Add a test for nix copy over ssh

Check that nix copy can copy stuff, refuses to copy unsigned paths by
default, and doesn't hide the ssh password prompt.

flake.nix

@@ -577,6 +577,8 @@
 
         tests.nix-copy-closure = runNixOSTestFor "x86_64-linux" ./tests/nixos/nix-copy-closure.nix;
 
+        tests.nix-copy = runNixOSTestFor "x86_64-linux" ./tests/nixos/nix-copy.nix;
+
         tests.nssPreload = runNixOSTestFor "x86_64-linux" ./tests/nixos/nss-preload.nix;
 
         tests.githubFlakes = runNixOSTestFor "x86_64-linux" ./tests/nixos/github-flakes.nix;

src/libmain/progress-bar.cc

@@ -129,6 +129,7 @@ public:
     void resume() override {
         state_.lock()->paused = false;
         writeToStderr("\r\e[K");
+        state_.lock()->haveUpdate = true;
         updateCV.notify_one();
     }
 
@@ -350,9 +351,8 @@ public:
     {
         auto nextWakeup = std::chrono::milliseconds::max();
 
-        if (state.paused) return nextWakeup;
         state.haveUpdate = false;
-        if (!state.active) return nextWakeup;
+        if (state.paused || !state.active) return nextWakeup;
 
         std::string line;
 

tests/nixos/nix-copy.nix

@@ -0,0 +1,85 @@
+# Test that ‘nix copy’ works over ssh.
+
+{ lib, config, nixpkgs, hostPkgs, ... }:
+
+let
+  pkgs = config.nodes.client.nixpkgs.pkgs;
+
+  pkgA = pkgs.cowsay;
+  pkgB = pkgs.wget;
+  pkgC = pkgs.hello;
+  pkgD = pkgs.tmux;
+
+in {
+  name = "nix-copy";
+
+  enableOCR = true;
+
+  nodes =
+    { client =
+        { config, lib, pkgs, ... }:
+        { virtualisation.writableStore = true;
+          virtualisation.additionalPaths = [ pkgA pkgD.drvPath ];
+          nix.settings.substituters = lib.mkForce [ ];
+          nix.settings.experimental-features = [ "nix-command" ];
+          services.getty.autologinUser = "root";
+        };
+
+      server =
+        { config, pkgs, ... }:
+        { services.openssh.enable = true;
+          services.openssh.permitRootLogin = "yes";
+					users.users.root.password = "foobar";
+          virtualisation.writableStore = true;
+          virtualisation.additionalPaths = [ pkgB pkgC ];
+        };
+    };
+
+  testScript = { nodes }: ''
+    # fmt: off
+    import subprocess
+
+    # Create an SSH key on the client.
+    subprocess.run([
+      "${pkgs.openssh}/bin/ssh-keygen", "-t", "ed25519", "-f", "key", "-N", ""
+    ], capture_output=True, check=True)
+
+    start_all()
+
+    server.wait_for_unit("sshd")
+    client.wait_for_unit("network.target")
+    client.wait_for_unit("getty@tty1.service")
+    client.wait_for_text("]#")
+
+    # Copy the closure of package A from the client to the server using password authentication,
+    # and check that all prompts are visible
+    server.fail("nix-store --check-validity ${pkgA}")
+    client.send_chars("nix copy --to ssh://server ${pkgA} >&2; echo done\n")
+    client.wait_for_text("continue connecting")
+    client.send_chars("yes\n")
+    client.wait_for_text("Password:")
+    client.send_chars("foobar\n")
+    client.wait_for_text("done")
+    server.succeed("nix-store --check-validity ${pkgA}")
+
+    client.copy_from_host("key", "/root/.ssh/id_ed25519")
+    client.succeed("chmod 600 /root/.ssh/id_ed25519")
+
+    # Install the SSH key on the server.
+    server.copy_from_host("key.pub", "/root/.ssh/authorized_keys")
+    server.succeed("systemctl restart sshd")
+    client.succeed(f"ssh -o StrictHostKeyChecking=no {server.name} 'echo hello world'")
+
+    # Copy the closure of package B from the server to the client, using ssh-ng.
+    client.fail("nix-store --check-validity ${pkgB}")
+    # Shouldn't download untrusted paths by default
+    client.fail("nix copy --from ssh-ng://server ${pkgB} >&2")
+    client.succeed("nix copy --no-check-sigs --from ssh-ng://server ${pkgB} >&2")
+    client.succeed("nix-store --check-validity ${pkgB}")
+
+    # Copy the derivation of package D's derivation from the client to the server.
+    server.fail("nix-store --check-validity ${pkgD.drvPath}")
+    client.succeed("nix copy --derivation --to ssh://server ${pkgD.drvPath} >&2")
+    server.succeed("nix-store --check-validity ${pkgD.drvPath}")
+  '';
+}