closes #39574 (but we should probably look if we can make it work on Windows)

This test is failing on Windows currently:

11:59:47 --- FAIL: TestHealthKillContainer (8.12s)
11:59:47     health_test.go:57: assertion failed: error is not nil: Error response from daemon: Invalid signal: SIGUSR1

That test was added recently in #39454, but
rewritten in a commit in the same PR:
f8aef6a

In that rewrite, there were some changes:

• originally it was skipped on Windows, but the rewritten test doesn't have that skip:

  testRequires(c, DaemonIsLinux) // busybox doesn't work on Windows

• the original test used SIGINT, but the new one uses SIGUSR1

Analysis:

• The Error bubbles up from:

  moby/pkg/signal/signal.go

  Lines 29 to 44 in 8e610b2

  	// ParseSignal translates a string to a valid syscall signal.
  	// It returns an error if the signal map doesn't include the given signal.
  	func ParseSignal(rawSignal string) (syscall.Signal, error) {
  	s, err := strconv.Atoi(rawSignal)
  	if err == nil {
  	if s == 0 {
  	return -1, fmt.Errorf("Invalid signal: %s", rawSignal)
  	}
  	return syscall.Signal(s), nil
  	}
  	signal, ok := SignalMap[strings.TrimPrefix(strings.ToUpper(rawSignal), "SIG")]
  	if !ok {
  	return -1, fmt.Errorf("Invalid signal: %s", rawSignal)
  	}
  	return signal, nil
  	}

• Interestingly; ContainerKill should validate if a signal is valid for the given platform, but somehow we don't hit that part;

  moby/daemon/kill.go

  Lines 40 to 48 in f1b5612

  	func (daemon *Daemon) ContainerKill(name string, sig uint64) error {
  	container, err := daemon.GetContainer(name)
  	if err != nil {
  	return err
  	}
  	if sig != 0 && !signal.ValidSignalForPlatform(syscall.Signal(sig)) {
  	return fmt.Errorf("The %s daemon does not support signal %d", runtime.GOOS, sig)
  	}

• Windows only looks to support 2 signals currently

  moby/pkg/signal/signal_windows.go

  Lines 17 to 26 in 8e610b2

  	// SignalMap is a map of "supported" signals. As per the comment in GOLang's
  	// ztypes_windows.go: "More invented values for signals". Windows doesn't
  	// really support signals in any way, shape or form that Unix does.
  	//
  	// We have these so that docker kill can be used to gracefully (TERM) and
  	// forcibly (KILL) terminate a container on Windows.
  	var SignalMap = map[string]syscall.Signal{
  	"KILL": syscall.SIGKILL,
  	"TERM": syscall.SIGTERM,
  	}

• Upstream Golang looks to define SIGINT as well; https://github.com/golang/go/blob/77f9b2728eb08456899e6500328e00ec4829dddf/src/runtime/defs_windows.go#L44
• This looks like the current list of Signals upstream in Go; https://github.com/golang/sys/blob/3b58ed4ad3395d483fc92d5d14123ce2c3581fec/windows/types_windows.go#L52-L67

const (
	// More invented values for signals
	SIGHUP  = Signal(0x1)
	SIGINT  = Signal(0x2)
	SIGQUIT = Signal(0x3)
	SIGILL  = Signal(0x4)
	SIGTRAP = Signal(0x5)
	SIGABRT = Signal(0x6)
	SIGBUS  = Signal(0x7)
	SIGFPE  = Signal(0x8)
	SIGKILL = Signal(0x9)
	SIGSEGV = Signal(0xb)
	SIGPIPE = Signal(0xd)
	SIGALRM = Signal(0xe)
	SIGTERM = Signal(0xf)
)