providers/docker: use a custom communicator to go through host VM

lib/vagrant/plugin/v2/communicator.rb

@@ -23,7 +23,7 @@ module Vagrant
         #
         # @return [Boolean]
         def self.match?(machine)
-          false
+          true
         end
 
         # Initializes the communicator with the machine that we will be

plugins/providers/docker/communicator.rb

@@ -0,0 +1,83 @@
+module VagrantPlugins
+  module DockerProvider
+    # This communicator uses the host VM as proxy to communicate to the
+    # actual Docker container via SSH.
+    class Communicator < Vagrant.plugin("2", :communicator)
+      def initialize(machine)
+        @machine = machine
+        @host_vm = machine.provider.host_vm
+
+        # We only work on the Docker provider
+        if machine.provider_name != :docker
+          raise Errors::CommunicatorNotDocker
+        end
+      end
+
+      #-------------------------------------------------------------------
+      # Communicator Methods
+      #-------------------------------------------------------------------
+
+      def ready?
+        # We can't be ready if we can't talk to the host VM
+        return false if !@host_vm.communicate.ready?
+
+        # We're ready if we can establish an SSH connection to the container
+        @host_vm.communicate.test("#{container_ssh_command} exit")
+      end
+
+      def download(from, to)
+        raise "NOT IMPLEMENTED YET"
+      end
+
+      def execute(command, opts=nil, &block)
+        @host_vm.communicate.execute(
+          "#{container_ssh_command} #{command}", opts, &block)
+      end
+
+      def sudo(command, opts=nil)
+      end
+
+      def test(command, **opts)
+        opts = { error_check: false }.merge(opts)
+        execute(command, opts) == 0
+      end
+
+      def upload(from, to)
+        # First, we upload this to the host VM to some temporary directory.
+        to_temp = "/tmp/docker_#{Time.now.to_i}_#{rand(100000)}"
+        @host_vm.communicate.upload(from, to_temp)
+
+        # Then, we use `cat` to get that file into the Docker container.
+        @host_vm.communicate.execute(
+          "#{container_ssh_command} 'cat >#{to}' <#{to_temp}")
+
+        # Remove the temporary file
+        @host_vm.communicate.execute("rm #{to_temp}", error_check: false)
+      end
+
+      #-------------------------------------------------------------------
+      # Other Methods
+      #-------------------------------------------------------------------
+
+      # This returns the raw SSH command string that can be used to
+      # connect via SSH to the container if you're on the same machine
+      # as the container.
+      #
+      # @return [String]
+      def container_ssh_command
+        # Get the container's SSH info
+        info = @machine.ssh_info
+        info[:port] ||= 22
+
+        # Build the SSH command
+        "ssh -i /home/vagrant/insecure " +
+          "-o Compression=yes " +
+          "-o ConnectTimeout=5 " +
+          "-o StrictHostKeyChecking=no " +
+          "-o UserKnownHostsFile=/dev/null " +
+          "-p#{info[:port]} " +
+          "#{info[:username]}@#{info[:host]}"
+      end
+    end
+  end
+end

plugins/providers/docker/errors.rb

@@ -5,6 +5,10 @@ module VagrantPlugins
         error_namespace("docker_provider.errors")
       end
 
+      class CommunicatorNonDocker < DockerError
+        error_key(:communicator_non_docker)
+      end
+
       class ExecuteError < DockerError
         error_key(:execute_error)
       end

plugins/providers/docker/plugin.rb

@@ -28,6 +28,12 @@ module VagrantPlugins
         Command::Logs
       end
 
+      communicator(:docker_hostvm) do
+        require_relative "communicator"
+        init!
+        Communicator
+      end
+
       config(:docker, :provider) do
         require_relative 'config'
         init!

plugins/providers/docker/provider.rb

@@ -11,6 +11,12 @@ module VagrantPlugins
       def initialize(machine)
         @logger  = Log4r::Logger.new("vagrant::provider::docker")
         @machine = machine
+
+        if host_vm?
+          # We need to use a special communicator that proxies our
+          # SSH requests over our host VM to the container itself.
+          @machine.config.vm.communicator = :docker_hostvm
+        end
       end
 
       # @see Vagrant::Plugin::V2::Provider#action

templates/locales/providers_docker.yml

@@ -63,6 +63,12 @@ en:
         run exits and doesn't keep running.
 
     errors:
+      communicator_non_docker: |-
+        The "docker_hostvm" communicator was specified on a machine that
+        is not provided by the Docker provider. This is a bug with your
+        Vagrantfile. Please contact the creator of your Vagrant environment
+        and notify them to not use this communicator for anything except the
+        "docker" provider.
       config:
         cmd_not_set: |-
           The Docker command has not been set!