tests/nixos: make the tarball-flakes test better reflect real use cases

In most real world cases, the Link header is set on the redirect, not on
the final file. This regressed in Lix earlier and while new unit tests
were added to cover it, this integration test should probably have also
caught it.

Source: https://git.lix.systems/lix-project/lix/commit/a3256a93759206dc64e597e2ad790ce582e84cf3

tests/nixos/tarball-flakes.nix

@@ -5,7 +5,7 @@ let
 
   root = pkgs.runCommand "nixpkgs-flake" {}
     ''
-      mkdir -p $out/stable
+      mkdir -p $out/{stable,tags}
 
       set -x
       dir=nixpkgs-${nixpkgs.shortRev}
@@ -14,9 +14,13 @@ let
       find $dir -print0 | xargs -0 touch -h -t ${builtins.substring 0 12 nixpkgs.lastModifiedDate}.${builtins.substring 12 2 nixpkgs.lastModifiedDate} --
       tar cfz $out/stable/${nixpkgs.rev}.tar.gz $dir --hard-dereference
 
-      echo 'Redirect "/latest.tar.gz" "/stable/${nixpkgs.rev}.tar.gz"' > $out/.htaccess
-
-      echo 'Header set Link "<http://localhost/stable/${nixpkgs.rev}.tar.gz?rev=${nixpkgs.rev}&revCount=1234>; rel=\"immutable\""' > $out/stable/.htaccess
+      # Set the "Link" header on the redirect but not the final response to
+      # simulate an S3-like serving environment where the final host cannot set
+      # arbitrary headers.
+      cat >$out/tags/.htaccess <<EOF
+      Redirect "/tags/latest.tar.gz" "/stable/${nixpkgs.rev}.tar.gz"
+      Header always set Link "<http://localhost/stable/${nixpkgs.rev}.tar.gz?rev=${nixpkgs.rev}&revCount=1234>; rel=\"immutable\""
+      EOF
     '';
 in
 
@@ -59,7 +63,7 @@ in
 
     machine.wait_for_unit("httpd.service")
 
-    out = machine.succeed("nix flake metadata --json http://localhost/latest.tar.gz")
+    out = machine.succeed("nix flake metadata --json http://localhost/tags/latest.tar.gz")
     print(out)
     info = json.loads(out)
 
@@ -71,14 +75,15 @@ in
     assert info["revCount"] == 1234
 
     # Check that fetching with rev/revCount/narHash succeeds.
-    machine.succeed("nix flake metadata --json http://localhost/latest.tar.gz?rev=" + info["revision"])
-    machine.succeed("nix flake metadata --json http://localhost/latest.tar.gz?revCount=" + str(info["revCount"]))
-    machine.succeed("nix flake metadata --json http://localhost/latest.tar.gz?narHash=" + info["locked"]["narHash"])
+
+    machine.succeed("nix flake metadata --json http://localhost/tags/latest.tar.gz?rev=" + info["revision"])
+    machine.succeed("nix flake metadata --json http://localhost/tags/latest.tar.gz?revCount=" + str(info["revCount"]))
+    machine.succeed("nix flake metadata --json http://localhost/tags/latest.tar.gz?narHash=" + info["locked"]["narHash"])
 
     # Check that fetching fails if we provide incorrect attributes.
-    machine.fail("nix flake metadata --json http://localhost/latest.tar.gz?rev=493300eb13ae6fb387fbd47bf54a85915acc31c0")
-    machine.fail("nix flake metadata --json http://localhost/latest.tar.gz?revCount=789")
-    machine.fail("nix flake metadata --json http://localhost/latest.tar.gz?narHash=sha256-tbudgBSg+bHWHiHnlteNzN8TUvI80ygS9IULh4rklEw=")
+    machine.fail("nix flake metadata --json http://localhost/tags/latest.tar.gz?rev=493300eb13ae6fb387fbd47bf54a85915acc31c0")
+    machine.fail("nix flake metadata --json http://localhost/tags/latest.tar.gz?revCount=789")
+    machine.fail("nix flake metadata --json http://localhost/tags/latest.tar.gz?narHash=sha256-tbudgBSg+bHWHiHnlteNzN8TUvI80ygS9IULh4rklEw=")
   '';
 
 }