Patch by Tadayoshi Funaba (with some changes) to be smarter about

guessing what happened when strftime() returns 0.  Is it buffer
overflow or was the result simply 0 bytes long?  (This happens for an
empty format string, or when the format string is a single %Z and the
timezone is unknown.)  if the buffer is at least 256 times as long as
the format, assume the latter.

diff --git a/Modules/timemodule.c b/Modules/timemodule.c
index 50abf00500127b183f93f156f1c44eb42b9e409f..b65bfbcee8ae58f83a0d3ae6dd57fce28f55bf9f 100644 (file)
--- a/Modules/timemodule.c
+++ b/Modules/timemodule.c
@@ -366,6 +366,7 @@ time_strftime(self, args)
        PyObject *tup;
        struct tm buf;
        const char *fmt;
+       int fmtlen, buflen;
        char *outbuf = 0;
        int i;
 
@@ -373,25 +374,30 @@ time_strftime(self, args)
 
        if (!PyArg_ParseTuple(args, "sO", &fmt, &tup) || !gettmarg(tup, &buf))
                return NULL;
+       fmtlen = strlen(fmt);
+
        /* I hate these functions that presume you know how big the output
         * will be ahead of time...
         */
-       for (i = 1024 ; i <= 8192 ; i += 1024) {
+       for (i = 1024; ; i += i) {
                outbuf = malloc(i);
                if (outbuf == NULL) {
                        return PyErr_NoMemory();
                }
-               if (strftime(outbuf, i-1, fmt, &buf) != 0) {
+               buflen = strftime(outbuf, i, fmt, &buf);
+               if (buflen > 0 || i >= 256 * fmtlen) {
+                       /* If the buffer is 256 times as long as the format,
+                          it's probably not failing for lack of room!
+                          More likely, the format yields an empty result,
+                          e.g. an empty format, or %Z when the timezone
+                          is unknown. */
                        PyObject *ret;
-                       ret = PyString_FromString(outbuf);
+                       ret = PyString_FromStringAndSize(outbuf, buflen);
                        free(outbuf);
                        return ret;
                }
                free(outbuf);
        }
-       PyErr_SetString(PyExc_ValueError,
-                       "bad strftime format or result too big");
-       return NULL;
 }
 
 static char strftime_doc[] =