Added install pkgs extension

.gitignore

@@ -5,4 +5,5 @@ deb_dist
 *.pyc
 .coverage
 build
-rocker_venv
+rocker_venv
+.vscode

README.md

@@ -37,6 +37,7 @@ You can get full details on the extensions from the main `rocker --help` command
 - home -- Mount the user's home directory into the container
 - pulse -- Mount pulse audio into the container
 - ssh -- Pass through ssh access to the container.
+- install_pkgs -- Install a list of additional packages not in the base image
 
 As well as access to many of the docker arguments as well such as `device`, `env`, `volume`, `name`, `network`, `ipc`, and `privileged`.
 

setup.py

@@ -55,6 +55,7 @@
             'home = rocker.extensions:HomeDir',
             'hostname = rocker.extensions:Hostname',
             'ipc = rocker.extensions:Ipc',
+            'install_pkgs = rocker.install_pkgs_extension:InstallPkgs',
             'name = rocker.extensions:Name',
             'network = rocker.extensions:Network',
             'nvidia = rocker.nvidia_extension:Nvidia',

src/rocker/install_pkgs_extension.py

@@ -0,0 +1,43 @@
+import em
+import pkgutil
+from rocker.extensions import RockerExtension
+
+
+class InstallPkgs(RockerExtension):
+
+    name = 'install_pkgs'
+
+    @classmethod
+    def get_name(cls):
+        return cls.name
+
+    def __init__(self):
+        self._env_subs = None
+        self.name = InstallPkgs.get_name()
+
+    def precondition_environment(self, cli_args):
+        pass
+
+    def validate_environment(self, cli_args):
+        pass
+
+    def get_preamble(self, cli_args):
+        return ''
+
+    def get_snippet(self, cli_args):
+        pkgs = set(cli_args['install_pkgs'])
+        args = {'packages': list(pkgs)}
+
+        snippet = pkgutil.get_data(
+            'rocker', 'templates/{}_snippet.Dockerfile.em'.format(self.name)).decode('utf-8')
+
+        return em.expand(snippet, args)
+
+    @staticmethod
+    def register_arguments(parser, defaults={}):
+        parser.add_argument('--install-pkgs',
+                            nargs='+',
+                            help='Installs specified packages in container')
+
+        # todo add argument to install common development packages by category 
+        # (e.g dev, debug, viz, sim, etc) that are not in the base image