bastion 0.53.2

client-go/console_windows.go

@@ -0,0 +1,53 @@
+//go:build windows
+
+package main
+
+import (
+	"os/exec"
+
+	"golang.org/x/sys/windows"
+)
+
+// hideConsole stops a child process from opening a console window.
+//
+// THE SYMPTOM: two flashing blue screens, seen again and again. Two, and
+// they flash, and they come back — that is the shape of this bug exactly.
+// Three Windows paths shell out to powershell.exe:
+//
+//	schedulers_windows.go:44   Get-ScheduledTask        (the scheduled-job inventory)
+//	origin_windows.go:79       Win32_Service 'Schedule' (the scheduler's own pid)
+//	computer_tree_windows.go:97 UIAutomation             (on demand, not on the beat)
+//
+// The first two sit on the heartbeat path and are each cached for
+// schedCacheFor = 10 minutes (schedulers.go:435), so they expire together and
+// respawn together: TWO windows, every ten minutes, for ever. The third only
+// runs when the host asks to read the screen.
+//
+// WHY IT ONLY STARTED NOW, AND WHY IT IS 0.24.0's DOING. A console child
+// INHERITS its parent's console when the parent has one — started from a
+// terminal, these three were invisible for as long as they have existed. 0.24.0
+// added relaunchAfterUpdate, which restarts the bastion with DETACHED_PROCESS
+// (relaunch_windows.go:47) because Windows has no service to do it. A detached
+// process has NO console, so there is none to inherit, and Windows allocates a
+// fresh one for each child — which is a window, on screen, in front of whatever
+// the user was doing. The same commit that made the bastion survive an update
+// is what made its shell-outs visible.
+//
+// CREATE_NO_WINDOW is the correct flag for a child whose output we capture and
+// whose input we never supply: it still gets a console object, so PowerShell
+// runs normally, but no window is created for it. HideWindow alone would ask
+// the child politely to start minimised and PowerShell does not always honour
+// it. Both are set because they cost nothing together.
+//
+// Not applied to relaunchAfterUpdate: that one sets DETACHED_PROCESS already
+// and must keep it — it is the flag that lets the replacement outlive us.
+func hideConsole(cmd *exec.Cmd) {
+	if cmd == nil {
+		return
+	}
+	if cmd.SysProcAttr == nil {
+		cmd.SysProcAttr = &windows.SysProcAttr{}
+	}
+	cmd.SysProcAttr.HideWindow = true
+	cmd.SysProcAttr.CreationFlags |= windows.CREATE_NO_WINDOW
+}