Synchronous ASIO and OpenSSL example

ASIO is a rather large and sprawling affair, made more complicated by having 11 ways of doing the same thing, in both synchronous and asynchronous fashion.

This pair of examples shows, I hope, the absolute minimum amount of code to get a working SSL connection between a client and server, the latter acting as an echo service.

ASIO itself is a header only affair (+1) and is contained in a submodule. Hence once the repo is cloned, do this:

cd asiotest
git submodule init
git submodule update --recursive

Windows

For Windows/Visual Studio, setup is critical and extremely tedious unless vcpkg is used.

For this sort of gig I like everything to be contained in a single binary, hence static linkage for both runtime and support libraries. The VS2022 project files are set up accordingly. See the vcpkg tab in the solution explorer.

Step by step:

1. git clone https://github.com/microsoft/vcpkg.git
2. cd vcpkg
3. bootstrap-vcpkg.bat
4. vcpkg integrate install
5. vcpkg install asio:x64-windows-static
6. vcpkg install openssl:x64-windows-static
7. Open asiotest.sln
8. Rebuild.

Linux/MacOS

Ensure libraries are installed:

1. sudo apt install libasio-dev libssl-dev libczmq-dev libsodium-dev
2. make -C ./server
3. make -C ./client

Operation

1. Run makcert.cmd (makcert.sh on Linux/MacOS) to generate required (self-signed) certificates. This is a once-off affair and may take some time.
2. Run the server: server 3456
3. Run the client: client localhost 3456
4. Send simple text messages, quit to shutdown client.

If you run the client on a different host, you will need to copy certs/rootca.pem which contain the relevant public keys.