cpython/Modules/_stringio.c

#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;
} StringIOObject;

#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(StringIOObject *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(StringIOObject *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                   positon

        */
        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(StringIOObject *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(StringIOObject *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(StringIOObject *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(StringIOObject *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(StringIOObject *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(StringIOObject *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().  Imply an absolute seek to pos.\n"
    "Returns the new absolute position.\n");

static PyObject *
stringio_truncate(StringIOObject *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;
    }
    self->pos = 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(StringIOObject *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(StringIOObject *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(StringIOObject *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(StringIOObject *self, visitproc visit, void *arg)
{
    Py_VISIT(self->dict);
    return 0;
}

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

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

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

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

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

    return (PyObject *)self;
}

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

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "|Oz:__init__", kwlist,
                                     &value, &newline))
        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: %s", newline);
        return -1;
    }
    if (value && value != Py_None && !PyUnicode_Check(value)) {
        PyErr_Format(PyExc_ValueError,
                     "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);

    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(StringIOObject *self, PyObject *args)
{
    CHECK_INITIALIZED(self);
    Py_RETURN_TRUE;
}

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

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

static PyObject *
stringio_buffer(StringIOObject *self, void *context)
{
    PyErr_SetString(IO_STATE->unsupported_operation,
                    "buffer attribute is unsupported on type StringIO");
    return NULL;
}

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

static PyObject *
stringio_encoding(StringIOObject *self, void *context)
{
    CHECK_INITIALIZED(self);
    CHECK_CLOSED(self);
    Py_RETURN_NONE;
}

static PyObject *
stringio_errors(StringIOObject *self, void *context)
{
    CHECK_INITIALIZED(self);
    CHECK_CLOSED(self);
    return PyUnicode_FromString("strict");
}

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

static PyObject *
stringio_newlines(StringIOObject *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_VARARGS, 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},
    {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.
    */
    {"buffer",         (getter)stringio_buffer,         NULL, NULL},
    {"encoding",       (getter)stringio_encoding,       NULL, NULL},
    {"errors",         (getter)stringio_errors,         NULL, NULL},
    {"line_buffering", (getter)stringio_line_buffering, NULL, NULL},
    {0}
};

PyTypeObject PyStringIO_Type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "_io.StringIO",                            /*tp_name*/
    sizeof(StringIOObject),                    /*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(StringIOObject, 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(StringIOObject, dict),            /*tp_dictoffset*/
    (initproc)stringio_init,                   /*tp_init*/
    0,                                         /*tp_alloc*/
    stringio_new,                              /*tp_new*/
};