+1) < end
+                && Py_UNICODE_IS_LOW_SURROGATE(iter[1]))
+            {
+                *ucs4_out++ = Py_UNICODE_JOIN_SURROGATES(iter[0], iter[1]);
+                iter += 2;
+            }
+            else {
+                *ucs4_out++ = *iter;
+                iter++;
+            }
+        }
+        assert(ucs4_out == ucs4_end);
+#else
+        assert(num_surrogates == 0);
+        memcpy(data, u, size * 4);
+#endif
+        break;
+    }
+    default:
+        Py_UNREACHABLE();
+    }
+}
+
+
 PyObject *
 PyUnicode_FromWideChar(const wchar_t *u, Py_ssize_t size)
 {
@@ -1989,36 +2005,65 @@ PyUnicode_FromWideChar(const wchar_t *u, Py_ssize_t size)
     if (!unicode)
         return NULL;
 
-    switch (PyUnicode_KIND(unicode)) {
-    case PyUnicode_1BYTE_KIND:
-        _PyUnicode_CONVERT_BYTES(wchar_t, unsigned char,
-                                u, u + size, PyUnicode_1BYTE_DATA(unicode));
-        break;
-    case PyUnicode_2BYTE_KIND:
-#if Py_UNICODE_SIZE == 2
-        memcpy(PyUnicode_2BYTE_DATA(unicode), u, size * 2);
-#else
-        _PyUnicode_CONVERT_BYTES(wchar_t, Py_UCS2,
-                                u, u + size, PyUnicode_2BYTE_DATA(unicode));
-#endif
-        break;
-    case PyUnicode_4BYTE_KIND:
-#if SIZEOF_WCHAR_T == 2
-        /* This is the only case which has to process surrogates, thus
-           a simple copy loop is not enough and we need a function. */
-        unicode_convert_wchar_to_ucs4(u, u + size, unicode);
-#else
-        assert(num_surrogates == 0);
-        memcpy(PyUnicode_4BYTE_DATA(unicode), u, size * 4);
+    unicode_write_widechar(PyUnicode_KIND(unicode), PyUnicode_DATA(unicode),
+                           u, size, num_surrogates);
+
+    return unicode_result(unicode);
+}
+
+
+int
+PyUnicodeWriter_WriteWideChar(PyUnicodeWriter *pub_writer,
+                              const wchar_t *str,
+                              Py_ssize_t size)
+{
+    _PyUnicodeWriter *writer = (_PyUnicodeWriter *)pub_writer;
+
+    if (size < 0) {
+        size = wcslen(str);
+    }
+
+    if (size == 0) {
+        return 0;
+    }
+
+#ifdef HAVE_NON_UNICODE_WCHAR_T_REPRESENTATION
+    /* Oracle Solaris uses non-Unicode internal wchar_t form for
+       non-Unicode locales and hence needs conversion to UCS-4 first. */
+    if (_Py_LocaleUsesNonUnicodeWchar()) {
+        wchar_t* converted = _Py_DecodeNonUnicodeWchar(str, size);
+        if (!converted) {
+            return -1;
+        }
+        PyObject *unicode = _PyUnicode_FromUCS4(converted, size);
+        PyMem_Free(converted);
+
+        int res = _PyUnicodeWriter_WriteStr(writer, unicode);
+        Py_DECREF(unicode);
+        return res;
+    }
 #endif
-        break;
-    default:
-        Py_UNREACHABLE();
+
+    Py_UCS4 maxchar = 0;
+    Py_ssize_t num_surrogates;
+    if (find_maxchar_surrogates(str, str + size,
+                                &maxchar, &num_surrogates) == -1) {
+        return -1;
     }
 
-    return unicode_result(unicode);
+    if (_PyUnicodeWriter_Prepare(writer, size - num_surrogates, maxchar) < 0) {
+        return -1;
+    }
+
+    int kind = writer->kind;
+    void *data = (Py_UCS1*)writer->data + writer->pos * kind;
+    unicode_write_widechar(kind, data, str, size, num_surrogates);
+
+    writer->pos += size - num_surrogates;
+    return 0;
 }
 
+
 PyObject *
 PyUnicode_FromStringAndSize(const char *u, Py_ssize_t size)
 {
@@ -13649,6 +13694,32 @@ PyUnicodeWriter_WriteUTF8(PyUnicodeWriter *writer,
     return res;
 }
 
+
+int
+PyUnicodeWriter_DecodeUTF8Stateful(PyUnicodeWriter *writer,
+                                   const char *string,
+                                   Py_ssize_t length,
+                                   const char *errors,
+                                   Py_ssize_t *consumed)
+{
+    if (length < 0) {
+        length = strlen(string);
+    }
+
+    _PyUnicodeWriter *_writer = (_PyUnicodeWriter*)writer;
+    Py_ssize_t old_pos = _writer->pos;
+    int res = unicode_decode_utf8_writer(_writer, string, length,
+                                         _Py_ERROR_UNKNOWN, errors, consumed);
+    if (res < 0) {
+        _writer->pos = old_pos;
+        if (consumed) {
+            *consumed = 0;
+        }
+    }
+    return res;
+}
+
+
 int
 _PyUnicodeWriter_WriteLatin1String(_PyUnicodeWriter *writer,
                                    const char *str, Py_ssize_t len)