Reuse an existing install or backup in router-setup

router-setup finds earlier installs and router-backup-*.tar.gz files and
reinstalls them with everything in /var/lib/router carried over.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AeFqV9dZrK6nipHkPfyM4F

tests/setup.nix

@@ -2,6 +2,12 @@
 # LAN address, web UI password), builds the router offline and installs it.
 # The installed box must come up with those settings, serve the web UI with
 # that password, and rebuild to exactly itself.
+#
+# Then the same box is reinstalled twice, everything carrying over (settings
+# with an unapplied change, passwords, the web UI's certificate): once from
+# the installed disk itself, once from a web UI backup on a USB stick after
+# the disk was wiped. The settings name an interface this machine lacks, so
+# setup asks which one takes its place.
 { self, pkgs }:
 let
   common = import ./common.nix;
@@ -35,6 +41,15 @@ let
 
     /dev/vda
   '';
+
+  # Reinstall the configuration found first, on /dev/vda; eth1 replaces the
+  # missing enp9s0.
+  reuseAnswers = pkgs.writeText "reuse-answers" ''
+    1
+    /dev/vda
+    eth1
+    /dev/vda
+  '';
 in
 pkgs.testers.runNixOSTest {
   name = "router-setup";
@@ -48,6 +63,7 @@ pkgs.testers.runNixOSTest {
           (self.lib.setupModule { inherit local; })
           common.tools
         ];
+        environment.systemPackages = [ pkgs.dosfstools ];
         environment.etc."router-test-local.nix".source = local;
         # The interfaces router-setup offers.
         virtualisation.vlans = [
@@ -55,8 +71,15 @@ pkgs.testers.runNixOSTest {
           2
         ];
         virtualisation.fileSystems."/".autoFormat = true;
-        virtualisation.emptyDiskImages = [ 1024 ];
+        # vdb: the installer's root; vdc: a USB stick for a backup.
+        virtualisation.emptyDiskImages = [
+          1024
+          64
+        ];
         virtualisation.rootDevice = "/dev/vdb";
+        # The installer boots several times on the same root disk, whose Nix
+        # database would list store paths left behind in a tmpfs overlay.
+        virtualisation.writableStoreUseTmpfs = false;
         nix.settings.substituters = lib.mkForce [ ];
       };
 
@@ -118,5 +141,60 @@ pkgs.testers.runNixOSTest {
     with subtest("the box rebuilds to exactly the installed system"):
         out = target.succeed("router-apply 2>&1")
         assert "no changes" in out, out
+
+    def install_again(prepare=None):
+        installer.start()
+        installer.wait_for_unit("multi-user.target")
+        if prepare:
+            prepare()
+        out = installer.succeed("router-setup --local /etc/router-test-local.nix < ${reuseAnswers} 2>&1")
+        installer.shutdown()
+        target.start()
+        target.wait_for_unit("multi-user.target")
+        return out
+
+    def check_carried_over():
+        assert target.succeed("hostname").strip() == "gw2"
+        settings = target.succeed("cat /var/lib/router/config/settings.json")
+        assert '"enp9s0"' not in settings and '"eth1"' in settings, settings
+        assert target.succeed("sha256sum /var/lib/router/webui/cert.pem").split()[0] == cert
+        target.wait_for_unit("router-webui.service")
+        target.wait_until_succeeds("curl -sk -o /dev/null https://127.0.0.1/login")
+        code = target.succeed("curl -sk -o /dev/null -w '%{http_code}' -d password=hunter2hunter2 https://127.0.0.1/login")
+        assert code == "303", code
+        assert "no changes" in target.succeed("router-apply 2>&1")
+
+    with subtest("reinstalling from the installed disk carries everything over"):
+        # Saved but not applied; and an interface this machine does not have.
+        target.succeed("sed -i 's/\"hostName\": \"gw\"/\"hostName\": \"gw2\"/; s/\"interface\": \"eth1\"/\"interface\": \"enp9s0\"/'"
+                       " /var/lib/router/config/settings.json")
+        cert = target.succeed("sha256sum /var/lib/router/webui/cert.pem").split()[0]
+        # A backup from the web UI, for the next subtest.
+        target.succeed("curl -sk -c /tmp/jar -o /dev/null -d password=hunter2hunter2 https://127.0.0.1/login")
+        token = target.succeed("curl -sk -b /tmp/jar https://127.0.0.1/advanced | grep -o 'name=\"csrf\" value=\"[^\"]*' | head -1 | cut -d'\"' -f4").strip()
+        target.succeed(f"curl -sfk -b /tmp/jar -d csrf={token} -o /tmp/router-backup-gw2.tar.gz https://127.0.0.1/backup")
+        assert "router/config/settings.json" in target.succeed("tar -tzf /tmp/router-backup-gw2.tar.gz").split()
+        # The installed system has no shared folder with the host: pass it as text.
+        backup = target.succeed("base64 -w0 /tmp/router-backup-gw2.tar.gz").strip()
+        target.shutdown()
+
+        out = install_again()
+        assert "installed on /dev/vda2: gw2" in out, out
+        assert "no interface enp9s0 (WAN)" in out, out
+        check_carried_over()
+
+    with subtest("a backup on a USB stick is found after the disk was wiped"):
+        target.shutdown()
+
+        def wipe_and_plug_in_stick():
+            installer.succeed("wipefs -a /dev/vda2 /dev/vda1 /dev/vda && blockdev --rereadpt /dev/vda && udevadm settle")
+            installer.succeed("mkfs.vfat /dev/vdc && udevadm settle && mount /dev/vdc /mnt")
+            installer.succeed(f"echo {backup} | base64 -d > /mnt/router-backup-gw2.tar.gz")
+            installer.succeed("umount /mnt")
+
+        out = install_again(wipe_and_plug_in_stick)
+        assert "backup router-backup-gw2.tar.gz on /dev/vdc: gw2" in out, out
+        assert "installed on" not in out, out
+        check_carried_over()
   '';
 }