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format-patch: RFC 2047 says multi-octet character may not be split
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Even though an earlier attempt (bafc478..41dd00b) cleaned
up RFC 2047 encoding, pretty.c::add_rfc2047() still decides
where to split the output line by going through the input
one byte at a time, and potentially splits a character in
the middle.  A subject line may end up showing like this:

     ".... fö?? bar".   (instead of  ".... föö bar".)

if split incorrectly.

RFC 2047, section 5 (3) explicitly forbids such beaviour

    Each 'encoded-word' MUST represent an integral number of
    characters.  A multi-octet character may not be split across
    adjacent 'encoded- word's.

that means that e.g. for

    Subject: .... föö bar

encoding

    Subject: =?UTF-8?q?....=20f=C3=B6=C3=B6?=
     =?UTF-8?q?=20bar?=

is correct, and

    Subject: =?UTF-8?q?....=20f=C3=B6=C3?=      <-- NOTE ö is broken here
     =?UTF-8?q?=B6=20bar?=

is not, because "ö" character UTF-8 encoding C3 B6 is split here across
adjacent encoded words.

To fix the problem, make the loop grab one _character_ at a time and
determine its output length to see where to break the output line.  Note
that this version only knows about UTF-8, but the logic to grab one
character is abstracted out in mbs_chrlen() function to make it possible
to extend it to other encodings with the help of iconv in the future.

Signed-off-by: Kirill Smelkov <kirr@mns.spb.ru>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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@gitster
Kirill Smelkov authored and gitster committed Mar 9, 2013
1 parent 1599999 commit 6cd3c05
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Showing 4 changed files with 77 additions and 25 deletions.
34 changes: 22 additions & 12 deletions pretty.c
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Original file line number Diff line number Diff line change
Expand Up @@ -345,7 +345,7 @@ static int needs_rfc2047_encoding(const char *line, int len,
return 0;
}

static void add_rfc2047(struct strbuf *sb, const char *line, int len,
static void add_rfc2047(struct strbuf *sb, const char *line, size_t len,
const char *encoding, enum rfc2047_type type)
{
static const int max_encoded_length = 76; /* per rfc2047 */
Expand All @@ -355,9 +355,22 @@ static void add_rfc2047(struct strbuf *sb, const char *line, int len,
strbuf_grow(sb, len * 3 + strlen(encoding) + 100);
strbuf_addf(sb, "=?%s?q?", encoding);
line_len += strlen(encoding) + 5; /* 5 for =??q? */
for (i = 0; i < len; i++) {
unsigned ch = line[i] & 0xFF;
int is_special = is_rfc2047_special(ch, type);

while (len) {
/*
* RFC 2047, section 5 (3):
*
* Each 'encoded-word' MUST represent an integral number of
* characters. A multi-octet character may not be split across
* adjacent 'encoded- word's.
*/
const unsigned char *p = (const unsigned char *)line;
int chrlen = mbs_chrlen(&line, &len, encoding);
int is_special = (chrlen > 1) || is_rfc2047_special(*p, type);

/* "=%02X" * chrlen, or the byte itself */
const char *encoded_fmt = is_special ? "=%02X" : "%c";
int encoded_len = is_special ? 3 * chrlen : 1;

/*
* According to RFC 2047, we could encode the special character
Expand All @@ -367,18 +380,15 @@ static void add_rfc2047(struct strbuf *sb, const char *line, int len,
* causes ' ' to be encoded as '=20', avoiding this problem.
*/

if (line_len + 2 + (is_special ? 3 : 1) > max_encoded_length) {
if (line_len + encoded_len + 2 > max_encoded_length) {
/* It won't fit with trailing "?=" --- break the line */
strbuf_addf(sb, "?=\n =?%s?q?", encoding);
line_len = strlen(encoding) + 5 + 1; /* =??q? plus SP */
}

if (is_special) {
strbuf_addf(sb, "=%02X", ch);
line_len += 3;
} else {
strbuf_addch(sb, ch);
line_len++;
}
for (i = 0; i < chrlen; i++)
strbuf_addf(sb, encoded_fmt, p[i]);
line_len += encoded_len;
}
strbuf_addstr(sb, "?=");
}
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27 changes: 14 additions & 13 deletions t/t4014-format-patch.sh
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Original file line number Diff line number Diff line change
Expand Up @@ -810,25 +810,26 @@ Subject: [PATCH] =?UTF-8?q?f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f?=
=?UTF-8?q?=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar?=
=?UTF-8?q?=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20?=
=?UTF-8?q?bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6?=
=?UTF-8?q?=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3?=
=?UTF-8?q?=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6?=
=?UTF-8?q?=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3?=
=?UTF-8?q?=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f?=
=?UTF-8?q?=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6?=
=?UTF-8?q?=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f?=
=?UTF-8?q?=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar?=
=?UTF-8?q?=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20?=
=?UTF-8?q?bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6?=
=?UTF-8?q?=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3?=
=?UTF-8?q?=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6?=
=?UTF-8?q?=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3?=
=?UTF-8?q?=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f?=
=?UTF-8?q?=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6?=
=?UTF-8?q?=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f?=
=?UTF-8?q?=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar?=
=?UTF-8?q?=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20?=
=?UTF-8?q?bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6?=
=?UTF-8?q?=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3?=
=?UTF-8?q?=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6?=
=?UTF-8?q?=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3?=
=?UTF-8?q?=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f?=
=?UTF-8?q?=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar?=
=?UTF-8?q?=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6?=
=?UTF-8?q?=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f?=
=?UTF-8?q?=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar?=
=?UTF-8?q?=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20?=
=?UTF-8?q?bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6?=
=?UTF-8?q?=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6?=
=?UTF-8?q?=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f?=
=?UTF-8?q?=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar?=
=?UTF-8?q?=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20bar=20f=C3=B6=C3=B6=20?=
=?UTF-8?q?bar?=
EOF
test_expect_success 'format-patch wraps extremely long subject (rfc2047)' '
rm -rf patches/ &&
Expand Down
39 changes: 39 additions & 0 deletions utf8.c
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Original file line number Diff line number Diff line change
Expand Up @@ -495,3 +495,42 @@ char *reencode_string(const char *in, const char *out_encoding, const char *in_e
return out;
}
#endif

/*
* Returns first character length in bytes for multi-byte `text` according to
* `encoding`.
*
* - The `text` pointer is updated to point at the next character.
* - When `remainder_p` is not NULL, on entry `*remainder_p` is how much bytes
* we can consume from text, and on exit `*remainder_p` is reduced by returned
* character length. Otherwise `text` is treated as limited by NUL.
*/
int mbs_chrlen(const char **text, size_t *remainder_p, const char *encoding)
{
int chrlen;
const char *p = *text;
size_t r = (remainder_p ? *remainder_p : SIZE_MAX);

if (r < 1)
return 0;

if (is_encoding_utf8(encoding)) {
pick_one_utf8_char(&p, &r);

chrlen = p ? (p - *text)
: 1 /* not valid UTF-8 -> raw byte sequence */;
}
else {
/*
* TODO use iconv to decode one char and obtain its chrlen
* for now, let's treat encodings != UTF-8 as one-byte
*/
chrlen = 1;
}

*text += chrlen;
if (remainder_p)
*remainder_p -= chrlen;

return chrlen;
}
2 changes: 2 additions & 0 deletions utf8.h
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Original file line number Diff line number Diff line change
Expand Up @@ -21,4 +21,6 @@ char *reencode_string(const char *in, const char *out_encoding, const char *in_e
#define reencode_string(a,b,c) NULL
#endif

int mbs_chrlen(const char **text, size_t *remainder_p, const char *encoding);

#endif

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