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utf8: add function to detect prohibited UTF-16/32 BOM

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Whenever a data stream is declared to be UTF-16BE, UTF-16LE, UTF-32BE
or UTF-32LE a BOM must not be used [1]. The function returns true if
this is the case.

This function is used in a subsequent commit.

[1] http://unicode.org/faq/utf_bom.html#bom10

Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Lars Schneider
2018-04-15 20:16:05 +02:00
committed by Junio C Hamano
parent 2f0c4a362c
commit 10ecb82e4f
2 changed files with 35 additions and 0 deletions
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26
utf8.c
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@ -560,6 +560,32 @@ char *reencode_string_len(const char *in, int insz,
}
#endif
static int has_bom_prefix(const char *data, size_t len,
const char *bom, size_t bom_len)
{
return data && bom && (len >= bom_len) && !memcmp(data, bom, bom_len);
}
static const char utf16_be_bom[] = {0xFE, 0xFF};
static const char utf16_le_bom[] = {0xFF, 0xFE};
static const char utf32_be_bom[] = {0x00, 0x00, 0xFE, 0xFF};
static const char utf32_le_bom[] = {0xFF, 0xFE, 0x00, 0x00};
int has_prohibited_utf_bom(const char *enc, const char *data, size_t len)
{
return (
(same_utf_encoding("UTF-16BE", enc) ||
same_utf_encoding("UTF-16LE", enc)) &&
(has_bom_prefix(data, len, utf16_be_bom, sizeof(utf16_be_bom)) ||
has_bom_prefix(data, len, utf16_le_bom, sizeof(utf16_le_bom)))
) || (
(same_utf_encoding("UTF-32BE", enc) ||
same_utf_encoding("UTF-32LE", enc)) &&
(has_bom_prefix(data, len, utf32_be_bom, sizeof(utf32_be_bom)) ||
has_bom_prefix(data, len, utf32_le_bom, sizeof(utf32_le_bom)))
);
}
/*
* Returns first character length in bytes for multi-byte `text` according to
* `encoding`.