generate tarball.nix with a script

Signed-off-by: Xe <me@christine.website>

flake.nix

@@ -25,25 +25,21 @@
         };
         version = builtins.substring 0 8 self.lastModifiedDate;
       in {
-        packages = rec {
+        packages = let tsmeta = import ./tarball.nix; in rec {
           imagebuilder = pkgs.buildGoModule {
             pname = "taildeck-imagebuilder";
-            inherit version;
+            inherit (tsmeta) version;
             src = ./.;
 
             vendorSha256 =
               "sha256-pQpattmS9VmO3ZIQUFn66az8GSmB4IvYhTTCFn6SUmo=";
           };
 
-          tsTarball = builtins.fetchurl {
+          tsTarball = tsmeta.tarball;
-            url =
-              "https://pkgs.tailscale.com/stable/tailscale_1.24.2_amd64.tgz";
-            sha256 = "1b697g694vigzmv5q48l1d3pjc9l5gwzazggnfi7z9prb9cvlnx2";
-          };
 
           image = pkgs.stdenv.mkDerivation {
             pname = "tailscale-image";
-            version = "1.24.2";
+            inherit (tsmeta) version;
             buildInputs = with pkgs; [ squashfsTools imagebuilder ];
             phases = "installPhase";
 

gen_tarball.sh

@@ -0,0 +1,17 @@
+#!/usr/bin/env nix-shell
+#! nix-shell -p curl -p jq -p nix -i bash
+
+set -euo pipefail
+
+version="$(curl https://pkgs.tailscale.com/stable/?mode=json | jq .Tarballs.amd64 -r)"
+url="https://pkgs.tailscale.com/stable/${version}"
+shasum="$(nix-prefetch-url "${url}")"
+
+rm -f tarball.nix
+echo "{
+  version = \"$(echo ${version} | cut -d_ -f2)\";
+  tarball = builtins.fetchurl {
+    url = \"${url}\";
+    sha256 = \"${shasum}\";
+  };
+}" >> tarball.nix

tarball.nix

@@ -0,0 +1,7 @@
+{
+  version = "1.24.2";
+  tarball = builtins.fetchurl {
+    url = "https://pkgs.tailscale.com/stable/tailscale_1.24.2_amd64.tgz";
+    sha256 = "1b697g694vigzmv5q48l1d3pjc9l5gwzazggnfi7z9prb9cvlnx2";
+  };
+}