Basic storage with C interop (#1)

* writer command design

* dune build with shared core lib

* port c lib project inside ocaml

* os specific dynamic link

* fix project name on flake

* fix: cmake cxx version breaking merklecpp

* finish write to disk and update maps func

* add non atomic commit to transaction graph

* merkle tree binding for generating root hash

* disk module refactor

---------

Co-authored-by: Renan Lopes <renans.l@icloud.com>

19 files changed, 443 insertions, 60 deletions

diff --git a/.gitignore b/.gitignore
index 2790b52..c0f3d8f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,5 @@
 result
-_build
\ No newline at end of file
+_build
+cmake-build-debug/
+*CMakeFiles
+*CMakeCache.txt
\ No newline at end of file
diff --git a/README.org b/README.org
new file mode 100644
index 0000000..dcd2b7c
--- /dev/null
+++ b/README.org
@@ -0,0 +1,24 @@
+#+TITLE: Relational Engine
+
+* About
+This is a relational engine.
+
+* Roadmap
+- [ ] Filesystem [0/6]
+  - [ ] Durability
+  - [ ] Immutable storage
+  - [ ] ARIES
+  - [ ] Merkle construction per virtual file
+  - [ ] Branching
+  - [ ] Branch merge strategies [0/3]
+    - [ ] Selected merge
+    - [ ] Union merge
+    - [ ] Biased union merge
+- [ ] Language [0/4]
+  - [ ] Lexer
+  - [ ] Parser
+  - [ ] AST
+  - [ ] Unification and query terms
+- [ ] Server [0/2]
+  - [ ] Authentication
+  - [ ] Multi-client coordination
diff --git a/bin/main.ml b/bin/main.ml
index 6fe3d69..289b4dd 100644
--- a/bin/main.ml
+++ b/bin/main.ml
@@ -1,3 +1,6 @@
-open Relational_engine.Hello
+open Relational_engine
 
-let _ = hello ()
+let () =
+  begin
+    print_endline @@ Interop.Merkle.merkle_generate_root [Disk.Executor._EMPTY_SHA_HASH_; Disk.Executor._EMPTY_SHA_HASH_]
+  end
diff --git a/deps/relational_engine_lib.nix b/deps/relational_engine_lib.nix
new file mode 100644
index 0000000..b1d0488
--- /dev/null
+++ b/deps/relational_engine_lib.nix
@@ -0,0 +1,28 @@
+{ pkgs, libressl ? pkgs.callPackage ./libressl.nix {}, merklecpp ? pkgs.callPackage ./merklecpp.nix {}, ... }:
+let
+  shared_lib_extension = if pkgs.stdenv.isDarwin then "dylib" else "so";
+in 
+pkgs.stdenv.mkDerivation {
+  name = "librelational_engine";
+  src = ../shared/librelational_engine;
+  nativeBuildInputs = [
+    pkgs.cmake
+    pkgs.gcc
+  ];
+  buildInputs = [ libressl merklecpp ];
+  env = {
+    MERKLECPP_INCLUDE_PATH="${merklecpp}/include";
+    LIBRESSL_INCLUDE_PATH="${libressl}/include";
+    LIBRESSL_LIB_PATH="${libressl}/lib";
+    OS_LIB_EXTENSION = shared_lib_extension;
+  };
+  buildPhase = ''
+      mkdir -p $out/lib
+      mkdir -p $out/include
+      cmake --build . --target relational_engine
+  '';
+  installPhase = ''
+      mv librelational_engine.${shared_lib_extension} $out/lib/librelational_engine.${shared_lib_extension}
+      cp $src/library.h $out/include/library.h
+  '';
+}
diff --git a/docs/architecture.plantuml b/docs/architecture.plantuml
new file mode 100644
index 0000000..90985ba
--- /dev/null
+++ b/docs/architecture.plantuml
@@ -0,0 +1,72 @@
+@startuml
+allowmixing
+
+package Client {
+    object "Query Interface" as query_interface
+}
+
+package Algebra {
+    object "Unifier" as unifier
+    object "Bytecode Builder" as bytecode_builder
+    object "Parser" as parser
+    object "Lexer" as lexer
+}
+
+query_interface --> lexer
+lexer --> parser
+parser --> unifier
+unifier --> bytecode_builder
+
+package Query {
+    object "Schema Builder" as schema_builder
+    object "Facts Builder" as facts_builder
+    object "Optimizer" as optimizer
+    object "Commands Generator" as commands_generator
+    object "B+ Tree" as b_plus_tree
+}
+
+bytecode_builder --> optimizer
+optimizer --> commands_generator
+facts_builder --> commands_generator
+schema_builder --> commands_generator
+commands_generator --> b_plus_tree
+b_plus_tree --> query_interface
+
+package Coordinator {
+    object "File Historical Hashes" as file_historical_hashes
+    object "Location Hashes" as location_hashes
+    object "Command Parser" as command_parser
+    object "Curator" as curator
+}
+
+commands_generator <-- command_parser
+
+package Disk {
+    object "Merkle Tree Root Generator" as merkle_tree
+    object "WAL Reader" as wal_reader
+    object "WAL Writer" as wal_writer
+    object "ARIES" as aries
+    object "SHA256 Hasher" as sha
+    object "Executor" as executor
+    map storage {
+        write => +λ
+        read => +λ
+    }
+    object "Courier" as courier
+    database Wal
+}
+
+executor *--> merkle_tree
+executor *--> sha
+curator --> command_parser
+command_parser --> executor
+location_hashes *--> curator
+file_historical_hashes *--> curator
+executor --> aries
+aries --> wal_reader
+aries --> wal_writer
+wal_writer --> Wal
+wal_reader --> Wal
+courier <-- wal_reader
+courier --> storage
+@enduml
\ No newline at end of file
diff --git a/dune-project b/dune-project
index 3e80424..661cecd 100644
--- a/dune-project
+++ b/dune-project
@@ -1,6 +1,6 @@
 (lang dune 3.16)
 
-;; (using ctypes 0.3)
+(using ctypes 0.3)
 
 (name relational_engine)
 
diff --git a/flake.nix b/flake.nix
index ac1cb49..9f0c182 100644
--- a/flake.nix
+++ b/flake.nix
@@ -1,5 +1,5 @@
 {
-  description = "A compiler for a statically-typed relational programming language";
+  description = "Relational Engine";
 
   # Flake dependency specification
   #
@@ -31,6 +31,7 @@
         lib = legacyPackages.lib;
         merklecpp = legacyPackages.callPackage ./deps/merklecpp.nix {};
         libressl = legacyPackages.callPackage ./deps/libressl.nix {};
+        librelational_engine = legacyPackages.callPackage ./deps/relational_engine_lib.nix { libressl = libressl; merklecpp = merklecpp; };
 
         # Filtered sources (prevents unecessary rebuilds)
         sources = {
@@ -78,12 +79,17 @@
                 MERKLECPP_INCLUDE_PATH="${merklecpp}/include";
                 LIBRESSL_INCLUDE_PATH="${libressl}/include";
                 LIBRESSL_LIB_PATH="${libressl}/lib";
+                OS_LIB_EXTENSION = if legacyPackages.stdenv.isDarwin then "dylib" else "so";
+                LIBRELATIONAL_ENGINE_LIB_PATH="${librelational_engine}/lib";
+                LIBRELATIONAL_ENGINE_INCLUDE_PATH="${librelational_engine}/include";
               };
 
               nativeInputs = [];
 
-              buildInputs = [
-                # Ocaml package dependencies needed to build go here.
+              buildInputs = with ocamlPackages; [
+                ctypes
+                ctypes-foreign
+                data-encoding
               ];
 
               strictDeps = true;
@@ -202,8 +208,9 @@
                 MERKLECPP_INCLUDE_PATH="${merklecpp}/include";
                 LIBRESSL_INCLUDE_PATH="${libressl}/include";
                 LIBRESSL_LIB_PATH="${libressl}/lib";
-                CAML_INCLUDE_PATH="${legacyPackages.ocaml}/include";
                 OS_LIB_EXTENSION = if legacyPackages.stdenv.isDarwin then "dylib" else "so";
+                LIBRELATIONAL_ENGINE_LIB_PATH="${librelational_engine}/lib";
+                LIBRELATIONAL_ENGINE_INCLUDE_PATH="${librelational_engine}/include";
             };
             
             # Development tools
@@ -225,8 +232,20 @@
               ocamlPackages.menhir
               ocamlPackages.ctypes
               ocamlPackages.ctypes-foreign
+              ocamlPackages.data-encoding
+              legacyPackages.cmake
+              legacyPackages.gcc
             ];
 
+            shellHook = ''
+                echo MERKLECPP_INCLUDE_PATH=$MERKLECPP_INCLUDE_PATH
+                echo LIBRESSL_INCLUDE_PATH=$LIBRESSL_INCLUDE_PATH
+                echo LIBRESSL_LIB_PATH=$LIBRESSL_LIB_PATH
+                echo OS_LIB_EXTENSION=$OS_LIB_EXTENSION 
+                echo LIBRELATIONAL_ENGINE_LIB_PATH=$LIBRELATIONAL_ENGINE_LIB_PATH
+                echo LIBRELATIONAL_ENGINE_INCLUDE_PATH=$LIBRELATIONAL_ENGINE_INCLUDE_PATH
+            '';
+
             # Tools from packages
             inputsFrom = [
               self.packages.${system}.relational_engine
diff --git a/lib/core_functions.ml b/lib/core_functions.ml
new file mode 100644
index 0000000..1e1af37
--- /dev/null
+++ b/lib/core_functions.ml
@@ -0,0 +1,21 @@
+(* open Ctypes *)
+
+module Types = Types_generated
+
+module Functions (F : Ctypes.FOREIGN) = struct
+  (* open F *)
+  open Ctypes_static
+  let os_extension =
+    if Sys.os_type = "Unix" then
+      let ic = Unix.open_process_in "uname" in
+      let uname = input_line ic in
+      let () = close_in ic in
+      if uname = "Darwin" then
+        "dylib"
+      else "so"
+    else "dll"
+  let libmerklecpp = Dl.dlopen ~flags:[RTLD_GLOBAL; RTLD_NOW] ~filename:((Sys.getenv "LIBRELATIONAL_ENGINE_LIB_PATH") ^ "/librelational_engine." ^ os_extension)
+  let compute_hash = Foreign.foreign ~from:libmerklecpp "compute_hash" (ptr char @-> Ctypes.string @-> returning void)
+  let merkle_generate_root = Foreign.foreign ~from:libmerklecpp "merkle_generate_root" (ptr Ctypes.string @-> int @-> ptr char @-> returning void)
+
+end
diff --git a/lib/core_types.ml b/lib/core_types.ml
new file mode 100644
index 0000000..45f5720
--- /dev/null
+++ b/lib/core_types.ml
@@ -0,0 +1,3 @@
+module Types (F : Ctypes.TYPE) = struct
+  let hash_size = F.constant "HASH_SIZE" F.int
+end
diff --git a/lib/disk.ml b/lib/disk.ml
new file mode 100644
index 0000000..3c5157b
--- /dev/null
+++ b/lib/disk.ml
@@ -0,0 +1,167 @@
+module type Configuration = sig
+  val base_dir: string
+  val storage: string
+  val transactions: string
+  val assure: unit -> unit
+end
+
+module DevelopmentConfiguration: Configuration = struct
+  let base_dir = "/tmp/relational-engine/"
+  let storage = base_dir ^ "storage/"
+  let transactions = base_dir ^ "transactions/"
+  let assure () =
+    if Sys.file_exists base_dir
+    then Sys.remove base_dir;
+    Sys.mkdir base_dir 0o700;
+    Sys.mkdir storage 0o700;
+    Sys.mkdir transactions 0o700;
+end
+
+module type FileSystem = sig
+  type target =
+    | Storage
+    | Transaction
+  val append: target -> bytes -> (int*int64, string) result
+end
+
+module FileSystem (C: Configuration): FileSystem = struct
+  type target =
+    | Storage
+    | Transaction
+  let target_to_string = function
+    | Storage -> "storage"
+    | Transaction -> "transaction"
+
+  (** [append target content] writes content to file in append only format, returning [content_length * offset_written] *)
+  let append target content =
+    let register channel =
+      let offset_written = Out_channel.length channel in
+      Out_channel.seek channel offset_written;
+      Out_channel.output_bytes channel content;
+      Out_channel.flush channel;
+      Out_channel.close channel;
+      Ok (Bytes.length content, offset_written)
+    in
+    try Out_channel.with_open_bin (target_to_string target) register
+    with _ -> Error (Printf.sprintf "Error on appending to target '%s'" (target_to_string target))
+end
+
+module Executor = struct
+  module StringMap = Map.Make(String)
+  module FS = FileSystem(DevelopmentConfiguration)
+  module Location = struct
+    type t =
+      { offset: int64;
+        size: int;
+        hash: string }
+  end
+  module Hashes = struct
+    type t = string list
+  end
+  type files = Hashes.t StringMap.t
+  type locations = Location.t StringMap.t
+  let _EMPTY_SHA_HASH_ = "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
+
+  (** Initializes the virtual file or opens it. *)
+  let init_file (files: Hashes.t StringMap.t) filename: Hashes.t StringMap.t =
+    match StringMap.find_opt filename files with
+    | None -> StringMap.add filename [_EMPTY_SHA_HASH_] files
+    | Some _ -> files
+  let write (files: files) (locations: locations) filename ?hash_to_replace (content: Bytes.t) =
+    let files = init_file files filename in
+    let computed_hash: string = Interop.Sha256.compute_hash content in
+    match StringMap.find_opt computed_hash locations with
+    | None ->
+        begin match hash_to_replace with
+        | None ->
+          begin
+            (* This instead should store a list of list to keep the history *)
+            let files =
+              StringMap.update
+                filename
+                (function Some file_hashes -> Some (computed_hash::file_hashes) | None -> Some [computed_hash])
+                files
+            in
+            let open Extensions.Result in
+            let+ (size, offset) = FS.append Storage content in
+            let locations = StringMap.add computed_hash ({size; offset; hash = computed_hash}: Location.t) locations in
+            Ok (files, locations)
+          end
+        | Some hash_to_replace ->
+           let files = StringMap.update filename (function Some file_hashes -> Some (List.map (fun hash -> if hash = hash_to_replace then computed_hash else hash) file_hashes) | None -> Some [computed_hash]) files in
+           let open Extensions.Result in
+           let+ (size, offset) = FS.append Storage content in
+           let locations = StringMap.add computed_hash ({size; offset; hash = computed_hash}: Location.t) locations in
+           Ok (files, locations)
+        end
+    | Some _ ->
+        begin match hash_to_replace with
+        | Some hash_to_replace ->
+           let files =
+             StringMap.update filename
+               (function
+                | Some file_hashes -> Some (List.map (fun hash -> if hash = hash_to_replace then computed_hash else hash) file_hashes)
+                | None -> Some [computed_hash])
+               files in
+           Ok (files, locations)
+        | None ->
+           Ok (files, locations)
+        end
+end
+
+module Startup = struct
+  let () = DevelopmentConfiguration.assure()
+end
+
+module Command = struct
+  module FS = FileSystem(DevelopmentConfiguration)
+  open Data_encoding
+  type command_kind =
+    | OPEN
+    | WRITE
+    | READ
+  let command_kind_encoding =
+    union [
+      case ~title:"open" (Tag 0)
+        Data_encoding.empty
+        (function OPEN -> Some () | _ -> None)
+        (function () -> OPEN);
+      case ~title:"write" (Tag 1)
+        Data_encoding.empty
+        (function WRITE -> Some () | _ -> None)
+        (function () -> WRITE);
+      case ~title:"read" (Tag 2)
+        Data_encoding.empty
+        (function READ -> Some () | _ -> None)
+        (function () -> READ);
+    ]
+  type t =
+    { kind: command_kind;
+      timestamp: float;
+      hash: string;
+      filename: string;
+      (* branch must be added here later *)
+      content: string }
+  let command_encoding =
+    conv 
+      (fun {kind; timestamp; hash; filename; content} -> (kind, timestamp, hash, filename, content))
+      (fun (kind, timestamp, hash, filename, content) -> {kind; timestamp; hash; filename; content})
+      Data_encoding.(tup5 command_kind_encoding float string string string)
+  
+  let parse_command ~data =
+    let contract_encoding = Data_encoding.(tup4 command_kind_encoding string string string) in
+    match Binary.of_bytes_opt contract_encoding data with
+    | Some (kind, hash, filename, content) -> Ok {kind; timestamp = Unix.time(); hash; filename; content}
+    | None -> Error "Failed to parse command"
+
+  (** TODO: This does not write atomically. If the system crashes while it attempts to write, it will corrupt.
+     Solve this with a temporary file and move later. *)
+  let commit 
+    (* (_files: Filesystem.files) (_locations: Filesystem.locations)  *)
+   command =
+      let open Extensions.Result in
+      let+ serialized_command =
+        Result.map_error (fun _ -> "Failed to serialize command to binary format.")
+        @@ Binary.to_bytes command_encoding command in
+      FS.append FS.Transaction serialized_command
+end
diff --git a/lib/dune b/lib/dune
index bdde443..a5d0378 100644
--- a/lib/dune
+++ b/lib/dune
@@ -1,31 +1,29 @@
 (library
  (name relational_engine)
- (libraries ctypes ctypes-foreign)
- (modes native)
-  (foreign_stubs
-   (language cxx)
-   (names merklecpp_stubs)
-   (flags
-    (:standard -lssl -lcrypto)
-    (-L %{env:LIBRESSL_LIB_PATH=})
-    (-I %{env:LIBRESSL_INCLUDE_PATH=})
-    (-I %{env:MERKLECPP_INCLUDE_PATH=})))
-  
-  ;; (ctypes
-  ;; (external_library_name merklecpp_stub)
-  ;; (headers (include "/Users/mmagueta/CLionProjects/merklecpp_stub/library.h"))
-  ;; (build_flags_resolver
-  ;;  (vendored
-  ;;   (c_flags
-  ;;     -L %{env:MERKLECPP_LIB_PATH=})))
-  ;; (type_description
-  ;;  (instance Types)
-  ;;  (functor Type_description))
-  ;; (function_description
-  ;;  (concurrency unlocked)
-  ;;  (instance Functions)
-  ;;  (functor Function_description))
-  ;; (generated_types Types_generated)
-  ;; (generated_entry_point C))
-
-  )
+ (libraries ctypes ctypes-foreign data-encoding)
+ ;; (c_library_flags -lssl -lcrypto -L %{env:LIBRESSL_LIB_PATH=})
+ ;; (foreign_stubs
+ ;;  (language cxx)
+ ;;  (names merklecpp_stubs)
+ ;;  (flags
+ ;;   (:standard -lssl -lcrypto)
+ ;;   (-L %{env:LIBRESSL_LIB_PATH=})
+ ;;   (-I %{env:LIBRESSL_INCLUDE_PATH=})
+ ;;   (-I %{env:MERKLECPP_INCLUDE_PATH=})))
+ 
+ (ctypes
+  (external_library_name relational_engine)
+  (headers (include %{env:LIBRELATIONAL_ENGINE_INCLUDE_PATH=}/library.h))
+  (build_flags_resolver
+   (vendored
+    (c_flags
+     -L %{env:LIBRELATIONAL_ENGINE_LIB_PATH=})))
+  (type_description
+   (instance Types)
+   (functor core_types))
+  (function_description
+   (concurrency unlocked)
+   (instance Functions)
+   (functor core_functions))
+  (generated_types Types_generated)
+  (generated_entry_point C)))
diff --git a/lib/extensions.ml b/lib/extensions.ml
new file mode 100644
index 0000000..c128f2a
--- /dev/null
+++ b/lib/extensions.ml
@@ -0,0 +1,7 @@
+module Option = struct
+  let ( let+ ) = Option.bind
+end
+
+module Result = struct
+  let ( let+ ) = Result.bind
+end
diff --git a/lib/hello.ml b/lib/hello.ml
deleted file mode 100644
index 1a3a138..0000000
--- a/lib/hello.ml
+++ /dev/null
@@ -1 +0,0 @@
-external hello : unit -> int = "hello_ocaml"
diff --git a/lib/interop.ml b/lib/interop.ml
new file mode 100644
index 0000000..fdfde5f
--- /dev/null
+++ b/lib/interop.ml
@@ -0,0 +1,19 @@
+open Ctypes
+
+module Sha256 = struct
+  let compute_hash content =
+    let size_with_null_terminator = C.Types.hash_size + 1 in
+    let buf = Ctypes.allocate_n char ~count:size_with_null_terminator in
+    let () = C.Functions.compute_hash buf (Bytes.to_string content) in
+    Ctypes.coerce (ptr char) Ctypes.string buf
+end
+
+module Merkle = struct
+  let merkle_generate_root hashes =
+    let size_with_null_terminator = C.Types.hash_size + 1 in
+    let buf = Ctypes.allocate_n char ~count:size_with_null_terminator in
+    let len = List.length hashes in
+    let hashes = CArray.of_list string hashes in
+    C.Functions.merkle_generate_root (CArray.start hashes) len buf;
+    Ctypes.coerce (ptr char) Ctypes.string buf
+end
diff --git a/lib/merklecpp_stubs.cpp b/lib/merklecpp_stubs.cpp
deleted file mode 100644
index 4ce427e..0000000
--- a/lib/merklecpp_stubs.cpp
+++ /dev/null
@@ -1,15 +0,0 @@
-#include <iostream>
-#include <merklecpp.h>
-
-void cpp_normal_function() {
-  std::cout << "HELLO OCAML! :)" << std::endl;
-}
-
-extern "C" {
-#include <caml/mlvalues.h>
-#include <caml/memory.h>
-  extern value hello_ocaml(value unit){
-    cpp_normal_function();
-    return 0;
-  }
-}
diff --git a/CMakeLists.txt b/shared/librelational_engine/CMakeLists.txt
index 98dbfc4..d22d0d0 100644
--- a/CMakeLists.txt
+++ b/shared/librelational_engine/CMakeLists.txt
@@ -1,16 +1,12 @@
 cmake_minimum_required(VERSION 3.29)
-project(relational_engine_ocaml)
-
-set(CMAKE_CXX_STANDARD 20)
+project(relational_engine)
 
 include_directories($ENV{LIBRESSL_INCLUDE_PATH})
 include_directories($ENV{MERKLECPP_INCLUDE_PATH})
-include_directories($ENV{CAML_INCLUDE_PATH})
 
-add_library(relational_engine_ocaml STATIC
-        lib/merklecpp_stubs.cpp)
+add_library(relational_engine SHARED library.cpp)
 
-target_link_libraries(relational_engine_ocaml
+target_link_libraries(relational_engine
         $ENV{LIBRESSL_LIB_PATH}/libssl.$ENV{OS_LIB_EXTENSION}
         $ENV{LIBRESSL_LIB_PATH}/libcrypto.$ENV{OS_LIB_EXTENSION}
 )
\ No newline at end of file
diff --git a/shared/librelational_engine/flake.nix b/shared/librelational_engine/flake.nix
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/shared/librelational_engine/flake.nix
diff --git a/shared/librelational_engine/library.cpp b/shared/librelational_engine/library.cpp
new file mode 100644
index 0000000..8048486
--- /dev/null
+++ b/shared/librelational_engine/library.cpp
@@ -0,0 +1,30 @@
+#include <iostream>
+#include <merklecpp.h>
+#include <openssl/sha.h>
+#include <iomanip>
+extern "C" {
+#include "library.h"
+    extern void merkle_generate_root(char** hashes, const int n, char* root) {
+        merkle::Tree tree;
+        for (int i = 0; i < n; i++){
+            tree.insert(merkle::Hash(hashes[i]));
+        }
+        std::memcpy(root, tree.root().to_string().c_str(), HASH_SIZE);
+    }
+    extern void compute_hash(char* computed_hash, const char *content) {
+
+        unsigned char hash[SHA256_DIGEST_LENGTH];
+        SHA256_CTX sha256;
+        SHA256_Init(&sha256);
+        SHA256_Update(&sha256, content, sizeof(content));
+        SHA256_Final(hash, &sha256);
+        std::stringstream ss;
+        for (int i = 0; i < SHA256_DIGEST_LENGTH; i++)
+            ss << std::hex << std::setw(2) << std::setfill('0') << static_cast<int>(hash[i]);
+
+        std::memcpy(computed_hash, ss.str().c_str(), HASH_SIZE);
+        std::cout << "⚙️ COMPUTED HASH: " << computed_hash << std::endl;
+    }
+
+    extern int trash() { return 100; }
+}
\ No newline at end of file
diff --git a/shared/librelational_engine/library.h b/shared/librelational_engine/library.h
new file mode 100644
index 0000000..ebf8497
--- /dev/null
+++ b/shared/librelational_engine/library.h
@@ -0,0 +1,9 @@
+#ifndef MERKLECPP_STUB_LIBRARY_H
+#define MERKLECPP_STUB_LIBRARY_H
+
+#define HASH_SIZE 64
+
+extern void merkle_generate_root(char**, const int, char*);
+extern void compute_hash(char*, const char*);
+
+#endif //MERKLECPP_STUB_LIBRARY_H