add session object and protocol with pinning

6 files changed, 67 insertions, 2 deletions

diff --git a/lib/concepts/Condition.ml b/lib/concepts/Condition.ml
index a9082ad..16f02d0 100644
--- a/lib/concepts/Condition.ml
+++ b/lib/concepts/Condition.ml
@@ -1,5 +1,3 @@
-(* @uses Value -- renders property values in to_string_hum *)
-
 type properties = (string, Value.value) BatMap.t
 type ps = properties -> properties
 
diff --git a/lib/kernel/Initialization.ml b/lib/kernel/Initialization.ml
index 25c2b3d..3c8addb 100644
--- a/lib/kernel/Initialization.ml
+++ b/lib/kernel/Initialization.ml
@@ -18,5 +18,6 @@ module Make (S : Abstract.Storage.STORAGE) = struct
         (Ok true) evaluators
     in
     let* _ = Registry.update registry "evaluator" None (Some evaluator_namespace) in
+    let* _ = Registry.update registry "session" None (Some (Namespace.make ())) in
     Ok root
 end
diff --git a/lib/kernel/Session.ml b/lib/kernel/Session.ml
new file mode 100644
index 0000000..75bf8c9
--- /dev/null
+++ b/lib/kernel/Session.ml
@@ -0,0 +1,27 @@
+module Make (S : Abstract.Storage.STORAGE) = struct
+  module SI = Storage.Make (S)
+  module B = Branch.Make (S)
+
+  class session storage state =
+    object (self)
+      inherit Lifecycle.null
+      inherit Identity.of_id
+      method to_string = "session"
+      val storage : S.connection = storage
+      val state : Protocols.Session.state Atomic.t = Atomic.make state
+      method state = Atomic.get state
+      method pin state' = Atomic.set state state'
+      method protocols = Protocols.[Directory.make self; Session.make self]
+      method list = Ok (BatFingerTree.singleton "branch")
+
+      method find =
+        function
+        | "branch" ->
+            SI.with_read storage (fun tx ->
+                B.load tx storage (Atomic.get state).Protocols.Session.snapshot )
+            |> Result.map Option.some
+        | _ -> Ok None
+    end
+
+  let make storage state = new session storage state |> Protocols.Handle.make
+end
diff --git a/lib/kernel/Session.mli b/lib/kernel/Session.mli
new file mode 100644
index 0000000..be4451b
--- /dev/null
+++ b/lib/kernel/Session.mli
@@ -0,0 +1,3 @@
+module Make (S : Abstract.Storage.STORAGE) : sig
+  val make : S.connection -> Protocols.Session.state -> Protocols.Handle.t
+end
diff --git a/lib/protocols/Session.ml b/lib/protocols/Session.ml
new file mode 100644
index 0000000..f740c1a
--- /dev/null
+++ b/lib/protocols/Session.ml
@@ -0,0 +1,23 @@
+module Error = struct
+  open Concepts.Condition
+
+  let not_a_session () =
+    condition "not-a-session" "A handle was expected to carry the session protocol and did not"
+      empty
+end
+
+type state = {branch: string; snapshot: Concepts.Hash.hash}
+
+class type implementation = object
+  method state : state
+  method pin : state -> unit
+end
+
+type Handle.protocol += Session of implementation
+type t = implementation
+
+let make impl = Session (impl :> implementation)
+let from handle = Handle.into handle (function Session impl -> Some impl | _ -> None)
+let require handle = from handle |> Option.to_result ~none:(Error.not_a_session ())
+let state i = Handle.invoke i (fun o -> o#state)
+let pin i state = Handle.invoke i (fun o -> o#pin state)
diff --git a/lib/protocols/Session.mli b/lib/protocols/Session.mli
new file mode 100644
index 0000000..141c250
--- /dev/null
+++ b/lib/protocols/Session.mli
@@ -0,0 +1,13 @@
+type state = {branch: string; snapshot: Concepts.Hash.hash}
+type t
+
+class type implementation = object
+  method state : state
+  method pin : state -> unit
+end
+
+val make : #implementation -> Handle.protocol
+val from : Handle.t -> t Handle.interface option
+val require : Handle.t -> (t Handle.interface, Concepts.Condition.condition) result
+val state : t Handle.interface -> state
+val pin : t Handle.interface -> state -> unit