Add a command line option for what interface to listen on

[tkluck]

This may be useful for exposing pac4cli to containers (cf. #33).

Choosing -s for the short form as that agrees with netcat.

This is WIP, so let's not merge until we hear back from the issue author.

[badp]

I couldn't manage to reach happiness, but it might be due to either me setting up the program incorrectly, or my bug report having fundamentally misunderstood how containers work.

$ git clone --recursive https://github.com/pacparser/pacparser.git
$ cd pac4cli
$ git checkout add-interface-option
$ pipenv install -r requirements.txt
$ pipenv run python main.py -p 3129 -s docker0
Traceback (most recent call last):
  File "main.py", line 17, in <module>
    import pacparser
ModuleNotFoundError: No module named 'pacparser'
$ git clone https://github.com/pacparser/pacparser.git
$ pipenv run python main.py -p 3129 -s docker0 &
ERROR [20682]: pac4cli: Problem starting the server
Traceback (most recent call last):
  File "main.py", line 95, in main
    pacparser.init()
AttributeError: module 'pacparser' has no attribute 'init'
# the proxy seems to be up and running now?
$ PROXY_IP_ADDRESS=172.17.0.1
$ jq '. + {"proxies": {"default": {"httpProxy": "http://'$PROXY_IP_ADDRESS':3129/", "httpsProxy": "http://'$PROXY_IP_ADDRESS':3129/"}}}' ~/.docker/config.json | tee tmp.$$.json && mv tmp.$$.json ~/.docker/config.json
{
  "auths": {...},
  "HttpHeaders": {
    "User-Agent": "Docker-Client/17.12.1-ce (linux)"
  },
  "proxies": {
    "default": {
      "httpProxy": "http://172.17.0.1:3129/",
      "httpsProxy": "http://172.17.0.1:3129/"
    }
  }
}
$ docker run -it python env | grep http
http_proxy=http://172.17.0.1:3129/
HTTPS_PROXY=http://172.17.0.1:3129/
https_proxy=http://172.17.0.1:3129/
HTTP_PROXY=http://172.17.0.1:3129/
$ docker run -it python pip install pipenv
Collecting pipenv
  Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProxyError('Cannot connect to proxy.', NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x7f4d08bfd470>: Failed to establish a new connection: [Errno 111] Connection refused'))': /simple/pipenv/

Indeed:

$ pipenv run python main.py -p 3129 -s 0.0.0.0 &
$ docker run -it python pip install pipenv
Collecting pipenv
  Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProxyError('Cannot connect to proxy.', NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x7f8f54967748>: Failed to establish a new connection: [Errno 111] Connection refused'))': /simple/pipenv/

[tkluck]

@badp that looks like an issue setting up the environment, indeed: there's an additional step to install pacparser (which has a build step) into the environment. If you prefer pipenv over virtualenv, then be sure to also suitably adjust the build step:
https://github.com/tkluck/pac4cli/blob/add-interface-option/Makefile#L38

[badp]

okay, that git clone https://github.com/pacparser/pacparser.git is where I took a wrong turn. Trying again...

[badp]

Starting over (I happened to have all of the required packages installed with apt anyway -- I did install the software!)

$ git clone https://github.com/pacparser/pacparser.git
$ cd pacparser
$ make -c src/
$ sudo make -C src install
$ make -C src pymod
$ sudo make -C src install-pymod
$ cd pac4cli
$ python3 main.py -p 3129 -s docker0
INFO [16176]: pac4cli: Updating WPAD configuration...
INFO [16176]: pac4cli: Trying to get wpad url from NetworkManager DHCP...
INFO [16176]: pac4cli: Trying to get wpad url from NetworkManager domains...
INFO [16176]: pac4cli: Trying http://wpad/wpad.dat...
INFO [16176]: pac4cli: ...found. Parsing configuration...
INFO [16176]: pac4cli: Updated configuration
INFO [16176]: pac4cli: Starting proxy server on docker0:3129
ERROR [16176]: pac4cli: Problem starting the server
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 1386, in _inlineCallbacks
    result = g.send(result)
StopIteration

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/twisted/internet/tcp.py", line 978, in startListening
    skt.bind(addr)
socket.gaierror: [Errno -2] Name or service not known

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "main.py", line 104, in main
    yield start_server(args.interface, args.port, reactor)
twisted.internet.error.CannotListenError: Couldn't listen on docker0:3129: [Errno -2] Name or service not known.
$ python3 main.py -p 3129 -s 172.17.0.1 &
$ docker run -it python pip install pipenv
Downloading https://files.pythonhosted.org/packages/eb/64/9b2747d54f2008ac3dfe86c0b1c8ec126042726fd8a540d5208d26732701/pipenv-2018.7.1-py3-none-any.whl (5.0MB)
    100% |████████████████████████████████| 5.0MB 6.0MB/s 

By the name of the parameter, "interface", I expected to be able to say "docker0" and have it work, but I don't suppose it's a huge deal breaker.

Stack Overflow says you may be able to get the IP address for a given interface with this:

 import netifaces; 
 ip = netifaces.ifaddresses('docker0')[netifaces.AF_INET][0]['addr']

Of course, that [0] is pretty scary hardcoding, and (more importantly) that's an additional dependency for your project, and your packaging, PPA, etc., so I'm happy to take the patch as-is and kludge the IP address myself with some ip address show dev docker0 | grep -o -P 'inet ([^ ]+)' | cut -d' ' -f2 | head -n1 incantation.

[tkluck]

Thanks @badp ! Maybe @lucrocha or @kdehairy can do a review as maintainers?

[tkluck]

@badp heads-up: I just changed the name for this option to -b, --bind to avoid the confusion you suffered. I stole that from python3 http.server.