This commit rewrites the log() function so that it will append a
newline at the end of the message if none is present. It doesn't make
sense to print a log message without a newline since the next log
message (which will write a prefix) expects to be starting at the
beginning of a line.

Although it isn't strictly necessary, this commit also removes any
newlines at the ends of messages. If I missed any, including the
newline at the end of the message will continue to work as it did
before.

Previously, some calls were missing the newline at the end even though
including it was necessary for subsequent messages to appear
correctly.

This code also cleans up some redundant prefixes. The log() method
will prepend the prefix and the different processes should set their
prefix as soon as they start.

Multiline messages are still supported (although the prefix for the
additional lines was changed to match the length of the prefix used
for the first line).

When users put parameters in a config file and pass them to sshuttle
using '@', they might copy the quotes from the command line into the
config file. This fix first ensures that we strip whitespace from the
beginning/end of each line in the config file. Then, if the line
begins and ends with a matching quote character, strip those too.

Fixes #573.

Add an "is_supported()" function to the different methods so that each
method can include whatever logic they wish to indicate if they are
supported on a particular machine. Previously, methods/__init__.py
contained all of the logic for selecting individual methods. Now, it
iterates through a list of possible options and stops on the first
method that it finds that is_supported().

Currently, the decision is made based on the presence of programs in
the PATH. In the future, things such as the platform sshuttle is
running on could be considered.

Signed-off-by: Samuel Bernardo <samuel@lip.pt>

Signed-off-by: Samuel Bernardo <samuel@lip.pt>

Signed-off-by: Samuel Bernardo <samuel@lip.pt>

Signed-off-by: Samuel Bernardo <samuel@lip.pt>

Signed-off-by: Samuel Bernardo <samuel@lip.pt>

Signed-off-by: Samuel Bernardo <samuel@lip.pt>

Add .gitignore .vscode/ path. Resolve the issue #374 adding tproxy mark option to allow different network mapping.
Signed-off-by: Samuel Bernardo <samuel@lip.pt>

Bumps [mock](https://github.com/testing-cabal/mock) from 2.0.0 to 4.0.3.
- [Release notes](https://github.com/testing-cabal/mock/releases)
- [Changelog](https://github.com/testing-cabal/mock/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/testing-cabal/mock/compare/2.0.0...4.0.3)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bump pytest from 6.2.0 to 6.2.1

Bumps [pytest](https://github.com/pytest-dev/pytest) from 6.2.0 to 6.2.1.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/pytest-dev/pytest/compare/6.2.0...6.2.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Due to message from CI:

DEPRECATION: Python 3.5 reached the end of its life on September 13th,
2020. Please upgrade your Python as Python 3.5 is no longer maintained.
pip 21.0 will drop support for Python 3.5 in January 2021. pip 21.0 will
remove support for this functionality.

Bump pytest from 6.1.2 to 6.2.0

Bump setuptools-scm from 4.1.2 to 5.0.1

Bumps [pytest](https://github.com/pytest-dev/pytest) from 6.1.2 to 6.2.0.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/pytest-dev/pytest/compare/6.1.2...6.2.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [setuptools-scm](https://github.com/pypa/setuptools_scm) from 4.1.2 to 5.0.1.
- [Release notes](https://github.com/pypa/setuptools_scm/releases)
- [Changelog](https://github.com/pypa/setuptools_scm/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/pypa/setuptools_scm/compare/v4.1.2...v5.0.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Fix handling OSError in FirewallClient#__init__

Bump attrs from 20.2.0 to 20.3.0

Bumps [attrs](https://github.com/python-attrs/attrs) from 20.2.0 to 20.3.0.
- [Release notes](https://github.com/python-attrs/attrs/releases)
- [Changelog](https://github.com/python-attrs/attrs/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/python-attrs/attrs/compare/20.2.0...20.3.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Fix "DNS request from ... to None" messages.

Intercept DNS requests sent by systemd-resolved.

Improve nft IPv6 support.

The server should just read from resolv.conf to find DNS servers to
use. This restores this behavior after the previous commit changed it.

The client now reads both /etc/resolv.conf and
/run/systemd/resolve/resolv.conf. The latter is required to more
reliably intercept regular DNS requests that systemd-resolved makes.

This commit makes two fixes:

1. If an IPv6 DNS server is used, an nft rule had "ip6 protocol" in it
which is invalid and caused sshuttle to exit.

2. I modified detection of udp vs tcp to follow the recommendation at
https://superuser.com/questions/1560376/match-ipv6-protocol-using-nftables

I also re-arranged the code slightly to reduce the number of
if-statements.

Improve consistency of PATH, environments, and which()

Bump pytest from 6.1.1 to 6.1.2

Bumps [pytest](https://github.com/pytest-dev/pytest) from 6.1.1 to 6.1.2.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/pytest-dev/pytest/compare/6.1.1...6.1.2)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Some methods are unable to determine the destination address of DNS
packets that we capture. When this happens, change the message so it
just shows where the DNS requests are from.

Previously, we would find DNS servers we wish to intercept traffic on
by reading /etc/resolv.conf. On systems using systemd-resolved,
/etc/resolv.conf points to localhost and then systemd-resolved
actually uses the DNS servers listed in
/run/systemd/resolve/resolv.conf. Many programs will route the DNS
traffic through localhost as /etc/resolv.conf indicates and sshuttle
would capture it. However, systemd-resolved also provides other
interfaces for programs to resolve hostnames besides the localhost
server in /etc/resolv.conf.

This patch adds systemd-resolved's servers into the list of DNS
servers when --dns is used.

Note that sshuttle will continue to fail to intercept any traffic sent
to port 853 for DNS over TLS (which systemd-resolved also supports).

For more info, see:
sshuttle issue #535
https://www.freedesktop.org/software/systemd/man/systemd-resolved.service.html
https://github.com/systemd/systemd/issues/6076

IPv6 support in nft method.