Add support for docker-outside-of-docker (#23)

* Add support for docker-outside-of-docker

This commit adds support for running testcontainers inside
Docker

* Address pep8 issues

* reverse update of Pipfile.lock

Author: tcwalther

Dockerfile

@@ -0,0 +1,9 @@
+FROM python:3.6
+
+COPY ./Pipfile* /workspace/
+WORKDIR /workspace
+
+RUN pip install pipenv && \
+    pipenv install --system --dev --deploy
+
+COPY . /workspace

testcontainers/core/container.py

@@ -4,7 +4,7 @@
 
 from testcontainers.core.docker_client import DockerClient
 from testcontainers.core.exceptions import ContainerStartException
-from testcontainers.core.utils import is_windows
+from testcontainers.core.utils import is_windows, inside_container
 
 
 class DockerContainer(object):
@@ -59,14 +59,31 @@ def __enter__(self):
     def __exit__(self, exc_type, exc_val, exc_tb):
         self.stop()
 
+    def __del__(self):
+        """
+        Try to remove the container in all circumstances
+        """
+        if self._container is not None:
+            try:
+                self.stop()
+            except:  # noqa: E722
+                pass
+
     def get_container_host_ip(self) -> str:
-        if is_windows():
+        # if testcontainers itself runs in docker, get the newly spawned
+        # container's IP address from the dockder "bridge" network
+        if inside_container():
+            return self.get_docker_client().bridge_ip(self._container.id)
+        elif is_windows():
             return "localhost"
         else:
             return "0.0.0.0"
 
     def get_exposed_port(self, port) -> str:
-        return self.get_docker_client().port(self._container.id, port)
+        if inside_container():
+            return port
+        else:
+            return self.get_docker_client().port(self._container.id, port)
 
     def with_command(self, command: str) -> 'DockerContainer':
         self._command = command

testcontainers/core/docker_client.py

@@ -38,3 +38,7 @@ def run(self, image: str,
 
     def port(self, container_id, port):
         return self.client.api.port(container_id, port)[0]["HostPort"]
+
+    def bridge_ip(self, container_id):
+        container = self.client.api.containers(filters={'id': container_id})[0]
+        return container['NetworkSettings']['Networks']['bridge']['IPAddress']

testcontainers/core/utils.py

@@ -1,3 +1,4 @@
+import os
 import sys
 
 LINUX = "linux"
@@ -25,3 +26,12 @@ def is_linux():
 
 def is_windows():
     return WIN == os_name()
+
+
+def inside_container():
+    """
+    Returns true if we are running inside a container.
+
+    https://github.com/docker/docker/blob/a9fa38b1edf30b23cae3eade0be48b3d4b1de14b/daemon/initlayer/setup_unix.go#L25
+    """
+    return os.path.exists('/.dockerenv')