+ /* Deal with buffer overruns. Instead of panicking, just
+ * truncate the resulting string. Note that some vsnprintf()s
+ * return -1 on truncation, e.g., glibc 2.0.6 and earlier. */
+ if (len > sizeof(buf)-1 || len < 0) {
+ const char ellipsis[] = "[...]";
+
+ /* Reset length, and zero-terminate the end of our buffer */
+ len = sizeof(buf)-1;
+ buf[len] = '\0';
+
+ /* Copy the ellipsis to the end of the string, but give
+ * us one extra character:
+ *
+ * v--- null byte at buf[sizeof(buf)-1]
+ * abcdefghij0
+ * -> abcd[...]00 <-- now two null bytes at end
+ *
+ * If the input format string has a trailing newline,
+ * we copy it into that extra null; if it doesn't, well,
+ * all we lose is one byte. */
+ strncpy(buf+len-sizeof(ellipsis), ellipsis, sizeof(ellipsis));
+ if (format[strlen(format)-1] == '\n') {
+ buf[len-1] = '\n';
+ }
+ }