From c632bcf1e85dab2183b2d54c0e82e2fecc905cb0 Mon Sep 17 00:00:00 2001
From: Matthew Oliver <mjo@google.com>
Date: Fri, 10 Apr 2026 18:20:58 -0700
Subject: [PATCH] The wsus.Init function now returns an error if an empty slice
 is provided for the WSUS servers, instead of defaulting to Windows Update.
 Added a test case to cover this scenario.

PiperOrigin-RevId: 897979585
---
 README.md            | 20 ++++++++++++++------
 wsus.go              | 26 +++++++++++++++++++++++++-
 wsus/wsus_test.go    |  7 +++++++
 wsus/wsus_windows.go |  3 +--
 4 files changed, 47 insertions(+), 9 deletions(-)

diff --git a/README.md b/README.md
index 0831f01..4f63909 100644
--- a/README.md
+++ b/README.md
@@ -145,18 +145,26 @@ Uninstall Cabbie service:
 
 ### Wsus
 
-Initializes the wsus server configuration and restarts the windows update
-service. If `--wsus_servers` flag is provided, Cabbie will check for
+Initializes the WSUS server configuration and restarts the Windows Update
+service. If the `--wsus_servers` flag is provided, Cabbie checks for
 connectivity to Windows Update endpoints. If it fails to connect, or if
-`--force` is true, it will write the provided list of servers to the
-`WsusServers` value in `HKLM:\SOFTWARE\Google\Cabbie` before initializing WSUS
-configuration and restarting the Windows Update service.
+`--force` is true, it writes the provided list of servers to the
+`WSUSServers` value in `HKLM:\SOFTWARE\Google\Cabbie`.
+
+By default, Cabbie pings the WSUS servers to find the fastest one. If `--force`
+is true, it skips this verification and unconditionally sets the first server.
+If no WSUS servers are reachable and `--force` is not active, it reverts to
+Windows Update and displays a warning.
+
+If no servers are provided and none are configured in the registry, a helpful
+message is displayed and the command will fail.
 
 `cabbie wsus [--wsus_servers=<server1>,<server2>] [--force]`
 
 Example:
 
-`cabbie wsus --wsus_servers=server1.google.com,server2.google.com`
+`"C:\Program Files\Google\Cabbie\cabbie.exe" wsus
+--wsus_servers="wsus1.example.com,wsus2.example.com"`
 
 `cabbie wsus`
 
diff --git a/wsus.go b/wsus.go
index 456532b..88fb2bf 100644
--- a/wsus.go
+++ b/wsus.go
@@ -99,13 +99,37 @@ func (c *wsusCmd) Execute(ctx context.Context, f *flag.FlagSet, args ...any) sub
 		}
 	}
 
-	if _, err := wsus.Init(config.WSUSServers); err != nil {
+	if len(config.WSUSServers) == 0 {
+		fmt.Println("No WSUS servers configured. Please provide servers using the --wsus_servers flag.")
+		return subcommands.ExitFailure
+	}
+
+	var w *wsus.WSUS
+	var err error
+
+	if c.force {
+		deck.Info("Forcing WSUS configuration, skipping verification.")
+		w = &wsus.WSUS{Servers: config.WSUSServers}
+		err = w.Set(0)
+		if err == nil {
+			w.ServerSelection = wsus.ManagedServer
+		}
+	} else {
+		w, err = wsus.Init(config.WSUSServers)
+	}
+
+	if err != nil {
 		msg := fmt.Sprintf("Failed to initialize WSUS: %v\n", err)
 		deck.ErrorfA("%s", msg).With(eventID(cablib.EvtErrMisc)).Go()
 		fmt.Print(msg)
 		return subcommands.ExitFailure
 	}
 
+	if w.ServerSelection == wsus.WindowsUpdate && !c.force {
+		deck.Warning("No WSUS servers were reachable. Reverted to Windows Update.")
+		fmt.Println("Warning: No WSUS servers were reachable. Reverted to Windows Update.")
+	}
+
 	deck.InfoA("WSUS configuration refreshed, restarting wuauserv to apply settings.").With(eventID(cablib.EvtMisc)).Go()
 	if err := helpers.RestartService("wuauserv"); err != nil {
 		msg := fmt.Sprintf("Failed to restart wuauserv: %v\n", err)
diff --git a/wsus/wsus_test.go b/wsus/wsus_test.go
index 21128eb..75d7da3 100644
--- a/wsus/wsus_test.go
+++ b/wsus/wsus_test.go
@@ -59,3 +59,10 @@ func TestSet(t *testing.T) {
 		}
 	}
 }
+
+func TestInit_EmptyServers(t *testing.T) {
+	_, err := Init([]string{})
+	if err == nil {
+		t.Error("Init([]) expected error for empty servers list, got nil")
+	}
+}
diff --git a/wsus/wsus_windows.go b/wsus/wsus_windows.go
index 37222ea..fd8bb16 100644
--- a/wsus/wsus_windows.go
+++ b/wsus/wsus_windows.go
@@ -59,8 +59,7 @@ func Init(servers []string) (*WSUS, error) {
 	var err error
 
 	if len(servers) == 0 {
-		w.ServerSelection = WindowsUpdate
-		return &w, w.Clear()
+		return nil, fmt.Errorf("servers list cannot be empty")
 	}
 
 	wlog, err = eventlog.Open("Cabbie WSUS")