bpo-27580: Add support of null characters in the csv module. (GH-28808)

3 files changed, 70 insertions, 38 deletions

diff --git a/Lib/test/test_csv.py b/Lib/test/test_csv.py
index 6e5dfc6..fb27ea3 100644
--- a/Lib/test/test_csv.py
+++ b/Lib/test/test_csv.py
@@ -217,6 +217,17 @@ class Test_Csv(unittest.TestCase):
         self._write_test(['C\\', '6', '7', 'X"'], 'C\\\\,6,7,"X"""',
                          escapechar='\\', quoting=csv.QUOTE_MINIMAL)
 
+    def test_write_lineterminator(self):
+        for lineterminator in '\r\n', '\n', '\r', '!@#', '\0':
+            with self.subTest(lineterminator=lineterminator):
+                with StringIO() as sio:
+                    writer = csv.writer(sio, lineterminator=lineterminator)
+                    writer.writerow(['a', 'b'])
+                    writer.writerow([1, 2])
+                    self.assertEqual(sio.getvalue(),
+                                     f'a,b{lineterminator}'
+                                     f'1,2{lineterminator}')
+
     def test_write_iterable(self):
         self._write_test(iter(['a', 1, 'p,q']), 'a,1,"p,q"')
         self._write_test(iter(['a', 1, None]), 'a,1,')
@@ -286,14 +297,10 @@ class Test_Csv(unittest.TestCase):
         self._read_test([''], [[]])
         self.assertRaises(csv.Error, self._read_test,
                           ['"ab"c'], None, strict = 1)
-        # cannot handle null bytes for the moment
-        self.assertRaises(csv.Error, self._read_test,
-                          ['ab\0c'], None, strict = 1)
         self._read_test(['"ab"c'], [['abc']], doublequote = 0)
 
         self.assertRaises(csv.Error, self._read_test,
-                          [b'ab\0c'], None)
-
+                          [b'abc'], None)
 
     def test_read_eol(self):
         self._read_test(['a,b'], [['a','b']])
@@ -313,6 +320,18 @@ class Test_Csv(unittest.TestCase):
         self.assertRaises(csv.Error, self._read_test,
                           ['^'], [], escapechar='^', strict=True)
 
+    def test_read_nul(self):
+        self._read_test(['\0'], [['\0']])
+        self._read_test(['a,\0b,c'], [['a', '\0b', 'c']])
+        self._read_test(['a,b\0,c'], [['a', 'b\0', 'c']])
+        self._read_test(['a,b\\\0,c'], [['a', 'b\0', 'c']], escapechar='\\')
+        self._read_test(['a,"\0b",c'], [['a', '\0b', 'c']])
+
+    def test_read_delimiter(self):
+        self._read_test(['a,b,c'], [['a', 'b', 'c']])
+        self._read_test(['a;b;c'], [['a', 'b', 'c']], delimiter=';')
+        self._read_test(['a\0b\0c'], [['a', 'b', 'c']], delimiter='\0')
+
     def test_read_escape(self):
         self._read_test(['a,\\b,c'], [['a', 'b', 'c']], escapechar='\\')
         self._read_test(['a,b\\,c'], [['a', 'b,c']], escapechar='\\')
@@ -320,6 +339,11 @@ class Test_Csv(unittest.TestCase):
         self._read_test(['a,"b,\\c"'], [['a', 'b,c']], escapechar='\\')
         self._read_test(['a,"b,c\\""'], [['a', 'b,c"']], escapechar='\\')
         self._read_test(['a,"b,c"\\'], [['a', 'b,c\\']], escapechar='\\')
+        self._read_test(['a,^b,c'], [['a', 'b', 'c']], escapechar='^')
+        self._read_test(['a,\0b,c'], [['a', 'b', 'c']], escapechar='\0')
+        self._read_test(['a,\\b,c'], [['a', '\\b', 'c']], escapechar=None)
+        self._read_test(['a,\\b,c'], [['a', '\\b', 'c']], escapechar='')
+        self._read_test(['a,\\b,c'], [['a', '\\b', 'c']])
 
     def test_read_quoting(self):
         self._read_test(['1,",3,",5'], [['1', ',3,', '5']])
@@ -334,6 +358,8 @@ class Test_Csv(unittest.TestCase):
         self.assertRaises(ValueError, self._read_test,
                           ['abc,3'], [[]],
                           quoting=csv.QUOTE_NONNUMERIC)
+        self._read_test(['1,@,3,@,5'], [['1', ',3,', '5']], quotechar='@')
+        self._read_test(['1,\0,3,\0,5'], [['1', ',3,', '5']], quotechar='\0')
 
     def test_read_bigfield(self):
         # This exercises the buffer realloc functionality and field size
@@ -1074,6 +1100,12 @@ Stonecutters Seafood and Chop House+ Lemont+ IL+ 12/19/02+ Week Back
                         a,b
                         """)
 
+    sample14 = """\
+abc\0def
+ghijkl\0mno
+ghi\0jkl
+"""
+
     def test_issue43625(self):
         sniffer = csv.Sniffer()
         self.assertTrue(sniffer.has_header(self.sample12))
@@ -1142,6 +1174,8 @@ Stonecutters Seafood and Chop House+ Lemont+ IL+ 12/19/02+ Week Back
         dialect = sniffer.sniff(self.sample9)
         self.assertEqual(dialect.delimiter, '+')
         self.assertEqual(dialect.quotechar, "'")
+        dialect = sniffer.sniff(self.sample14)
+        self.assertEqual(dialect.delimiter, '\0')
 
     def test_doublequote(self):
         sniffer = csv.Sniffer()
diff --git a/Misc/NEWS.d/next/Library/2021-10-07-21-11-48.bpo-27580.tGcBTH.rst b/Misc/NEWS.d/next/Library/2021-10-07-21-11-48.bpo-27580.tGcBTH.rst
new file mode 100644
index 0000000..15a8ff2
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-10-07-21-11-48.bpo-27580.tGcBTH.rst
@@ -0,0 +1 @@
+Add support of null characters in :mod:`csv`.
diff --git a/Modules/_csv.c b/Modules/_csv.c
index 72f0791..469c1a1 100644
--- a/Modules/_csv.c
+++ b/Modules/_csv.c
@@ -14,6 +14,9 @@ module instead.
 #include "structmember.h"         // PyMemberDef
 #include <stdbool.h>
 
+#define NOT_SET ((Py_UCS4)-1)
+#define EOL ((Py_UCS4)-2)
+
 
 typedef struct {
     PyObject *error_obj;   /* CSV exception */
@@ -153,9 +156,9 @@ get_dialect_from_registry(PyObject *name_obj, _csvstate *module_state)
 }
 
 static PyObject *
-get_nullchar_as_None(Py_UCS4 c)
+get_char_or_None(Py_UCS4 c)
 {
-    if (c == '\0') {
+    if (c == NOT_SET) {
         Py_RETURN_NONE;
     }
     else
@@ -172,19 +175,19 @@ Dialect_get_lineterminator(DialectObj *self, void *Py_UNUSED(ignored))
 static PyObject *
 Dialect_get_delimiter(DialectObj *self, void *Py_UNUSED(ignored))
 {
-    return get_nullchar_as_None(self->delimiter);
+    return get_char_or_None(self->delimiter);
 }
 
 static PyObject *
 Dialect_get_escapechar(DialectObj *self, void *Py_UNUSED(ignored))
 {
-    return get_nullchar_as_None(self->escapechar);
+    return get_char_or_None(self->escapechar);
 }
 
 static PyObject *
 Dialect_get_quotechar(DialectObj *self, void *Py_UNUSED(ignored))
 {
-    return get_nullchar_as_None(self->quotechar);
+    return get_char_or_None(self->quotechar);
 }
 
 static PyObject *
@@ -235,7 +238,7 @@ _set_char_or_none(const char *name, Py_UCS4 *target, PyObject *src, Py_UCS4 dflt
         *target = dflt;
     }
     else {
-        *target = '\0';
+        *target = NOT_SET;
         if (src != Py_None) {
             if (!PyUnicode_Check(src)) {
                 PyErr_Format(PyExc_TypeError,
@@ -254,7 +257,7 @@ _set_char_or_none(const char *name, Py_UCS4 *target, PyObject *src, Py_UCS4 dflt
                 return -1;
             }
             /* PyUnicode_READY() is called in PyUnicode_GetLength() */
-            else {
+            else if (len > 0) {
                 *target = PyUnicode_READ_CHAR(src, 0);
             }
         }
@@ -269,7 +272,7 @@ _set_char(const char *name, Py_UCS4 *target, PyObject *src, Py_UCS4 dflt)
         *target = dflt;
     }
     else {
-        *target = '\0';
+        *target = NOT_SET;
         if (!PyUnicode_Check(src)) {
             PyErr_Format(PyExc_TypeError,
                          "\"%s\" must be string, not %.200s", name,
@@ -287,7 +290,7 @@ _set_char(const char *name, Py_UCS4 *target, PyObject *src, Py_UCS4 dflt)
             return -1;
         }
         /* PyUnicode_READY() is called in PyUnicode_GetLength() */
-        else {
+        else if (len > 0) {
             *target = PyUnicode_READ_CHAR(src, 0);
         }
     }
@@ -481,7 +484,7 @@ dialect_new(PyTypeObject *type, PyObject *args, PyObject *kwargs)
         goto err
     DIASET(_set_char, "delimiter", &self->delimiter, delimiter, ',');
     DIASET(_set_bool, "doublequote", &self->doublequote, doublequote, true);
-    DIASET(_set_char_or_none, "escapechar", &self->escapechar, escapechar, 0);
+    DIASET(_set_char_or_none, "escapechar", &self->escapechar, escapechar, NOT_SET);
     DIASET(_set_str, "lineterminator", &self->lineterminator, lineterminator, "\r\n");
     DIASET(_set_char_or_none, "quotechar", &self->quotechar, quotechar, '"');
     DIASET(_set_int, "quoting", &self->quoting, quoting, QUOTE_MINIMAL);
@@ -491,19 +494,19 @@ dialect_new(PyTypeObject *type, PyObject *args, PyObject *kwargs)
     /* validate options */
     if (dialect_check_quoting(self->quoting))
         goto err;
-    if (self->delimiter == 0) {
+    if (self->delimiter == NOT_SET) {
         PyErr_SetString(PyExc_TypeError,
                         "\"delimiter\" must be a 1-character string");
         goto err;
     }
     if (quotechar == Py_None && quoting == NULL)
         self->quoting = QUOTE_NONE;
-    if (self->quoting != QUOTE_NONE && self->quotechar == 0) {
+    if (self->quoting != QUOTE_NONE && self->quotechar == NOT_SET) {
         PyErr_SetString(PyExc_TypeError,
                         "quotechar must be set if quoting enabled");
         goto err;
     }
-    if (self->lineterminator == 0) {
+    if (self->lineterminator == NULL) {
         PyErr_SetString(PyExc_TypeError, "lineterminator must be set");
         goto err;
     }
@@ -670,7 +673,7 @@ parse_process_char(ReaderObj *self, _csvstate *module_state, Py_UCS4 c)
     switch (self->state) {
     case START_RECORD:
         /* start of record */
-        if (c == '\0')
+        if (c == EOL)
             /* empty line - return [] */
             break;
         else if (c == '\n' || c == '\r') {
@@ -682,11 +685,11 @@ parse_process_char(ReaderObj *self, _csvstate *module_state, Py_UCS4 c)
         /* fallthru */
     case START_FIELD:
         /* expecting field */
-        if (c == '\n' || c == '\r' || c == '\0') {
+        if (c == '\n' || c == '\r' || c == EOL) {
             /* save empty field - return [fields] */
             if (parse_save_field(self) < 0)
                 return -1;
-            self->state = (c == '\0' ? START_RECORD : EAT_CRNL);
+            self->state = (c == EOL ? START_RECORD : EAT_CRNL);
         }
         else if (c == dialect->quotechar &&
                  dialect->quoting != QUOTE_NONE) {
@@ -722,7 +725,7 @@ parse_process_char(ReaderObj *self, _csvstate *module_state, Py_UCS4 c)
             self->state = AFTER_ESCAPED_CRNL;
             break;
         }
-        if (c == '\0')
+        if (c == EOL)
             c = '\n';
         if (parse_add_char(self, module_state, c) < 0)
             return -1;
@@ -730,17 +733,17 @@ parse_process_char(ReaderObj *self, _csvstate *module_state, Py_UCS4 c)
         break;
 
     case AFTER_ESCAPED_CRNL:
-        if (c == '\0')
+        if (c == EOL)
             break;
         /*fallthru*/
 
     case IN_FIELD:
         /* in unquoted field */
-        if (c == '\n' || c == '\r' || c == '\0') {
+        if (c == '\n' || c == '\r' || c == EOL) {
             /* end of line - return [fields] */
             if (parse_save_field(self) < 0)
                 return -1;
-            self->state = (c == '\0' ? START_RECORD : EAT_CRNL);
+            self->state = (c == EOL ? START_RECORD : EAT_CRNL);
         }
         else if (c == dialect->escapechar) {
             /* possible escaped character */
@@ -761,7 +764,7 @@ parse_process_char(ReaderObj *self, _csvstate *module_state, Py_UCS4 c)
 
     case IN_QUOTED_FIELD:
         /* in quoted field */
-        if (c == '\0')
+        if (c == EOL)
             ;
         else if (c == dialect->escapechar) {
             /* Possible escape character */
@@ -786,7 +789,7 @@ parse_process_char(ReaderObj *self, _csvstate *module_state, Py_UCS4 c)
         break;
 
     case ESCAPE_IN_QUOTED_FIELD:
-        if (c == '\0')
+        if (c == EOL)
             c = '\n';
         if (parse_add_char(self, module_state, c) < 0)
             return -1;
@@ -808,11 +811,11 @@ parse_process_char(ReaderObj *self, _csvstate *module_state, Py_UCS4 c)
                 return -1;
             self->state = START_FIELD;
         }
-        else if (c == '\n' || c == '\r' || c == '\0') {
+        else if (c == '\n' || c == '\r' || c == EOL) {
             /* end of line - return [fields] */
             if (parse_save_field(self) < 0)
                 return -1;
-            self->state = (c == '\0' ? START_RECORD : EAT_CRNL);
+            self->state = (c == EOL ? START_RECORD : EAT_CRNL);
         }
         else if (!dialect->strict) {
             if (parse_add_char(self, module_state, c) < 0)
@@ -831,7 +834,7 @@ parse_process_char(ReaderObj *self, _csvstate *module_state, Py_UCS4 c)
     case EAT_CRNL:
         if (c == '\n' || c == '\r')
             ;
-        else if (c == '\0')
+        else if (c == EOL)
             self->state = START_RECORD;
         else {
             PyErr_Format(module_state->error_obj,
@@ -909,12 +912,6 @@ Reader_iternext(ReaderObj *self)
         linelen = PyUnicode_GET_LENGTH(lineobj);
         while (linelen--) {
             c = PyUnicode_READ(kind, data, pos);
-            if (c == '\0') {
-                Py_DECREF(lineobj);
-                PyErr_Format(module_state->error_obj,
-                             "line contains NUL");
-                goto err;
-            }
             if (parse_process_char(self, module_state, c) < 0) {
                 Py_DECREF(lineobj);
                 goto err;
@@ -922,7 +919,7 @@ Reader_iternext(ReaderObj *self)
             pos++;
         }
         Py_DECREF(lineobj);
-        if (parse_process_char(self, module_state, 0) < 0)
+        if (parse_process_char(self, module_state, EOL) < 0)
             goto err;
     } while (self->state != START_RECORD);
 
@@ -1127,7 +1124,7 @@ join_append_data(WriterObj *self, unsigned int field_kind, const void *field_dat
                     *quoted = 1;
             }
             if (want_escape) {
-                if (!dialect->escapechar) {
+                if (dialect->escapechar == NOT_SET) {
                     PyErr_Format(self->error_obj,
                                  "need to escape, but no escapechar set");
                     return -1;