[pargue]

Handle a decimal point longer than one byte

get_decimal_point() writes "1" and the locale's decimal point with sprintf into char buf[3] and returns buf[1]. In a locale whose decimal point is more than one byte, such as ps_AF.UTF-8 (U+066B, 2 bytes in UTF-8):

• the sprintf writes 4 bytes into the 3-byte buffer (ASan: stack-buffer-overflow in get_decimal_point);
• only the first byte of the point is used, so to_locale() puts a partial UTF-8 sequence where the . was, strtod() stops early, and json_loads("[1.5]") fails the assert in jsonp_strtod();
• with USE_DTOA off, from_locale() makes the same one-byte assumption when printing.

It only happens when the program has set LC_NUMERIC to such a locale.

The change: get_decimal_point() returns the whole point as a string, in a buffer of MB_LEN_MAX bytes (the most one character can take). to_locale() grows the buffer when the point is longer than ., and jsonp_strtod() returns -2 if it cannot, which the lexer reports as "out of memory" instead of "real number overflow". from_locale() replaces the whole point and shortens the output.

Test: test_multibyte_decimal_point in test/suites/api/test_number.c loads reals under ps_AF.UTF-8 (including ones long enough to grow the buffer), dumps them, checks the output holds no byte of the locale's point, and reloads it in the C locale to compare values. It restores the caller's LC_NUMERIC. When the locale is not installed it prints that it skipped, which is likely on CI; locally it was built with localedef -i ps_AF -f UTF-8 <dir>/ps_AF.UTF-8 and run with LOCPATH=<dir>. On master it fails under ASan with the stack-buffer-overflow above; with the fix the full suite passes (215 tests) with USE_DTOA on and off, under ASan/UBSan.

Not changed here: as before, jsonp_strtod converts saved_text in place, so a "real number overflow near '...'" message under such a locale shows the locale's point rather than the input's .. Parsing with strtod_l and a C locale where available would avoid the rewrite entirely; that is a larger change than this fix.