add forwarder service

Co-authored-by: Gelu Vrabie <gelu@exolabs.net>

flake.nix

@@ -1,46 +1,64 @@
 {
-  description = "The development environment for Exo";
+  description = "Exo development flake";
 
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
   };
 
-  outputs = { self, nixpkgs }:
-    let
-      supportedSystems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];
-      forAllSystems = nixpkgs.lib.genAttrs supportedSystems;
-    in
-    {
-      devShells = forAllSystems (system:
-        let
-          pkgs = import nixpkgs { inherit system; };
-        in
-        {
-          default = pkgs.mkShell {
-            packages = [
-              pkgs.python313
-              pkgs.uv
-              pkgs.just
-              pkgs.protobuf
-              pkgs.rustc
-              pkgs.cargo
-              pkgs.basedpyright
-              pkgs.ruff
-            ];
-          };
-        }
-      );
-      
-      apps = forAllSystems (system:
-        let
-          pkgs = import nixpkgs { inherit system; };
-        in
-        {
-          python-lsp = {
-            type = "app";
-            program = "${pkgs.basedpyright}/bin/basedpyright-langserver";
-          };
-        }
-      );
-    };
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs { inherit system; };
+
+        # Go 1.23 compiler – align with go.mod
+        go = pkgs.go_1_23;
+
+        # Build the networking/forwarder Go utility.
+        forwarder = pkgs.buildGoModule {
+          pname = "exo-forwarder";
+          version = "0.1.0";
+          src = ./networking/forwarder;
+
+          vendorHash = "sha256-BXIGg2QYqHDz2TNe8hLAGC6jVlffp9766H+WdkkuVgA=";
+
+          # Only the main package at the repository root needs building.
+          subPackages = [ "." ];
+        };
+      in
+      {
+        packages = {
+          inherit forwarder;
+          default = forwarder;
+        };
+
+        apps.forwarder = {
+          type = "app";
+          program = "${forwarder}/bin/forwarder";
+        };
+        apps.python-lsp = {
+          type = "app";
+          program = "${pkgs.basedpyright}/bin/basedpyright-langserver";
+        };
+        apps.default = self.apps.${system}.forwarder;
+
+        devShells.default = pkgs.mkShell {
+          packages = [
+            pkgs.python313
+            pkgs.uv
+            pkgs.just
+            pkgs.protobuf
+            pkgs.rustc
+            pkgs.cargo
+            pkgs.basedpyright
+            pkgs.ruff
+            go
+          ];
+
+          shellHook = ''
+            export GOPATH=$(mktemp -d)
+          '';
+        };
+      }
+    );
 }