Question

This is with regard to data sent over a socket to a C application residing on a remote POS system.

Binary data is sent from a php application, in the C app packet structure there is 64bytes stored for a string e.g. a product name.

Now when I send the product name across network through php sockets, I use pack to convert data to binary

$value = 'product name' 
$qty = 2;
$len = strlen($value);
$output = '';
for($i=0; $i<$len; $i++) {
        $output .= pack('c', ord(substr($value, $i, 1))).pack('c',$qty) 
}

When the data is received by the C application the string contains a lot of garbage data, including numbers and special characters.

Which of the pack options i have to use to pack the product name into a 64byte binary string that will be interpreted by the C application in the correct format.

Answer 1

Your loop to build $output produces a string like "p\x02r\x02o\x02d\x02u\x02c\x02t\x02 \x02n\x02a\x02m\x02e\x02"

If your C program expects something like "product name\0\x02", then the loop should be:

$output = '';
for($i=0; $i<$len; $i++) {
        $output .= pack('c', ord(substr($value, $i, 1))); 
}
$output .= pack('c',0).pack('c',$qty);