Do not assume that the hash of an object is its storage address

9 files changed, 64 insertions, 18 deletions

diff --git a/lib/Utilities.ml b/lib/Utilities.ml
index 9bff69b..404d8aa 100644
--- a/lib/Utilities.ml
+++ b/lib/Utilities.ml
@@ -4,6 +4,14 @@ module Ordering = struct
   let of_int x = if x < 0 then Smaller else if x > 0 then Greater else Equal
 end
 
+module Option = struct
+  let ( let* ) = Option.bind
+  let fmap f m = Option.bind m f
+  let sequence = function
+    | None -> Ok None
+    | Some x -> Result.map Option.some x
+end
+
 module Result = struct
   let ( let* ) = Result.bind
   let fmap f m = Result.bind m f
@@ -80,11 +88,6 @@ module FingerTree = struct
     |> Fun.flip BatIO.to_string ss
 end
 
-module Option = struct
-  let ( let* ) = Option.bind
-  let fmap f m = Option.bind m f
-end
-
 module Atomic = struct
   let rec swap atom f =
     let v = Atomic.get atom in
diff --git a/lib/Utilities.mli b/lib/Utilities.mli
index eae59f9..11c4487 100644
--- a/lib/Utilities.mli
+++ b/lib/Utilities.mli
@@ -17,6 +17,7 @@ end
 module Option : sig
   val ( let* ) : 'a option -> ('a -> 'b option) -> 'b option
   val fmap : ('a -> 'b option) -> 'a option -> 'b option
+  val sequence : ('a, 'b) result option -> ('a option, 'b) result
 end
 
 module Atomic : sig
diff --git a/lib/kernel/Branch.ml b/lib/kernel/Branch.ml
index 64f9689..3832a07 100644
--- a/lib/kernel/Branch.ml
+++ b/lib/kernel/Branch.ml
@@ -59,7 +59,7 @@ module Make (S : Abstract.Storage.STORAGE) = struct
       Ok { multigroups; previous }
   end
 
-  class branch storage value node = object
+  class branch storage value node = object (self)
     inherit Lifecycle.null
 
     val storage : S.connection = storage
@@ -67,15 +67,18 @@ module Make (S : Abstract.Storage.STORAGE) = struct
     val node = node (* FIXME: can we not place this inside `t`? *)
 
     method protocols : Protocols.Handle.protocol list =
-      [ Prototype.Directory.of_properties
-          [ "multigroup", Prototype.mixture
-                            [ MMDirectory.make
-                                ~storage ~node
-                                ~constructor:(M.wrap storage) ] ] ]
+      Protocols.[ Addressable.make self;
+                  Prototype.Directory.of_properties
+                    [ "multigroup", Prototype.mixture
+                                      [ MMDirectory.make
+                                          ~storage ~node
+                                          ~constructor:(M.wrap storage) ] ] ]
 
     method hash =
       Representation.to_blob branch
       |> Concepts.Hash.hash_of_blob
+
+    method address = self#hash
   end
 
   let load tx conn addr =
diff --git a/lib/kernel/BranchManager.ml b/lib/kernel/BranchManager.ml
index 016f75a..1162b40 100644
--- a/lib/kernel/BranchManager.ml
+++ b/lib/kernel/BranchManager.ml
@@ -51,13 +51,21 @@ module Make (S : Abstract.Storage.STORAGE) = struct
 
     method update key reference value =
       let open Utilities.Result in
+      let open Protocols in
       SI.with_transaction storage (fun tx ->
           match
             Utilities.Atomic.mswap head (fun head ->
+                let address_of h =
+                  let* i = Handle.require Addressable.from h in
+                  Ok (Addressable.address i)
+                in
                 let* branch = M.lookup tx key head |> Result.map_error (fun e -> Some e) in
-                (* FIXME: we should have an addressable protocol rather than assuming the hash is the content store address *)
-                let reference = Option.map Protocols.Handle.hash reference in
-                let value = Option.map Protocols.Handle.hash value in
+                let* reference = Option.map address_of reference
+                                 |> Utilities.Option.sequence
+                                 |> Result.map_error (fun e -> Some e) in
+                let* value = Option.map address_of value
+                             |> Utilities.Option.sequence
+                             |> Result.map_error (fun e -> Some e) in
                 if branch = reference then
                   begin
                     let* new_head = match value with
diff --git a/lib/protocols/Addressable.ml b/lib/protocols/Addressable.ml
new file mode 100644
index 0000000..7e97f08
--- /dev/null
+++ b/lib/protocols/Addressable.ml
@@ -0,0 +1,13 @@
+class type implementation = object
+  method address : Concepts.Hash.hash
+end
+
+type Handle.protocol += Addressable of implementation
+
+type t = implementation
+
+let make impl = Addressable (impl :> implementation)
+
+let from handle = Handle.into handle (function Addressable impl -> Some impl | _ -> None)
+
+let address i = Handle.invoke i (fun o -> o#address)
diff --git a/lib/protocols/Addressable.mli b/lib/protocols/Addressable.mli
new file mode 100644
index 0000000..2d9c14d
--- /dev/null
+++ b/lib/protocols/Addressable.mli
@@ -0,0 +1,11 @@
+type t
+
+class type implementation = object
+  method address : Concepts.Hash.hash
+end
+
+val make : #implementation -> Handle.protocol
+
+val from : Handle.t -> t Handle.interface option
+
+val address : t Handle.interface -> Concepts.Hash.hash
diff --git a/lib/protocols/Context.ml b/lib/protocols/Context.ml
deleted file mode 100644
index b7c8a37..0000000
--- a/lib/protocols/Context.ml
+++ /dev/null
@@ -1,4 +0,0 @@
-type t =
-  { snapshot : Concepts.Hash.hash
-  ; root : Handle.t
-  ; status : unit -> [`Live | `Cancelled | `Exhausted] }
diff --git a/lib/protocols/Handle.ml b/lib/protocols/Handle.ml
index 524386b..313a3d4 100644
--- a/lib/protocols/Handle.ml
+++ b/lib/protocols/Handle.ml
@@ -1,5 +1,12 @@
 type protocol = ..
 
+module Error = struct
+  open Concepts.Condition
+
+  let unimplemented_protocol () = condition "unimplemented-protocol" "A required protocol was not implemented by the specified object"
+                                    empty
+end
+
 class type obj = object
   method reference : bool
   method release : unit
@@ -45,3 +52,5 @@ let release ({ valid; _ } as handle) =
   let o = object_of handle in
   valid := false;
   o#release
+
+let require f h = Option.to_result ~none:(Error.unimplemented_protocol ()) (f h)
diff --git a/lib/protocols/Handle.mli b/lib/protocols/Handle.mli
index f36c95e..f63bbea 100644
--- a/lib/protocols/Handle.mli
+++ b/lib/protocols/Handle.mli
@@ -22,3 +22,5 @@ val equal : t -> t -> bool
 val release : t -> unit
 
 val hash : t -> Concepts.Hash.hash
+
+val require : (t -> 'a interface option) -> t -> ('a interface, Concepts.Condition.condition) result