cache getClusters in Annex state

Annex.hs

@@ -74,6 +74,7 @@ import Types.CatFileHandles
 import Types.RemoteConfig
 import Types.TransferrerPool
 import Types.VectorClock
+import Types.Cluster
 import Annex.VectorClock.Utility
 import Annex.Debug.Utility
 import qualified Database.Keys.Handle as Keys
@@ -194,6 +195,7 @@ data AnnexState = AnnexState
 	, preferredcontentmap :: Maybe (FileMatcherMap Annex)
 	, requiredcontentmap :: Maybe (FileMatcherMap Annex)
 	, remoteconfigmap :: Maybe (M.Map UUID RemoteConfig)
+	, clusters :: Maybe Clusters
 	, forcetrust :: TrustMap
 	, trustmap :: Maybe TrustMap
 	, groupmap :: Maybe GroupMap
@@ -248,6 +250,7 @@ newAnnexState c r = do
 		, preferredcontentmap = Nothing
 		, requiredcontentmap = Nothing
 		, remoteconfigmap = Nothing
+		, clusters = Nothing
 		, forcetrust = M.empty
 		, trustmap = Nothing
 		, groupmap = Nothing

Logs/Cluster.hs

@@ -30,15 +30,19 @@ import qualified Data.Attoparsec.ByteString as A
 import qualified Data.Attoparsec.ByteString.Char8 as A8
 import qualified Data.ByteString.Lazy as L
 
--- TODO caching
 getClusters :: Annex Clusters
-getClusters = do
+getClusters = maybe loadClusters return =<< Annex.getState Annex.clusters
+
+loadClusters :: Annex Clusters
+loadClusters = do
 	m <- convclusteruuids . M.map value . fromMapLog . parseClusterLog
 		<$> Annex.Branch.get clusterLog
-	return $ Clusters
+	let clusters = Clusters
 		{ clusterUUIDs = m
 		, clusterNodeUUIDs = M.foldlWithKey inverter mempty m
 		}
+	Annex.changeState $ \s -> s { Annex.clusters = Just clusters }
+	return clusters
   where
 	convclusteruuids :: M.Map UUID (S.Set ClusterNodeUUID) -> M.Map ClusterUUID (S.Set ClusterNodeUUID)
 	convclusteruuids = M.fromList 

doc/design/passthrough_proxy.mdwn

@@ -218,9 +218,10 @@ UUID, all random except the first octet set to 'a' and the second to 'c'.
 
 The proxy log contains the cluster UUID (with a remote name like
 "cluster"), as well as the UUIDs of the nodes of the cluster.
-This makes the client access the cluster using the proxy. Note that more
+This lets the client access the cluster using the proxy, and it lets the
-than one proxy can be in front of the same cluster, and multiple clusters
+client access individual nodes (so it can lock content on them while
-can be accessed via the same proxy.
+dropping). Note that more than one proxy can be in front of the same
+cluster, and multiple clusters can be accessed via the same proxy.
 
 The cluster UUID is recorded in the git-annex branch, along with a list of
 the UUIDs of nodes of the cluster (which can change at any time).