summaryrefslogtreecommitdiff
path: root/Modules/_io/stringio.c
blob: c9d14b114b181786f582a1840a370ca4b5e62279 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
#define PY_SSIZE_T_CLEAN
#include "Python.h"
#include "structmember.h"
#include "_iomodule.h"

/* Implementation note: the buffer is always at least one character longer
   than the enclosed string, for proper functioning of _PyIO_find_line_ending.
*/

typedef struct {
    PyObject_HEAD
    Py_UNICODE *buf;
    Py_ssize_t pos;
    Py_ssize_t string_size;
    size_t buf_size;

    char ok; /* initialized? */
    char closed;
    char readuniversal;
    char readtranslate;
    PyObject *decoder;
    PyObject *readnl;
    PyObject *writenl;
    
    PyObject *dict;
    PyObject *weakreflist;
} stringio;

#define CHECK_INITIALIZED(self) \
    if (self->ok <= 0) { \
        PyErr_SetString(PyExc_ValueError, \
            "I/O operation on uninitialized object"); \
        return NULL; \
    }

#define CHECK_CLOSED(self) \
    if (self->closed) { \
        PyErr_SetString(PyExc_ValueError, \
            "I/O operation on closed file"); \
        return NULL; \
    }

PyDoc_STRVAR(stringio_doc,
    "Text I/O implementation using an in-memory buffer.\n"
    "\n"
    "The initial_value argument sets the value of object.  The newline\n"
    "argument is like the one of TextIOWrapper's constructor.");


/* Internal routine for changing the size, in terms of characters, of the
   buffer of StringIO objects.  The caller should ensure that the 'size'
   argument is non-negative.  Returns 0 on success, -1 otherwise. */
static int
resize_buffer(stringio *self, size_t size)
{
    /* Here, unsigned types are used to avoid dealing with signed integer
       overflow, which is undefined in C. */
    size_t alloc = self->buf_size;
    Py_UNICODE *new_buf = NULL;

    assert(self->buf != NULL);

    /* Reserve one more char for line ending detection. */
    size = size + 1;
    /* For simplicity, stay in the range of the signed type. Anyway, Python
       doesn't allow strings to be longer than this. */
    if (size > PY_SSIZE_T_MAX)
        goto overflow;

    if (size < alloc / 2) {
        /* Major downsize; resize down to exact size. */
        alloc = size + 1;
    }
    else if (size < alloc) {
        /* Within allocated size; quick exit */
        return 0;
    }
    else if (size <= alloc * 1.125) {
        /* Moderate upsize; overallocate similar to list_resize() */
        alloc = size + (size >> 3) + (size < 9 ? 3 : 6);
    }
    else {
        /* Major upsize; resize up to exact size */
        alloc = size + 1;
    }

    if (alloc > ((size_t)-1) / sizeof(Py_UNICODE))
        goto overflow;
    new_buf = (Py_UNICODE *)PyMem_Realloc(self->buf,
                                          alloc * sizeof(Py_UNICODE));
    if (new_buf == NULL) {
        PyErr_NoMemory();
        return -1;
    }
    self->buf_size = alloc;
    self->buf = new_buf;

    return 0;

  overflow:
    PyErr_SetString(PyExc_OverflowError,
                    "new buffer size too large");
    return -1;
}

/* Internal routine for writing a whole PyUnicode object to the buffer of a
   StringIO object. Returns 0 on success, or -1 on error. */
static Py_ssize_t
write_str(stringio *self, PyObject *obj)
{
    Py_UNICODE *str;
    Py_ssize_t len;
    PyObject *decoded = NULL;
    assert(self->buf != NULL);
    assert(self->pos >= 0);

    if (self->decoder != NULL) {
        decoded = _PyIncrementalNewlineDecoder_decode(
            self->decoder, obj, 1 /* always final */);
    }
    else {
        decoded = obj;
        Py_INCREF(decoded);
    }
    if (self->writenl) {
        PyObject *translated = PyUnicode_Replace(
            decoded, _PyIO_str_nl, self->writenl, -1);
        Py_DECREF(decoded);
        decoded = translated;
    }
    if (decoded == NULL)
        return -1;

    assert(PyUnicode_Check(decoded));
    str = PyUnicode_AS_UNICODE(decoded);
    len = PyUnicode_GET_SIZE(decoded);

    assert(len >= 0);

    /* This overflow check is not strictly necessary. However, it avoids us to
       deal with funky things like comparing an unsigned and a signed
       integer. */
    if (self->pos > PY_SSIZE_T_MAX - len) {
        PyErr_SetString(PyExc_OverflowError,
                        "new position too large");
        goto fail;
    }
    if (self->pos + len > self->string_size) {
        if (resize_buffer(self, self->pos + len) < 0)
            goto fail;
    }

    if (self->pos > self->string_size) {
        /* In case of overseek, pad with null bytes the buffer region between
           the end of stream and the current position.

          0   lo      string_size                           hi
          |   |<---used--->|<----------available----------->|
          |   |            <--to pad-->|<---to write--->    |
          0   buf                   position

        */
        memset(self->buf + self->string_size, '\0',
               (self->pos - self->string_size) * sizeof(Py_UNICODE));
    }

    /* Copy the data to the internal buffer, overwriting some of the
       existing data if self->pos < self->string_size. */
    memcpy(self->buf + self->pos, str, len * sizeof(Py_UNICODE));
    self->pos += len;

    /* Set the new length of the internal string if it has changed. */
    if (self->string_size < self->pos) {
        self->string_size = self->pos;
    }

    Py_DECREF(decoded);
    return 0;

fail:
    Py_XDECREF(decoded);
    return -1;
}

PyDoc_STRVAR(stringio_getvalue_doc,
    "Retrieve the entire contents of the object.");

static PyObject *
stringio_getvalue(stringio *self)
{
    CHECK_INITIALIZED(self);
    CHECK_CLOSED(self);
    return PyUnicode_FromUnicode(self->buf, self->string_size);
}

PyDoc_STRVAR(stringio_tell_doc,
    "Tell the current file position.");

static PyObject *
stringio_tell(stringio *self)
{
    CHECK_INITIALIZED(self);
    CHECK_CLOSED(self);
    return PyLong_FromSsize_t(self->pos);
}

PyDoc_STRVAR(stringio_read_doc,
    "Read at most n characters, returned as a string.\n"
    "\n"
    "If the argument is negative or omitted, read until EOF\n"
    "is reached. Return an empty string at EOF.\n");

static PyObject *
stringio_read(stringio *self, PyObject *args)
{
    Py_ssize_t size, n;
    Py_UNICODE *output;
    PyObject *arg = Py_None;

    CHECK_INITIALIZED(self);
    if (!PyArg_ParseTuple(args, "|O:read", &arg))
        return NULL;
    CHECK_CLOSED(self);

    if (PyNumber_Check(arg)) {
        size = PyNumber_AsSsize_t(arg, PyExc_OverflowError);
        if (size == -1 && PyErr_Occurred())
            return NULL;
    }
    else if (arg == Py_None) {
        /* Read until EOF is reached, by default. */
        size = -1;
    }
    else {
        PyErr_Format(PyExc_TypeError, "integer argument expected, got '%s'",
                     Py_TYPE(arg)->tp_name);
        return NULL;
    }

    /* adjust invalid sizes */
    n = self->string_size - self->pos;
    if (size < 0 || size > n) {
        size = n;
        if (size < 0)
            size = 0;
    }

    output = self->buf + self->pos;
    self->pos += size;
    return PyUnicode_FromUnicode(output, size);
}

/* Internal helper, used by stringio_readline and stringio_iternext */
static PyObject *
_stringio_readline(stringio *self, Py_ssize_t limit)
{
    Py_UNICODE *start, *end, old_char;
    Py_ssize_t len, consumed;

    /* In case of overseek, return the empty string */
    if (self->pos >= self->string_size)
        return PyUnicode_FromString("");

    start = self->buf + self->pos;
    if (limit < 0 || limit > self->string_size - self->pos)
        limit = self->string_size - self->pos;

    end = start + limit;
    old_char = *end;
    *end = '\0';
    len = _PyIO_find_line_ending(
        self->readtranslate, self->readuniversal, self->readnl,
        start, end, &consumed);
    *end = old_char;
    /* If we haven't found any line ending, we just return everything
       (`consumed` is ignored). */
    if (len < 0)
        len = limit;
    self->pos += len;
    return PyUnicode_FromUnicode(start, len);
}

PyDoc_STRVAR(stringio_readline_doc,
    "Read until newline or EOF.\n"
    "\n"
    "Returns an empty string if EOF is hit immediately.\n");

static PyObject *
stringio_readline(stringio *self, PyObject *args)
{
    PyObject *arg = Py_None;
    Py_ssize_t limit = -1;

    CHECK_INITIALIZED(self);
    if (!PyArg_ParseTuple(args, "|O:readline", &arg))
        return NULL;
    CHECK_CLOSED(self);

    if (PyNumber_Check(arg)) {
        limit = PyNumber_AsSsize_t(arg, PyExc_OverflowError);
        if (limit == -1 && PyErr_Occurred())
            return NULL;
    }
    else if (arg != Py_None) {
        PyErr_Format(PyExc_TypeError, "integer argument expected, got '%s'",
                     Py_TYPE(arg)->tp_name);
        return NULL;
    }
    return _stringio_readline(self, limit);
}

static PyObject *
stringio_iternext(stringio *self)
{
    PyObject *line;

    CHECK_INITIALIZED(self);
    CHECK_CLOSED(self);

    if (Py_TYPE(self) == &PyStringIO_Type) {
        /* Skip method call overhead for speed */
        line = _stringio_readline(self, -1);
    }
    else {
        /* XXX is subclassing StringIO really supported? */
        line = PyObject_CallMethodObjArgs((PyObject *)self,
                                           _PyIO_str_readline, NULL);
        if (line && !PyUnicode_Check(line)) {
            PyErr_Format(PyExc_IOError,
                         "readline() should have returned an str object, "
                         "not '%.200s'", Py_TYPE(line)->tp_name);
            Py_DECREF(line);
            return NULL;
        }
    }

    if (line == NULL)
        return NULL;

    if (PyUnicode_GET_SIZE(line) == 0) {
        /* Reached EOF */
        Py_DECREF(line);
        return NULL;
    }

    return line;
}

PyDoc_STRVAR(stringio_truncate_doc,
    "Truncate size to pos.\n"
    "\n"
    "The pos argument defaults to the current file position, as\n"
    "returned by tell().  The current file position is unchanged.\n"
    "Returns the new absolute position.\n");

static PyObject *
stringio_truncate(stringio *self, PyObject *args)
{
    Py_ssize_t size;
    PyObject *arg = Py_None;

    CHECK_INITIALIZED(self);
    if (!PyArg_ParseTuple(args, "|O:truncate", &arg))
        return NULL;
    CHECK_CLOSED(self);

    if (PyNumber_Check(arg)) {
        size = PyNumber_AsSsize_t(arg, PyExc_OverflowError);
        if (size == -1 && PyErr_Occurred())
            return NULL;
    }
    else if (arg == Py_None) {
        /* Truncate to current position if no argument is passed. */
        size = self->pos;
    }
    else {
        PyErr_Format(PyExc_TypeError, "integer argument expected, got '%s'",
                     Py_TYPE(arg)->tp_name);
        return NULL;
    }

    if (size < 0) {
        PyErr_Format(PyExc_ValueError,
                     "Negative size value %zd", size);
        return NULL;
    }

    if (size < self->string_size) {
        if (resize_buffer(self, size) < 0)
            return NULL;
        self->string_size = size;
    }

    return PyLong_FromSsize_t(size);
}

PyDoc_STRVAR(stringio_seek_doc,
    "Change stream position.\n"
    "\n"
    "Seek to character offset pos relative to position indicated by whence:\n"
    "    0  Start of stream (the default).  pos should be >= 0;\n"
    "    1  Current position - pos must be 0;\n"
    "    2  End of stream - pos must be 0.\n"
    "Returns the new absolute position.\n");

static PyObject *
stringio_seek(stringio *self, PyObject *args)
{
    Py_ssize_t pos;
    int mode = 0;

    CHECK_INITIALIZED(self);
    if (!PyArg_ParseTuple(args, "n|i:seek", &pos, &mode))
        return NULL;
    CHECK_CLOSED(self);

    if (mode != 0 && mode != 1 && mode != 2) {
        PyErr_Format(PyExc_ValueError,
                     "Invalid whence (%i, should be 0, 1 or 2)", mode);
        return NULL;
    }
    else if (pos < 0 && mode == 0) {
        PyErr_Format(PyExc_ValueError,
                     "Negative seek position %zd", pos);
        return NULL;
    }
    else if (mode != 0 && pos != 0) {
        PyErr_SetString(PyExc_IOError,
                        "Can't do nonzero cur-relative seeks");
        return NULL;
    }

    /* mode 0: offset relative to beginning of the string.
       mode 1: no change to current position.
       mode 2: change position to end of file. */
    if (mode == 1) {
        pos = self->pos;
    }
    else if (mode == 2) {
        pos = self->string_size;
    }

    self->pos = pos;

    return PyLong_FromSsize_t(self->pos);
}

PyDoc_STRVAR(stringio_write_doc,
    "Write string to file.\n"
    "\n"
    "Returns the number of characters written, which is always equal to\n"
    "the length of the string.\n");

static PyObject *
stringio_write(stringio *self, PyObject *obj)
{
    Py_ssize_t size;

    CHECK_INITIALIZED(self);
    if (!PyUnicode_Check(obj)) {
        PyErr_Format(PyExc_TypeError, "string argument expected, got '%s'",
                     Py_TYPE(obj)->tp_name);
        return NULL;
    }
    CHECK_CLOSED(self);
    size = PyUnicode_GET_SIZE(obj);

    if (size > 0 && write_str(self, obj) < 0)
        return NULL;

    return PyLong_FromSsize_t(size);
}

PyDoc_STRVAR(stringio_close_doc,
    "Close the IO object. Attempting any further operation after the\n"
    "object is closed will raise a ValueError.\n"
    "\n"
    "This method has no effect if the file is already closed.\n");

static PyObject *
stringio_close(stringio *self)
{
    self->closed = 1;
    /* Free up some memory */
    if (resize_buffer(self, 0) < 0)
        return NULL;
    Py_CLEAR(self->readnl);
    Py_CLEAR(self->writenl);
    Py_CLEAR(self->decoder);
    Py_RETURN_NONE;
}

static int
stringio_traverse(stringio *self, visitproc visit, void *arg)
{
    Py_VISIT(self->dict);
    return 0;
}

static int
stringio_clear(stringio *self)
{
    Py_CLEAR(self->dict);
    return 0;
}

static void
stringio_dealloc(stringio *self)
{
    _PyObject_GC_UNTRACK(self);
    self->ok = 0;
    if (self->buf) {
        PyMem_Free(self->buf);
        self->buf = NULL;
    }
    Py_CLEAR(self->readnl);
    Py_CLEAR(self->writenl);
    Py_CLEAR(self->decoder);
    Py_CLEAR(self->dict);
    if (self->weakreflist != NULL)
        PyObject_ClearWeakRefs((PyObject *) self);
    Py_TYPE(self)->tp_free(self);
}

static PyObject *
stringio_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    stringio *self;

    assert(type != NULL && type->tp_alloc != NULL);
    self = (stringio *)type->tp_alloc(type, 0);
    if (self == NULL)
        return NULL;

    /* tp_alloc initializes all the fields to zero. So we don't have to
       initialize them here. */

    self->buf = (Py_UNICODE *)PyMem_Malloc(0);
    if (self->buf == NULL) {
        Py_DECREF(self);
        return PyErr_NoMemory();
    }

    return (PyObject *)self;
}

static int
stringio_init(stringio *self, PyObject *args, PyObject *kwds)
{
    char *kwlist[] = {"initial_value", "newline", NULL};
    PyObject *value = NULL;
    PyObject *newline_obj = NULL;
    char *newline = "\n";

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "|OO:__init__", kwlist,
                                     &value, &newline_obj))
        return -1;

    /* Parse the newline argument. This used to be done with the 'z'
       specifier, however this allowed any object with the buffer interface to
       be converted. Thus we have to parse it manually since we only want to
       allow unicode objects or None. */
    if (newline_obj == Py_None) {
        newline = NULL;
    }
    else if (newline_obj) {
        if (!PyUnicode_Check(newline_obj)) {
            PyErr_Format(PyExc_TypeError,
                         "newline must be str or None, not %.200s",
                         Py_TYPE(newline_obj)->tp_name);
            return -1;
        }
        newline = _PyUnicode_AsString(newline_obj);
        if (newline == NULL)
            return -1;
    }

    if (newline && newline[0] != '\0'
        && !(newline[0] == '\n' && newline[1] == '\0')
        && !(newline[0] == '\r' && newline[1] == '\0')
        && !(newline[0] == '\r' && newline[1] == '\n' && newline[2] == '\0')) {
        PyErr_Format(PyExc_ValueError,
                     "illegal newline value: %R", newline_obj);
        return -1;
    }
    if (value && value != Py_None && !PyUnicode_Check(value)) {
        PyErr_Format(PyExc_TypeError,
                     "initial_value must be str or None, not %.200s",
                     Py_TYPE(value)->tp_name);
        return -1;
    }

    self->ok = 0;

    Py_CLEAR(self->readnl);
    Py_CLEAR(self->writenl);
    Py_CLEAR(self->decoder);

    assert((newline != NULL && newline_obj != Py_None) ||
           (newline == NULL && newline_obj == Py_None));

    if (newline) {
        self->readnl = PyUnicode_FromString(newline);
        if (self->readnl == NULL)
            return -1;
    }
    self->readuniversal = (newline == NULL || newline[0] == '\0');
    self->readtranslate = (newline == NULL);
    /* If newline == "", we don't translate anything.
       If newline == "\n" or newline == None, we translate to "\n", which is
       a no-op.
       (for newline == None, TextIOWrapper translates to os.sepline, but it
       is pointless for StringIO)
    */
    if (newline != NULL && newline[0] == '\r') {
        self->writenl = self->readnl;
        Py_INCREF(self->writenl);
    }

    if (self->readuniversal) {
        self->decoder = PyObject_CallFunction(
            (PyObject *)&PyIncrementalNewlineDecoder_Type,
            "Oi", Py_None, (int) self->readtranslate);
        if (self->decoder == NULL)
            return -1;
    }

    /* Now everything is set up, resize buffer to size of initial value,
       and copy it */
    self->string_size = 0;
    if (value && value != Py_None) {
        Py_ssize_t len = PyUnicode_GetSize(value);
        /* This is a heuristic, for newline translation might change
           the string length. */
        if (resize_buffer(self, len) < 0)
            return -1;
        self->pos = 0;
        if (write_str(self, value) < 0)
            return -1;
    }
    else {
        if (resize_buffer(self, 0) < 0)
            return -1;
    }
    self->pos = 0;

    self->closed = 0;
    self->ok = 1;
    return 0;
}

/* Properties and pseudo-properties */
static PyObject *
stringio_seekable(stringio *self, PyObject *args)
{
    CHECK_INITIALIZED(self);
    Py_RETURN_TRUE;
}

static PyObject *
stringio_readable(stringio *self, PyObject *args)
{
    CHECK_INITIALIZED(self);
    Py_RETURN_TRUE;
}

static PyObject *
stringio_writable(stringio *self, PyObject *args)
{
    CHECK_INITIALIZED(self);
    Py_RETURN_TRUE;
}

/* Pickling support.

   The implementation of __getstate__ is similar to the one for BytesIO,
   except that we also save the newline parameter. For __setstate__ and unlike
   BytesIO, we call __init__ to restore the object's state. Doing so allows us
   to avoid decoding the complex newline state while keeping the object
   representation compact.

   See comment in bytesio.c regarding why only pickle protocols and onward are
   supported.
*/

static PyObject *
stringio_getstate(stringio *self)
{
    PyObject *initvalue = stringio_getvalue(self);
    PyObject *dict;
    PyObject *state;

    if (initvalue == NULL)
        return NULL;
    if (self->dict == NULL) {
        Py_INCREF(Py_None);
        dict = Py_None;
    }
    else {
        dict = PyDict_Copy(self->dict);
        if (dict == NULL)
            return NULL;
    }

    state = Py_BuildValue("(OOnN)", initvalue,
                          self->readnl ? self->readnl : Py_None,
                          self->pos, dict);
    Py_DECREF(initvalue);
    return state;
}

static PyObject *
stringio_setstate(stringio *self, PyObject *state)
{
    PyObject *initarg;
    PyObject *position_obj;
    PyObject *dict;
    Py_ssize_t pos;

    assert(state != NULL);
    CHECK_CLOSED(self);

    /* We allow the state tuple to be longer than 4, because we may need
       someday to extend the object's state without breaking
       backward-compatibility. */
    if (!PyTuple_Check(state) || Py_SIZE(state) < 4) {
        PyErr_Format(PyExc_TypeError,
                     "%.200s.__setstate__ argument should be 4-tuple, got %.200s",
                     Py_TYPE(self)->tp_name, Py_TYPE(state)->tp_name);
        return NULL;
    }

    /* Initialize the object's state. */
    initarg = PyTuple_GetSlice(state, 0, 2);
    if (initarg == NULL)
        return NULL;
    if (stringio_init(self, initarg, NULL) < 0) {
        Py_DECREF(initarg);
        return NULL;
    }
    Py_DECREF(initarg);

    /* Restore the buffer state. Even if __init__ did initialize the buffer,
       we have to initialize it again since __init__ may translates the
       newlines in the inital_value string. We clearly do not want that
       because the string value in the state tuple has already been translated
       once by __init__. So we do not take any chance and replace object's
       buffer completely. */
    {
        Py_UNICODE *buf = PyUnicode_AS_UNICODE(PyTuple_GET_ITEM(state, 0));
        Py_ssize_t bufsize = PyUnicode_GET_SIZE(PyTuple_GET_ITEM(state, 0));
        if (resize_buffer(self, bufsize) < 0)
            return NULL;
        memcpy(self->buf, buf, bufsize * sizeof(Py_UNICODE));
        self->string_size = bufsize;
    }

    /* Set carefully the position value. Alternatively, we could use the seek
       method instead of modifying self->pos directly to better protect the
       object internal state against errneous (or malicious) inputs. */
    position_obj = PyTuple_GET_ITEM(state, 2);
    if (!PyLong_Check(position_obj)) {
        PyErr_Format(PyExc_TypeError,
                     "third item of state must be an integer, got %.200s",
                     Py_TYPE(position_obj)->tp_name);
        return NULL;
    }
    pos = PyLong_AsSsize_t(position_obj);
    if (pos == -1 && PyErr_Occurred())
        return NULL;
    if (pos < 0) {
        PyErr_SetString(PyExc_ValueError,
                        "position value cannot be negative");
        return NULL;
    }
    self->pos = pos;

    /* Set the dictionary of the instance variables. */
    dict = PyTuple_GET_ITEM(state, 3);
    if (dict != Py_None) {
        if (!PyDict_Check(dict)) {
            PyErr_Format(PyExc_TypeError,
                         "fourth item of state should be a dict, got a %.200s",
                         Py_TYPE(dict)->tp_name);
            return NULL;
        }
        if (self->dict) {
            /* Alternatively, we could replace the internal dictionary
               completely. However, it seems more practical to just update it. */
            if (PyDict_Update(self->dict, dict) < 0)
                return NULL;
        }
        else {
            Py_INCREF(dict);
            self->dict = dict;
        }
    }

    Py_RETURN_NONE;
}


static PyObject *
stringio_closed(stringio *self, void *context)
{
    CHECK_INITIALIZED(self);
    return PyBool_FromLong(self->closed);
}

static PyObject *
stringio_line_buffering(stringio *self, void *context)
{
    CHECK_INITIALIZED(self);
    CHECK_CLOSED(self);
    Py_RETURN_FALSE;
}

static PyObject *
stringio_newlines(stringio *self, void *context)
{
    CHECK_INITIALIZED(self);
    CHECK_CLOSED(self);
    if (self->decoder == NULL)
        Py_RETURN_NONE;
    return PyObject_GetAttr(self->decoder, _PyIO_str_newlines);
}

static struct PyMethodDef stringio_methods[] = {
    {"close",    (PyCFunction)stringio_close,    METH_NOARGS,  stringio_close_doc},
    {"getvalue", (PyCFunction)stringio_getvalue, METH_NOARGS,  stringio_getvalue_doc},
    {"read",     (PyCFunction)stringio_read,     METH_VARARGS, stringio_read_doc},
    {"readline", (PyCFunction)stringio_readline, METH_VARARGS, stringio_readline_doc},
    {"tell",     (PyCFunction)stringio_tell,     METH_NOARGS,  stringio_tell_doc},
    {"truncate", (PyCFunction)stringio_truncate, METH_VARARGS, stringio_truncate_doc},
    {"seek",     (PyCFunction)stringio_seek,     METH_VARARGS, stringio_seek_doc},
    {"write",    (PyCFunction)stringio_write,    METH_O,       stringio_write_doc},

    {"seekable", (PyCFunction)stringio_seekable, METH_NOARGS},
    {"readable", (PyCFunction)stringio_readable, METH_NOARGS},
    {"writable", (PyCFunction)stringio_writable, METH_NOARGS},

    {"__getstate__", (PyCFunction)stringio_getstate, METH_NOARGS},
    {"__setstate__", (PyCFunction)stringio_setstate, METH_O},
    {NULL, NULL}        /* sentinel */
};

static PyGetSetDef stringio_getset[] = {
    {"closed",         (getter)stringio_closed,         NULL, NULL},
    {"newlines",       (getter)stringio_newlines,       NULL, NULL},
    /*  (following comments straight off of the original Python wrapper:)
        XXX Cruft to support the TextIOWrapper API. This would only
        be meaningful if StringIO supported the buffer attribute.
        Hopefully, a better solution, than adding these pseudo-attributes,
        will be found.
    */
    {"line_buffering", (getter)stringio_line_buffering, NULL, NULL},
    {NULL}
};

PyTypeObject PyStringIO_Type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "_io.StringIO",                            /*tp_name*/
    sizeof(stringio),                    /*tp_basicsize*/
    0,                                         /*tp_itemsize*/
    (destructor)stringio_dealloc,              /*tp_dealloc*/
    0,                                         /*tp_print*/
    0,                                         /*tp_getattr*/
    0,                                         /*tp_setattr*/
    0,                                         /*tp_reserved*/
    0,                                         /*tp_repr*/
    0,                                         /*tp_as_number*/
    0,                                         /*tp_as_sequence*/
    0,                                         /*tp_as_mapping*/
    0,                                         /*tp_hash*/
    0,                                         /*tp_call*/
    0,                                         /*tp_str*/
    0,                                         /*tp_getattro*/
    0,                                         /*tp_setattro*/
    0,                                         /*tp_as_buffer*/
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
                       | Py_TPFLAGS_HAVE_GC,   /*tp_flags*/
    stringio_doc,                              /*tp_doc*/
    (traverseproc)stringio_traverse,           /*tp_traverse*/
    (inquiry)stringio_clear,                   /*tp_clear*/
    0,                                         /*tp_richcompare*/
    offsetof(stringio, weakreflist),            /*tp_weaklistoffset*/
    0,                                         /*tp_iter*/
    (iternextfunc)stringio_iternext,           /*tp_iternext*/
    stringio_methods,                          /*tp_methods*/
    0,                                         /*tp_members*/
    stringio_getset,                           /*tp_getset*/
    0,                                         /*tp_base*/
    0,                                         /*tp_dict*/
    0,                                         /*tp_descr_get*/
    0,                                         /*tp_descr_set*/
    offsetof(stringio, dict),                  /*tp_dictoffset*/
    (initproc)stringio_init,                   /*tp_init*/
    0,                                         /*tp_alloc*/
    stringio_new,                              /*tp_new*/
};