OpenVPN 3
=========
OpenVPN 3 is a C++ class library that implements the functionality
of an OpenVPN client, and is protocol-compatible with the OpenVPN
2.x branch.
OpenVPN 3 includes a minimal client wrapper (``cli``) that links in with
the library and provides basic command line functionality.
OpenVPN 3 is currently used in production as the core of the
OpenVPN Connect clients for iOS, Android, Linux, Windows, and Mac OS X.
NOTE: As of 2017, OpenVPN 3 is primarily of interest to developers,
as it does not yet replicate the full functionality of OpenVPN 2.x.
In particular, server functionality is not yet implemented.
.. contents:: Table of Contents
OpenVPN 3 Client API
--------------------
OpenVPN 3 is organized as a C++ class library, and the API is defined in
`<client/ovpncli.hpp>`_.
A simple command-line wrapper for the API is provided in
`<test/ovpncli/cli.cpp>`_.
Building the OpenVPN 3 client on Linux
--------------------------------------
These instructions were tested on Ubuntu 20.
Prepare directory structure:
::
$ sudo apt install g++ make libmbedtls-dev libssl-dev liblz4-dev cmake
$ export O3=~/O3 && mkdir $O3
$ export DEP_DIR=$O3/deps && mkdir $DEP_DIR
$ export DL=$O3/dl && mkdir $DL
Clone the OpenVPN 3 source repo:
::
$ cd $O3
$ git clone https://github.com/OpenVPN/openvpn3.git core
Build dependencies:
::
$ cd core/scripts/linux/
$ ./build-all
Build the OpenVPN 3 client wrapper (cli) with OpenSSL library:
::
$ cd $O3/core && mkdir build && cd build
$ cmake ..
$ cmake --build .
To use mbed TLS, use:
::
$ cmake -DUSE_MBEDTLS=on ..
Run OpenVPN 3 client:
::
$ sudo test/ovpncli/ovpncli myprofile.ovpn route-nopull
Options used:
- :code:`myprofile.ovpn` : OpenVPN config file (must have .ovpn extension)
- :code:`route-nopull` : if you are connected via ssh, prevent ssh session lockout
Using cli with ovpn-dco
"""""""""""""""""""""""
ovpn-dco is a kernel module which optimises data channel encryption and
transport, providing better performance.
Download, build and install ovpn-dco:
::
$ cd $O3
$ git clone https://github.com/OpenVPN/ovpn-dco.git
$ cd ovpn-dco
$ make && sudo make install
$ sudo modprobe ovpn-dco
Install core dependencies:
::
$ sudo apt install pkg-config libnl-genl-3-dev
Build cli with ovpn-dco support:
::
$ cd $O3/core/build
$ cmake -DCLI_OVPNDCO=on .. && make
$ sudo test/ovpncli/ovpncliovpndco --dco myprofile.ovpn
Options used:
- :code:`myprofile.ovpn` : OpenVPN config file (must have .ovpn extension)
- :code:`--dco` : enable data channel offload
Building the OpenVPN 3 client on Mac OS X
-----------------------------------------
OpenVPN 3 should be built in a non-root Mac OS X account.
Make sure that Xcode is installed with optional command-line tools.
(These instructions have been tested with Xcode 5.1.1).
Create the directories ``~/src`` and ``~/src/mac``:
::
$ mkdir -p ~/src/mac
Clone the OpenVPN 3 repo:
::
$ cd ~/src
$ mkdir ovpn3
$ cd ovpn3
$ git clone https://github.com/OpenVPN/openvpn3.git core
Export the shell variable ``O3`` to point to the OpenVPN 3 top level
directory:
::
$ export O3=~/src/ovpn3
Download source tarballs (``.tar.gz`` or ``.tgz``) for these dependency
libraries into ``~/Downloads``
See the file ``$O3/core/deps/lib-versions`` for the expected
version numbers of each dependency. If you want to use a different
version of the library than listed here, you can edit this file.
1. Asio - https://github.com/chriskohlhoff/asio
2. mbed TLS (2.3.0 or higher) - https://tls.mbed.org/
3. LZ4 - https://github.com/Cyan4973/lz4
For dependencies that are typically cloned from github vs.
provided as a .tar.gz file, tools are provided to convert
the github to a .tar.gz file. See "snapshot" scripts under
``$O3/core/deps``
Note that while OpenSSL is listed in lib-versions, it is
not required for Mac builds.
Build the dependencies:
::
$ DL=~/Downloads
$ OSX_ONLY=1 $O3/core/scripts/mac/build-all
Now build the OpenVPN 3 client executable:
::
$ cd $O3/core
$ . vars/vars-osx64
$ . vars/setpath
$ cd test/ovpncli
$ MTLS=1 LZ4=1 ASIO=1 build cli
This will build the OpenVPN 3 client library with a small client
wrapper (``cli``). It will also statically link in all external
dependencies (Asio, mbed TLS, and LZ4), so ``cli`` may be distributed
to other Macs and will run as a standalone executable.
These build scripts will create a **x86_x64** Mac OS X executable,
with a minimum deployment target of 10.8.x. The Mac OS X tuntap driver is not
required, as OpenVPN 3 can use the integrated utun interface if
available.
To view the client wrapper options:
::
$ ./cli -h
To connect:
::
$ ./cli client.ovpn
Building the OpenVPN 3 client on Windows
----------------------------------------
Prerequisites:
* Visual Studio 2019
* CMake
* vcpkg
Download and build dependencies:
::
> git clone https://github.com/Microsoft/vcpkg.git
> cd vcpkg
> bootstrap-vcpkg.bat
> vcpkg integrate install
> vcpkg install openssl-windows:x64-windows asio:x64-windows tap-windows6:x64-windows lz4:x64-windows gtest:x64-windows
Download and build core test client:
::
> git clone https://github.com/OpenVPN/openvpn3.git
> cmake -DCMAKE_TOOLCHAIN_FILE=<path_to_vcpkg>\scripts\buildsystems\vcpkg.cmake -A x64 -B build openvpn3
> cmake --build build --config Release --target ovpncli
Testing
-------
The OpenVPN 3 core includes a stress/performance test of
the OpenVPN protocol implementation. The test basically
creates a virtualized lossy network between two OpenVPN
protocol objects, triggers TLS negotiations between them,
passes control/data channel messages, and measures the ability
of the OpenVPN protocol objects to perform and remain in
a valid state.
The OpenVPN protocol implementation that is being tested
is here: `<openvpn/ssl/proto.hpp>`_
The test code itself is here: `<test/ssl/proto.cpp>`_
Build the test:
::
$ cd ovpn3/core/test/ssl
$ ECHO=1 PROF=linux ASIO_DIR=~/asio MTLS_SYS=1 NOSSL=1 $O3/core/scripts/build proto
Run the test:
::
$ time ./proto
*** app bytes=72777936 net_bytes=122972447 data_bytes=415892854 prog=0000216599/0000216598 D=12700/600/12700/600 N=109/109 SH=17400/15300 HE=0/0
real 0m15.813s
user 0m15.800s
sys 0m0.004s
The OpenVPN 3 core also includes unit tests, which are based on
Google Test framework. To run unit tests, you need to install
CMake and build Google Test.
Building Google Test on Linux:
::
$ git clone https://github.com/google/googletest.git
$ cd googletest
$ cmake . && cmake --build .
Building Google Test on Windows:
::
> git clone https://github.com/google/googletest.git
> cd googletest
> cmake -G "Visual Studio 14 2015 Win64" .
> cmake --build .
After Google Test is built you are ready to build and run unit tests.
Build and run tests on Linux:
::
$ cd ovpn3/core/test/unittests
$ GTEST_DIR=~/googletest ECHO=1 PROF=linux ASIO_DIR=~/asio MTLS_SYS=1 LZ4_SYS=1 NOSSL=1 $O3/core/scripts/build test_log
$ ./test_log
Build and run tests on Windows:
::
$ cd ovpn3/core/win
$ python build.py ../test/unittests/test_log.cpp unittest
$ test_log.exe
Developer Guide
---------------
OpenVPN 3 is written in C++11 and developers who are moving
from C to C++ should take some time to familiarize themselves with
key C++ design patterns such as *RAII*:
https://en.wikipedia.org/wiki/Resource_acquisition_is_initialization
OpenVPN 3 Client Core
"""""""""""""""""""""
OpenVPN 3 is designed as a class library, with an API that
is essentially defined inside of namespace ``ClientAPI``
with headers and implementation in `<client>`_ and
header-only library files under `<openvpn>`_.
The consise definition of the client API is essentially ``class OpenVPNClient``
in `<client/ovpncli.hpp>`_ with several imporant extensions to
the API found in:
* :code:`class TunBuilderBase` in `<openvpn/tun/builder/base.hpp>`_ —
Provides an abstraction layer defining the *tun* interface,
and is especially useful for interfacing with an OS-layer VPN API.
* :code:`class ExternalPKIBase` in `<openvpn/pki/epkibase.hpp>`_ —
Provides a callback for external private key operations, and
is useful for interfacing with an OS-layer Keychain such as
the Keychain on iOS, Mac OS X, and Android, and the Crypto API
on Windows.
* :code:`class LogReceiver` in `<client/ovpncli.hpp>`_ —
Provides an abstraction layer for the delivery of logging messages.
OpenVPN 3 includes a command-line reference client (``cli``) for
testing the API. See `<test/ovpncli/cli.cpp>`_.
The basic approach to building an OpenVPN 3 client is
to define a client class that derives from
:code:`ClientAPI::OpenVPNClient`, then provide implementations
for callbacks including event and logging notifications:
::
class Client : public ClientAPI::OpenVPNClient
{
public:
virtual void event(const Event&) override { // events delivered here
...
}
virtual void log(const LogInfo&) override { // logging delivered here
...
}
...
};
To start the client, first create a :code:`ClientAPI::Config` object
and initialize it with the OpenVPN config file and other options:
::
ClientAPI::Config config;
config.content = <config_file_content_as_multiline_string>;
...
Next, create a client object and evaluate the configuration:
::
Client client;
ClientAPI::EvalConfig eval = client.eval_config(config);
if (eval.error)
throw ...;
Finally, in a new worker thread, start the connection:
::
ClientAPI::Status connect_status = client.connect();
Note that :code:`client.connect()` will not return until
the session has terminated.
Top Layer
"""""""""
The top layer of the OpenVPN 3 client is implemented
in `<test/ovpncli/cli.cpp>`_ and `<openvpn/client/cliopt.hpp>`_.
Most of what this code does is marshalling the configuration and
dispatching the higher-level objects that implement the OpenVPN
client session.
Connection
""""""""""
:code:`class ClientConnect` in `<openvpn/client/cliconnect.hpp>`_
implements the top-level connection logic for an OpenVPN client
connection. It is concerned with starting, stopping, pausing, and resuming
OpenVPN client connections. It deals with retrying a connection and handles
the connection timeout. It also deals with connection exceptions and understands
the difference between an exception that should halt any further reconnection
attempts (such as ``AUTH_FAILED``), and other exceptions such as network errors
that would justify a retry.
Some of the methods in the class
(such as ``stop``, ``pause``, and ``reconnect``) are often
called by another thread that is controlling the connection, therefore
thread-safe methods are provided where the thread-safe function posts a message
to the actual connection thread.
In an OpenVPN client connection, the following object stack would be used:
1. :code:`class ClientConnect` in `<openvpn/client/cliconnect.hpp>`_ —
The top-layer object in an OpenVPN client connection.
2. :code:`class ClientProto::Session` in `<openvpn/client/cliproto.hpp>`_ —
The OpenVPN client protocol object that subinstantiates the transport
and tun layer objects.
3. :code:`class ProtoContext` in `<openvpn/ssl/proto.hpp>`_ —
The core OpenVPN protocol implementation that is common to both
client and server.
4. :code:`class ProtoStackBase<Packet>` in `<openvpn/ssl/protostack.hpp>`_ —
The bottom-layer class that implements
the basic functionality of tunneling a protocol over a reliable or
unreliable transport layer, but isn't specific to OpenVPN per-se.
Transport Layer
"""""""""""""""
OpenVPN 3 defines abstract base classes for Transport layer
implementations in `<openvpn/transport/client/transbase.hpp>`_.
Currently, transport layer implementations are provided for:
* **UDP** — `<openvpn/transport/client/udpcli.hpp>`_
* **TCP** — `<openvpn/transport/client/tcpcli.hpp>`_
* **HTTP Proxy** — `<openvpn/transport/client/httpcli.hpp>`_
Tun Layer
"""""""""
OpenVPN 3 defines abstract base classes for Tun layer
implementations in `<openvpn/tun/client/tunbase.hpp>`_.
There are two possible approaches to define a Tun
layer implementation:
1. Use a VPN API-centric model (such as for Android
or iOS). These models derive from **class TunBuilderBase**
in `<openvpn/tun/builder/base.hpp>`_
2. Use an OS-specific model such as:
* **Linux** — `<openvpn/tun/linux/client/tuncli.hpp>`_
* **Windows** — `<openvpn/tun/win/client/tuncli.hpp>`_
* **Mac OS X** — `<openvpn/tun/mac/client/tuncli.hpp>`_
Protocol Layer
""""""""""""""
The OpenVPN protocol is implemented in **class ProtoContext**
in `<openvpn/ssl/proto.hpp>`_.
Options Processing
""""""""""""""""""
The parsing and query of the OpenVPN config file
is implemented by :code:`class OptionList` in
`<openvpn/common/options.hpp>`_.
Note that OpenVPN 3 always assumes an *inline* style of
configuration, where all certs, keys, etc. are
defined inline rather than through an external file
reference.
For config files that do use external file references,
:code:`class ProfileMerge` in `<openvpn/options/merge.hpp>`_
is provided to merge those external
file references into an inline form.
Calling the Client API from other languages
"""""""""""""""""""""""""""""""""""""""""""
The OpenVPN 3 client API, as defined by :code:`class OpenVPNClient`
in `<client/ovpncli.hpp>`_, can be wrapped by the
Swig_ tool to create bindings for other languages.
.. _Swig: http://www.swig.org/
For example, OpenVPN Connect for Android creates a Java
binding of the API using `<javacli/ovpncli.i>`_.
Security
--------
When developing security software in C++, it's very important to
take advantage of the language and OpenVPN library code
to insulate code from the kinds of
bugs that can introduce security vulnerabilities.
Here is a brief set of guidelines:
* When dealing with strings, use a :code:`std::string`
rather than a :code:`char *`.
* When dealing with binary data or buffers, always try to use a
:code:`Buffer`, :code:`ConstBuffer`, :code:`BufferAllocated`, or
:code:`BufferPtr` object to provide managed access to the buffer, to
protect against security bugs that arise when using raw buffer pointers.
See `<openvpn/buffer/buffer.hpp>`_ for the OpenVPN :code:`Buffer` classes.
* When it's necessary to have a pointer to an object, use
:code:`std::unique_ptr<>` for non-shared objects and reference-counted
smart pointers for shared objects. For shared-pointers,
OpenVPN code should use the smart pointer classes defined
in `<openvpn/common/rc.hpp>`_. Please see the comments in
this file for documentation.
* Never use :code:`malloc` or :code:`free`. When allocating objects,
use the C++ :code:`new` operator and then immediately construct
a smart pointer to reference the object:
::
std::unique_ptr<MyObject> ptr = new MyObject();
ptr->method();
* When interfacing with C functions that deal with
raw pointers, memory allocation, etc., consider wrapping
the functionality in C++. For an example, see :code:`enum_dir()`
in `<openvpn/common/enumdir.hpp>`_,
a function that returns a list of files in
a directory (Unix only) via a high-level
string vector, while internally calling
the low level libc methods
:code:`opendir`, :code:`readdir`, and :code:`closedir`.
Notice how :code:`unique_ptr_del` is used to wrap the
``DIR`` struct in a smart pointer with a custom
deletion function.
* When grabbing random entropy that is to be used
for cryptographic purposes (i.e. for keys, tokens, etc.),
always ensure that the RNG is crypto-grade by calling
:code:`assert_crypto()` on the RNG. This will throw
an exception if the RNG is not crypto-grade:
::
void set_rng(RandomAPI::Ptr rng_arg) {
rng_arg->assert_crypto();
rng = std::move(rng_arg);
}
* Any variable whose value is not expected to change should
be declared :code:`const`.
* Don't use non-const global or static variables unless absolutely
necessary.
* When formatting strings, don't use :code:`snprintf`. Instead, use
:code:`std::ostringstream` or build the string using the :code:`+`
:code:`std::string` operator:
::
std::string format_reconnecting(const int n_seconds) {
return "Reconnecting in " + openvpn::to_string(n_seconds) + " seconds.";
}
or:
::
std::string format_reconnecting(const int n_seconds) {
std::ostringstream os;
os << "Reconnecting in " << n_seconds << " seconds.";
return os.str();
}
* OpenVPN 3 is a "header-only" library, therefore all free functions
outside of classes should have the :code:`inline` attribute.
Conventions
"""""""""""
* Use the **Asio** library for I/O and timers.
Don't deal with sockets directly.
* Never block. If you need to wait for something, use **Asio** timers
or sockets.
* Use the :code:`OPENVPN_LOG()` macro to log stuff. Don't use :code:`printf`.
* Don't call crypto/ssl libraries directly. Instead use the abstraction
layers (`<openvpn/crypto>`_ and `<openvpn/ssl>`_) that allow OpenVPN
to link with different crypto/ssl libraries (such as **OpenSSL**
or **mbed TLS**).
* Use :code:`RandomAPI` as a wrapper for random number
generators (`<openvpn/random/randapi.hpp>`_).
* If you need to deal with configuration file options,
see :code:`class OptionList` in `<openvpn/common/options.hpp>`_.
* If you need to deal with time or time durations, use the
classes under `<openvpn/time>`_.
* If you need to deal with IP addresses, see the comprehensive classes
under `<openvpn/addr>`_.
* In general, if you need a general-purpose library class or function,
look under `<openvpn/common>`_. Chances are good that it's already
been implemented.
* The OpenVPN 3 approach to errors is to count them, rather than
unconditionally log them. If you need to add a new error
counter, see `<openvpn/error/error.hpp>`_.
* If you need to create a new event type which can be transmitted
as a notification back to the client API user, see
`<openvpn/client/clievent.hpp>`_.
* Raw pointers or references can be okay when used by an object to
point back to its parent (or container), if you can guarantee that
the object will not outlive its parent. Backreferences to a parent
object is also a common use case for weak pointers.
* Use C++ exceptions for error handling and as an alternative
to :code:`goto`. See OpenVPN's general exception classes
and macros in `<openvpn/common/exception.hpp>`_.
* Use C++ destructors for automatic object cleanup, and so
that thrown exceptions will not leak objects. Alternatively,
use :code:`Cleanup` in `<openvpn/common/cleanup.hpp>`_ when
you need to specify a code block to execute prior to scope
exit. For example, ensure that the file :code:`pid_fn` is
deleted before scope exit:
::
auto clean = Cleanup([pid_fn]() {
if (pid_fn)
::unlink(pid_fn);
});
* When calling global methods (such as libc :code:`fork`),
prepend :code:`::` to the symbol name, e.g.:
::
struct dirent *e;
while ((e = ::readdir(dir.get())) != nullptr) {
...
}
* Use :code:`nullptr` instead of :code:`NULL`.
Threading
"""""""""
The OpenVPN 3 client core is designed to run in a single thread, with
the UI or controller driving the OpenVPN API running in a different
thread.
It's almost never necessary to create additional threads within
the OpenVPN 3 client core.
Contributing
------------
See `<CONTRIBUTING.rst>`_.
License
-------
See `<LICENSE.rst>`_.
