(** Physical storage abstraction.
This module defines a functor-based storage interface that can be backed by
any key-value store (etcd, Redis, DynamoDB, PostgreSQL, filesystem, etc.).
All data is content-addressed: keys are hashes, values are serialized
objects. The storage is append-only - objects are never modified, only new
versions are written with new hashes. *)
(** Backend module signature that any storage driver must implement *)
module type BACKEND = sig
include Configuration.CONFIGURABLE
type connection
type error
val connect : configuration -> (connection, error) result
(** Connect to the storage backend *)
val disconnect : connection -> unit
(** Disconnect from the backend *)
val get : connection -> Conventions.Hash.t -> (bytes option, error) result
(** Get a value by its hash. Returns None if not found. *)
val put : connection -> Conventions.Hash.t -> bytes -> (unit, error) result
(** Store a value at its hash *)
val exists : connection -> Conventions.Hash.t -> (bool, error) result
(** Check if a hash exists *)
val with_transaction : connection -> (unit -> 'a) -> ('a option, error) result
(** Execute a function within a transaction *)
val abort : connection -> unit
(** Abort the currently executing transaction. This performs a non-local transfer of control to the nearest `with_transaction` *)
val get_many :
connection -> Conventions.Hash.t BatEnum.t -> (bytes option BatEnum.t, error) result
(** Batch get multiple values *)
val put_many :
connection -> (Conventions.Hash.t * bytes) BatEnum.t -> (unit, error) result
(** Batch put multiple values *)
end
(** Storage operations built on top of a backend *)
module type S = sig
include Configuration.CONFIGURABLE
type t
type error
val create : configuration -> (t, error) result
(** Create a storage instance from a backend connection *)
val close : t -> unit
(** Close the storage *)
val store_attribute :
t -> Conventions.AbstractValue.t -> (Conventions.Hash.t, error) result
(** Store an attribute value, returns its hash *)
val load_attribute :
t ->
Conventions.Hash.t ->
(Conventions.AbstractValue.t option, error) result
(** Load an attribute value by hash *)
val store_raw : t -> Conventions.Hash.t -> bytes -> (unit, error) result
(** Store raw bytes at a hash *)
val load_raw : t -> Conventions.Hash.t -> (bytes option, error) result
(** Load raw bytes by hash *)
val exists : t -> Conventions.Hash.t -> (bool, error) result
(** Check if a hash exists *)
val with_transaction : t -> (unit -> 'a) -> ('a option, error) result
(** Execute a function within a transaction *)
end
(** Functor to create storage operations from a backend *)
module Make (B : BACKEND) :
S with type error = B.error and type configuration = B.configuration = struct
type configuration = B.configuration
type t = B.connection
type error = B.error
let parse = B.parse
let create config = B.connect config
let close = B.disconnect
let store_attribute conn value =
let bytes = Marshal.to_bytes value [] in
let hash = Conventions.AbstractValue.hash value in
match B.put conn hash bytes with Ok () -> Ok hash | Error e -> Error e
let load_attribute conn hash =
match B.get conn hash with
| Ok (Some bytes) -> Ok (Some (Marshal.from_bytes bytes 0))
| Ok None -> Ok None
| Error e -> Error e
let store_raw conn hash bytes = B.put conn hash bytes
let load_raw conn hash = B.get conn hash
let exists conn hash = B.exists conn hash
let with_transaction = B.with_transaction
end
