$rows = $db->query('SELECT message FROM messages WHERE id = 1');
$obj = $rows->fetch(PDO::FETCH_OBJ);
$tabbed = str_replace(' ' , "\t", $obj->message);
$spaced = str_replace("\t", ' ' , $obj->message);
print "With Tabs: <pre>$tabbed</pre>";
print "With Spaces: <pre>$spaced</pre>";

function tab_expand($text) {
	while (strstr($text,"\t")) {
		$text = preg_replace_callback('/^([^\t\n]*)(\t+)/m','tab_expand_helper', $text);
	}
	return $text;
}

function tab_expand_helper($matches) {
	$tab_stop = 8;
	return $matches[1] .str_repeat(' ',strlen($matches[2]) *$tab_stop - (strlen($matches[1]) % $tab_stop));
}
$spaced = tab_expand($obj->message);

function tab_unexpand($text) {
	$tab_stop = 8;
	$lines = explode("\n",$text);
	foreach ($lines as $i => $line) {
		// 把所有的制表符都转化为空格
		$line = tab_expand($line);
		$chunks = str_split($line, $tab_stop);
		$chunkCount = count($chunks);
		// 扫描除了最后一个元素的所有元素
		for ($j = 0; $j < $chunkCount - 1; $j++) {
			$chunks[$j] = preg_replace('/ {2,}$/',"\t",$chunks[$j]);
		}
		// 如果最后的制表位是一个空格
		// 转成 tab，或者不动
		if ($chunks[$chunkCount-1] == str_repeat(' ', $tab_stop)) {
			$chunks[$chunkCount-1] = "\t";
		}
		// 重组数组
		$lines[$i] = implode('',$chunks);
	}
	// 重组字符串
	return implode("\n",$lines);
}

$tabbed = tab_unexpand($obj->message);