Translate UDP packet data into human-readable form in PHP - php

Question

I am receiving data over UDP in PHP.
After passing the buffer through bin2hex function in PHP I end up with something resembling the Raw Data as indicated below in the example
Here is my PHP code:
$socket = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP);
socket_bind($socket, "0.0.0.0" , 20500);
$from = '';
$port = 0;
socket_recvfrom($socket, $buf, 512, 0, $from, $port);
$file = 'testudp.txt';
// Open the file to get existing content
$current = file_get_contents($file);
// Append a new log line(s) to file
$current .= "New Connection " . date('Y-m-d H:i:s') . " \n" . bin2hex($buf) . "\n";
// Write the contents back to the file
file_put_contents($file, $current);
echo "Received connection from remote address $from and remote port $port" . PHP_EOL;
Which results in something like 83 05 01 02 03 04 05 01 01 01 02 00 01 4F B4 64 88 4F B4 64 88 13 BF 71 A8 BA 18 A5 06 00 00 1333 00 00 00 00 11 11 02 ...
but without the spaces.
Example of Data and what it ought to translate to: note that the translation only begins after ther first 9 bytes, then address 2, then skips 2 again.
Raw Data:
83 05 01 02 03 04 05 01 01 01 02 00 01 4F B4 64 88 4F B4 64
88 13 BF 71 A8 BA 18 A5 06 00 00 1333 00 00 00 00 11 11 02
33 44 44 55 55 66 77 88 99 10 11 ?? 00 ??
Decoded:
-------Message Header--------
01 Service Type, for this message 1 = Acknowledged Request
02 Message Type, for this message 2 = Event Report
-------Event Report----------
4FB46488 Update Time (5/17/12 # 2:38pm)
4FB46488 Time of Fix (5/17/12 # 2:38pm)
13BF71A8 Latitude (33.1313576)
BA18A506 Longitude (-117.2790010)
00001333 Altitude
00000000 Speed
1111 Heading
02 Satellites
33 Fix Status
4444 Carrier
5555 RSSI
66 Comm State
77 HDOP
88 Inputs
99 Unit Status
10 Event Index
11 Event Code
?? Accums (# of 4-byte Accum List values)
00 Spare
?? Accum List (Varies depending on the # of Accums reporting)
I have tried various decoders hexadecimal to ascii, I've also tried unpack() in PHP all to no avail.
How do you translate the data into something resembling the example via PHP?
i.e. how would BA18A506 end up giving me the data (unformatted or not) to correspond to Longitude (-117.2790010) in a human readable form?
EDIT:
The docs specify Note that all bytes in multi-byte fields are transmitted in Net Endian format (Big Endian) where the most significant bits are transmitted first. For example, for a 32-bit field, bits 31-24 are transmitted first, 16-23 second, 8-15 third and 0-7 last
if that helps at all.

Answer 1

unpack() or unpack() per substr() of the binary data should in the end get you where you want. But as HamZa mentions, you have to know what format it is...
$test = "\x06\xA5\x18\xBA";
var_dump(unpack('l',$test));
result:
-1172790010
Just add the . on the correct place
Sample code to unpack first part (extend / correct where needed)
Change your code to recieve into a buffer instead of a file:
socket_recv($socket, $buf, 512, 0);
Then you can use the buffer $buf (for now i enter the sample data you provided)
// Now we use some test data
$buf = "\x83\x05\x01\x02\x03\x04\x05\x01\x01\x01\x02\x00\x01\x4F\xB4\x64\x88\x4F\xB4\x64\x88\x13\xBF\x71\xA8\xBA\x18\xA5\x06\x00\x00\x13\x33\x00\x00\x00\x00\x11\x11\x02\x33\x44\x44\x55\x55\x66\x77\x88\x99\x10\x11";
// field definition
$fields = array();
$fields['header'] = array(9, 'c*');
$fields['serviceType'] = array(1, 'c');
$fields['messageType'] = array(1, 'c');
$fields['skip'] = array(2, 'c');
$fields['updateTime'] = array(4, 'l');
$fields['fixTime'] = array(4, 'l');
$fields['longitude'] = array(4, 'l');
$fields['latitude'] = array(4, 'l');
$fields['altitude'] = array(4, 'l');
$fields['speed'] = array(4, 'l');
// etc.
$values = array();
$start = 0;
foreach($fields as $type=>$setting) {
list($len, $format) = $setting;
$values[$type] = unpack($format, strrev(substr($buf, $start, $len)));
$start += $len;
}
var_dump($values);
Will output something like:
["serviceType"]=>
array(1) {
[1]=>
int(1)
}
["messageType"]=>
array(1) {
[1]=>
int(2)
}
["skip"]=>
array(1) {
[1]=>
int(1)
}
["updateTime"]=>
array(1) {
[1]=>
int(1337222280)
}
["fixTime"]=>
array(1) {
[1]=>
int(1337222280)
}
["longitude"]=>
array(1) {
[1]=>
int(331313576)
}
["latitude"]=>
array(1) {
[1]=>
int(-1172790010)
}
["altitude"]=>
array(1) {
[1]=>
int(4915)
}
["speed"]=>
array(1) {
[1]=>
int(0)
}
Just divide latitude and longitude by 10000000 (10M) to get the real longitude and latitude