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LICENSE

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+GNU GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
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+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.

README.md

@@ -0,0 +1,63 @@
+# Natter
+帮助 Full cone NAT (NAT 1) 用户打开公网 TCP 端口。  
+
+
+## 使用例
+在本地 3456 号 TCP 端口上实行 TCP 打洞，并开启测试用 HTTP 服务：
+```
+python natter.py -t 3456
+```
+成功打洞后：
+![](.img/img01.png)
+
+使用外部网络访问该公网地址 `http://203.0.113.10:14500/`，可见 `It works!` 字样：
+![](.img/img02.png)
+
+打洞测试成功后，可以去掉 `-t` 选项，然后使用防火墙规则（如 iptables）将 3456 端口转发至您想要的目标地址上。
+
+
+## 方案
+
+- **推荐方案：**  
+    光猫设置桥接模式，在路由器系统如 OpenWRT 上直接运行 Natter（仅经过一层 NAT）
+
+- **可行方案：**  
+    在子网中的主机上运行 Natter，在光猫或路由器上对其开启 DMZ 功能，或对需要开放的端口设置端口转发。（经过多层NAT）
+
+
+## 大概率会失败的情形
+- **不满足基本条件：**  
+    经过测试，我的网络不是 NAT 1；
+
+- **多层非可控 NAT：**  
+    光猫处于路由模式，我无法关闭光猫的防火墙，并对其设置 DMZ 主机或改桥接；
+
+- **运营商设置了防火墙：**  
+    我在外部网络使用 `nmap` 对出口 IP 地址进行 TCP 全端口扫描，发现均为 `filtered` 。
+
+
+## 错误解读 & 解决方法
+
+```
+This OS or Python does not support reusing ports!
+```
+此操作系统或者 Python 不支持端口重用。  
+**解决方法：** 推荐使用内核版本 4.0+ 的 Linux 系统。
+
+```
+No public STUN server is avaliable. Please check your Internet connection.
+```
+没有可用的公共 STUN 服务器。请检查您的网络连接。  
+**解决方法：** 检查网络，检查防火墙是否阻止 TCP/UDP 端口 3478。如果是脚本内置列表中的服务器不可用，请提 issue。
+
+```
+You cannot perform TCP hole punching in a symmetric NAT network.
+```
+您无法在一个对称型 NAT 网络中实行 TCP 打洞。  
+**解决方法：** 此网络无法打洞。检查您的网络拓扑。检查您是否处于多层 NAT 下。
+
+```
+TCP hole punching seems to fail. Maybe you are behind a firewall.
+```
+TCP 打洞似乎失败了。您可能处于防火墙下。  
+**解决方法：** 如果外部网络可以访问 Natter 提供的地址，请忽略此条信息。尝试关闭光猫的防火墙。如果处于多层 NAT 下，请在光猫或路由器下设置 DMZ 主机或者端口转发。如果上述方案不能解决改问题，则是运营商设置了防火墙，此网络无法开放 TCP 端口。

natter.py

@@ -0,0 +1,583 @@
+import threading
+import socket
+import struct
+import codecs
+import time
+import sys
+import os
+
+
+# Fix OpenWRT Python codecs issues:
+#   Always fallback to ASCII when specified codec is not available.
+try:
+    codecs.lookup('idna')
+    codecs.lookup('utf-8')
+except LookupError:
+    def search_codec(_):
+        return codecs.CodecInfo(codecs.ascii_encode, codecs.ascii_decode, name='ascii')
+    codecs.register(search_codec)
+
+
+class Logger(object):
+    DEBUG = 1
+    INFO = 2
+    WARNING = 3
+    ERROR = 4
+
+    def __init__(self, level = INFO):
+        self.level = level
+
+    def debug(self, msg):
+        if self.level <= Logger.DEBUG:
+            sys.stdout.write("[DEBUG] - " + str(msg) + "\n")
+            sys.stdout.flush()
+
+    def info(self, msg):
+        if self.level <= Logger.INFO:
+            sys.stdout.write("[INFO] - " + str(msg) + "\n")
+            sys.stdout.flush()
+
+    def warning(self, msg):
+        if self.level <= Logger.WARNING:
+            sys.stderr.write("[WARNING] - " + str(msg) + "\n")
+            sys.stderr.flush()
+
+    def error(self, msg):
+        if self.level <= Logger.ERROR:
+            sys.stderr.write("[ERROR] - " + str(msg) + "\n")
+            sys.stderr.flush()
+
+
+class StunClient(object):
+    # Note: IPv4 Only.
+    # Reference:
+    #     https://www.rfc-editor.org/rfc/rfc3489
+    #     https://www.rfc-editor.org/rfc/rfc5389
+    #     https://www.rfc-editor.org/rfc/rfc8489
+
+    # Servers in this list must be compatible with rfc5389 or rfc8489
+    stun_server_tcp = [
+        "fwa.lifesizecloud.com",
+        "stun.isp.net.au",
+        "stun.freeswitch.org",
+        "stun.voip.blackberry.com",
+        "stun.nextcloud.com",
+        "stun.stunprotocol.org",
+        "stun.sipnet.com",
+        "stun.radiojar.com",
+        "stun.sonetel.com",
+        "stun.voipgate.com"
+    ]
+    # Servers in this list must be compatible with rfc3489, with "change IP" and "change port" functions available
+    stun_server_udp = [
+        "stun.miwifi.com",
+        "stun.qq.com"
+    ]
+    MTU         = 1500
+    STUN_PORT   = 3478
+    MAGIC_COOKIE    = 0x2112a442
+    BIND_REQUEST    = 0x0001
+    BIND_RESPONSE   = 0x0101
+    FAMILY_IPV4     = 0x01
+    FAMILY_IPV6     = 0x02
+    CHANGE_PORT     = 0x0002
+    CHANGE_IP       = 0x0004
+    ATTRIB_MAPPED_ADDRESS      = 0x0001
+    ATTRIB_CHANGE_REQUEST      = 0x0003
+    ATTRIB_XOR_MAPPED_ADDRESS  = 0x0020
+    NAT_OPEN_INTERNET    = 0
+    NAT_FULL_CONE        = 1
+    NAT_RESTRICTED       = 2
+    NAT_PORT_RESTRICTED  = 3
+    NAT_SYMMETRIC        = 4
+    NAT_SYM_UDP_FIREWALL = 5
+
+    def __init__(self, source_ip = "0.0.0.0", log_level = Logger.INFO):
+        self.logger = Logger(log_level)
+        self.source_ip = source_ip
+        self.stun_ip_tcp = []
+        self.stun_ip_udp = []
+        if not self.check_reuse_ability():
+            raise OSError("This OS or Python does not support reusing ports!")
+        self.logger.info("Getting STUN server IP...")
+        for hostname in self.stun_server_tcp:
+            self.stun_ip_tcp.extend(self.resolve_hostname(hostname))
+        for hostname in self.stun_server_udp:
+            self.stun_ip_udp.extend(self.resolve_hostname(hostname))
+        if not self.stun_ip_tcp or not self.stun_ip_udp:
+            raise Exception("No public STUN server is avaliable. Please check your Internet connection.")
+
+    def get_free_port(self, udp=False):
+        if udp:
+            sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+        else:
+            sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+        if 'SO_REUSEPORT' in dir(socket):
+            sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
+        sock.bind(('', 0))
+        ret = sock.getsockname()[1]
+        sock.close()
+        return ret
+
+    def check_reuse_ability(self):
+        try:
+            test_port = self.get_free_port()
+            s1 = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+            s1.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+            if 'SO_REUSEPORT' in dir(socket):
+                s1.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
+            s1.bind(("0.0.0.0", test_port))
+            s1.listen(1)
+            s2 = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+            s2.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+            if 'SO_REUSEPORT' in dir(socket):
+                s2.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
+            s2.bind(("0.0.0.0", test_port))
+            s2.listen(1)
+            s1.close()
+            s2.close()
+            return True
+        except OSError as e:
+            self.logger.debug("%s: %s" % (e.__class__.__name__, e))
+            return False
+
+    def resolve_hostname(self, hostname):
+        self.logger.debug("Resolving hostname [%s]..." % hostname)
+        try:
+            host, alias, ip_addresses = socket.gethostbyname_ex(hostname)
+            return ip_addresses
+        except Exception as e:
+            self.logger.debug("%s: %s" % (e.__class__.__name__, e))
+            return []
+
+    def random_tran_id(self, use_magic_cookie = False):
+        if use_magic_cookie:
+            # Compatible with rfc3489, rfc5389 and rfc8489
+            return struct.pack("!L", self.MAGIC_COOKIE) + os.urandom(12)
+        else:
+            # Compatible with rfc3489
+            return os.urandom(16)
+
+    def pack_stun_message(self, msg_type, tran_id, payload = b""):
+        return struct.pack("!HH", msg_type, len(payload)) + tran_id + payload
+
+    def unpack_stun_message(self, data):
+        msg_type, msg_length = struct.unpack("!HH", data[:4])
+        tran_id = data[4:20]
+        payload = data[20:20 + msg_length]
+        return msg_type, tran_id, payload
+
+    def get_mapped_addr(self, payload):
+        while payload:
+            attrib_type, attrib_length = struct.unpack("!HH", payload[:4])
+            attrib_value = payload[4:4 + attrib_length]
+            payload = payload[4 + attrib_length:]
+            if attrib_type == self.ATTRIB_MAPPED_ADDRESS:
+                _, family, port = struct.unpack("!BBH", attrib_value[:4])
+                if family == self.FAMILY_IPV4:
+                    ip = socket.inet_ntoa(attrib_value[4:8])
+                    return ip, port
+            elif attrib_type == self.ATTRIB_XOR_MAPPED_ADDRESS:
+                # rfc5389 and rfc8489
+                _, family, xor_port = struct.unpack("!BBH", attrib_value[:4])
+                if family == self.FAMILY_IPV4:
+                    xor_iip, = struct.unpack("!L", attrib_value[4:8])
+                    ip = socket.inet_ntoa(struct.pack("!L", self.MAGIC_COOKIE ^ xor_iip))
+                    port = (self.MAGIC_COOKIE >> 16) ^ xor_port
+                    return ip, port
+        return None
+
+    def tcp_test(self, stun_host, source_port, timeout = 1):
+        # rfc5389 and rfc8489 only
+        self.logger.debug("Trying TCP STUN: %s" % stun_host)
+        tran_id = self.random_tran_id(use_magic_cookie = True)
+        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        try:
+            sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
+            sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+            if 'SO_REUSEPORT' in dir(socket):
+                sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
+            sock.settimeout(timeout)
+            sock.bind((self.source_ip, source_port))
+            sock.connect((stun_host, self.STUN_PORT))
+            data = self.pack_stun_message(self.BIND_REQUEST, tran_id)
+            sock.sendall(data)
+            buf = sock.recv(self.MTU)
+            msg_type, msg_id, payload = self.unpack_stun_message(buf)
+            if tran_id == msg_id and msg_type == self.BIND_RESPONSE:
+                source_addr  = sock.getsockname()
+                mapped_addr = self.get_mapped_addr(payload)
+                ret = source_addr, mapped_addr
+                self.logger.debug("(TCP) %s says: %s" % (stun_host, mapped_addr))
+            else:
+                ret = None
+            sock.shutdown(socket.SHUT_RDWR)
+            sock.close()
+        except Exception as e:
+            self.logger.debug("%s: %s" % (e.__class__.__name__, e))
+            sock.close()
+            ret = None
+        return ret
+
+    def udp_test(self, stun_host, source_port, change_ip = False, change_port = False, timeout = 1, repeat = 3):
+        # Note:
+        #     Assuming STUN is being multiplexed with other protocols,
+        #     the packet must be inspected to check if it is a STUN packet.
+        self.logger.debug("Trying UDP STUN: %s (change ip:%d/port:%d)" % (stun_host, change_ip, change_port))
+        time_start = time.time()
+        tran_id = self.random_tran_id()
+        sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+        try:
+            sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+            if 'SO_REUSEPORT' in dir(socket):
+                sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
+            sock.settimeout(timeout)
+            sock.bind((self.source_ip, source_port))
+            flags = 0
+            if change_ip:
+                flags |= self.CHANGE_IP
+            if change_port:
+                flags |= self.CHANGE_PORT
+            if flags:
+                payload = struct.pack("!HHL", self.ATTRIB_CHANGE_REQUEST, 0x4, flags)
+                data = self.pack_stun_message(self.BIND_REQUEST, tran_id, payload)
+            else:
+                data = self.pack_stun_message(self.BIND_REQUEST, tran_id)
+            # Send packets repeatedly to avoid packet loss.
+            for _ in range(repeat):
+                sock.sendto(data, (stun_host, self.STUN_PORT))
+            while True:
+                time_left = time_start + timeout - time.time()
+                if time_left <= 0:
+                    raise socket.timeout("timed out")
+                sock.settimeout(time_left)
+                buf, recv_addr = sock.recvfrom(self.MTU)
+                recv_host, recv_port = recv_addr
+                # check STUN packet
+                if len(buf) < 20:
+                    continue
+                msg_type, msg_id, payload = self.unpack_stun_message(buf)
+                if tran_id != msg_id or msg_type != self.BIND_RESPONSE:
+                    continue
+                source_addr  = sock.getsockname()
+                mapped_addr  = self.get_mapped_addr(payload)
+                ip_changed   = (recv_host != self.STUN_PORT)
+                port_changed = (recv_port != self.STUN_PORT)
+                self.logger.debug("(UDP) %s says: %s" % (recv_addr, mapped_addr))
+                return source_addr, mapped_addr, ip_changed, port_changed
+        except Exception as e:
+            self.logger.debug("%s: %s" % (e.__class__.__name__, e))
+            return None
+        finally:
+            sock.close()
+
+    def get_tcp_mapping(self, source_port):
+        server_ip = first = self.stun_ip_tcp[0]
+        while True:
+            ret = self.tcp_test(server_ip, source_port)
+            if ret is None:
+                # server unavailable, put it at the end of the list
+                self.stun_ip_tcp.append(self.stun_ip_tcp.pop(0))
+                server_ip = self.stun_ip_tcp[0]
+                if server_ip == first:
+                    raise Exception("No public STUN server is avaliable. Please check your Internet connection.")
+            else:
+                source_addr, mapped_addr = ret
+                return source_addr, mapped_addr
+
+    def get_udp_mapping(self, source_port):
+        server_ip = first = self.stun_ip_udp[0]
+        while True:
+            ret = self.udp_test(server_ip, source_port)
+            if ret is None:
+                # server unavailable, put it at the end of the list
+                self.stun_ip_udp.append(self.stun_ip_udp.pop(0))
+                server_ip = self.stun_ip_udp[0]
+                if server_ip == first:
+                    raise Exception("No public STUN server is avaliable. Please check your Internet connection.")
+            else:
+                source_addr, mapped_addr, ip_changed, port_changed = ret
+                return source_addr, mapped_addr
+
+    def check_nat_type(self, source_port = 0):
+        # Like classic STUN (rfc3489). Detect NAT behavior for UDP.
+        # Modified from rfc3489. Requires at least two STUN servers.
+        ret_test1_1 = None
+        ret_test1_2 = None
+        ret_test2 = None
+        ret_test3 = None
+        if source_port == 0:
+            source_port = self.get_free_port(udp=True)
+
+        for server_ip in self.stun_ip_udp:
+            ret = self.udp_test(server_ip, source_port, change_ip=False, change_port=False)
+            if ret is None:
+                self.logger.debug("No response. Trying another STUN server...")
+                continue
+            if ret_test1_1 is None:
+                ret_test1_1 = ret
+                continue
+            ret_test1_2 = ret
+            ret = self.udp_test(server_ip, source_port, change_ip=True, change_port=True)
+            if ret is not None:
+                source_addr, mapped_addr, ip_changed, port_changed = ret
+                if not ip_changed or not port_changed:
+                    self.logger.debug("Trying another STUN server because current server do not have another available IP or port...")
+                    continue
+            ret_test2 = ret
+            ret_test3 = self.udp_test(server_ip, source_port, change_ip=False, change_port=True)
+            break
+        else:
+            raise Exception("UDP Blocked or not enough STUN servers available.")
+
+        source_addr_1_1, mapped_addr_1_1, _, _ = ret_test1_1
+        source_addr_1_2, mapped_addr_1_2, _, _ = ret_test1_2
+        if mapped_addr_1_1 != mapped_addr_1_2:
+            return StunClient.NAT_SYMMETRIC
+        if source_addr_1_1 == mapped_addr_1_1:
+            if ret_test2 is not None:
+                return StunClient.NAT_OPEN_INTERNET
+            else:
+                return StunClient.NAT_SYM_UDP_FIREWALL
+        else:
+            if ret_test2 is not None:
+                return StunClient.NAT_FULL_CONE
+            else:
+                if ret_test3 is not None:
+                    return StunClient.NAT_RESTRICTED
+                else:
+                    return StunClient.NAT_PORT_RESTRICTED
+
+    def is_tcp_cone(self, source_port = 0):
+        # Detect NAT behavior for TCP. Requires at least three STUN servers for accuracy.
+        if source_port == 0:
+            source_port = self.get_free_port()
+        mapped_addr_first = None
+        count = 0
+        for server_ip in self.stun_ip_tcp:
+            if count >= 3:
+                return True
+            ret = self.tcp_test(server_ip, source_port)
+            if ret is not None:
+                source_addr, mapped_addr = ret
+                if mapped_addr_first is not None and mapped_addr != mapped_addr_first:
+                    return False
+                mapped_addr_first = ret[1]
+                count += 1
+        raise Exception("Not enough STUN servers available.")
+
+
+class HttpTestServer(object):
+    # HTTP Server for testing purpose
+    # On success, you can see the text "It works!".
+
+    def __init__(self, listen_addr):
+        self.running = False
+        self.listen_addr = listen_addr
+        self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        self.sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+        if 'SO_REUSEPORT' in dir(socket):
+            self.sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
+
+    def run(self):
+        self.running = True
+        self.sock.bind(self.listen_addr)
+        self.sock.listen(1)
+        while self.running:
+            try:
+                conn, addr = self.sock.accept()
+            except Exception:
+                return
+            try:
+                conn.recv(4096)
+                conn.sendall(b"HTTP/1.1 200 OK\r\n")
+                conn.sendall(b"Content-Type: text/html\r\n")
+                conn.sendall(b"\r\n")
+                conn.sendall(b"<h1>It works!</h1><hr/>Natter\r\n")
+                conn.shutdown(socket.SHUT_RDWR)
+            except Exception:
+                pass
+            finally:
+                conn.close()
+
+    def start(self):
+        threading.Thread(target=self.run).start()
+
+    def stop(self):
+        self.running = False
+        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        sock.settimeout(0.1)
+        result = sock.connect_ex(self.listen_addr)
+        sock.close()
+        self.sock.close()
+
+
+class Natter(object):
+    def __init__(self, source_ip, source_port, test_http = False,
+                 keep_alive_host = "www.qq.com", keep_alive_interval = 10, retry_sec = 3, log_level = Logger.INFO):
+        self.logger = Logger(log_level)
+        self.source_ip = source_ip
+        self.source_port = source_port
+        self.test_http = test_http
+        self.keep_alive_host = keep_alive_host
+        self.keep_alive_interval = keep_alive_interval
+        self.retry_sec = retry_sec
+        self.stun_client = StunClient(source_ip, log_level = log_level)
+        self.keep_alive_sock = self._init_keep_alive_sock()
+        self.http_test_server = HttpTestServer((source_ip, source_port))
+
+    def _init_keep_alive_sock(self):
+        s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        s.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
+        s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+        if 'SO_REUSEPORT' in dir(socket):
+            s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
+        s.bind((self.source_ip, self.source_port))
+        s.connect((self.keep_alive_host, 80))
+        s.settimeout(self.keep_alive_interval)
+        return s
+
+    def _keep_alive(self):
+        s = self.keep_alive_sock
+        try:
+            s.sendall(b"GET /~ HTTP/1.1\r\n")
+            s.sendall(b"Host: %s\r\n" % self.keep_alive_host.encode())
+            s.sendall(b"Connection: keep-alive\r\n")
+            s.sendall(b"\r\n")
+        except Exception as e:
+            self.logger.debug("%s: %s" % (e.__class__.__name__, e))
+            return False
+        try:
+            while s.recv(4096):
+                self.logger.debug("[%s] Keep-Alive OK!" % time.asctime())
+            self.logger.debug("Server closed connection")
+            return False
+        except socket.timeout:
+            return True
+        except Exception as e:
+            self.logger.debug("%s: %s" % (e.__class__.__name__, e))
+            return False
+
+    def test_port_open(self, dst_addr, timeout = 3):
+        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        sock.settimeout(timeout)
+        result = sock.connect_ex(dst_addr)
+        sock.close()
+        return result == 0
+
+    def tcp_punch(self):
+        self.logger.info("Checking NAT Type for UDP...")
+        nat_type = self.stun_client.check_nat_type()
+        if nat_type == StunClient.NAT_OPEN_INTERNET:
+            nat_type_txt = "Open Internet"
+        elif nat_type == StunClient.NAT_SYM_UDP_FIREWALL:
+            nat_type_txt = "Symmetric UDP firewall"
+        elif nat_type == StunClient.NAT_FULL_CONE:
+            nat_type_txt = "Full cone (NAT 1)"
+        elif nat_type == StunClient.NAT_RESTRICTED:
+            nat_type_txt = "Restricted (NAT 2)"
+        elif nat_type == StunClient.NAT_PORT_RESTRICTED:
+            nat_type_txt = "Port restricted (NAT 3)"
+        elif nat_type == StunClient.NAT_SYMMETRIC:
+            nat_type_txt = "Symmetric (NAT 4)"
+        else:
+            nat_type_txt = "Unknown"
+        self.logger.info("NAT Type for UDP: [ %s ]" % nat_type_txt)
+        if nat_type == StunClient.NAT_OPEN_INTERNET:
+            self.logger.warning("It looks like you are not in a NAT network, so there is no need to use this tool.")
+        elif nat_type != StunClient.NAT_FULL_CONE:
+            self.logger.warning("The NAT type of your network is not full cone (NAT 1). TCP hole punching may fail.")
+
+        self.logger.info("Checking NAT Type for TCP...")
+        if self.stun_client.is_tcp_cone():
+            self.logger.info("NAT Type for TCP: [ Cone NAT ]")
+        else:
+            self.logger.info("NAT Type for TCP: [ Symmetric ]")
+            self.logger.error("You cannot perform TCP hole punching in a symmetric NAT network.")
+            return
+
+        self.logger.info("Start punching...")
+        self.http_test_server.start()
+        source_addr, mapped_addr = self.stun_client.get_tcp_mapping(self.source_port)
+        if not self.test_port_open(source_addr):
+            self.logger.error("Local address %s is not available. Check your firewall settings." % source_addr)
+            return
+        if self.test_port_open(mapped_addr):
+            self.logger.info(
+                "The TCP hole punching appears to be successful. "
+                "Please test this address from another network: %s" % str(mapped_addr)
+            )
+            print("\n================================\n    %s\n================================\n"% str(mapped_addr))
+            if self.test_http:
+                print("HTTP test server is enabled. Please check [ http://%s:%d/ ]\n" % mapped_addr)
+        else:
+            self.logger.warning(
+                "TCP hole punching seems to fail. Maybe you are behind a firewall. "
+                "However, you may check this address from another network: %s" % str(mapped_addr)
+            )
+        if not self.test_http:
+            self.http_test_server.stop()
+        # Keep alive
+        self.logger.info("TCP keep-alive...")
+        while True:
+            ok = self._keep_alive()
+            if not ok:
+                self.keep_alive_sock.close()
+                time.sleep(self.retry_sec)
+                self.keep_alive_sock = self._init_keep_alive_sock()
+                self._keep_alive()
+                source_addr, mapped_addr = self.stun_client.get_tcp_mapping(self.source_port)
+                self.logger.info("Mapped address: %s" % str(mapped_addr))
+    
+    def close(self):
+        try:
+            self.keep_alive_sock.shutdown(socket.SHUT_RDWR)
+        except Exception:
+            pass
+        self.keep_alive_sock.close()
+        self.http_test_server.stop()
+
+
+def main():
+    try:
+        src_host = "0.0.0.0"
+        src_port = -1
+        verbose = False
+        test_http = False
+        l = []
+        for arg in sys.argv[1:]:
+            if arg[0] == "-":
+                if arg == "-v":
+                    verbose = True
+                elif arg == "-t":
+                    test_http = True
+                else:
+                    raise ValueError
+            else:
+                l.append(arg)
+        if len(l) == 1:
+            src_port = int(l[0])
+        elif len(l) == 2:
+            src_host = l[0]
+            src_port = int(l[1])
+        else:
+            raise ValueError
+    except ValueError:
+        print("Usage: python natter.py [-v] [-t] [SRC_HOST] SRC_PORT\n")
+        return
+    
+    if verbose:
+        log_level=Logger.DEBUG
+    else:
+        log_level=Logger.INFO
+    natter = Natter(src_host, src_port, test_http=test_http, log_level=log_level)
+    try:
+        natter.tcp_punch()
+    except KeyboardInterrupt:
+        print("\nExiting...\n")
+        natter.close()
+
+
+if __name__ == '__main__':
+    main()