Sending and receiving multiple JSON literals via PHP sockets - php

Question

I am trying send JSON data from one PHP script to another through sockets. The following is the client code
$socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
#socket_connect($socket, "localhost", 2429) or die("Connect could not be opened");
$arr = ["Hello", "I", "am", "a", "client"];
$count = 10;
while($count-- > 0) {
$msg = json_encode(["msg" => $arr[rand(0, 4)]]);
// tried appending \n & \0
// $msg .= "\0"; // "\n";
echo "sending $msg \n";
socket_write($socket, $msg, strlen($msg));
}
The following code is a piece of server that handles the reception:
$count = 0;
while(socket_recv($feed, $buf, 1024, 0) >= 1) {
echo "Obj ".++$count." : $buf";
// $obj = json_decode($buf); // error
}
The problem is, on the socket server side, the json_decode is unable to parse the data because of the following situation:
Expected Output:
Obj 1: {"msg":"I"}
Obj 2: {"msg":"a"}
Obj 3: {"msg":"a"}
Obj 4: {"msg":"I"}
Obj 5: {"msg":"a"}
Obj 6: {"msg":"client"}
Obj 7: {"msg":"am"}
Obj 8: {"msg":"am"}
Obj 9: {"msg":"am"}
The output I get:
Obj 1: {"msg":"I"}{"msg":"a"}{"msg":"a"}{"msg":"I"}
Obj 2: {"msg":"a"}{"msg":"client"}{"msg":"am"}{"msg":"am"}
Obj 3: {"msg":"am"}
I understand I need to tell the server end of object before sending the next one, but I do not know how. I tried to append "\n" and "\0" to tell the server end of stream, but it doesn't work. Please help me friends. Thank you in advance!

Answer 1

Let's try adding a length header, as that's the safest way to go when strings are involved.
Your client needs to send that information, so a slight change to your original code is in order: $msg = strlen($msg) . $msg; (right after $msg = json_encode(["msg" => $arr[rand(0, 4)]]);.
Then, assuming $socket is opened, try this as the server code (don't forget to close your sockets):
$lengthHeader = '';
$jsonLiteral = '';
while ($byte = socket_read($socket, 1)) { // reading one number at a time
echo "Read $byte\n";
if (is_numeric($byte)) { //
$lengthHeader .= $byte;
} else if ($lengthHeader) {
echo "JSON seems to start here. So...\n";
$nextMsgLength = $lengthHeader - 1; // except the current one we've just read (usually "[" or "{")
echo "Will grab the next $nextMsgLength bytes\n";
if (($partialJson = socket_read($socket, $nextMsgLength)) === false) {
die("Bad host, bad!");
}
$jsonLiteral = $byte . $partialJson;
$lengthHeader = ''; // reset the length header
echo "Grabbed JSON: $jsonLiteral\n";
} else {
echo "Nothing to grab\n";
}
}

Answer 2

you use socket_write function for other socket. When you add EOF char, is just for other socket recv. But you must know EOF char with that socket_write for your recv and explode it.