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string-util: tweak cellescape() a bit 

For short buffer sizes cellescape() was a bit wasteful, as it might
suffice to to drop a single character to find enough place for the full
four byte ellipsis, if that one character was a four character escape.
With this rework we'll guarantee to drop the minimum number of
characters from the end to fit in the ellipsis.

If the buffers we write to are large this doesn't matter much. However,
if they are short (as they are when talking about the process comm
field) then it starts to matter that we put as much information as we
can in the space we get.
This commit is contained in:
Lennart Poettering 2018-06-01 21:45:23 +02:00
parent 76a359736f
commit 61f6e27671
2 changed files with 112 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

57
src/basic/string-util.c
View File

@ -627,25 +627,58 @@ char *cellescape(char *buf, size_t len, const char *s) {
* very end.
*/
size_t i;
const char *t = s;
size_t i = 0, last_char_width[4] = {}, k = 0, j;
assert(len > 4 + 4 + 1); /* two chars and the terminator */
assert(len > 0); /* at least a terminating NUL */
for (i = 0; i < len - 9; t++) {
if (!*t)
for (;;) {
char four[4];
int w;
if (*s == 0) /* terminating NUL detected? then we are done! */
goto done;
i += cescape_char(*t, buf + i);
w = cescape_char(*s, four);
if (i + w + 1 > len) /* This character doesn't fit into the buffer anymore? In that case let's
* ellipsize at the previous location */
break;
/* OK, there was space, let's add this escaped character to the buffer */
memcpy(buf + i, four, w);
i += w;
/* And remember its width in the ring buffer */
last_char_width[k] = w;
k = (k + 1) % 4;
s++;
}
/* We have space for one more char and terminating nul at this point */
if (*t) {
if (*(t+1))
i += write_ellipsis(buf + i, false);
else
i += cescape_char(*t, buf + i);
/* Ellipsation is necessary. This means we might need to truncate the string again to make space for 4
* characters ideally, but the buffer is shorter than that in the first place take what we can get */
for (j = 0; j < ELEMENTSOF(last_char_width); j++) {
if (i + 4 <= len) /* nice, we reached our space goal */
break;
k = k == 0 ? 3 : k - 1;
if (last_char_width[k] == 0) /* bummer, we reached the beginning of the strings */
break;
assert(i >= last_char_width[k]);
i -= last_char_width[k];
}
if (i + 4 <= len) /* yay, enough space */
i += write_ellipsis(buf + i, false);
else if (i + 3 <= len) { /* only space for ".." */
buf[i++] = '.';
buf[i++] = '.';
} else if (i + 2 <= len) /* only space for a single "." */
buf[i++] = '.';
else
assert(i + 1 <= len);
done:
buf[i] = '\0';
return buf;

76
src/test/test-string-util.c
View File

@ -81,21 +81,79 @@ static void test_ascii_strcasecmp_nn(void) {
static void test_cellescape(void) {
char buf[40];
assert_se(streq(cellescape(buf, 10, "1"), "1"));
assert_se(streq(cellescape(buf, 10, "12"), "12"));
assert_se(streq(cellescape(buf, 10, "123"), is_locale_utf8() ? "1…" : "1..."));
assert_se(streq(cellescape(buf, 1, ""), ""));
assert_se(streq(cellescape(buf, 1, "1"), ""));
assert_se(streq(cellescape(buf, 1, "12"), ""));
assert_se(streq(cellescape(buf, 10, "1\011"), "1\\t"));
assert_se(streq(cellescape(buf, 10, "1\020"), "1\\020"));
assert_se(streq(cellescape(buf, 10, "1\020x"), is_locale_utf8() ? "1…" : "1..."));
assert_se(streq(cellescape(buf, 2, ""), ""));
assert_se(streq(cellescape(buf, 2, "1"), "1"));
assert_se(streq(cellescape(buf, 2, "12"), "."));
assert_se(streq(cellescape(buf, 2, "123"), "."));
assert_se(streq(cellescape(buf, 3, ""), ""));
assert_se(streq(cellescape(buf, 3, "1"), "1"));
assert_se(streq(cellescape(buf, 3, "12"), "12"));
assert_se(streq(cellescape(buf, 3, "123"), ".."));
assert_se(streq(cellescape(buf, 3, "1234"), ".."));
assert_se(streq(cellescape(buf, 4, ""), ""));
assert_se(streq(cellescape(buf, 4, "1"), "1"));
assert_se(streq(cellescape(buf, 4, "12"), "12"));
assert_se(streq(cellescape(buf, 4, "123"), "123"));
assert_se(streq(cellescape(buf, 4, "1234"), is_locale_utf8() ? "…" : "..."));
assert_se(streq(cellescape(buf, 4, "12345"), is_locale_utf8() ? "…" : "..."));
assert_se(streq(cellescape(buf, 5, ""), ""));
assert_se(streq(cellescape(buf, 5, "1"), "1"));
assert_se(streq(cellescape(buf, 5, "12"), "12"));
assert_se(streq(cellescape(buf, 5, "123"), "123"));
assert_se(streq(cellescape(buf, 5, "1234"), "1234"));
assert_se(streq(cellescape(buf, 5, "12345"), is_locale_utf8() ? "1…" : "1..."));
assert_se(streq(cellescape(buf, 5, "123456"), is_locale_utf8() ? "1…" : "1..."));
assert_se(streq(cellescape(buf, 1, "\020"), ""));
assert_se(streq(cellescape(buf, 2, "\020"), "."));
assert_se(streq(cellescape(buf, 3, "\020"), ".."));
assert_se(streq(cellescape(buf, 4, "\020"), "…"));
assert_se(streq(cellescape(buf, 5, "\020"), "\\020"));
assert_se(streq(cellescape(buf, 5, "1234\020"), "1…"));
assert_se(streq(cellescape(buf, 6, "1234\020"), "12…"));
assert_se(streq(cellescape(buf, 7, "1234\020"), "123…"));
assert_se(streq(cellescape(buf, 8, "1234\020"), "1234…"));
assert_se(streq(cellescape(buf, 9, "1234\020"), "1234\\020"));
assert_se(streq(cellescape(buf, 1, "\t\n"), ""));
assert_se(streq(cellescape(buf, 2, "\t\n"), "."));
assert_se(streq(cellescape(buf, 3, "\t\n"), ".."));
assert_se(streq(cellescape(buf, 4, "\t\n"), "…"));
assert_se(streq(cellescape(buf, 5, "\t\n"), "\\t\\n"));
assert_se(streq(cellescape(buf, 5, "1234\t\n"), "1…"));
assert_se(streq(cellescape(buf, 6, "1234\t\n"), "12…"));
assert_se(streq(cellescape(buf, 7, "1234\t\n"), "123…"));
assert_se(streq(cellescape(buf, 8, "1234\t\n"), "1234…"));
assert_se(streq(cellescape(buf, 9, "1234\t\n"), "1234\\t\\n"));
assert_se(streq(cellescape(buf, 4, "x\t\020\n"), "…"));
assert_se(streq(cellescape(buf, 5, "x\t\020\n"), "x…"));
assert_se(streq(cellescape(buf, 6, "x\t\020\n"), "x…"));
assert_se(streq(cellescape(buf, 7, "x\t\020\n"), "x\\t…"));
assert_se(streq(cellescape(buf, 8, "x\t\020\n"), "x\\t…"));
assert_se(streq(cellescape(buf, 9, "x\t\020\n"), "x\\t…"));
assert_se(streq(cellescape(buf, 10, "x\t\020\n"), "x\\t\\020\\n"));
assert_se(streq(cellescape(buf, 6, "1\011"), "1\\t"));
assert_se(streq(cellescape(buf, 6, "1\020"), "1\\020"));
assert_se(streq(cellescape(buf, 6, "1\020x"), is_locale_utf8() ? "1…" : "1..."));
assert_se(streq(cellescape(buf, 40, "1\020"), "1\\020"));
assert_se(streq(cellescape(buf, 40, "1\020x"), "1\\020x"));
assert_se(streq(cellescape(buf, 40, "\a\b\f\n\r\t\v\\\"'"), "\\a\\b\\f\\n\\r\\t\\v\\\\\\\"\\'"));
assert_se(streq(cellescape(buf, 10, "\a\b\f\n\r\t\v\\\"'"), is_locale_utf8() ? "\\a…" : "\\a..."));
assert_se(streq(cellescape(buf, 11, "\a\b\f\n\r\t\v\\\"'"), is_locale_utf8() ? "\\a…" : "\\a..."));
assert_se(streq(cellescape(buf, 12, "\a\b\f\n\r\t\v\\\"'"), is_locale_utf8() ? "\\a\\b…" : "\\a\\b..."));
assert_se(streq(cellescape(buf, 6, "\a\b\f\n\r\t\v\\\"'"), is_locale_utf8() ? "\\a…" : "\\a..."));
assert_se(streq(cellescape(buf, 7, "\a\b\f\n\r\t\v\\\"'"), is_locale_utf8() ? "\\a…" : "\\a..."));
assert_se(streq(cellescape(buf, 8, "\a\b\f\n\r\t\v\\\"'"), is_locale_utf8() ? "\\a\\b…" : "\\a\\b..."));
assert_se(streq(cellescape(buf, sizeof buf, "1\020"), "1\\020"));
assert_se(streq(cellescape(buf, sizeof buf, "1\020x"), "1\\020x"));