Commit d32b08af authored by cypherpunks's avatar cypherpunks
Browse files

string: add string_is_utf8() helper

Ticket #27373.
parent 1c62adb6
......@@ -451,3 +451,93 @@ string_is_C_identifier(const char *string)
return 1;
}
/** A byte with the top <b>x</b> bits set. */
#define TOP_BITS(x) ((uint8_t)(0xFF << (8 - (x))))
/** A byte with the lowest <b>x</b> bits set. */
#define LOW_BITS(x) ((uint8_t)(0xFF >> (8 - (x))))
/** Given the leading byte <b>b</b>, return the total number of bytes in the
* UTF-8 character. Returns 0 if it's an invalid leading byte.
*/
static uint8_t
bytes_in_char(uint8_t b)
{
if ((TOP_BITS(1) & b) == 0x00)
return 1; // a 1-byte UTF-8 char, aka ASCII
if ((TOP_BITS(3) & b) == TOP_BITS(2))
return 2; // a 2-byte UTF-8 char
if ((TOP_BITS(4) & b) == TOP_BITS(3))
return 3; // a 3-byte UTF-8 char
if ((TOP_BITS(5) & b) == TOP_BITS(4))
return 4; // a 4-byte UTF-8 char
// Invalid: either the top 2 bits are 10, or the top 5 bits are 11111.
return 0;
}
/** Returns true iff <b>b</b> is a UTF-8 continuation byte. */
static bool
is_continuation_byte(uint8_t b)
{
uint8_t top2bits = b & TOP_BITS(2);
return top2bits == TOP_BITS(1);
}
/** Returns true iff the <b>len</b> bytes in <b>c</b> are a valid UTF-8
* character.
*/
static bool
validate_char(const uint8_t *c, uint8_t len)
{
if (len == 1)
return true; // already validated this is an ASCII char earlier.
uint8_t mask = LOW_BITS(7 - len); // bitmask for the leading byte.
uint32_t codepoint = c[0] & mask;
mask = LOW_BITS(6); // bitmask for continuation bytes.
for (uint8_t i = 1; i < len; i++) {
if (!is_continuation_byte(c[i]))
return false;
codepoint <<= 6;
codepoint |= (c[i] & mask);
}
if (len == 2 && codepoint <= 0x7f)
return false; // Invalid, overly long encoding, should have fit in 1 byte.
if (len == 3 && codepoint <= 0x7ff)
return false; // Invalid, overly long encoding, should have fit in 2 bytes.
if (len == 4 && codepoint <= 0xffff)
return false; // Invalid, overly long encoding, should have fit in 3 bytes.
if (codepoint >= 0xd800 && codepoint <= 0xdfff)
return false; // Invalid, reserved for UTF-16 surrogate pairs.
return codepoint <= 0x10ffff; // Check if within maximum.
}
/** Returns true iff the first <b>len</b> bytes in <b>str</b> are a
valid UTF-8 string. */
int
string_is_utf8(const char *str, size_t len)
{
for (size_t i = 0; i < len;) {
uint8_t num_bytes = bytes_in_char(str[i]);
if (num_bytes == 0) // Invalid leading byte found.
return false;
size_t next_char = i + num_bytes;
if (next_char > len)
return false;
// Validate the continuation bytes in this multi-byte character,
// and advance to the next character in the string.
if (!validate_char((const uint8_t*)&str[i], num_bytes))
return false;
i = next_char;
}
return true;
}
......@@ -52,4 +52,6 @@ const char *find_str_at_start_of_line(const char *haystack,
int string_is_C_identifier(const char *string);
int string_is_utf8(const char *str, size_t len);
#endif /* !defined(TOR_UTIL_STRING_H) */
......@@ -4011,6 +4011,53 @@ test_util_string_is_C_identifier(void *ptr)
;
}
static void
test_util_string_is_utf8(void *ptr)
{
(void)ptr;
tt_int_op(1, OP_EQ, string_is_utf8(NULL, 0));
tt_int_op(1, OP_EQ, string_is_utf8("", 1));
tt_int_op(1, OP_EQ, string_is_utf8("\uFEFF", 3));
tt_int_op(1, OP_EQ, string_is_utf8("\uFFFE", 3));
tt_int_op(1, OP_EQ, string_is_utf8("ascii\x7f\n", 7));
tt_int_op(1, OP_EQ, string_is_utf8("Risqu\u00e9=1", 9));
// Validate exactly 'len' bytes.
tt_int_op(0, OP_EQ, string_is_utf8("\0\x80", 2));
tt_int_op(0, OP_EQ, string_is_utf8("Risqu\u00e9=1", 6));
// Reject sequences with missing bytes.
tt_int_op(0, OP_EQ, string_is_utf8("\x80", 1));
tt_int_op(0, OP_EQ, string_is_utf8("\xc2", 1));
tt_int_op(0, OP_EQ, string_is_utf8("\xc2 ", 2));
tt_int_op(0, OP_EQ, string_is_utf8("\xe1\x80", 2));
tt_int_op(0, OP_EQ, string_is_utf8("\xe1\x80 ", 3));
tt_int_op(0, OP_EQ, string_is_utf8("\xf1\x80\x80", 3));
tt_int_op(0, OP_EQ, string_is_utf8("\xf1\x80\x80 ", 4));
// Reject encodings that are overly long.
tt_int_op(0, OP_EQ, string_is_utf8("\xc1\xbf", 2));
tt_int_op(1, OP_EQ, string_is_utf8("\xc2\x80", 2));
tt_int_op(0, OP_EQ, string_is_utf8("\xe0\x9f\xbf", 3));
tt_int_op(1, OP_EQ, string_is_utf8("\xe0\xa0\x80", 3));
tt_int_op(0, OP_EQ, string_is_utf8("\xf0\x8f\xbf\xbf", 4));
tt_int_op(1, OP_EQ, string_is_utf8("\xf0\x90\x80\x80", 4));
// Reject UTF-16 surrogate halves.
tt_int_op(1, OP_EQ, string_is_utf8("\xed\x9f\xbf", 3));
tt_int_op(0, OP_EQ, string_is_utf8("\xed\xa0\x80", 3));
tt_int_op(0, OP_EQ, string_is_utf8("\xed\xbf\xbf", 3));
tt_int_op(1, OP_EQ, string_is_utf8("\xee\x80\x80", 3));
// The maximum legal codepoint, 10FFFF.
tt_int_op(1, OP_EQ, string_is_utf8("\xf4\x8f\xbf\xbf", 4));
tt_int_op(0, OP_EQ, string_is_utf8("\xf4\x90\x80\x80", 4));
done:
;
}
static void
test_util_asprintf(void *ptr)
{
......@@ -6398,6 +6445,7 @@ struct testcase_t util_tests[] = {
UTIL_TEST(clamp_double_to_int64, 0),
UTIL_TEST(find_str_at_start_of_line, 0),
UTIL_TEST(string_is_C_identifier, 0),
UTIL_TEST(string_is_utf8, 0),
UTIL_TEST(asprintf, 0),
UTIL_TEST(listdir, 0),
UTIL_TEST(parent_dir, 0),
......
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