Motivation for this change

I have been using shellinabox but the terminal implementation leaves something to be desired. And since ttyd is already in nixpkgs i decided to give it a go and write a module for it.
TLDR:
ttyd enables you (like shellinabox) to expose a shell over a websocket.

Tested out on nixos 19.03 by including this module and adding ttyd to pkgs in override.

Sample service configuration:

  services.ttyd = {
    enable = true;
    clientOptions = {
      "fontFamily" = "Fira Code";
      "fontSize" = "16";
    };
  };

Relevant part of the nginx configuration

services.nginx = {
  virtualHosts."mydomain.tld" = {
    locations = {
      "/console" = {
        proxyPass = "http://localhost:7681/";
        proxyWebsockets = true;
        extraConfig = ''
          if ($scheme = 'http') {
              rewrite ^ https://$http_host$request_uri? permanent;
          };
        '';
      };
    };
  };
};

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Notify maintainers

cc @