masscan 扫描端口时靠什么检测，为什么这么快? 请详述.

import socket
import struct
import random

def send_syn_packet(ip, port):
    # 创建原始套接字
    s = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_TCP)
    s.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1)

    # 构建 IP 头
    ip_header = build_ip_header(ip)

    # 构建 TCP 头
    tcp_header = build_tcp_header(port)

    # 构建完整的数据包
    packet = ip_header + tcp_header

    # 发送数据包
    s.sendto(packet, (ip, 0))

def build_ip_header(ip):
    # IP 头结构
    ip_header = struct.pack('!BBHHHBBH4s4s', 
                            69, 0, 0, 0, 0, 64, 6, 0, 
                            socket.inet_aton('0.0.0.0'), socket.inet_aton(ip))
    return ip_header

def build_tcp_header(port):
    # TCP 头结构
    source_port = random.randint(1024, 65535)
    dest_port = port
    seq = 0
    ack_seq = 0
    doff = 5
    flags = 0x02  # SYN 标志
    window = socket.htons(5840)
    checksum = 0
    urg_ptr = 0

    tcp_header = struct.pack('!HHLLBBHHH', 
                             source_port, dest_port, seq, ack_seq, 
                             (doff << 4) + 0, flags, window, checksum, urg_ptr)
    return tcp_header

def receive_response(s):
    # 接收响应
    while True:
        packet = s.recvfrom(65565)
        ip_header = packet[0][0:20]
        iph = struct.unpack('!BBHHHBBH4s4s', ip_header)
        
        version_ihl = iph[0]
        version = version_ihl >> 4
        ihl = version_ihl & 0xF
        iph_length = ihl * 4
        
        tcp_header = packet[0][iph_length:iph_length+20]
        tcph = struct.unpack('!HHLLBBHHH', tcp_header)
        
        source_port = tcph[0]
        dest_port = tcph[1]
        sequence = tcph[2]
        acknowledgement = tcph[3]
        doff_reserved = tcph[4]
        tcph_length = doff_reserved >> 4
        
        flags = tcph[5]
        if flags & 0x12 == 0x12:  # SYN-ACK
            print(f"Port {dest_port} is open")
        elif flags & 0x14 == 0x14:  # RST-ACK
            print(f"Port {dest_port} is closed")

# 示例使用
send_syn_packet('192.168.1.1', 80)