Repair widespread misuse of _PyString_Resize. Since it's clear people
don't understand how this function works, also beefed up the docs. The
most common usage error is of this form (often spread out across gotos):
if (_PyString_Resize(&s, n) < 0) {
Py_DECREF(s);
s = NULL;
goto outtahere;
}
The error is that if _PyString_Resize runs out of memory, it automatically
decrefs the input string object s (which also deallocates it, since its
refcount must be 1 upon entry), and sets s to NULL. So if the "if"
branch ever triggers, it's an error to call Py_DECREF(s): s is already
NULL! A correct way to write the above is the simpler (and intended)
if (_PyString_Resize(&s, n) < 0)
goto outtahere;
Bugfix candidate.
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index c4c8d8d..9a3e456 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -927,10 +927,7 @@
*out++ = '-';
}
- if (_PyString_Resize(&v, out - start)) {
- Py_DECREF(v);
- return NULL;
- }
+ _PyString_Resize(&v, out - start);
return v;
}
@@ -1764,7 +1761,7 @@
/* Resize the string if necessary */
if (offset + 12 > PyString_GET_SIZE(repr)) {
if (_PyString_Resize(&repr, PyString_GET_SIZE(repr) + 100))
- goto onError;
+ return NULL;
p = PyString_AS_STRING(repr) + offset;
}
@@ -1847,14 +1844,8 @@
*p++ = PyString_AS_STRING(repr)[1];
*p = '\0';
- if (_PyString_Resize(&repr, p - PyString_AS_STRING(repr)))
- goto onError;
-
+ _PyString_Resize(&repr, p - PyString_AS_STRING(repr));
return repr;
-
- onError:
- Py_DECREF(repr);
- return NULL;
}
PyObject *PyUnicode_EncodeUnicodeEscape(const Py_UNICODE *s,
@@ -1985,14 +1976,8 @@
*p++ = (char) ch;
}
*p = '\0';
- if (_PyString_Resize(&repr, p - q))
- goto onError;
-
+ _PyString_Resize(&repr, p - q);
return repr;
-
- onError:
- Py_DECREF(repr);
- return NULL;
}
PyObject *PyUnicode_AsRawUnicodeEscapeString(PyObject *unicode)
@@ -2092,8 +2077,7 @@
}
/* Resize if error handling skipped some characters */
if (s - start < PyString_GET_SIZE(repr))
- if (_PyString_Resize(&repr, s - start))
- goto onError;
+ _PyString_Resize(&repr, s - start);
return repr;
onError:
@@ -2240,8 +2224,7 @@
}
/* Resize if error handling skipped some characters */
if (s - start < PyString_GET_SIZE(repr))
- if (_PyString_Resize(&repr, s - start))
- goto onError;
+ _PyString_Resize(&repr, s - start);
return repr;
onError:
@@ -2588,12 +2571,11 @@
Py_DECREF(x);
}
if (s - PyString_AS_STRING(v) < PyString_GET_SIZE(v))
- if (_PyString_Resize(&v, (int)(s - PyString_AS_STRING(v))))
- goto onError;
+ _PyString_Resize(&v, (int)(s - PyString_AS_STRING(v)));
return v;
onError:
- Py_DECREF(v);
+ Py_XDECREF(v);
return NULL;
}