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Bug #49361 wordwrap works incorrectly
Submitted: 2009-08-25 15:58 UTC Modified: 2009-08-31 12:28 UTC
From: code-it at mail dot ru Assigned:
Status: Closed Package: Strings related
PHP Version: 5.*, 6 OS: *
Private report: No CVE-ID:
 [2009-08-25 15:58 UTC] code-it at mail dot ru
wordwrapping suppose that

wordwrap(wordwrap($s,$n,$d),$n,$d) is equal to wordwrap($s,$n,$d) and yes, sometimes php works that way:

$s0 = 'a a a a a a a a';
$s1 = wordwrap($s0,7,'XX');
$s2 = wordwrap($s1,7,'XX');

gives $s1==$s2=='a a a aXXa a a a'

but if we add an extra space to the end of $s0, the result will be
'a a a aXXa a a aXX' != 'a a a aXXa a aXXaXX'

if we construct $s0 as (a )+a? we get $s1!=$s2 if and only if strlen($s0)%8==0. more, the diff between $s1 and $s2 every time is the same: trailing 'XXaXX' in $s2 instead of ' aXX' in $s1.


now lets take a look at the case of 1-char-length thing as the 3rd argument to wordwrap

$s0 = 'a a a a a a a a a a a'; // as above, $s0 is constructed as (a )+a?
$s1 = wordwrap($s0,5,'X');
$s2 = wordwrap($s1,5,'X');

here we only get $s1==$s2 having strlen($s0)<11!

this bug is related to line 828 in /php-src/branches/PHP_5_3/ext/standard/string.c?revision=287264:

current line: 	laststart = lastspace = current;
should be:		laststart = lastspace = current+1;

+1 is obviuos: if we found a breakchar in the string, we can forget about everything to the left of it INCLUDING itself and restart the whole algorythm at the NEXT character as the first character in our new string. so the very first `laststart = lastspace = 0;` to start becomes `laststart = lastspace = current+1;` to restart. this patch completely removes the strange behaviour.

when strlen(3rd argument to wordwrap)>1 another section of code works and the above patch doesnt affect it

Reproduce code:
function f( $len, $breakstr, $n) {
	echo "\n-------- \$len=$len, \$breakstr='$breakstr', \$n=$n -------\n";
	for ( $i=1, $c = 'a ', $s0='', $x=1, $k=0; $i<=$n; $i++) {
		$s0 .= $c[$x^=1];
		$s1 = wordwrap($s0,$len,$breakstr);
		$s2 = wordwrap($s1,$len,$breakstr);
		if ($s1==$s2) {
		echo "strlen(\$s0)=$i -> FAIL\n";
	if ($k==$n) {
		echo "passed all, no fails\n";

Expected result:
-------- $len=5, $breakstr='X', $n=20 -------
passed all, no fails

-------- $len=7, $breakstr='XX', $n=50 -------
passed all, no fails

Actual result:
-------- $len=5, $breakstr='X', $n=20 -------
strlen($s0)=11 -> FAIL
strlen($s0)=12 -> FAIL
strlen($s0)=13 -> FAIL
strlen($s0)=14 -> FAIL
strlen($s0)=15 -> FAIL
strlen($s0)=16 -> FAIL
strlen($s0)=17 -> FAIL
strlen($s0)=18 -> FAIL
strlen($s0)=19 -> FAIL
strlen($s0)=20 -> FAIL

-------- $len=7, $breakstr='XX', $n=50 -------
strlen($s0)=8 -> FAIL
strlen($s0)=16 -> FAIL
strlen($s0)=24 -> FAIL
strlen($s0)=32 -> FAIL
strlen($s0)=40 -> FAIL
strlen($s0)=48 -> FAIL


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 [2009-08-27 16:45 UTC]
Thank you for your bug report.

Your report is too long and too hard to understand. However, I did the best I could to make a simple script which reproduces the problem you describe and is more like real-life usage of wordwrap.

$lines = array(
	"The quick brown fox just",
	"jumped over the lazy dog",
	"which laid on the ground"

$text = implode("\n", $lines);
$wrapped = wordwrap($text, 24);

echo "Expected:\n".$text."\n";
echo "Actual:\n".$wrapped."\n";

The quick brown fox just
jumped over the lazy dog
which laid on the ground
The quick brown fox just
jumped over the lazy
which laid on the

 [2009-08-27 17:01 UTC] code-it at mail dot ru
sjoerd, your example looks very similar to what ive got in my real-life script when i discovered the problem for the first time. but you missed one thing

when you use "\n" to wrap strings, there is just a small piece of code that does all the work in strings.c and the bug can be easy killed with the patch i provided in my report. but when you try 2+ length strings instead of "\n", another code works and it works incorrectly too
 [2009-08-31 12:28 UTC]
Automatic comment from SVN on behalf of iliaa
Log: Fixed bug #49361 (wordwrap() wraps incorrectly on end of line boundaries).
 [2009-08-31 12:28 UTC]
This bug has been fixed in SVN.

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