strawman implementation of launch script

repo2docker/buildpacks/base.py

@@ -118,6 +118,14 @@ RUN ./{{ s }}
 {% endfor %}
 {% endif -%}
 
+# Run launch script
+{% if launch_scripts -%}
+{% for s in launch_scripts -%}
+RUN chmod +x {{ s }}
+ENTRYPOINT ./{{ s }}
+{% endfor %}
+{% endif -%}
+
 # Specify the default command to run
 CMD ["jupyter", "notebook", "--ip", "0.0.0.0"]
 
@@ -283,6 +291,21 @@ class BuildPack:
         """
         return []
 
+    def get_launch_scripts(self):
+        """
+        An ordered list of executable scripts to be executated at runtime.
+        These scripts are added as an `ENTRYPOINT` to the container.
+
+        Is run as a non-root user, and must be executable. Used for doing
+        things that are currently not supported by other means and need to be
+        applied at runtime (set environment variables).
+
+        The scripts should be as deterministic as possible - running it twice
+        should not produce different results.!
+
+        """
+        return []
+
     def binder_path(self, path):
         """Locate a file"""
         if os.path.exists('binder'):
@@ -329,6 +352,7 @@ class BuildPack:
             build_script_files=self.get_build_script_files(),
             base_packages=sorted(self.get_base_packages()),
             post_build_scripts=self.get_post_build_scripts(),
+            launch_scripts=self.get_launch_scripts(),
             appendix=self.appendix,
         )
 
@@ -432,3 +456,9 @@ class BaseImage(BuildPack):
         if os.path.exists(post_build):
             return [post_build]
         return []
+
+    def get_launch_scripts(self):
+        launch = self.binder_path('launch')
+        if os.path.exists(launch):
+            return [launch]
+        return []