enhanced HexToAscii() to handle anomaly in a hexadecimal string

codepot/src/codepot/libraries/converter.php

@@ -67,11 +67,46 @@ class Converter
 	function HexToAscii($hex)
 	{
 		$ascii = '';
+		$is_hex = FALSE;
    
 		$len = strlen($hex);
-		if ($len > 0 && $hex[0] == '!')
+		if ($len <= 0) return $ascii;
+
+
+		if ($hex[0] != '!')
 		{
-			for ($i = 1; $i < $len; $i++)
+			$orglen = $len;
+			$is_hex = 1;
+			if ($len % 2 == 1) 
+			{
+				$hex = '0' . $hex;
+				$len++;
+			}
+   
+			for($i = 0; $i < $len; $i += 2)
+			{
+				if (!ctype_xdigit($hex[$i])  || !ctype_xdigit($hex[$i + 1]))
+				{
+					$ascii = '';
+					$is_hex = FALSE;
+					break;		
+				}
+				$ascii .= chr(base_convert(substr($hex, $i, 2), 16, 10));
+			}
+
+			if ($is_hex > 0) return $ascii;
+
+			# if the string not prefixed with '!' contains non-hexadecimal character,
+			# arrange it to treat it as if it's prefixed with '!'.
+			$startpos = $len - $orglen;
+		}
+		else 
+		{
+			$startpos = 1;
+		}
+
+	
+		for ($i = $startpos; $i < $len; $i++)
 		{
 			if ($hex[$i] == '!')
 			{
@@ -109,14 +144,6 @@ class Converter
 
 			$ascii .= $seg;
 		}	
-		}
-		else
-		{
-			if (strlen($hex) % 2 == 1) $hex = '0' . $hex;
-   
-			for($i = 0; $i < strlen($hex); $i += 2)
-				$ascii .= chr(base_convert(substr($hex, $i, 2), 16, 10));
-		}
    
 		return $ascii;
 	}