Minimal PHP packet sniffer

sniff.php

<?php declare(strict_types=1);

$socket = socket_create(AF_INET, SOCK_RAW, SOL_TCP);

if (!$socket) {
    $errorCode = socket_last_error();
    throw new \RuntimeException(socket_strerror($errorCode), $errorCode);
}

const IP_HDR = 'Cversion_ihl/Ctos/ntot_len/nid/nfrag_off/Cttl/Cprotocol/ncheck/Nsaddr/Ndaddr/';
const TCP_HDR = 'nsource/ndest/Nseq/Nack_seq/Cdoff_res/Cflags/nwindow/ncheck/nurg_ptr/';

while (socket_recv($socket, $data, 4096, 0)) {
    $unpackedIPHeader = unpack(IP_HDR, $data);
    // TCP check.
    if ($unpackedIPHeader['protocol'] !== 6) {
        continue;
    }

    $version = $unpackedIPHeader['version_ihl'] >> 4;
    // IPv4 check.
    if ($version !== 4) {
        continue;
    }

    $ipHdrLen = ($unpackedIPHeader['version_ihl'] & 0x0f) << 2;
    // Ignore options data
    $data = substr($data, $ipHdrLen);

    $unpackedTCPHeader = unpack(TCP_HDR, $data);
    $tcpHdrLen = ($unpackedTCPHeader['doff_res'] >> 4) << 2;
    // Ignore options data
    $data = substr($data, $tcpHdrLen);

    var_dump($data);
}