Raise UnknownConfigError when a server is configured with an unknown storage plugin

src/allmydata/client.py

@@ -355,8 +355,13 @@ class _StoragePlugins(object):
         """
         storage_plugin_names = cls._get_enabled_storage_plugin_names(config)
         plugins = list(cls._collect_storage_plugins(storage_plugin_names))
-        # TODO Handle missing plugins
+        unknown_plugin_names = storage_plugin_names - {plugin.name for plugin in plugins}
-        # https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3118
+        if unknown_plugin_names:
+            raise configutil.UnknownConfigError(
+                "Storage plugins {} are enabled but not known on this system.".format(
+                    unknown_plugin_names,
+                ),
+            )
         announceable_storage_servers = yield cls._create_plugin_storage_servers(
             get_anonymous_storage_server,
             config,
@@ -375,7 +380,7 @@ class _StoragePlugins(object):
             config.get_config(
                 "storage", "plugins", b""
             ).decode("ascii").split(u",")
-        )
+        ) - {u""}
 
     @classmethod
     def _collect_storage_plugins(cls, storage_plugin_names):

src/allmydata/test/test_client.py

@@ -54,6 +54,7 @@ from allmydata.util import (
     base32,
     fileutil,
     encodingutil,
+    configutil,
 )
 from allmydata.util.fileutil import abspath_expanduser_unicode
 from allmydata.interfaces import IFilesystemNode, IFileNode, \
@@ -1496,3 +1497,30 @@ introducer.furl = pb://abcde@nowhere/fake
             ),
             failed(Always()),
         )
+
+    def test_storage_plugin_not_found(self):
+        """
+        ``client.create_client_from_config`` raises ``UnknownConfigError`` when
+        called with a configuration which enables a storage plugin that is not
+        available on the system.
+        """
+        config = client.config_from_string(
+            self.basedir,
+            u"tub.port",
+            self.get_config(
+                storage_enabled=True,
+                more_storage=b"plugins=tahoe-lafs-dummy-vX",
+            ),
+        )
+        self.assertThat(
+            client.create_client_from_config(
+                config,
+                _introducer_factory=MemoryIntroducerClient,
+            ),
+            failed(
+                AfterPreprocessing(
+                    lambda f: f.type,
+                    Equals(configutil.UnknownConfigError),
+                ),
+            ),
+        )