Extract YAML loading and parsing into config module

Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>

compose/config.py

@@ -0,0 +1,180 @@
+import os
+import yaml
+import six
+
+
+DOCKER_CONFIG_KEYS = [
+    'cap_add',
+    'cap_drop',
+    'cpu_shares',
+    'command',
+    'detach',
+    'dns',
+    'dns_search',
+    'domainname',
+    'entrypoint',
+    'env_file',
+    'environment',
+    'hostname',
+    'image',
+    'links',
+    'mem_limit',
+    'net',
+    'ports',
+    'privileged',
+    'restart',
+    'stdin_open',
+    'tty',
+    'user',
+    'volumes',
+    'volumes_from',
+    'working_dir',
+]
+
+ALLOWED_KEYS = DOCKER_CONFIG_KEYS + [
+    'build',
+    'expose',
+    'external_links',
+    'name',
+]
+
+DOCKER_CONFIG_HINTS = {
+    'cpu_share' : 'cpu_shares',
+    'link'      : 'links',
+    'port'      : 'ports',
+    'privilege' : 'privileged',
+    'priviliged': 'privileged',
+    'privilige' : 'privileged',
+    'volume'    : 'volumes',
+    'workdir'   : 'working_dir',
+}
+
+
+def load(filename):
+    return from_dictionary(load_yaml(filename))
+
+
+def load_yaml(filename):
+    try:
+        with open(filename, 'r') as fh:
+            return yaml.safe_load(fh)
+    except IOError as e:
+        raise ConfigurationError(six.text_type(e))
+
+
+def from_dictionary(dictionary):
+    service_dicts = []
+
+    for service_name, service_dict in list(dictionary.items()):
+        if not isinstance(service_dict, dict):
+            raise ConfigurationError('Service "%s" doesn\'t have any configuration options. All top level keys in your docker-compose.yml must map to a dictionary of configuration options.' % service_name)
+        service_dict = make_service_dict(service_name, service_dict)
+        service_dicts.append(service_dict)
+
+    return service_dicts
+
+
+def make_service_dict(name, options):
+    service_dict = options.copy()
+    service_dict['name'] = name
+    return process_container_options(service_dict)
+
+
+def process_container_options(service_dict):
+    for k in service_dict:
+        if k not in ALLOWED_KEYS:
+            msg = "Unsupported config option for %s service: '%s'" % (service_dict['name'], k)
+            if k in DOCKER_CONFIG_HINTS:
+                msg += " (did you mean '%s'?)" % DOCKER_CONFIG_HINTS[k]
+            raise ConfigurationError(msg)
+
+    for filename in get_env_files(service_dict):
+        if not os.path.exists(filename):
+            raise ConfigurationError("Couldn't find env file for service %s: %s" % (service_dict['name'], filename))
+
+    if 'environment' in service_dict or 'env_file' in service_dict:
+        service_dict['environment'] = build_environment(service_dict)
+
+    return service_dict
+
+
+def parse_links(links):
+    return dict(parse_link(l) for l in links)
+
+
+def parse_link(link):
+    if ':' in link:
+        source, alias = link.split(':', 1)
+        return (alias, source)
+    else:
+        return (link, link)
+
+
+def get_env_files(options):
+    env_files = options.get('env_file', [])
+    if not isinstance(env_files, list):
+        env_files = [env_files]
+    return env_files
+
+
+def build_environment(options):
+    env = {}
+
+    for f in get_env_files(options):
+        env.update(env_vars_from_file(f))
+
+    env.update(parse_environment(options.get('environment')))
+    return dict(resolve_env(k, v) for k, v in six.iteritems(env))
+
+
+def parse_environment(environment):
+    if not environment:
+        return {}
+
+    if isinstance(environment, list):
+        return dict(split_env(e) for e in environment)
+
+    if isinstance(environment, dict):
+        return environment
+
+    raise ConfigurationError(
+        "environment \"%s\" must be a list or mapping," %
+        environment
+    )
+
+
+def split_env(env):
+    if '=' in env:
+        return env.split('=', 1)
+    else:
+        return env, None
+
+
+def resolve_env(key, val):
+    if val is not None:
+        return key, val
+    elif key in os.environ:
+        return key, os.environ[key]
+    else:
+        return key, ''
+
+
+def env_vars_from_file(filename):
+    """
+    Read in a line delimited file of environment variables.
+    """
+    env = {}
+    for line in open(filename, 'r'):
+        line = line.strip()
+        if line and not line.startswith('#'):
+            k, v = split_env(line)
+            env[k] = v
+    return env
+
+
+class ConfigurationError(Exception):
+    def __init__(self, msg):
+        self.msg = msg
+
+    def __str__(self):
+        return self.msg