Issue #6218: Make io.BytesIO and io.StringIO picklable.

1 files changed, 119 insertions, 3 deletions

diff --git a/Modules/_io/bytesio.c b/Modules/_io/bytesio.c
index daef78f..7b56551 100644
--- a/Modules/_io/bytesio.c
+++ b/Modules/_io/bytesio.c
@@ -606,6 +606,120 @@ bytesio_close(bytesio *self)
     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)
+            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;
+    }
+    /* 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)
 {
@@ -630,9 +744,9 @@ bytesio_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     if (self == NULL)
         return NULL;
 
-    self->string_size = 0;
-    self->pos = 0;
-    self->buf_size = 0;
+    /* tp_alloc initializes all the fields to zero. So we don't have to
+       initialize them here. */
+
     self->buf = (char *)PyMem_Malloc(0);
     if (self->buf == NULL) {
         Py_DECREF(self);
@@ -705,6 +819,8 @@ static struct PyMethodDef bytesio_methods[] = {
     {"getvalue",   (PyCFunction)bytesio_getvalue,   METH_VARARGS, 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},
     {NULL, NULL}        /* sentinel */
 };