Code cleanup and tests

pre_commit/languages/docker.py

@@ -1,8 +1,10 @@
+from __future__ import absolute_import
 from __future__ import unicode_literals
 
 import hashlib
 import os
 
+from pre_commit import five
 from pre_commit.languages import helpers
 from pre_commit.util import clean_path_on_failure
 from pre_commit.util import mkdirp
@@ -10,12 +12,11 @@ from pre_commit.xargs import xargs
 
 
 ENVIRONMENT_DIR = 'docker'
+PRE_COMMIT_LABEL = 'PRE_COMMIT'
 
 
 def md5(s):
-    m = hashlib.md5()
-    m.update(s)
-    return m.hexdigest()
+    return five.to_text(hashlib.md5(s).hexdigest())
 
 
 def docker_tag(repo_cmd_runner):
@@ -24,39 +25,62 @@ def docker_tag(repo_cmd_runner):
     ).lower()
 
 
+def docker_is_running():
+    return xargs(('docker',), ['ps'])[0] == 0
+
+
+def assert_docker_available():
+    assert docker_is_running(), (
+        'Docker is either not running or not configured in this environment'
+    )
+
+
+def build_docker_image(repo_cmd_runner):
+    cmd = (
+        'docker', 'build', '--pull',
+        '--tag', docker_tag(repo_cmd_runner),
+        '--label', PRE_COMMIT_LABEL,
+        '.'
+    )
+    helpers.run_setup_cmd(repo_cmd_runner, cmd)
+
+
 def install_environment(
         repo_cmd_runner,
         version='default',
         additional_dependencies=(),
 ):
-    assert repo_cmd_runner.exists('Dockerfile')
-    # I don't know of anybody trying to juggle multiple docker installations
-    # so this seems sufficient
+    assert repo_cmd_runner.exists('Dockerfile'), (
+        'No Dockerfile was found in the hook repository'
+    )
+    assert version == 'default', (
+        'Pre-commit does not support language_version for docker '
+    )
+    assert_docker_available()
+
     directory = helpers.environment_dir(ENVIRONMENT_DIR, 'default')
     mkdirp(os.path.join(repo_cmd_runner.path(), directory))
 
-    cmd = (
-        'docker', 'build', '--pull',
-        '--tag', docker_tag(repo_cmd_runner),
-        '.'
-    )
-
     # Docker doesn't really have relevant disk environment, but pre-commit
     # still needs to cleanup it's state files on failure
     env_dir = repo_cmd_runner.path(directory)
     with clean_path_on_failure(env_dir):
-        helpers.run_setup_cmd(repo_cmd_runner, cmd)
+        build_docker_image(repo_cmd_runner)
 
 
 def run_hook(repo_cmd_runner, hook, file_args):
+    assert_docker_available()
+    # Rebuild the docker image in case it has gone missing, as many people do
+    # automated cleanup of docker images.
+    build_docker_image(repo_cmd_runner)
+    # the docker lib doesn't return stdout on non-zero exit codes,
+    # so we run the container directly on the command line
     cmd = (
         'docker', 'run',
-        '-t',
+        '--rm',
         '-v', '{}:/src'.format(os.getcwd()),
         '--workdir', '/src',
+        '--entrypoint', hook['entry'],
         docker_tag(repo_cmd_runner)
     )
-
-    return xargs(
-        cmd + (hook['entry'],) + tuple(hook['args']), file_args,
-    )
+    return xargs(cmd + tuple(hook['args']), file_args)