PHP. Forward request to another server as is

Question

Server A is sending messages to Server B. I need to insert Server C with PHP script between them.

So I want it to work like this:

Server A -> Server C (do some stuff with data and forward request further) -> Server B.

I need Server B to recieve exactly the same request, that was sent from server A. I don't need Server C acting as proxy, just send request as is, and that's all

How could I do it?

I've tried something like this, but in did not work:

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, 'Server B URL');  
curl_setopt($ch, CURLOPT_HEADER, 1);  
curl_setopt($ch, CURLOPT_POST, 1);  
curl_setopt($ch, CURLOPT_VERBOSE, 1);  
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);  
curl_setopt($ch, CURLOPT_FRESH_CONNECT, 1);  
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);  
curl_setopt($ch, CURLINFO_HEADER_OUT, 1);  
curl_setopt($ch, CURLOPT_POSTFIELDS, $_POST);
$response = curl_exec($ch);

Server B returned 200, but did nothing. I don't have access to it, so I don't know what blocked the request.

Answer 1

making sure curl exactly replicates any request to the smallest detail? that's not really a job for curl, but for socket_*. i bet some would say that this is not really a job for PHP either, but PHP surely is capable of doing it, in a single-threaded manner. use the socket api to accept connections from server A, read the request, do your processing, forward the request to server B as it was received, read the response from server B, and send that response back to server A.

example (could call this ServerC.php):

<?php
declare(strict_types = 1);
if(php_sapi_name() !== 'cli'){die('this script must run in cli mode.');}
$port = 9999;
$targetIP = gethostbyname ( 'example.org' );
$targetPort = 80;
assert ( false !== filter_var ( $targetIP, FILTER_VALIDATE_IP ) );
var_dump ( $targetIP, $targetPort );

y ( ($listen = socket_create ( AF_INET, SOCK_STREAM, SOL_TCP )) );
register_shutdown_function ( function () use (&$listen) {
    socket_close ( $listen );
} );
y ( socket_bind ( $listen, '0.0.0.0', $port ) );
y ( socket_listen ( $listen ) );
y ( socket_set_block ( $listen ) );
echo 'listening for connections... ', PHP_EOL;
while ( false !== ($newconn = socket_accept ( $listen )) ) {
    echo 'new connection from ';
    socket_getpeername ( $newconn, $peername, $peerport );
    echo $peername . ':' . $peerport . PHP_EOL;
    y ( socket_set_block ( $newconn ) );
    $data = '';
    echo 'reading request... ';
    $data = socket_read_all ( $newconn, 2 );
    var_dump ( $data );
    echo 'done.' . PHP_EOL;
    // client didnt send any bytes in a while, assume we got the whole request...
    {
        // do whatever processing you need to do between requests in here.
    }
    {
        // now to forward the request.
        y ( ($targetSock = socket_create ( AF_INET, SOCK_STREAM, SOL_TCP )) );
        y ( socket_set_block ( $targetSock ) );
        y ( socket_connect ( $targetSock, $targetIP, $targetPort ) );
        echo 'connected to target. forwarding request... ';
        socket_write_all ( $targetSock, $data );
        echo 'done.', PHP_EOL;
        unset ( $data, $newdata );
        $data = '';
        echo 'reading response... ';
        $data = socket_read_all ( $targetSock, 2 );
        var_dump ( $data );
        echo 'done.', PHP_EOL;
        socket_close ( $targetSock );
    }
    echo 'sending response back to client... ';
    socket_write_all ( $newconn, $data );
    echo 'done.', PHP_EOL;
    socket_close ( $newconn );
}
function y($in) {
    if (! $in) {
        $str = hhb_return_var_dump ( socket_last_error (), socket_strerror ( socket_last_error () ) );
        throw new \Exception ( $str );
    }
    return $in;
}
function n($in) {
    if (! ! $in) {
        throw new \Exception ();
    }
    return $in;
}
function hhb_return_var_dump(): string // works like var_dump, but returns a string instead of printing it.
{
    $args = func_get_args ();
    ob_start ();
    call_user_func_array ( 'var_dump', $args );
    return ob_get_clean ();
}
function socket_write_all($sock, string $data) {
    $len = strlen ( $data );
    while ( $len > 0 ) {
        $written = socket_write ( $sock, $data );
        if ($written === false) {
            throw new RuntimeException ( 'socket_write failed. errno: ' . socket_last_error ( $sock ) . '. error: ' . socket_strerror ( socket_last_error ( $sock ) ) );
        }
        $len -= $written;
        $data = substr ( $data, $written );
    }
    return; // all data written
}
function socket_read_all($sock, int $sleep_sec = 2): string {
    $ret = '';
    while ( true ) {
        sleep ( $sleep_sec ); // ...
        $buf = '';
        $read = socket_recv ( $sock, $buf, 9999, MSG_DONTWAIT );
        if ($read === false || $read < 1) {
            return $ret;
        }
        $ret .= $buf;
    }
}

(this script is slow, processes only 1 request at a time (concurrent requests are buffered by the OS for socket_accept, though), and synchronous. but it could be optimized and made fully async with socket_select & co, if its worth optimizing)

Answer 2

Try changing this line

curl_setopt($ch, CURLOPT_POSTFIELDS, $_POST);

to:

curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($_POST));

When you make a regular cURL request, you cannot use an array ($_POST is an array) directly as a value for CURLOPT_POSTFIELDS. You have to transform that array into a postdata string, which is exactly what http_build_query() does. It converts for example

["name" => "my first name", "email" => "my@email.com"]

into:

name=my%20first%20name&email=my@email.com