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gfileutils: Improve performance of g_canonicalize_filename()

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Improve the performance of canonicalising filenames with many `..` or
`.` components, by modifying the path inline rather than calling
`memmove()`.

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

Fixes: #2541
This commit is contained in:
Sebastian Wilhelmi
2021-11-26 13:43:56 +00:00
committed by Philip Withnall
parent 72377e3b6e
commit 9a30a495ec
2 changed files with 94 additions and 57 deletions
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115
glib/gfileutils.c
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@@ -2736,8 +2736,7 @@ gchar *
g_canonicalize_filename (const gchar *filename,
const gchar *relative_to)
{
gchar *canon, *start, *p, *q;
guint i;
gchar *canon, *input, *output, *start;
g_return_val_if_fail (relative_to == NULL || g_path_is_absolute (relative_to), NULL);
@@ -2770,74 +2769,76 @@ g_canonicalize_filename (const gchar *filename,
return g_build_filename (G_DIR_SEPARATOR_S, filename, NULL);
}
/* POSIX allows double slashes at the start to
* mean something special (as does windows too).
* So, "//" != "/", but more than two slashes
/* Find the first dir separator and use the canonical dir separator. */
for (output = start - 1;
(output >= canon) && G_IS_DIR_SEPARATOR (*output);
output--)
*output = G_DIR_SEPARATOR;
output += 2;
/* POSIX allows double slashes at the start to mean something special
* (as does windows too). So, "//" != "/", but more than two slashes
* is treated as "/".
*/
i = 0;
for (p = start - 1;
(p >= canon) &&
G_IS_DIR_SEPARATOR (*p);
p--)
i++;
if (i > 2)
{
i -= 1;
start -= i;
memmove (start, start+i, strlen (start+i) + 1);
}
if (start - output == 1)
output++;
/* Make sure we're using the canonical dir separator */
p++;
while (p < start && G_IS_DIR_SEPARATOR (*p))
*p++ = G_DIR_SEPARATOR;
p = start;
while (*p != 0)
input = start;
while (*input)
{
if (p[0] == '.' && (p[1] == 0 || G_IS_DIR_SEPARATOR (p[1])))
/* input points to the next non-separator to be processed. */
/* output points to the next location to write to. */
g_assert (input > canon && G_IS_DIR_SEPARATOR (input[-1]));
g_assert (output > canon && G_IS_DIR_SEPARATOR (output[-1]));
g_assert (input >= output);
/* Ignore repeated dir separators. */
while (G_IS_DIR_SEPARATOR (input[0]))
input++;
/* Ignore single dot directory components. */
if (input[0] == '.' && (input[1] == 0 || G_IS_DIR_SEPARATOR (input[1])))
{
memmove (p, p+1, strlen (p+1)+1);
if (input[1] == 0)
break;
input += 2;
}
else if (p[0] == '.' && p[1] == '.' && (p[2] == 0 || G_IS_DIR_SEPARATOR (p[2])))
/* Remove double-dot directory components along with the preceding
* path component. */
else if (input[0] == '.' && input[1] == '.' &&
(input[2] == 0 || G_IS_DIR_SEPARATOR (input[2])))
{
q = p + 2;
/* Skip previous separator */
p = p - 2;
if (p < start)
p = start;
while (p > start && !G_IS_DIR_SEPARATOR (*p))
p--;
if (G_IS_DIR_SEPARATOR (*p))
*p++ = G_DIR_SEPARATOR;
memmove (p, q, strlen (q)+1);
if (output > start)
{
do
{
output--;
}
while (!G_IS_DIR_SEPARATOR (output[-1]) && output > start);
}
if (input[2] == 0)
break;
input += 3;
}
/* Copy the input to the output until the next separator,
* while converting it to canonical separator */
else
{
/* Skip until next separator */
while (*p != 0 && !G_IS_DIR_SEPARATOR (*p))
p++;
if (*p != 0)
{
/* Canonicalize one separator */
*p++ = G_DIR_SEPARATOR;
}
while (*input && !G_IS_DIR_SEPARATOR (*input))
*output++ = *input++;
if (input[0] == 0)
break;
input++;
*output++ = G_DIR_SEPARATOR;
}
/* Remove additional separators */
q = p;
while (*q && G_IS_DIR_SEPARATOR (*q))
q++;
if (p != q)
memmove (p, q, strlen (q) + 1);
}
/* Remove trailing slashes */
if (p > start && G_IS_DIR_SEPARATOR (*(p-1)))
*(p-1) = 0;
/* Remove a potentially trailing dir separator */
if (output > start && G_IS_DIR_SEPARATOR (output[-1]))
output--;
*output = '\0';
return canon;
}