consensus plugin

bigchaindb/config_utils.py

@@ -16,11 +16,15 @@ import copy
 import json
 import logging
 import collections
+from functools import lru_cache
+
+from pkg_resources import iter_entry_points, ResolutionError
 
 from bigchaindb.common import exceptions
 
 import bigchaindb
 
+from bigchaindb.consensus import BaseConsensusRules
 
 # TODO: move this to a proper configuration file for logging
 logging.getLogger('requests').setLevel(logging.WARNING)
@@ -240,3 +244,39 @@ def autoconfigure(filename=None, config=None, force=False):
         newconfig = update(newconfig, config)
 
     set_config(newconfig)  # sets bigchaindb.config
+
+@lru_cache()
+def load_consensus_plugin(name=None):
+    """Find and load the chosen consensus plugin.
+
+    Args:
+        name (string): the name of the entry_point, as advertised in the
+            setup.py of the providing package.
+
+    Returns:
+        an uninstantiated subclass of ``bigchaindb.consensus.AbstractConsensusRules``
+    """
+    if not name:
+        return BaseConsensusRules;
+
+    # TODO: This will return the first plugin with group `bigchaindb.consensus`
+    #       and name `name` in the active WorkingSet.
+    #       We should probably support Requirements specs in the config, e.g.
+    #       consensus_plugin: 'my-plugin-package==0.0.1;default'
+    plugin = None
+    for entry_point in iter_entry_points('bigchaindb.consensus', name):
+        plugin = entry_point.load()
+
+    # No matching entry_point found
+    if not plugin:
+        raise ResolutionError(
+            'No plugin found in group `bigchaindb.consensus` with name `{}`'.
+            format(name))
+
+    # Is this strictness desireable?
+    # It will probably reduce developer headaches in the wild.
+    if not issubclass(plugin, (BaseConsensusRules)):
+        raise TypeError("object of type '{}' does not implement `bigchaindb."
+                        "consensus.BaseConsensusRules`".format(type(plugin)))
+
+    return plugin

bigchaindb/consensus.py

@@ -10,6 +10,11 @@ logger = logging.getLogger(__name__)
 
 class BaseConsensusRules():
     """Base consensus rules for Bigchain.
+
+    A consensus plugin must expose a class inheriting from this one via an entry_point.
+
+    All methods listed below must be implemented.
+
     """
 
     @staticmethod

bigchaindb/core.py

@@ -56,7 +56,14 @@ class Bigchain(object):
         self.me_private = private_key or bigchaindb.config['keypair']['private']
         self.nodes_except_me = keyring or bigchaindb.config['keyring']
         self.backlog_reassign_delay = backlog_reassign_delay or bigchaindb.config['backlog_reassign_delay']
-        self.consensus = BaseConsensusRules
+
+        consensusPlugin = bigchaindb.config.get('consensus_plugin')
+
+        if consensusPlugin:
+            self.consensus = config_utils.load_consensus_plugin(consensusPlugin)
+        else:
+            self.consensus = BaseConsensusRules
+
         self.connection = connection if connection else backend.connect(**bigchaindb.config['database'])
         if not self.me or not self.me_private:
             raise exceptions.KeypairNotFoundException()

bigchaindb/pipelines/vote.py

@@ -13,6 +13,7 @@ from bigchaindb.common import exceptions
 import bigchaindb
 from bigchaindb import Bigchain
 from bigchaindb import backend
+from bigchaindb import config_utils
 from bigchaindb.backend.changefeed import ChangeFeed
 from bigchaindb.consensus import BaseConsensusRules
 from bigchaindb.models import Transaction, Block
@@ -31,7 +32,14 @@ class Vote:
         # Since cannot share a connection to RethinkDB using multiprocessing,
         # we need to create a temporary instance of BigchainDB that we use
         # only to query RethinkDB
-        self.consensus = BaseConsensusRules
+        #self.consensus = BaseConsensusRules
+
+        consensusPlugin = bigchaindb.config.get('consensus_plugin')
+
+        if consensusPlugin:
+          self.consensus = config_utils.load_consensus_plugin(consensusPlugin)
+        else:
+          self.consensus = BaseConsensusRules
 
         # This is the Bigchain instance that will be "shared" (aka: copied)
         # by all the subprocesses

docs/server/source/server-reference/configuration.md

@@ -23,6 +23,7 @@ For convenience, here's a list of all the relevant environment variables (docume
 `BIGCHAINDB_STATSD_RATE`<br>
 `BIGCHAINDB_CONFIG_PATH`<br>
 `BIGCHAINDB_BACKLOG_REASSIGN_DELAY`<br>
+`BIGCHAINDB_CONSENSUS_PLUGIN`<br>
 
 The local config file is `$HOME/.bigchaindb` by default (a file which might not even exist), but you can tell BigchainDB to use a different file by using the `-c` command-line option, e.g. `bigchaindb -c path/to/config_file.json start`
 or using the `BIGCHAINDB_CONFIG_PATH` environment variable, e.g. `BIGHAINDB_CONFIG_PATH=.my_bigchaindb_config bigchaindb start`.
@@ -56,7 +57,7 @@ Internally (i.e. in the Python code), both keys have a default value of `None`,
 
 ## keyring
 
-A list of the public keys of all the nodes in the cluster, excluding the public key of this node. 
+A list of the public keys of all the nodes in the cluster, excluding the public key of this node.
 
 **Example using an environment variable**
 ```text
@@ -67,7 +68,7 @@ Note how the keys in the list are separated by colons.
 
 **Example config file snippet**
 ```js
-"keyring": ["BnCsre9MPBeQK8QZBFznU2dJJ2GwtvnSMdemCmod2XPB", 
+"keyring": ["BnCsre9MPBeQK8QZBFznU2dJJ2GwtvnSMdemCmod2XPB",
             "4cYQHoQrvPiut3Sjs8fVR1BMZZpJjMTC4bsMTt9V71aQ"]
 ```
 
@@ -170,9 +171,23 @@ Specifies how long, in seconds, transactions can remain in the backlog before be
 **Example using environment variables**
 ```text
 export BIGCHAINDB_BACKLOG_REASSIGN_DELAY=30
-``` 
+```
 
 **Default value (from a config file)**
 ```js
-"backlog_reassign_delay": 120 
+"backlog_reassign_delay": 120
+```
+
+## consensus_plugin
+
+The [consensus plugin](../appendices/consensus.html) to use.
+
+**Example using an environment variable**
+```text
+export BIGCHAINDB_CONSENSUS_PLUGIN=default
+```
+
+**Example config file snippet: the default**
+```js
+"consensus_plugin": "default"
 ```

tests/test_config_utils.py

@@ -39,6 +39,34 @@ def test_bigchain_instance_raises_when_not_configured(monkeypatch):
     with pytest.raises(exceptions.KeypairNotFoundException):
         bigchaindb.Bigchain()
 
+def test_load_consensus_plugin_loads_default_rules_without_name():
+    from bigchaindb import config_utils
+    from bigchaindb.consensus import BaseConsensusRules
+
+    assert config_utils.load_consensus_plugin() == BaseConsensusRules
+
+
+def test_load_consensus_plugin_raises_with_unknown_name():
+    from pkg_resources import ResolutionError
+    from bigchaindb import config_utils
+
+    with pytest.raises(ResolutionError):
+        config_utils.load_consensus_plugin('bogus')
+
+
+def test_load_consensus_plugin_raises_with_invalid_subclass(monkeypatch):
+    # Monkeypatch entry_point.load to return something other than a
+    # ConsensusRules instance
+    from bigchaindb import config_utils
+    import time
+    monkeypatch.setattr(config_utils,
+                        'iter_entry_points',
+                        lambda *args: [type('entry_point', (object), {'load': lambda: object})])
+
+    with pytest.raises(TypeError):
+        # Since the function is decorated with `lru_cache`, we need to
+        # "miss" the cache using a name that has not been used previously
+        config_utils.load_consensus_plugin(str(time.time()))
 
 def test_map_leafs_iterator():
     from bigchaindb import config_utils