https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108976
Bug ID: 108976
Summary: codecvt for Unicode allows surrogate code points
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: dmjpp at hotmail dot com
Target Milestone: ---
Text in valid Unicode should never contain surrogate code POINTS. Those are
only allowed in UTF-16, but only as code UNITS and must be properly paired.
UTF-8 text in its strictest form must not contain surrogates but in a slightly
relaxed form surrogates can be easily encoded as 3-byte sequences. Same can be
said for UTF-32 and UCS-2. Only UTF-16 is immune to the error of surrogate code
POINT (they are treated as UNITS).
Codecvts in libstdc++ currently allow surrogate code points in some cases. Here
is a minimal reproduction (asserts are the correct behavior):
#include <locale>
#include <cassert>
void u32()
{
using namespace std;
auto& f = use_facet<codecvt<char32_t, char, mbstate_t>>(locale::classic());
char u8str[] = "\uC800\uCBFF\uCC00\uCFFF";
u8str[0] = u8str[3] = u8str[6] = u8str[9] = 0xED; // turn the C into D.
// now the string is D800, DBFF, DC00 and DFFF encoded in relaxed UTF-8
// that allows surrogate code points.
char32_t u32str[] = {0xD800, 0xDBFF, 0xDC00, 0xDFFF, 0};
char32_t u32out[1];
const char* from_next;
char32_t* to_next;
mbstate_t st = {};
auto res = f.in(st, u8str, u8str+3, from_next, u32out, u32out+1, to_next);
assert(res == f.error);
assert(from_next == u8str);
assert(to_next == u32out);
st = {};
auto l = f.length(st, u8str, u8str+3, 1);
assert(l == 0);
char u8out[3];
const char32_t* from_next2;
char* to_next2;
st = {};
res = f.out(st, u32str, u32str+1, from_next2, u8out, u8out+3, to_next2);
assert(res == f.error);
assert(from_next2 == u32str);
assert(to_next2 == u8out);
}
void u16()
{
using namespace std;
auto& f = use_facet<codecvt<char16_t, char, mbstate_t>>(locale::classic());
char u8str[] = "\uC800\uCBFF\uCC00\uCFFF";
u8str[0] = u8str[3] = u8str[6] = u8str[9] = 0xED; // turn the C into D.
// now the string is D800, DBFF, DC00 and DFFF encoded in relaxed UTF-8
// that allows surrogates.
char16_t u16out[1];
const char* from_next;
char16_t* to_next;
mbstate_t st = {};
auto res = f.in(st, u8str, u8str+3, from_next, u16out, u16out+1, to_next);
assert(res == f.error);
assert(from_next == u8str);
assert(to_next == u16out);
st = {};
auto l = f.length(st, u8str, u8str+3, 1);
assert(l == 0);
}
int main()
{
u32();
u16();
}
>From reading the file codecvt.cc the following conversions have the bug:
- From UTF-8 to any other encoding.
- From UTF-32/UCS-4 to any other encoding.
Those that read from UCS-2 seem to me like they properly report the error.
Reading from UTF-16 can not have this bug by definition. From what I checked,
the functions for reading UTF-16 properly treat unpaired surrogate code units
as error.
