├── .idea ├── encodings.xml ├── vcs.xml ├── misc.xml ├── inspectionProfiles │ └── profiles_settings.xml ├── modules.xml └── pyportredirector.iml ├── Dockerfile ├── Dockerfile.pypy ├── docker_build.sh ├── docker_entry.sh ├── test └── testserver.py ├── .gitignore ├── README.md ├── portredirector.py └── LICENSE /.idea/encodings.xml: -------------------------------------------------------------------------------- 1 | 2 | 3 | 4 | 5 | 6 | -------------------------------------------------------------------------------- /.idea/vcs.xml: -------------------------------------------------------------------------------- 1 | 2 | 3 | 4 | 5 | 6 | -------------------------------------------------------------------------------- /.idea/misc.xml: -------------------------------------------------------------------------------- 1 | 2 | 3 | 4 | -------------------------------------------------------------------------------- /.idea/inspectionProfiles/profiles_settings.xml: -------------------------------------------------------------------------------- 1 | 2 | 3 | 7 | -------------------------------------------------------------------------------- /.idea/modules.xml: -------------------------------------------------------------------------------- 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | -------------------------------------------------------------------------------- /Dockerfile: -------------------------------------------------------------------------------- 1 | FROM python:3.6-alpine 2 | 3 | MAINTAINER Adam Wallner 4 | 5 | COPY portredirector.py /opt/ 6 | COPY docker_entry.sh /opt/ 7 | 8 | RUN \ 9 | # Install needed packages 10 | apk add --no-cache iptables bash gcc musl-dev make \ 11 | # Install python modules 12 | && pip3 install uvloop async_timeout \ 13 | # Clean unneeded packages 14 | && apk del gcc musl-dev make 15 | 16 | WORKDIR /opt 17 | 18 | ENTRYPOINT ["/opt/docker_entry.sh"] 19 | -------------------------------------------------------------------------------- /.idea/pyportredirector.iml: -------------------------------------------------------------------------------- 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 11 | -------------------------------------------------------------------------------- /Dockerfile.pypy: -------------------------------------------------------------------------------- 1 | FROM pypy:3-slim 2 | 3 | MAINTAINER Adam Wallner 4 | 5 | COPY portredirector.py /opt/ 6 | COPY docker_entry.sh /opt/ 7 | 8 | RUN \ 9 | # Install needed packages 10 | apt-get update && apt-get install -y iptables \ 11 | # Make entry script working with pypy 12 | && ln -s /usr/local/bin/pypy3 /usr/local/bin/python3 \ 13 | # Install python modules 14 | && pip3 install async_timeout \ 15 | # Clean unneeded packages 16 | && apt-get clean \ 17 | && rm -rf /var/lib/apt/lists/* 18 | 19 | WORKDIR /opt 20 | 21 | ENTRYPOINT ["/opt/docker_entry.sh"] 22 | -------------------------------------------------------------------------------- /docker_build.sh: -------------------------------------------------------------------------------- 1 | #!/bin/bash 2 | 3 | NAME="pickapp/pyportredirector" 4 | VERSION=`cat ./portredirector.py | grep "__version__" | cut -d '"' -f2` 5 | 6 | [ "$1" == "pypy" ] && VERSION="$VERSION-pypy" 7 | 8 | if [ "$1" != "pypy" ]; then 9 | docker build --rm -t ${NAME}:${VERSION} -t ${NAME}:latest . \ 10 | && docker push ${NAME}:latest 11 | fi 12 | if [ "$1" == "pypy" ]; then 13 | docker build -f Dockerfile.pypy --rm -t ${NAME}:${VERSION} -t ${NAME}:pypy . \ 14 | && docker push ${NAME}:pypy 15 | fi 16 | 17 | [ $? -eq 0 ] && docker push ${NAME}:${VERSION} 18 | 19 | # Remove untagged images 20 | docker images --no-trunc | grep "" | awk "{print \$3}" | xargs docker rmi -f -------------------------------------------------------------------------------- /docker_entry.sh: -------------------------------------------------------------------------------- 1 | #!/bin/bash 2 | 3 | server=0; 4 | interface="" 5 | 6 | # TODO: make no require Bash 7 | 8 | # Parse params 9 | _interface=0 10 | args=() 11 | for arg in "$@"; do 12 | # Interface 13 | [ "$arg" == "-i" ] && [ ${_interface} -eq 0 ] && _interface=1 && continue 14 | [ ${_interface} -eq 1 ] && _interface=0 && interface="$arg" && continue 15 | 16 | # Is it server? 17 | [ "$arg" == "-l" ] && server=1; 18 | 19 | args+=(${arg}) 20 | done 21 | 22 | if [ ${server} -ne 0 ]; then 23 | # Check if iptables is usable on server 24 | iptables -L &>/dev/null 25 | if [ $? -ne 0 ]; then 26 | echo "You need to start docker in privileged mode and with host networking:" >&2 27 | echo " docker run --net=host --privileged ..." >&2 28 | exit 1 29 | fi 30 | 31 | # Enable local routing 32 | [ "$interface" != "" ] && eval "echo -n 1 >/proc/sys/net/ipv4/conf/${interface}/route_localnet" 33 | fi 34 | 35 | exec /usr/local/bin/python3 -u -OO /opt/portredirector.py ${args[@]} 36 | -------------------------------------------------------------------------------- /test/testserver.py: -------------------------------------------------------------------------------- 1 | #!/usr/bin/env python3 2 | # -*- coding: utf-8 -*- 3 | 4 | import argparse 5 | import asyncio 6 | 7 | __author__ = "Adam Wallner" 8 | __copyright__ = "Copyright 2017, Adam Wallner" 9 | __credits__ = [] 10 | __license__ = "GPLv3" 11 | __version__ = "0.1" 12 | __maintainer__ = "Adam Wallner" 13 | __email__ = "adam.wallner@gmail.com" 14 | __status__ = "Beta" 15 | __doc__ = "Test server for testing if port redirection is working" 16 | 17 | 18 | class ServerProtocol(asyncio.Protocol): 19 | transport = None 20 | peer = "" 21 | 22 | def connection_made(self, transport): 23 | peername = transport.get_extra_info('peername') 24 | self.peer = peername[0] + ':' + str(peername[1]) 25 | print('Connection from ' + self.peer) 26 | self.transport = transport 27 | 28 | def data_received(self, data): 29 | message = data.decode() 30 | print('Data received from {}: {!r}'.format(self.peer, message)) 31 | # Echo data back with the detected ip of the peer 32 | self.transport.write(str.encode(self.peer + ': ') + data) 33 | # Exit if asked from the client 34 | if message.strip() == 'exit': 35 | self.transport.close() 36 | 37 | def connection_lost(self, exc): 38 | print(self.peer + ' disconnected') 39 | 40 | parser = argparse.ArgumentParser(description=__doc__) 41 | parser.add_argument('port', help='The port where the server will listen on.') 42 | 43 | args = parser.parse_args() 44 | 45 | 46 | loop = asyncio.get_event_loop() 47 | # Each client connection will create a new protocol instance 48 | coro = loop.create_server(ServerProtocol, '0.0.0.0', args.port) 49 | server = loop.run_until_complete(coro) 50 | 51 | # Serve requests until CTRL+c is pressed 52 | sockname = server.sockets[0].getsockname() 53 | print('Serving on {}:{}'.format(sockname[0], sockname[1])) 54 | try: 55 | loop.run_forever() 56 | except KeyboardInterrupt: 57 | pass 58 | 59 | # Close the server 60 | server.close() 61 | loop.run_until_complete(server.wait_closed()) 62 | loop.close() 63 | -------------------------------------------------------------------------------- /.gitignore: -------------------------------------------------------------------------------- 1 | test/test.sh 2 | 3 | # Created by .ignore support plugin (hsz.mobi) 4 | ### macOS template 5 | *.DS_Store 6 | .AppleDouble 7 | .LSOverride 8 | 9 | # Icon must end with two \r 10 | Icon 11 | 12 | 13 | # Thumbnails 14 | ._* 15 | 16 | # Files that might appear in the root of a volume 17 | .DocumentRevisions-V100 18 | .fseventsd 19 | .Spotlight-V100 20 | .TemporaryItems 21 | .Trashes 22 | .VolumeIcon.icns 23 | .com.apple.timemachine.donotpresent 24 | 25 | # Directories potentially created on remote AFP share 26 | .AppleDB 27 | .AppleDesktop 28 | Network Trash Folder 29 | Temporary Items 30 | .apdisk 31 | ### Python template 32 | # Byte-compiled / optimized / DLL files 33 | __pycache__/ 34 | *.py[cod] 35 | *$py.class 36 | 37 | # C extensions 38 | *.so 39 | 40 | # Distribution / packaging 41 | .Python 42 | env/ 43 | build/ 44 | develop-eggs/ 45 | dist/ 46 | downloads/ 47 | eggs/ 48 | .eggs/ 49 | lib/ 50 | lib64/ 51 | parts/ 52 | sdist/ 53 | var/ 54 | wheels/ 55 | *.egg-info/ 56 | .installed.cfg 57 | *.egg 58 | 59 | # PyInstaller 60 | # Usually these files are written by a python script from a template 61 | # before PyInstaller builds the exe, so as to inject date/other infos into it. 62 | *.manifest 63 | *.spec 64 | 65 | # Installer logs 66 | pip-log.txt 67 | pip-delete-this-directory.txt 68 | 69 | # Unit test / coverage reports 70 | htmlcov/ 71 | .tox/ 72 | .coverage 73 | .coverage.* 74 | .cache 75 | nosetests.xml 76 | coverage.xml 77 | *,cover 78 | .hypothesis/ 79 | 80 | # Translations 81 | *.mo 82 | *.pot 83 | 84 | # Django stuff: 85 | *.log 86 | local_settings.py 87 | 88 | # Flask stuff: 89 | instance/ 90 | .webassets-cache 91 | 92 | # Scrapy stuff: 93 | .scrapy 94 | 95 | # Sphinx documentation 96 | docs/_build/ 97 | 98 | # PyBuilder 99 | target/ 100 | 101 | # Jupyter Notebook 102 | .ipynb_checkpoints 103 | 104 | # pyenv 105 | .python-version 106 | 107 | # celery beat schedule file 108 | celerybeat-schedule 109 | 110 | # SageMath parsed files 111 | *.sage.py 112 | 113 | # dotenv 114 | .env 115 | 116 | # virtualenv 117 | .venv 118 | venv/ 119 | ENV/ 120 | 121 | # Spyder project settings 122 | .spyderproject 123 | 124 | # Rope project settings 125 | .ropeproject 126 | ### JetBrains template 127 | # Covers JetBrains IDEs: IntelliJ, RubyMine, PhpStorm, AppCode, PyCharm, CLion, Android Studio and Webstorm 128 | # Reference: https://intellij-support.jetbrains.com/hc/en-us/articles/206544839 129 | 130 | # User-specific stuff: 131 | .idea/**/workspace.xml 132 | .idea/**/tasks.xml 133 | .idea/dictionaries 134 | 135 | # Sensitive or high-churn files: 136 | .idea/**/dataSources/ 137 | .idea/**/dataSources.ids 138 | .idea/**/dataSources.xml 139 | .idea/**/dataSources.local.xml 140 | .idea/**/sqlDataSources.xml 141 | .idea/**/dynamic.xml 142 | .idea/**/uiDesigner.xml 143 | 144 | # Gradle: 145 | .idea/**/gradle.xml 146 | .idea/**/libraries 147 | 148 | # Mongo Explorer plugin: 149 | .idea/**/mongoSettings.xml 150 | 151 | ## File-based project format: 152 | *.iws 153 | 154 | ## Plugin-specific files: 155 | 156 | # IntelliJ 157 | /out/ 158 | 159 | # mpeltonen/sbt-idea plugin 160 | .idea_modules/ 161 | 162 | # JIRA plugin 163 | atlassian-ide-plugin.xml 164 | 165 | # Crashlytics plugin (for Android Studio and IntelliJ) 166 | com_crashlytics_export_strings.xml 167 | crashlytics.properties 168 | crashlytics-build.properties 169 | fabric.properties 170 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # PyPortRedirector 2 | 3 | A simple Linux TCP client-server proxy able to redirect all data from one address to another by preserving source IP address written in Python 4 | 5 | ## About 6 | 7 | The client can listen on one or more ports then transfer all data to the server. The server accepts connections from the client(s) on a specified port. On new connections client sends the original source IP address and port with the original destination port to the server. Then server creates iptables specific SNAT and DNAT rules for all connections to be able to return packets on the same route back. This way the service will see the original address as source address and think it communicates with that. From this point both server and client(s) act as a TCP proxy between the peers and the service. When peer disconnects or server stops all related rules are deleted. 8 | 9 | Both client and server are asynchronous, so it is very lightweight and has low latency. No threads or forking. Theroretically it can handle 10k peers, but it is not tested (yet). 10 | 11 | ### What is it good for 12 | 13 | Mainly it is good for if you have services with different default routes than the entry firewall. 14 | E.g. you have a firewall with ISP1 and another one with ISP2. The service port should be redirected from ISP1, but the machine which has the service application has default route through ISP2. This way DNAT won't work, because TCP packets arrive at the ISP1 firewall, but leave on ISP2. You can create SNAT to make packets back to ISP1, but this way your service application will see ISP1 firewall as source address, not the original sender. This is a problem if you need logging or filtering based on source IP. 15 | 16 | Also DNAT/SNAT rules won't work if you have one interface to route. So multi ISP DNAT is not an option. 17 | 18 | Of course you can use proxy servers for HTTP traffic, where the proxy can set "X-Forwarded-For" like headers. But what about the other kind of services e.g. HTTPS, SMTP, IMAP, etc? PyPortRedirector is working with these protocols too. 19 | 20 | You can use SSH tunnel for TCP traffics, but all connections will have the same IP address again. You can try to create VPN, but the same problem is you need to route all traffic back through VPN interface to make DNAT work. But what if you need both ISP... 21 | 22 | Another use case if you need to make a service available on another machine as well e.g. because you changed your service provider, but you need to serve on the original IP address too. 23 | 24 | Because multiple clients can connect to one server, you can make a service available as seemingly different ones from different places. 25 | 26 | ### What about security 27 | 28 | PyPortRedirector transfers the same data as arrived on the client part of it. So if the data is encrypted, it will be encrypted as well, no further encryption is needed. But the server needs to know the original sender's IP address. Because of this the 1st packet of every connection will contain these informations. If a malicious person can access the redirector server, he can easily send spoofed packets and the service will see the spoofed IP addresses. So he can bypass source IP filters and logging on the service. Of course it can be logged because the server can log where the connection is from. 29 | 30 | The solution or best practice is to create firewall rules to make server be able to communicate only with the client(s). For this you need to know the IP address of the client(s). 31 | Another solution could be to create an SSH tunnel between the 2 machines. For this solution you don't need fix client IPs, but of course the tunnel has overhead. 32 | 33 | ## Dependencies 34 | 35 | - Python >= v3.5 (works with PyPy3 as well) 36 | - async_timeout >= 1.3.0: https://github.com/aio-libs/async-timeout/releases 37 | 38 | Optional: 39 | - uvloop: https://github.com/MagicStack/uvloop (it makes PyPortRedirector even faster) 40 | 41 | ## Usage 42 | 43 | In the example 1.1.1.1 is the IP of machine1 (M1), 2.2.2.2 is machine2 (M2). The server should listen on the service machine on port 12345. The service is on port 80 and 443. 44 | 45 | On the server you need to enable local routing, to make DNAT rules originated from localhost work: 46 | ```bash 47 | sysctl -w net.ipv4.conf.eth0.route_localnet=1 48 | # Or 49 | # echo "1" >/proc/sys/net/ipv4/conf/eth0/route_localnet 50 | ``` 51 | 52 | Start the client on M1: 53 | ```bash 54 | portredirector.py -c 2.2.2.2:12345 -p 80 -p 443 55 | ``` 56 | 57 | Start the server on M2 58 | ```bash 59 | portredirector.py -l 0.0.0.0:12345 -p 80 -p 443 60 | ``` 61 | 62 | If your service on M2 is listening on other port (e.g. 10080 and 10443), you can replace ports got from client: 63 | ```bash 64 | portredirector.py -l 0.0.0.0:12345 -p 80 -p 443 -r 80.10080 -r 443.10443 65 | ``` 66 | 67 | More info in the help: 68 | ```bash 69 | portredirector.py -h 70 | ``` 71 | Or of course in the source code. 72 | 73 | Both the client and the server can be stopped by pressing CTRL+C, or by sending TERM signal. 74 | 75 | ### Using with Docker 76 | 77 | You can use PyPortRedirector with docker but you need to enable host networking and privileged mode on the server side for making iptables working. 78 | 79 | The image uses Python 3.6 on Alpine Linux to be as small as possible. It contains all the dependencies. It also enable local routing on the server automatically on eth0 by default. You can specify thi interfave with "-i" option e.g. "-i eth1". 80 | 81 | Start client: 82 | ```bash 83 | docker run -ti --rm -p 80:80 -p 443:443 pickapp/pyportredirector -c 2.2.2.2:12345 -p 80 -p 443 84 | ``` 85 | 86 | Start server: 87 | ```bash 88 | docker run -ti --rm --privileged --net=host pickapp/pyportredirector -l 0.0.0.0:12345 -p 80 -p 443 89 | ``` 90 | 91 | #### If the service runs in docker as well 92 | 93 | If you run a service in a docker container with port bindings e.g. `docker run -p 80:80 ...`, docker will create some masquerade rule which changes original source address if the destination is not in docker network. The solution is using 172.17.0.1 as service host, which is the default host IP for Docker: 94 | 95 | ```bash 96 | docker run -ti --rm --privileged --net=host pickapp/pyportredirector -l 0.0.0.0:12345 -p 172.17.0.1:80 -p 172.17.0.1:443 97 | ``` 98 | 99 | It will work in this special case, because the packets are originated from the docker proxy, so packets will be routed back and our DNAT rules can redirect them to PyPortRedirector. 100 | Of course you need to change the address if you have your own docker network created. 101 | 102 | It is good practice to bind the service only on the docker interface by specifying the host before port like this: `docker run -p 172.17.0.1:80:80`. This way the service cannot be accessed from outside world. 127.0.0.1 won't work, because of docker's own iptables rules. 103 | 104 | #### PyPy version 105 | 106 | I created an experimental PyPy version too, which can be used the same way as the original just with "pypy" tag (or version-pypy, e.g. 0.1-pypy): 107 | 108 | ```bash 109 | docker run -ti --rm --privileged --net=host pickapp/pyportredirector:pypy -l 0.0.0.0:12345 -p 80 -p 443 110 | ``` 111 | -------------------------------------------------------------------------------- /portredirector.py: -------------------------------------------------------------------------------- 1 | #!/usr/bin/env python3 2 | # -*- coding: utf-8 -*- 3 | 4 | import sys 5 | import argparse 6 | import asyncio 7 | import async_timeout 8 | import socket 9 | import signal 10 | 11 | try: 12 | # noinspection PyPackageRequirements 13 | import uvloop 14 | asyncio.set_event_loop_policy(uvloop.EventLoopPolicy()) 15 | except ImportError: 16 | uvloop = None 17 | 18 | 19 | __doc__ = """ 20 | PyPortRedirector is a Linux TCP client-server proxy able to redirect all data from one address to another by 21 | preserving source IP address. The client can listen on one or more ports then transfer data to the server. 22 | The server creates Linux iptables SNAT and DNAT rules for all connections to be able to return packets on the same 23 | route back. On server you need to enable "route_localnet" with the following command: 24 | sysctl -w net.ipv4.conf.eth0.route_localnet=1 25 | """ 26 | __author__ = "Adam Wallner" 27 | __copyright__ = "Copyright 2017, Adam Wallner" 28 | __credits__ = [] 29 | __license__ = "GPLv3" 30 | __version__ = "0.3" 31 | __maintainer__ = "Adam Wallner" 32 | __email__ = "adam.wallner@gmail.com" 33 | __status__ = "Production" 34 | 35 | 36 | # The name of redirector iptables chain 37 | IPTABLES_CHAIN_PREFIX = 'PYPORTREDIRECT_' 38 | 39 | # Timeouts 40 | CONNECT_TIMEOUT = 15 # sec - Timeout waiting for a good connection 41 | READ_TIMEOUT = 120 # sec - The maximum time a connection can be opened without communication 42 | 43 | # Socket read size, the maximum number of bytes can be read at once 44 | READ_SIZE = 65536 45 | 46 | 47 | def error(*args, **kwargs): 48 | """ Shortcut for printing errors """ 49 | print(*args, file=sys.stderr, **kwargs) 50 | 51 | 52 | class GoToEnd(Exception): 53 | """ Dummy exception to go to function exit and finalize if needed. """ 54 | 55 | 56 | class Server(object): 57 | """ 58 | Server listening for redirector clients 59 | """ 60 | 61 | def __init__(self, lhost: str, lport: int, servicePorts: list, replacePorts: list, loop=None): 62 | self.loop = loop or asyncio.get_event_loop() 63 | 64 | self.servicePorts = {} 65 | self.replacePorts = {} 66 | 67 | try: 68 | # Process service ports 69 | for sport in servicePorts: 70 | if ':' in sport: 71 | fhost, sport = sport.split(':') 72 | else: 73 | fhost = '127.0.0.1' 74 | sport = int(sport) 75 | self.servicePorts[sport] = (fhost, sport) 76 | 77 | # Process replace prots 78 | if replacePorts is not None: 79 | for rport in replacePorts: 80 | rport = rport.split('.') 81 | if len(rport) != 2: continue 82 | self.replacePorts[int(rport[0])] = int(rport[1]) 83 | 84 | except ValueError: 85 | error("Port numbers must be integer!") 86 | return 87 | 88 | # Initialize iptables 89 | self.loop.run_until_complete(Server.Iptables.createChains()) 90 | 91 | # Create listen socket 92 | make_server = asyncio.start_server(self.handleConnection, lhost, int(lport), 93 | reuse_address=True, reuse_port=True, loop=self.loop) 94 | server = self.loop.run_until_complete(make_server) 95 | 96 | self.listenAddress = lhost + ':' + str(lport) 97 | print('Waiting for redirector client connections on {}…'.format(self.listenAddress)) 98 | 99 | # Waiting until an end signal 100 | self.loop.run_forever() 101 | 102 | # Close server gracefully 103 | server.close() 104 | self.loop.run_until_complete(server.wait_closed()) 105 | 106 | # Finalize iptables 107 | self.loop.run_until_complete(Server.Iptables.deleteChains()) 108 | 109 | # Close the loop 110 | self.loop.close() 111 | 112 | async def handleConnection(self, redirectorClientReader: asyncio.StreamReader, 113 | redirectorClientWriter: asyncio.StreamWriter): 114 | """ Handle connections from redirector clients """ 115 | line = b'' 116 | sport = pport = shost = phost = None 117 | serviceAddress = peerAddress = None 118 | serviceReader = serviceWriter = None 119 | redirectorClientAddress = None 120 | tasks = [] 121 | 122 | try: 123 | # fix buffering issues (backpressure effect) 124 | redirectorClientWriter.transport.set_write_buffer_limits(0) 125 | # Get client address from socket 126 | peername = redirectorClientWriter.transport.get_extra_info('peername') 127 | redirectorClientAddress = peername[0] + ':' + str(peername[1]) 128 | print('Redirector client connected from', redirectorClientAddress, 'to', self.listenAddress) 129 | 130 | try: 131 | with async_timeout.timeout(CONNECT_TIMEOUT, loop=self.loop): 132 | try: 133 | # Wait for the 1st packet (line), which is 134 | line = await redirectorClientReader.readline() 135 | ll = len(line) 136 | 137 | # Validate message 138 | if ll < 11 or ll > 28 or line[-1:] != b"\n" or b":" not in line: 139 | raise ValueError() 140 | 141 | peerData = line[:-1].decode() 142 | phost, pport, sport = peerData.split(':') 143 | # The address of the peer 144 | peerAddress = phost + ':' + pport 145 | pport = int(pport) 146 | # Parse service port 147 | shost, sport = self.servicePorts[int(sport)] 148 | # Replace ports 149 | if sport in self.replacePorts: 150 | sport = self.replacePorts[sport] 151 | serviceAddress = shost + ':' + str(sport) 152 | 153 | except ValueError: pass 154 | 155 | except KeyError: 156 | error("Error: No service is on the specified port: {!r}".format(line)) 157 | raise GoToEnd() 158 | 159 | except asyncio.TimeoutError: 160 | error('Error: Client', redirectorClientAddress, 'protocol error, no data in time!') 161 | raise GoToEnd() 162 | 163 | except BrokenPipeError: 164 | error('Client has immediately closed connection!') 165 | raise GoToEnd() 166 | 167 | if sport is None: 168 | error('Error: Client', redirectorClientAddress, 'protocol error!') 169 | raise GoToEnd() 170 | 171 | # Here we know the peer address and port and the destination port as well so we can create the iptables 172 | # rules and connect to 173 | try: 174 | # Create a socket and get a free port to communicate with. We need to use our own socket to be able to 175 | # get listening port and create iptables rules before connection 176 | csock = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 177 | csock.bind((shost, 0)) 178 | scport = csock.getsockname()[1] 179 | serviceClientAddress = shost + ':' + str(scport) 180 | except socket.error as e: 181 | error("Socket error: ", e) 182 | raise GoToEnd() 183 | 184 | try: 185 | with async_timeout.timeout(CONNECT_TIMEOUT, loop=self.loop): 186 | print(peerAddress, "connecting through", redirectorClientAddress + '…') 187 | # Add IPTables rules 188 | res = await Server.Iptables.addNatRules(redirectorClientAddress, serviceClientAddress, 189 | scport, shost, sport, phost, pport) 190 | # Exit if not connected or no rules 191 | if res != 0: raise GoToEnd() 192 | try: 193 | # Use our own socket to connect 194 | csock.setblocking(False) 195 | await self.loop.sock_connect(csock, (shost, sport)) 196 | serviceReader, serviceWriter = await asyncio.open_connection(sock=csock) 197 | except (ConnectionError, BrokenPipeError, OSError, GeneratorExit): 198 | error("Error: service connection from", peerAddress, 'to', serviceAddress, 'is failed!') 199 | raise GoToEnd() 200 | 201 | except asyncio.TimeoutError: 202 | error('Error: service', serviceAddress, 'connection error timeout!') 203 | raise GoToEnd() 204 | 205 | if not serviceReader or not serviceWriter: 206 | error('Error: service', serviceAddress, 'connection error!') 207 | raise GoToEnd() 208 | 209 | # Here connection successfull 210 | print(peerAddress, 'through', redirectorClientAddress, 'connected to', serviceAddress) 211 | 212 | async def relayStream(reader, writer, otherWriter): 213 | """ Transfer data from reader to writer """ 214 | try: 215 | while True: 216 | # Stop if no data has received in time 217 | with async_timeout.timeout(READ_TIMEOUT, loop=self.loop): 218 | try: 219 | await writer.drain() 220 | data = await reader.read(READ_SIZE) 221 | l = len(data) 222 | if l == 0: # EOF 223 | if not otherWriter.transport.is_closing(): 224 | if reader == redirectorClientReader: 225 | print('Peer ', peerAddress, 'through', redirectorClientAddress, 226 | 'has closed connection to', serviceAddress) 227 | else: 228 | print('Service', serviceAddress, 229 | 'has closed connection from peer', peerAddress, 230 | 'through', redirectorClientAddress) 231 | break 232 | writer.write(data) 233 | except (ConnectionError, BrokenPipeError): 234 | if reader == redirectorClientReader: 235 | error('Peer', peerAddress, 'through', redirectorClientAddress, 236 | 'has disconnected from service', serviceAddress) 237 | else: 238 | error('Service', serviceAddress, 'has disconnected from peer', peerAddress, 239 | 'through', redirectorClientAddress) 240 | break 241 | except OSError as err: 242 | error('Error: OS error:', str(err)) 243 | 244 | except asyncio.TimeoutError: 245 | if reader == redirectorClientReader: 246 | error('Peer', peerAddress, 'through', redirectorClientAddress, 247 | 'read timeout occured. Closing connection.') 248 | else: 249 | error('Service', serviceAddress, 'read timeout occured. Closing connection.') 250 | 251 | except asyncio.CancelledError: pass 252 | 253 | # Close connection 254 | if not writer.transport.is_closing(): 255 | await writer.drain() 256 | writer.close() 257 | # To let the socket actually close 258 | await asyncio.sleep(0, loop=self.loop) 259 | 260 | # Create relay tasks 261 | tasks = [ 262 | asyncio.ensure_future(relayStream(redirectorClientReader, serviceWriter, redirectorClientWriter), 263 | loop=self.loop), 264 | asyncio.ensure_future(relayStream(serviceReader, redirectorClientWriter, serviceWriter), 265 | loop=self.loop) 266 | ] 267 | 268 | # Stop waiting when any connection endpoint has closed 269 | done, pending = await asyncio.wait(tasks, loop=self.loop, return_when=asyncio.FIRST_COMPLETED) 270 | # Cancel remaining task 271 | for task in pending: task.cancel() 272 | if pending: await asyncio.wait(pending, loop=self.loop, timeout=1) 273 | tasks = [] 274 | 275 | except asyncio.CancelledError: pass 276 | except GoToEnd: pass 277 | 278 | finally: 279 | # If we have pending tasks, close them 280 | if tasks: 281 | for task in tasks: task.cancel() 282 | await asyncio.wait(tasks, loop=self.loop, timeout=1) 283 | # Close connection from the client if still connected 284 | if not redirectorClientWriter.transport.is_closing(): 285 | await redirectorClientWriter.drain() 286 | redirectorClientWriter.close() 287 | # Close connection to the service if still connected 288 | if serviceWriter and not serviceWriter.transport.is_closing(): 289 | await serviceWriter.drain() 290 | serviceWriter.close() 291 | # Delete iptables rules 292 | if redirectorClientAddress and Server.Iptables.hasNatRule(redirectorClientAddress): 293 | await Server.Iptables.deleteNatRules(redirectorClientAddress) 294 | 295 | class Iptables(object): 296 | """ 297 | Asynchronous IPTables handling 298 | """ 299 | 300 | # Iptables command 301 | IPTABLES = 'iptables' 302 | 303 | # Rules by redirectorClientAddress 304 | rules = {} 305 | 306 | @classmethod 307 | async def call(cls, rule): 308 | while True: 309 | # All our rules are in the "nat" table 310 | rule = ('-t', 'nat') + rule 311 | creator = asyncio.create_subprocess_exec(cls.IPTABLES, *rule, stderr=asyncio.subprocess.PIPE) 312 | proc = await creator 313 | # Wait for exit and get exit code 314 | res = await proc.wait() 315 | # Read error messages 316 | err = await proc.stderr.readline() 317 | # Handle errors 318 | if res: 319 | # On lock (res == 4) or resource error we need to try again 320 | if res == 4 or err == b"iptables: Resource temporarily unavailable.\n": 321 | continue 322 | # Expected errors 323 | if res != 1 or (err != b"iptables: No chain/target/match by that name.\n" and 324 | err != b"iptables: Chain already exists.\n"): 325 | error("Error (" + str(res) + "): " + err.rstrip().decode()) 326 | # We are done 327 | break 328 | return res 329 | 330 | @classmethod 331 | def hasNatRule(cls, redirectorClientAddress): 332 | return redirectorClientAddress in cls.rules 333 | 334 | @classmethod 335 | async def addNatRules(cls, redirectorClientAddress, clientAddress, cport, shost, sport, phost, pport): 336 | dnatRule = (IPTABLES_CHAIN_PREFIX + 'DNAT', '-s', shost, '-d', phost, '-p', 'tcp', '-m', 'tcp', 337 | '--sport', str(sport), '--dport', str(pport), '-j', 'DNAT', '--to-destination', clientAddress) 338 | res = await cls.call(('-I',) + dnatRule) 339 | 340 | if res == 0: 341 | snatRule = (IPTABLES_CHAIN_PREFIX + 'SNAT', '-s', shost, '-p', 'tcp', '-m', 'tcp', 342 | '--sport', str(cport), '--dport', str(sport), '-j', 'SNAT', '--to-source', 343 | phost + ':' + str(pport)) 344 | res = await cls.call(('-I',) + snatRule) 345 | 346 | cls.rules[redirectorClientAddress] = (dnatRule, snatRule) 347 | if res != 0: 348 | cls.deleteNatRules(redirectorClientAddress) 349 | 350 | return res 351 | 352 | @classmethod 353 | async def deleteNatRules(cls, redirectorClientAddress): 354 | try: 355 | dnatRule, snatRule = cls.rules[redirectorClientAddress] 356 | await cls.call(('-D',) + dnatRule) 357 | await cls.call(('-D',) + snatRule) 358 | 359 | # Delete from rule cache 360 | del cls.rules[redirectorClientAddress] 361 | 362 | # If the address is not in the list of rules 363 | except KeyError: pass 364 | 365 | @classmethod 366 | async def createChains(cls): 367 | # Create chains 368 | await cls.call(('-N', IPTABLES_CHAIN_PREFIX + 'DNAT')) 369 | await cls.call(('-N', IPTABLES_CHAIN_PREFIX + 'SNAT')) 370 | # Create NAT rules 371 | await cls.call(('-D', 'OUTPUT', '-j', IPTABLES_CHAIN_PREFIX + 'DNAT')) # Try deleting 1st 372 | await cls.call(('-I', 'OUTPUT', '-j', IPTABLES_CHAIN_PREFIX + 'DNAT')) 373 | await cls.call(('-D', 'POSTROUTING', '-j', IPTABLES_CHAIN_PREFIX + 'SNAT')) # Try deleting 1st 374 | await cls.call(('-I', 'POSTROUTING', '-j', IPTABLES_CHAIN_PREFIX + 'SNAT')) 375 | # Create RETURN rules 376 | await cls.call(('-A', IPTABLES_CHAIN_PREFIX + 'DNAT', '-j', 'RETURN')) 377 | await cls.call(('-A', IPTABLES_CHAIN_PREFIX + 'SNAT', '-j', 'RETURN')) 378 | 379 | @classmethod 380 | async def deleteChains(cls): 381 | await cls.call(('-D', 'OUTPUT', '-j' + IPTABLES_CHAIN_PREFIX + 'DNAT')) 382 | await cls.call(('-D', 'POSTROUTING', '-j' + IPTABLES_CHAIN_PREFIX + 'SNAT')) 383 | # Flush chains 384 | await cls.call(('-F', IPTABLES_CHAIN_PREFIX + 'DNAT')) 385 | await cls.call(('-F', IPTABLES_CHAIN_PREFIX + 'SNAT')) 386 | # Remove chains 387 | await cls.call(('-X', IPTABLES_CHAIN_PREFIX + 'DNAT')) 388 | await cls.call(('-X', IPTABLES_CHAIN_PREFIX + 'SNAT')) 389 | 390 | 391 | class Client(object): 392 | """ 393 | Client accepting and forwarding connections and data to the server 394 | """ 395 | 396 | def __init__(self, host: str, port: int, redirectingPorts: list, loop=None): 397 | self.loop = loop or asyncio.get_event_loop() 398 | 399 | servers = [] 400 | 401 | try: 402 | self.redirectorServerHost = host 403 | self.redirectorServerPort = int(port) 404 | self.redirectorServerAddress = host + ':' + str(port) 405 | 406 | # Create listen sockets for forwarding ports 407 | for forwardPort in redirectingPorts: 408 | if type(forwardPort) is str and ':' in forwardPort: 409 | forwardHost, forwardPort = forwardPort.split(':') 410 | else: 411 | forwardHost = '0.0.0.0' 412 | 413 | make_server = asyncio.start_server(self.handleConnection, forwardHost, int(forwardPort), 414 | reuse_address=True, reuse_port=True, loop=self.loop) 415 | server = self.loop.run_until_complete(make_server) 416 | 417 | listenAddress = forwardHost + ':' + str(forwardPort) 418 | print('Waiting for peer connections on {}…'.format(listenAddress)) 419 | 420 | servers.append(server) 421 | 422 | # Waiting until an end signal 423 | self.loop.run_forever() 424 | 425 | # Tasks for closing connections 426 | closeTasks = [] 427 | 428 | # Close server connections 429 | for server in servers: 430 | server.close() 431 | closeTasks.append(server.wait_closed()) 432 | 433 | self.loop.run_until_complete(asyncio.wait(closeTasks, loop=self.loop, timeout=5)) 434 | 435 | except RuntimeError: 436 | pass 437 | 438 | # Close the loop 439 | self.loop.close() 440 | 441 | async def handleConnection(self, peerReader: asyncio.StreamReader, peerWriter: asyncio.StreamWriter): 442 | """ Accepts peer connections """ 443 | redirectorReader = redirectorWriter = None 444 | tasks = [] 445 | try: 446 | # fix buffering issues (backpressure effect) 447 | peerWriter.transport.set_write_buffer_limits(0) 448 | # Get socket info 449 | peername = peerWriter.get_extra_info('peername') 450 | sockname = peerWriter.get_extra_info('sockname') 451 | # Calculate peer and liten address info 452 | peerAddress = peername[0] + ':' + str(peername[1]) 453 | listenPort = str(sockname[1]) 454 | listenAddress = sockname[0] + ':' + listenPort 455 | print('Peer', peerAddress, 'connected to', listenAddress) 456 | 457 | # Connect to redirector server 458 | try: 459 | with async_timeout.timeout(CONNECT_TIMEOUT, loop=self.loop): 460 | try: 461 | redirectorReader, redirectorWriter = await asyncio.open_connection(self.redirectorServerHost, 462 | self.redirectorServerPort, 463 | ssl=False) 464 | # fix buffering issues (backpressure effect) 465 | redirectorWriter.transport.set_write_buffer_limits(0) 466 | # Send peer info to the redirector server as 1st message 467 | redirectorWriter.write(str.encode(peerAddress + ':' + listenPort + '\n')) 468 | 469 | except (ConnectionError, BrokenPipeError, GeneratorExit, OSError): 470 | error('Error: Redirecting connection from ' + peerAddress + ' to ' + 471 | listenAddress + ' is failed!') 472 | 473 | except asyncio.TimeoutError: 474 | error('Error: Redirecting connection from ' + peerAddress + ' to ' + listenAddress + 475 | ' was failed because of timeout!') 476 | 477 | # If connection was unsuccessfull 478 | if not redirectorReader or not redirectorWriter: raise GoToEnd() 479 | 480 | print("Peer", peerAddress, 'redirected to', self.redirectorServerAddress) 481 | 482 | async def relayStream(reader, writer, otherWriter): 483 | """ Transfer data from reader to writer """ 484 | try: 485 | while True: 486 | # Stop if no data has received in time 487 | with async_timeout.timeout(READ_TIMEOUT, loop=self.loop): 488 | try: 489 | await writer.drain() 490 | data = await reader.read(READ_SIZE) 491 | l = len(data) 492 | if l == 0: # EOF 493 | if not otherWriter.transport.is_closing(): 494 | if reader == peerReader: 495 | print('Peer', peerAddress, 'has closed connection to', 496 | self.redirectorServerAddress) 497 | else: 498 | print('Redirector', self.redirectorServerAddress, 499 | 'has closed connection from peer', peerAddress) 500 | break 501 | writer.write(data) 502 | except (ConnectionError, BrokenPipeError): 503 | if reader == peerReader: 504 | error('Peer', peerAddress, 'has disconnected from', self.redirectorServerAddress) 505 | else: 506 | error('Redirector', self.redirectorServerAddress, 507 | 'has disconnected from', peerAddress) 508 | break 509 | 510 | except OSError as e: 511 | error('Error: OS error:', str(e)) 512 | 513 | except asyncio.TimeoutError: 514 | if reader == peerReader: 515 | error('Peer', peerAddress, 'read timeout occured. Closing connection.') 516 | else: 517 | error('Redirector', self.redirectorServerAddress, 'read timeout occured. Closing connection.') 518 | 519 | except asyncio.CancelledError: pass 520 | 521 | # Close connection 522 | if not writer.transport.is_closing(): 523 | await writer.drain() 524 | writer.close() 525 | # To let the socket actually close 526 | await asyncio.sleep(0, loop=self.loop) 527 | 528 | # Create relay tasks 529 | tasks = [ 530 | asyncio.ensure_future(relayStream(peerReader, redirectorWriter, peerWriter), loop=self.loop), 531 | asyncio.ensure_future(relayStream(redirectorReader, peerWriter, redirectorWriter), loop=self.loop) 532 | ] 533 | 534 | # Stop waiting when any connection endpoint has closed 535 | done, pending = await asyncio.wait(tasks, loop=self.loop, return_when=asyncio.FIRST_COMPLETED) 536 | # Cancel remaining task 537 | for task in pending: task.cancel() 538 | if pending: await asyncio.wait(pending, loop=self.loop, timeout=1) 539 | tasks = [] 540 | 541 | except BrokenPipeError: 542 | error('Error: Peer has immediately closed connection!') 543 | 544 | except asyncio.CancelledError: pass 545 | except GoToEnd: pass 546 | 547 | finally: 548 | # If we have pending tasks close them 549 | if tasks: 550 | for task in tasks: task.cancel() 551 | await asyncio.wait(tasks, loop=self.loop, timeout=1) 552 | # Close peer connection if still opened 553 | if not peerWriter.transport.is_closing(): 554 | await peerWriter.drain() 555 | peerWriter.close() 556 | # Close redirector connection if still opened 557 | if redirectorWriter and not redirectorWriter.transport.is_closing(): 558 | await redirectorWriter.drain() 559 | redirectorWriter.close() 560 | 561 | 562 | def main(): 563 | # Parse command line arguments 564 | parser = argparse.ArgumentParser(description=__doc__) 565 | 566 | parser.add_argument('-l', '--listen', type=str, help='Start server on the specified interface and port (e.g ' 567 | '0.0.0.0:1234). If only port is specified 0.0.0.0 is used as ' 568 | 'host.') 569 | parser.add_argument('-c', '--connect', type=str, help='Connect to the given server (e.g. 1.2.3.4:1234)') 570 | parser.add_argument('-p', '--port', action='append', type=str, 571 | help='The original service port. The server will connect to this local port,' 572 | 'the client will listen on it and forward data to the server. ' 573 | 'Multiple ports can be specified by more, separated --port parameters.' 574 | 'On client the ports can contain a listen address as well if not need to listen on all ' 575 | 'interfaces (e.g. --port 1.1.1.1:443 --port 80).') 576 | parser.add_argument('-r', '--replace', action='append', type=str, 577 | help='If the local port on the redirector client is not the same as the listen port on server ' 578 | 'side, this parameter can replace the remote port sent by client to a new one. ' 579 | 'The old and new port should be separated by comma (e.g. 80.1080)') 580 | 581 | args = parser.parse_args() 582 | 583 | if (not args.listen and not args.connect) or not args.port: 584 | parser.print_usage() 585 | exit(1) 586 | 587 | if args.listen and args.connect: 588 | error("Either client or server must be selected, not both!") 589 | parser.print_usage() 590 | exit(2) 591 | 592 | forwardPorts = args.port 593 | replacePorts = args.replace 594 | 595 | # The event loop 596 | loop = asyncio.get_event_loop() 597 | 598 | # Signal handler for exiting the loop 599 | async def shutdown(): 600 | print("\r", end='') # Remove ^C from command line 601 | print("Shutting down…") 602 | 603 | # Find all running tasks: 604 | pending = asyncio.Task.all_tasks() 605 | # Cancel all still running tasks (except this shutdown task) 606 | for task in pending: 607 | if task is not asyncio.Task.current_task(): 608 | task.cancel() 609 | 610 | # Stop loop 611 | loop.stop() 612 | 613 | # Add signal handlers 614 | for sig in (signal.SIGINT, signal.SIGTERM, signal.SIGABRT): 615 | loop.add_signal_handler(sig, lambda: loop.create_task(shutdown())) 616 | 617 | # Start client or server based on listen or connect arguments 618 | if args.listen: # Server 619 | try: 620 | if ':' in args.listen: 621 | host, port = args.listen.split(":") 622 | else: 623 | host = '0.0.0.0' 624 | port = int(args.listen) 625 | Server(host, port, forwardPorts, replacePorts, loop=loop) 626 | except ValueError: 627 | error("Wrong listen address format! It should be like 0.0.0.0:1234…") 628 | parser.print_usage() 629 | exit(4) 630 | else: # Client 631 | try: 632 | host, port = args.connect.split(":") 633 | Client(host, port, forwardPorts, loop=loop) 634 | except ValueError: 635 | error("Wrong address format! It should be like 0.0.0.0:1234…") 636 | parser.print_usage() 637 | exit(4) 638 | 639 | 640 | if __name__ == '__main__': main() 641 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | GNU GENERAL PUBLIC LICENSE 2 | Version 3, 29 June 2007 3 | 4 | Copyright (C) 2007 Free Software Foundation, Inc. 5 | Everyone is permitted to copy and distribute verbatim copies 6 | of this license document, but changing it is not allowed. 7 | 8 | Preamble 9 | 10 | The GNU General Public License is a free, copyleft license for 11 | software and other kinds of works. 12 | 13 | The licenses for most software and other practical works are designed 14 | to take away your freedom to share and change the works. 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No Surrender of Others' Freedom. 541 | 542 | If conditions are imposed on you (whether by court order, agreement or 543 | otherwise) that contradict the conditions of this License, they do not 544 | excuse you from the conditions of this License. If you cannot convey a 545 | covered work so as to satisfy simultaneously your obligations under this 546 | License and any other pertinent obligations, then as a consequence you may 547 | not convey it at all. For example, if you agree to terms that obligate you 548 | to collect a royalty for further conveying from those to whom you convey 549 | the Program, the only way you could satisfy both those terms and this 550 | License would be to refrain entirely from conveying the Program. 551 | 552 | 13. Use with the GNU Affero General Public License. 553 | 554 | Notwithstanding any other provision of this License, you have 555 | permission to link or combine any covered work with a work licensed 556 | under version 3 of the GNU Affero General Public License into a single 557 | combined work, and to convey the resulting work. The terms of this 558 | License will continue to apply to the part which is the covered work, 559 | but the special requirements of the GNU Affero General Public License, 560 | section 13, concerning interaction through a network will apply to the 561 | combination as such. 562 | 563 | 14. Revised Versions of this License. 564 | 565 | The Free Software Foundation may publish revised and/or new versions of 566 | the GNU General Public License from time to time. Such new versions will 567 | be similar in spirit to the present version, but may differ in detail to 568 | address new problems or concerns. 569 | 570 | Each version is given a distinguishing version number. If the 571 | Program specifies that a certain numbered version of the GNU General 572 | Public License "or any later version" applies to it, you have the 573 | option of following the terms and conditions either of that numbered 574 | version or of any later version published by the Free Software 575 | Foundation. If the Program does not specify a version number of the 576 | GNU General Public License, you may choose any version ever published 577 | by the Free Software Foundation. 578 | 579 | If the Program specifies that a proxy can decide which future 580 | versions of the GNU General Public License can be used, that proxy's 581 | public statement of acceptance of a version permanently authorizes you 582 | to choose that version for the Program. 583 | 584 | Later license versions may give you additional or different 585 | permissions. However, no additional obligations are imposed on any 586 | author or copyright holder as a result of your choosing to follow a 587 | later version. 588 | 589 | 15. Disclaimer of Warranty. 590 | 591 | THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY 592 | APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT 593 | HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY 594 | OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, 595 | THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 596 | PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM 597 | IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF 598 | ALL NECESSARY SERVICING, REPAIR OR CORRECTION. 599 | 600 | 16. Limitation of Liability. 601 | 602 | IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING 603 | WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS 604 | THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY 605 | GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE 606 | USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF 607 | DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD 608 | PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), 609 | EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF 610 | SUCH DAMAGES. 611 | 612 | 17. Interpretation of Sections 15 and 16. 613 | 614 | If the disclaimer of warranty and limitation of liability provided 615 | above cannot be given local legal effect according to their terms, 616 | reviewing courts shall apply local law that most closely approximates 617 | an absolute waiver of all civil liability in connection with the 618 | Program, unless a warranty or assumption of liability accompanies a 619 | copy of the Program in return for a fee. 620 | 621 | END OF TERMS AND CONDITIONS 622 | 623 | How to Apply These Terms to Your New Programs 624 | 625 | If you develop a new program, and you want it to be of the greatest 626 | possible use to the public, the best way to achieve this is to make it 627 | free software which everyone can redistribute and change under these terms. 628 | 629 | To do so, attach the following notices to the program. It is safest 630 | to attach them to the start of each source file to most effectively 631 | state the exclusion of warranty; and each file should have at least 632 | the "copyright" line and a pointer to where the full notice is found. 633 | 634 | {one line to give the program's name and a brief idea of what it does.} 635 | Copyright (C) {year} {name of author} 636 | 637 | This program is free software: you can redistribute it and/or modify 638 | it under the terms of the GNU General Public License as published by 639 | the Free Software Foundation, either version 3 of the License, or 640 | (at your option) any later version. 641 | 642 | This program is distributed in the hope that it will be useful, 643 | but WITHOUT ANY WARRANTY; without even the implied warranty of 644 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 645 | GNU General Public License for more details. 646 | 647 | You should have received a copy of the GNU General Public License 648 | along with this program. If not, see . 649 | 650 | Also add information on how to contact you by electronic and paper mail. 651 | 652 | If the program does terminal interaction, make it output a short 653 | notice like this when it starts in an interactive mode: 654 | 655 | {project} Copyright (C) {year} {fullname} 656 | This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'. 657 | This is free software, and you are welcome to redistribute it 658 | under certain conditions; type `show c' for details. 659 | 660 | The hypothetical commands `show w' and `show c' should show the appropriate 661 | parts of the General Public License. Of course, your program's commands 662 | might be different; for a GUI interface, you would use an "about box". 663 | 664 | You should also get your employer (if you work as a programmer) or school, 665 | if any, to sign a "copyright disclaimer" for the program, if necessary. 666 | For more information on this, and how to apply and follow the GNU GPL, see 667 | . 668 | 669 | The GNU General Public License does not permit incorporating your program 670 | into proprietary programs. If your program is a subroutine library, you 671 | may consider it more useful to permit linking proprietary applications with 672 | the library. If this is what you want to do, use the GNU Lesser General 673 | Public License instead of this License. But first, please read 674 | . 675 | --------------------------------------------------------------------------------