Modules/_io/bytesio.c

#include "Python.h"
#include "structmember.h"       /* for offsetof() */
#include "_iomodule.h"

typedef struct {
    PyObject_HEAD
    PyObject *buf;
    Py_ssize_t pos;
    Py_ssize_t string_size;
    PyObject *dict;
    PyObject *weakreflist;
    Py_ssize_t exports;
} bytesio;

typedef struct {
    PyObject_HEAD
    bytesio *source;
} bytesiobuf;

/* The bytesio object can be in three states:
  * Py_REFCNT(buf) == 1, exports == 0.
  * Py_REFCNT(buf) > 1.  exports == 0,
    first modification or export causes the internal buffer copying.
  * exports > 0.  Py_REFCNT(buf) == 1, any modifications are forbidden.
*/

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

#define CHECK_EXPORTS(self) \
    if ((self)->exports > 0) { \
        PyErr_SetString(PyExc_BufferError, \
                        "Existing exports of data: object cannot be re-sized"); \
        return NULL; \
    }

#define SHARED_BUF(self) (Py_REFCNT((self)->buf) > 1)


/* Internal routine to get a line from the buffer of a BytesIO
   object. Returns the length between the current position to the
   next newline character. */
static Py_ssize_t
scan_eol(bytesio *self, Py_ssize_t len)
{
    const char *start, *n;
    Py_ssize_t maxlen;

    assert(self->buf != NULL);

    /* Move to the end of the line, up to the end of the string, s. */
    start = PyBytes_AS_STRING(self->buf) + self->pos;
    maxlen = self->string_size - self->pos;
    if (len < 0 || len > maxlen)
        len = maxlen;

    if (len) {
        n = memchr(start, '\n', len);
        if (n)
            /* Get the length from the current position to the end of
               the line. */
            len = n - start + 1;
    }
    assert(len >= 0);
    assert(self->pos < PY_SSIZE_T_MAX - len);

    return len;
}

/* Internal routine for detaching the shared buffer of BytesIO objects.
   The caller should ensure that the 'size' argument is non-negative and
   not lesser than self->string_size.  Returns 0 on success, -1 otherwise. */
static int
unshare_buffer(bytesio *self, size_t size)
{
    PyObject *new_buf, *old_buf;
    assert(SHARED_BUF(self));
    assert(self->exports == 0);
    assert(size >= (size_t)self->string_size);
    new_buf = PyBytes_FromStringAndSize(NULL, size);
    if (new_buf == NULL)
        return -1;
    memcpy(PyBytes_AS_STRING(new_buf), PyBytes_AS_STRING(self->buf),
           self->string_size);
    old_buf = self->buf;
    self->buf = new_buf;
    Py_DECREF(old_buf);
    return 0;
}

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

    assert(self->buf != NULL);

    /* 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(char))
        goto overflow;

    if (SHARED_BUF(self)) {
        if (unshare_buffer(self, alloc) < 0)
            return -1;
    }
    else {
        if (_PyBytes_Resize(&self->buf, alloc) < 0)
            return -1;
    }

    return 0;

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

/* Internal routine for writing a string of bytes to the buffer of a BytesIO
   object. Returns the number of bytes written, or -1 on error. */
static Py_ssize_t
write_bytes(bytesio *self, const char *bytes, Py_ssize_t len)
{
    size_t endpos;
    assert(self->buf != NULL);
    assert(self->pos >= 0);
    assert(len >= 0);

    endpos = (size_t)self->pos + len;
    if (endpos > (size_t)PyBytes_GET_SIZE(self->buf)) {
        if (resize_buffer(self, endpos) < 0)
            return -1;
    }
    else if (SHARED_BUF(self)) {
        if (unshare_buffer(self, Py_MAX(endpos, (size_t)self->string_size)) < 0)
            return -1;
    }

    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(PyBytes_AS_STRING(self->buf) + self->string_size, '\0',
               (self->pos - self->string_size) * sizeof(char));
    }

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

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

    return len;
}

static PyObject *
bytesio_get_closed(bytesio *self)
{
    if (self->buf == NULL) {
        Py_RETURN_TRUE;
    }
    else {
        Py_RETURN_FALSE;
    }
}

PyDoc_STRVAR(readable_doc,
"readable() -> bool. Returns True if the IO object can be read.");

PyDoc_STRVAR(writable_doc,
"writable() -> bool. Returns True if the IO object can be written.");

PyDoc_STRVAR(seekable_doc,
"seekable() -> bool. Returns True if the IO object can be seeked.");

/* Generic getter for the writable, readable and seekable properties */
static PyObject *
return_not_closed(bytesio *self)
{
    CHECK_CLOSED(self);
    Py_RETURN_TRUE;
}

PyDoc_STRVAR(flush_doc,
"flush() -> None.  Does nothing.");

static PyObject *
bytesio_flush(bytesio *self)
{
    CHECK_CLOSED(self);
    Py_RETURN_NONE;
}

PyDoc_STRVAR(getbuffer_doc,
"getbuffer() -> bytes.\n"
"\n"
"Get a read-write view over the contents of the BytesIO object.");

static PyObject *
bytesio_getbuffer(bytesio *self)
{
    PyTypeObject *type = &_PyBytesIOBuffer_Type;
    bytesiobuf *buf;
    PyObject *view;

    CHECK_CLOSED(self);

    buf = (bytesiobuf *) type->tp_alloc(type, 0);
    if (buf == NULL)
        return NULL;
    Py_INCREF(self);
    buf->source = self;
    view = PyMemoryView_FromObject((PyObject *) buf);
    Py_DECREF(buf);
    return view;
}

PyDoc_STRVAR(getval_doc,
"getvalue() -> bytes.\n"
"\n"
"Retrieve the entire contents of the BytesIO object.");

static PyObject *
bytesio_getvalue(bytesio *self)
{
    CHECK_CLOSED(self);
    if (self->string_size <= 1 || self->exports > 0)
        return PyBytes_FromStringAndSize(PyBytes_AS_STRING(self->buf),
                                         self->string_size);

    if (self->string_size != PyBytes_GET_SIZE(self->buf)) {
        if (SHARED_BUF(self)) {
            if (unshare_buffer(self, self->string_size) < 0)
                return NULL;
        }
        else {
            if (_PyBytes_Resize(&self->buf, self->string_size) < 0)
                return NULL;
        }
    }
    Py_INCREF(self->buf);
    return self->buf;
}

PyDoc_STRVAR(isatty_doc,
"isatty() -> False.\n"
"\n"
"Always returns False since BytesIO objects are not connected\n"
"to a tty-like device.");

static PyObject *
bytesio_isatty(bytesio *self)
{
    CHECK_CLOSED(self);
    Py_RETURN_FALSE;
}

PyDoc_STRVAR(tell_doc,
"tell() -> current file position, an integer\n");

static PyObject *
bytesio_tell(bytesio *self)
{
    CHECK_CLOSED(self);
    return PyLong_FromSsize_t(self->pos);
}

static PyObject *
read_bytes(bytesio *self, Py_ssize_t size)
{
    char *output;

    assert(self->buf != NULL);
    assert(size <= self->string_size);
    if (size > 1 &&
        self->pos == 0 && size == PyBytes_GET_SIZE(self->buf) &&
        self->exports == 0) {
        self->pos += size;
        Py_INCREF(self->buf);
        return self->buf;
    }

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

PyDoc_STRVAR(read_doc,
"read([size]) -> read at most size bytes, returned as a string.\n"
"\n"
"If the size argument is negative, read until EOF is reached.\n"
"Return an empty string at EOF.");

static PyObject *
bytesio_read(bytesio *self, PyObject *args)
{
    Py_ssize_t size, n;
    PyObject *arg = Py_None;

    CHECK_CLOSED(self);

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

    if (PyLong_Check(arg)) {
        size = PyLong_AsSsize_t(arg);
        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;
    }

    return read_bytes(self, size);
}


PyDoc_STRVAR(read1_doc,
"read1(size) -> read at most size bytes, returned as a string.\n"
"\n"
"If the size argument is negative or omitted, read until EOF is reached.\n"
"Return an empty string at EOF.");

static PyObject *
bytesio_read1(bytesio *self, PyObject *n)
{
    PyObject *arg, *res;

    arg = PyTuple_Pack(1, n);
    if (arg == NULL)
        return NULL;
    res  = bytesio_read(self, arg);
    Py_DECREF(arg);
    return res;
}

PyDoc_STRVAR(readline_doc,
"readline([size]) -> next line from the file, as a string.\n"
"\n"
"Retain newline.  A non-negative size argument limits the maximum\n"
"number of bytes to return (an incomplete line may be returned then).\n"
"Return an empty string at EOF.\n");

static PyObject *
bytesio_readline(bytesio *self, PyObject *args)
{
    Py_ssize_t size, n;
    PyObject *arg = Py_None;

    CHECK_CLOSED(self);

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

    if (PyLong_Check(arg)) {
        size = PyLong_AsSsize_t(arg);
        if (size == -1 && PyErr_Occurred())
            return NULL;
    }
    else if (arg == Py_None) {
        /* No size limit, by default. */
        size = -1;
    }
    else {
        PyErr_Format(PyExc_TypeError, "integer argument expected, got '%s'",
                     Py_TYPE(arg)->tp_name);
        return NULL;
    }

    n = scan_eol(self, size);

    return read_bytes(self, n);
}

PyDoc_STRVAR(readlines_doc,
"readlines([size]) -> list of strings, each a line from the file.\n"
"\n"
"Call readline() repeatedly and return a list of the lines so read.\n"
"The optional size argument, if given, is an approximate bound on the\n"
"total number of bytes in the lines returned.\n");

static PyObject *
bytesio_readlines(bytesio *self, PyObject *args)
{
    Py_ssize_t maxsize, size, n;
    PyObject *result, *line;
    char *output;
    PyObject *arg = Py_None;

    CHECK_CLOSED(self);

    if (!PyArg_ParseTuple(args, "|O:readlines", &arg))
        return NULL;

    if (PyLong_Check(arg)) {
        maxsize = PyLong_AsSsize_t(arg);
        if (maxsize == -1 && PyErr_Occurred())
            return NULL;
    }
    else if (arg == Py_None) {
        /* No size limit, by default. */
        maxsize = -1;
    }
    else {
        PyErr_Format(PyExc_TypeError, "integer argument expected, got '%s'",
                     Py_TYPE(arg)->tp_name);
        return NULL;
    }

    size = 0;
    result = PyList_New(0);
    if (!result)
        return NULL;

    output = PyBytes_AS_STRING(self->buf) + self->pos;
    while ((n = scan_eol(self, -1)) != 0) {
        self->pos += n;
        line = PyBytes_FromStringAndSize(output, n);
        if (!line)
            goto on_error;
        if (PyList_Append(result, line) == -1) {
            Py_DECREF(line);
            goto on_error;
        }
        Py_DECREF(line);
        size += n;
        if (maxsize > 0 && size >= maxsize)
            break;
        output += n;
    }
    return result;

  on_error:
    Py_DECREF(result);
    return NULL;
}

PyDoc_STRVAR(readinto_doc,
"readinto(bytearray) -> int.  Read up to len(b) bytes into b.\n"
"\n"
"Returns number of bytes read (0 for EOF), or None if the object\n"
"is set not to block as has no data to read.");

static PyObject *
bytesio_readinto(bytesio *self, PyObject *arg)
{
    Py_buffer buffer;
    Py_ssize_t len, n;

    CHECK_CLOSED(self);

    if (!PyArg_Parse(arg, "w*", &buffer))
        return NULL;

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

    memcpy(buffer.buf, PyBytes_AS_STRING(self->buf) + self->pos, len);
    assert(self->pos + len < PY_SSIZE_T_MAX);
    assert(len >= 0);
    self->pos += len;
    PyBuffer_Release(&buffer);

    return PyLong_FromSsize_t(len);
}

PyDoc_STRVAR(truncate_doc,
"truncate([size]) -> int.  Truncate the file to at most size bytes.\n"
"\n"
"Size defaults to the current file position, as returned by tell().\n"
"The current file position is unchanged.  Returns the new size.\n");

static PyObject *
bytesio_truncate(bytesio *self, PyObject *args)
{
    Py_ssize_t size;
    PyObject *arg = Py_None;

    CHECK_CLOSED(self);
    CHECK_EXPORTS(self);

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

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

    return PyLong_FromSsize_t(size);
}

static PyObject *
bytesio_iternext(bytesio *self)
{
    Py_ssize_t n;

    CHECK_CLOSED(self);

    n = scan_eol(self, -1);

    if (n == 0)
        return NULL;

    return read_bytes(self, n);
}

PyDoc_STRVAR(seek_doc,
"seek(pos, whence=0) -> int.  Change stream position.\n"
"\n"
"Seek to byte offset pos relative to position indicated by whence:\n"
"     0  Start of stream (the default).  pos should be >= 0;\n"
"     1  Current position - pos may be negative;\n"
"     2  End of stream - pos usually negative.\n"
"Returns the new absolute position.");

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

    CHECK_CLOSED(self);

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

    if (pos < 0 && mode == 0) {
        PyErr_Format(PyExc_ValueError,
                     "negative seek value %zd", pos);
        return NULL;
    }

    /* mode 0: offset relative to beginning of the string.
       mode 1: offset relative to current position.
       mode 2: offset relative the end of the string. */
    if (mode == 1) {
        if (pos > PY_SSIZE_T_MAX - self->pos) {
            PyErr_SetString(PyExc_OverflowError,
                            "new position too large");
            return NULL;
        }
        pos += self->pos;
    }
    else if (mode == 2) {
        if (pos > PY_SSIZE_T_MAX - self->string_size) {
            PyErr_SetString(PyExc_OverflowError,
                            "new position too large");
            return NULL;
        }
        pos += self->string_size;
    }
    else if (mode != 0) {
        PyErr_Format(PyExc_ValueError,
                     "invalid whence (%i, should be 0, 1 or 2)", mode);
        return NULL;
    }

    if (pos < 0)
        pos = 0;
    self->pos = pos;

    return PyLong_FromSsize_t(self->pos);
}

PyDoc_STRVAR(write_doc,
"write(bytes) -> int.  Write bytes to file.\n"
"\n"
"Return the number of bytes written.");

static PyObject *
bytesio_write(bytesio *self, PyObject *obj)
{
    Py_ssize_t n = 0;
    Py_buffer buf;
    PyObject *result = NULL;

    CHECK_CLOSED(self);
    CHECK_EXPORTS(self);

    if (PyObject_GetBuffer(obj, &buf, PyBUF_CONTIG_RO) < 0)
        return NULL;

    if (buf.len != 0)
        n = write_bytes(self, buf.buf, buf.len);
    if (n >= 0)
        result = PyLong_FromSsize_t(n);

    PyBuffer_Release(&buf);
    return result;
}

PyDoc_STRVAR(writelines_doc,
"writelines(sequence_of_strings) -> None.  Write strings to the file.\n"
"\n"
"Note that newlines are not added.  The sequence can be any iterable\n"
"object producing strings. This is equivalent to calling write() for\n"
"each string.");

static PyObject *
bytesio_writelines(bytesio *self, PyObject *v)
{
    PyObject *it, *item;
    PyObject *ret;

    CHECK_CLOSED(self);

    it = PyObject_GetIter(v);
    if (it == NULL)
        return NULL;

    while ((item = PyIter_Next(it)) != NULL) {
        ret = bytesio_write(self, item);
        Py_DECREF(item);
        if (ret == NULL) {
            Py_DECREF(it);
            return NULL;
        }
        Py_DECREF(ret);
    }
    Py_DECREF(it);

    /* See if PyIter_Next failed */
    if (PyErr_Occurred())
        return NULL;

    Py_RETURN_NONE;
}

PyDoc_STRVAR(close_doc,
"close() -> None.  Disable all I/O operations.");

static PyObject *
bytesio_close(bytesio *self)
{
    CHECK_EXPORTS(self);
    Py_CLEAR(self->buf);
    Py_RETURN_NONE;
}

/* Pickling support.

   Note that only pickle protocol 2 and onward are supported since we use
   extended __reduce__ API of PEP 307 to make BytesIO instances picklable.

   Providing support for protocol < 2 would require the __reduce_ex__ method
   which is notably long-winded when defined properly.

   For BytesIO, the implementation would similar to one coded for
   object.__reduce_ex__, but slightly less general. To be more specific, we
   could call bytesio_getstate directly and avoid checking for the presence of
   a fallback __reduce__ method. However, we would still need a __newobj__
   function to use the efficient instance representation of PEP 307.
 */

static PyObject *
bytesio_getstate(bytesio *self)
{
    PyObject *initvalue = bytesio_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) {
            Py_DECREF(initvalue);
            return NULL;
        }
    }

    state = Py_BuildValue("(OnN)", initvalue, self->pos, dict);
    Py_DECREF(initvalue);
    return state;
}

static PyObject *
bytesio_setstate(bytesio *self, PyObject *state)
{
    PyObject *result;
    PyObject *position_obj;
    PyObject *dict;
    Py_ssize_t pos;

    assert(state != NULL);

    /* We allow the state tuple to be longer than 3, because we may need
       someday to extend the object's state without breaking
       backward-compatibility. */
    if (!PyTuple_Check(state) || Py_SIZE(state) < 3) {
        PyErr_Format(PyExc_TypeError,
                     "%.200s.__setstate__ argument should be 3-tuple, got %.200s",
                     Py_TYPE(self)->tp_name, Py_TYPE(state)->tp_name);
        return NULL;
    }
    CHECK_EXPORTS(self);
    /* Reset the object to its default state. This is only needed to handle
       the case of repeated calls to __setstate__. */
    self->string_size = 0;
    self->pos = 0;

    /* Set the value of the internal buffer. If state[0] does not support the
       buffer protocol, bytesio_write will raise the appropriate TypeError. */
    result = bytesio_write(self, PyTuple_GET_ITEM(state, 0));
    if (result == NULL)
        return NULL;
    Py_DECREF(result);

    /* 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, 1);
    if (!PyLong_Check(position_obj)) {
        PyErr_Format(PyExc_TypeError,
                     "second item of state must be an integer, not %.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, 2);
    if (dict != Py_None) {
        if (!PyDict_Check(dict)) {
            PyErr_Format(PyExc_TypeError,
                         "third 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 void
bytesio_dealloc(bytesio *self)
{
    _PyObject_GC_UNTRACK(self);
    if (self->exports > 0) {
        PyErr_SetString(PyExc_SystemError,
                        "deallocated BytesIO object has exported buffers");
        PyErr_Print();
    }
    Py_CLEAR(self->buf);
    Py_CLEAR(self->dict);
    if (self->weakreflist != NULL)
        PyObject_ClearWeakRefs((PyObject *) self);
    Py_TYPE(self)->tp_free(self);
}

static PyObject *
bytesio_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    bytesio *self;

    assert(type != NULL && type->tp_alloc != NULL);
    self = (bytesio *)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 = PyBytes_FromStringAndSize(NULL, 0);
    if (self->buf == NULL) {
        Py_DECREF(self);
        return PyErr_NoMemory();
    }

    return (PyObject *)self;
}

static int
bytesio_init(bytesio *self, PyObject *args, PyObject *kwds)
{
    char *kwlist[] = {"initial_bytes", NULL};
    PyObject *initvalue = NULL;

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "|O:BytesIO", kwlist,
                                     &initvalue))
        return -1;

    /* In case, __init__ is called multiple times. */
    self->string_size = 0;
    self->pos = 0;

    if (self->exports > 0) {
        PyErr_SetString(PyExc_BufferError,
                        "Existing exports of data: object cannot be re-sized");
        return -1;
    }
    if (initvalue && initvalue != Py_None) {
        if (PyBytes_CheckExact(initvalue)) {
            Py_INCREF(initvalue);
            Py_XDECREF(self->buf);
            self->buf = initvalue;
            self->string_size = PyBytes_GET_SIZE(initvalue);
        }
        else {
            PyObject *res;
            res = bytesio_write(self, initvalue);
            if (res == NULL)
                return -1;
            Py_DECREF(res);
            self->pos = 0;
        }
    }

    return 0;
}

static PyObject *
bytesio_sizeof(bytesio *self, void *unused)
{
    Py_ssize_t res;

    res = sizeof(bytesio);
    if (self->buf && !SHARED_BUF(self))
        res += _PySys_GetSizeOf(self->buf);
    return PyLong_FromSsize_t(res);
}

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

static int
bytesio_clear(bytesio *self)
{
    Py_CLEAR(self->dict);
    return 0;
}


static PyGetSetDef bytesio_getsetlist[] = {
    {"closed",  (getter)bytesio_get_closed, NULL,
     "True if the file is closed."},
    {NULL},            /* sentinel */
};

static struct PyMethodDef bytesio_methods[] = {
    {"readable",   (PyCFunction)return_not_closed,  METH_NOARGS, readable_doc},
    {"seekable",   (PyCFunction)return_not_closed,  METH_NOARGS, seekable_doc},
    {"writable",   (PyCFunction)return_not_closed,  METH_NOARGS, writable_doc},
    {"close",      (PyCFunction)bytesio_close,      METH_NOARGS, close_doc},
    {"flush",      (PyCFunction)bytesio_flush,      METH_NOARGS, flush_doc},
    {"isatty",     (PyCFunction)bytesio_isatty,     METH_NOARGS, isatty_doc},
    {"tell",       (PyCFunction)bytesio_tell,       METH_NOARGS, tell_doc},
    {"write",      (PyCFunction)bytesio_write,      METH_O, write_doc},
    {"writelines", (PyCFunction)bytesio_writelines, METH_O, writelines_doc},
    {"read1",      (PyCFunction)bytesio_read1,      METH_O, read1_doc},
    {"readinto",   (PyCFunction)bytesio_readinto,   METH_O, readinto_doc},
    {"readline",   (PyCFunction)bytesio_readline,   METH_VARARGS, readline_doc},
    {"readlines",  (PyCFunction)bytesio_readlines,  METH_VARARGS, readlines_doc},
    {"read",       (PyCFunction)bytesio_read,       METH_VARARGS, read_doc},
    {"getbuffer",  (PyCFunction)bytesio_getbuffer,  METH_NOARGS,  getbuffer_doc},
    {"getvalue",   (PyCFunction)bytesio_getvalue,   METH_NOARGS,  getval_doc},
    {"seek",       (PyCFunction)bytesio_seek,       METH_VARARGS, seek_doc},
    {"truncate",   (PyCFunction)bytesio_truncate,   METH_VARARGS, truncate_doc},
    {"__getstate__",  (PyCFunction)bytesio_getstate,  METH_NOARGS, NULL},
    {"__setstate__",  (PyCFunction)bytesio_setstate,  METH_O, NULL},
    {"__sizeof__", (PyCFunction)bytesio_sizeof,     METH_NOARGS, NULL},
    {NULL, NULL}        /* sentinel */
};

PyDoc_STRVAR(bytesio_doc,
"BytesIO([buffer]) -> object\n"
"\n"
"Create a buffered I/O implementation using an in-memory bytes\n"
"buffer, ready for reading and writing.");

PyTypeObject PyBytesIO_Type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "_io.BytesIO",                             /*tp_name*/
    sizeof(bytesio),                     /*tp_basicsize*/
    0,                                         /*tp_itemsize*/
    (destructor)bytesio_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*/
    bytesio_doc,                               /*tp_doc*/
    (traverseproc)bytesio_traverse,            /*tp_traverse*/
    (inquiry)bytesio_clear,                    /*tp_clear*/
    0,                                         /*tp_richcompare*/
    offsetof(bytesio, weakreflist),      /*tp_weaklistoffset*/
    PyObject_SelfIter,                         /*tp_iter*/
    (iternextfunc)bytesio_iternext,            /*tp_iternext*/
    bytesio_methods,                           /*tp_methods*/
    0,                                         /*tp_members*/
    bytesio_getsetlist,                        /*tp_getset*/
    0,                                         /*tp_base*/
    0,                                         /*tp_dict*/
    0,                                         /*tp_descr_get*/
    0,                                         /*tp_descr_set*/
    offsetof(bytesio, dict),             /*tp_dictoffset*/
    (initproc)bytesio_init,                    /*tp_init*/
    0,                                         /*tp_alloc*/
    bytesio_new,                               /*tp_new*/
};


/*
 * Implementation of the small intermediate object used by getbuffer().
 * getbuffer() returns a memoryview over this object, which should make it
 * invisible from Python code.
 */

static int
bytesiobuf_getbuffer(bytesiobuf *obj, Py_buffer *view, int flags)
{
    bytesio *b = (bytesio *) obj->source;

    if (view == NULL) {
        PyErr_SetString(PyExc_BufferError,
            "bytesiobuf_getbuffer: view==NULL argument is obsolete");
        return -1;
    }
    if (SHARED_BUF(b)) {
        if (unshare_buffer(b, b->string_size) < 0)
            return -1;
    }

    /* cannot fail if view != NULL and readonly == 0 */
    (void)PyBuffer_FillInfo(view, (PyObject*)obj,
                            PyBytes_AS_STRING(b->buf), b->string_size,
                            0, flags);
    b->exports++;
    return 0;
}

static void
bytesiobuf_releasebuffer(bytesiobuf *obj, Py_buffer *view)
{
    bytesio *b = (bytesio *) obj->source;
    b->exports--;
}

static int
bytesiobuf_traverse(bytesiobuf *self, visitproc visit, void *arg)
{
    Py_VISIT(self->source);
    return 0;
}

static void
bytesiobuf_dealloc(bytesiobuf *self)
{
    Py_CLEAR(self->source);
    Py_TYPE(self)->tp_free(self);
}

static PyBufferProcs bytesiobuf_as_buffer = {
    (getbufferproc) bytesiobuf_getbuffer,
    (releasebufferproc) bytesiobuf_releasebuffer,
};

PyTypeObject _PyBytesIOBuffer_Type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "_io._BytesIOBuffer",                      /*tp_name*/
    sizeof(bytesiobuf),                        /*tp_basicsize*/
    0,                                         /*tp_itemsize*/
    (destructor)bytesiobuf_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*/
    &bytesiobuf_as_buffer,                     /*tp_as_buffer*/
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,   /*tp_flags*/
    0,                                         /*tp_doc*/
    (traverseproc)bytesiobuf_traverse,         /*tp_traverse*/
    0,                                         /*tp_clear*/
    0,                                         /*tp_richcompare*/
    0,                                         /*tp_weaklistoffset*/
    0,                                         /*tp_iter*/
    0,                                         /*tp_iternext*/
    0,                                         /*tp_methods*/
    0,                                         /*tp_members*/
    0,                                         /*tp_getset*/
    0,                                         /*tp_base*/
    0,                                         /*tp_dict*/
    0,                                         /*tp_descr_get*/
    0,                                         /*tp_descr_set*/
    0,                                         /*tp_dictoffset*/
    0,                                         /*tp_init*/
    0,                                         /*tp_alloc*/
    0,                                         /*tp_new*/
};