1#pylint: disable-msg=C0111
2
3# Copyright (c) 2014 The Chromium OS Authors. All rights reserved.
4# Use of this source code is governed by a BSD-style license that can be
5# found in the LICENSE file.
6
7"""Helpers to load database settings.
8
9Four databases are used with django (a default and one for tko tables,
10which always must be the global database, a readonly connection to the
11global database, and a connection to server database).
12
13In order to save configuration overhead, settings that aren't set for the
14desired database type, should be obtained from the setting with the next lower
15priority. The order is:
16readonly -> global -> local.
17I.e. this means if `readonly_host` is not set, `global_db_host` will be used. If
18that is also not set, `host` (the local one) will be used.
19
20server database setting falls back to local database setting. That is, if
21`server_db_host` is not set, `host`(the local one) will be used.
22
23In case an instance is running on a shard, a global database must explicitly
24be set. Instead of failing over from global to local, an exception will be
25raised in that case.
26
27The complexity to do this, is combined in this file.
28"""
29
30
31# Don't import anything that needs django here: Django may not be configured
32# on the builders, and this is also used by tko/db.py so failures like this
33# may occur: http://crbug.com/421565
34import common
35from autotest_lib.client.common_lib import global_config
36
37config = global_config.global_config
38SHARD_HOSTNAME = config.get_config_value('SHARD', 'shard_hostname',
39                                         default=None)
40
41
42def _get_config(config_key, section='AUTOTEST_WEB', **kwargs):
43    """Retrieves a config value for the specified key.
44
45    @param config_key: The string key associated with the desired config value.
46    @param section: Section of global config to read config. Default is set to
47                    AUTOTEST_WEB.
48    @param **kwargs: Additional arguments to be passed to
49                     global_config.get_config_value.
50
51    @return: The config value, as returned by
52             global_config.global_config.get_config_value().
53    """
54    return config.get_config_value(section, config_key, **kwargs)
55
56
57def _get_global_config(config_key, default=config._NO_DEFAULT_SPECIFIED,
58                       **kwargs):
59    """Retrieves a global config value for the specified key.
60
61    If the value can't be found, this will happen:
62    - if no default value was specified, and this is run on a shard instance,
63      a ConfigError will be raised.
64    - if a default value is set or this is run on a non-shard instancee, the
65      non-global value is returned
66
67    @param config_key: The string key associated with the desired config value.
68    @param default: The default value to return if the value couldn't be looked
69                    up; neither with global_db_ nor no prefix.
70    @param **kwargs: Additional arguments to be passed to
71                     global_config.get_config_value.
72
73    @return: The config value, as returned by
74             global_config.global_config.get_config_value().
75    """
76    try:
77        return _get_config('global_db_' + config_key, **kwargs)
78    except global_config.ConfigError:
79        if SHARD_HOSTNAME and default == config._NO_DEFAULT_SPECIFIED:
80            # When running on a shard, fail loudly if the global_db_ prefixed
81            # settings aren't present.
82            raise
83        return _get_config(config_key, default=default, **kwargs)
84
85
86def _get_readonly_config(config_key, default=config._NO_DEFAULT_SPECIFIED,
87                         **kwargs):
88    """Retrieves a readonly config value for the specified key.
89
90    If no value can be found, the value of non readonly but global value
91    is returned instead.
92
93    @param config_key: The string key associated with the desired config value.
94    @param default: The default value to return if the value couldn't be looked
95                    up; neither with readonly_, global_db_ nor no prefix.
96    @param **kwargs: Additional arguments to be passed to
97                     global_config.get_config_value.
98
99    @return: The config value, as returned by
100             global_config.global_config.get_config_value().
101    """
102    try:
103        return _get_config('readonly_' + config_key, **kwargs)
104    except global_config.ConfigError:
105        return _get_global_config(config_key, default=default, **kwargs)
106
107
108def _get_server_db_config(config_key, default=config._NO_DEFAULT_SPECIFIED,
109                          **kwargs):
110    """Retrieves a config value for the specified key for server database.
111
112    The order of searching for the specified config_key is:
113        section: AUTOTEST_SERVER_DB
114        section: AUTOTEST_WEB
115        supplied default
116
117    @param config_key: The string key associated with the desired config value.
118    @param default: The default value to return if the value couldn't be looked
119                    up; neither with global_db_ nor no prefix.
120    @param **kwargs: Additional arguments to be passed to
121                     global_config.get_config_value.
122
123    @return: The config value, as returned by
124             global_config.global_config.get_config_value().
125    """
126    try:
127        return _get_config(config_key, section='AUTOTEST_SERVER_DB', **kwargs)
128    except global_config.ConfigError:
129        return _get_config(config_key, default=default, **kwargs)
130
131
132def _get_database_config(getter):
133    """Create a configuration dictionary that can be passed to Django.
134
135    @param getter: A function to call to get configuration values.
136
137    @return A dictionary that can be used in the Django DATABASES setting.
138    """
139    config = {
140        'ENGINE': 'autotest_lib.frontend.db.backends.afe',
141        'PORT': getter('port', default=''),
142        'HOST': getter('host'),
143        'NAME': getter('database'),
144        'USER': getter('user'),
145        'PASSWORD': getter('password', default=''),
146        'READONLY_HOST': getter('readonly_host', default=getter('host')),
147        'READONLY_USER': getter('readonly_user', default=getter('user')),
148    }
149    if config['READONLY_USER'] != config['USER']:
150        config['READONLY_PASSWORD'] = getter('readonly_password', default='')
151    else:
152        config['READONLY_PASSWORD'] = config['PASSWORD']
153    return config
154
155
156def get_global_db_config():
157    """Returns settings for the global database as required by django.
158
159    @return: A dictionary that can be used in the Django DATABASES setting.
160    """
161    return _get_database_config(getter=_get_global_config)
162
163
164def get_default_db_config():
165    """Returns settings for the default/local database as required by django.
166
167    @return: A dictionary that can be used in the Django DATABASES setting.
168    """
169    return _get_database_config(getter=_get_config)
170
171
172def get_readonly_db_config():
173    """Returns settings for the readonly database as required by django.
174
175    @return: A dictionary that can be used in the Django DATABASES setting.
176    """
177    return _get_database_config(getter=_get_readonly_config)
178
179
180def get_server_db_config():
181    """Returns settings for the server database as required by django.
182
183    @return: A dictionary that can be used in the Django DATABASES setting.
184    """
185    return _get_database_config(getter=_get_server_db_config)
186