portlist: use win32 calls instead of running netstat process [windows]

Turns out using win32 instead of shelling out to child processes is a
bit faster:

    name                  old time/op    new time/op    delta
    GetListIncremental-4     278ms ± 2%       0ms ± 7%  -99.93%  (p=0.000 n=8+10)

    name                  old alloc/op   new alloc/op   delta
    GetListIncremental-4     238kB ± 0%       9kB ± 0%  -96.12%  (p=0.000 n=10+8)

    name                  old allocs/op  new allocs/op  delta
    GetListIncremental-4     1.19k ± 0%     0.02k ± 0%  -98.49%  (p=0.000 n=10+10)

Fixes #3876 (sadly)

Change-Id: I1195ac5de21a8a8b3cdace5871d263e81aa27e91
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tailscaled/depaware.txt

@@ -226,7 +226,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/net/neterror                                   from tailscale.com/net/dns/resolver+
         tailscale.com/net/netknob                                    from tailscale.com/net/netns+
         tailscale.com/net/netns                                      from tailscale.com/derp/derphttp+
-     💣 tailscale.com/net/netstat                                    from tailscale.com/ipn/ipnserver
+     💣 tailscale.com/net/netstat                                    from tailscale.com/ipn/ipnserver+
         tailscale.com/net/netutil                                    from tailscale.com/ipn/ipnlocal+
         tailscale.com/net/packet                                     from tailscale.com/net/tstun+
         tailscale.com/net/ping                                       from tailscale.com/net/netcheck

portlist/netstat_exec.go

@@ -15,22 +15,12 @@ import (
 	"strings"
 )
 
-var osHideWindow func(*exec.Cmd) // non-nil on Windows; see portlist_windows.go
-
-// hideWindow returns c. On Windows it first sets SysProcAttr.HideWindow.
-func hideWindow(c *exec.Cmd) *exec.Cmd {
-	if osHideWindow != nil {
-		osHideWindow(c)
-	}
-	return c
-}
-
 func appendListeningPortsNetstat(base []Port, arg string) ([]Port, error) {
 	exe, err := exec.LookPath("netstat")
 	if err != nil {
 		return nil, fmt.Errorf("netstat: lookup: %v", err)
 	}
-	output, err := hideWindow(exec.Command(exe, arg)).Output()
+	output, err := exec.Command(exe, arg).Output()
 	if err != nil {
 		xe, ok := err.(*exec.ExitError)
 		stderr := ""

portlist/portlist_windows.go

@@ -5,39 +5,122 @@
 package portlist
 
 import (
-	"os/exec"
+	"path/filepath"
+	"strings"
 	"syscall"
 	"time"
 
 	"golang.org/x/sys/windows"
+	"tailscale.com/net/netstat"
 )
 
 // Forking on Windows is insanely expensive, so don't do it too often.
 const pollInterval = 5 * time.Second
 
-func appendListeningPorts(base []Port) ([]Port, error) {
-	// TODO(bradfitz): stop shelling out to netstat and use the
-	// net/netstat package instead. When doing so, be sure to filter
-	// out all of 127.0.0.0/8 and not just 127.0.0.1.
-	return appendListeningPortsNetstat(base, "-na")
+func init() {
+	newOSImpl = newWindowsImpl
 }
 
-func addProcesses(pl []Port) ([]Port, error) {
-	// OpenCurrentProcessToken instead of GetCurrentProcessToken,
-	// as GetCurrentProcessToken only works on Windows 8+.
-	tok, err := windows.OpenCurrentProcessToken()
+type famPort struct {
+	proto string
+	port  uint16
+	pid   uintptr
+}
+
+type windowsImpl struct {
+	known map[famPort]*portMeta // inode string => metadata
+}
+
+type portMeta struct {
+	port Port
+	keep bool
+}
+
+func newWindowsImpl() osImpl {
+	return &windowsImpl{
+		known: map[famPort]*portMeta{},
+	}
+}
+
+func (*windowsImpl) Close() error { return nil }
+
+func (im *windowsImpl) AppendListeningPorts(base []Port) ([]Port, error) {
+	// TODO(bradfitz): netstat.Get makes a bunch of garbage. Add an Append-style
+	// API to that package instead/additionally.
+	tab, err := netstat.Get()
 	if err != nil {
 		return nil, err
 	}
-	defer tok.Close()
-	if !tok.IsElevated() {
-		return appendListeningPortsNetstat(nil, "-na")
+
+	for _, pm := range im.known {
+		pm.keep = false
 	}
-	return appendListeningPortsNetstat(nil, "-nab")
+
+	ret := base
+	for _, e := range tab.Entries {
+		if e.State != "LISTEN" {
+			continue
+		}
+		if !e.Local.Addr().IsUnspecified() {
+			continue
+		}
+		fp := famPort{
+			proto: "tcp", // TODO(bradfitz): UDP too; add to netstat
+			port:  e.Local.Port(),
+			pid:   uintptr(e.Pid),
+		}
+		pm, ok := im.known[fp]
+		if ok {
+			pm.keep = true
+			continue
+		}
+		pm = &portMeta{
+			keep: true,
+			port: Port{
+				Proto:   "tcp",
+				Port:    e.Local.Port(),
+				Process: procNameOfPid(e.Pid),
+			},
+		}
+		im.known[fp] = pm
+	}
+
+	for k, m := range im.known {
+		if !m.keep {
+			delete(im.known, k)
+			continue
+		}
+		ret = append(ret, m.port)
+	}
+	return sortAndDedup(ret), nil
 }
 
-func init() {
-	osHideWindow = func(c *exec.Cmd) {
-		c.SysProcAttr = &syscall.SysProcAttr{HideWindow: true}
+func procNameOfPid(pid int) string {
+	const da = windows.PROCESS_QUERY_LIMITED_INFORMATION
+	h, err := syscall.OpenProcess(da, false, uint32(pid))
+	if err != nil {
+		return ""
 	}
+	defer syscall.CloseHandle(h)
+
+	var buf [512]uint16
+	var size = uint32(len(buf))
+	if err := windows.QueryFullProcessImageName(windows.Handle(h), 0, &buf[0], &size); err != nil {
+		return ""
+	}
+	name := filepath.Base(windows.UTF16ToString(buf[:]))
+	if name == "." {
+		return ""
+	}
+	name = strings.TrimSuffix(name, ".exe")
+	name = strings.TrimSuffix(name, ".EXE")
+	return name
+}
+
+func appendListeningPorts([]Port) ([]Port, error) {
+	panic("unused on windows; needed to compile for now")
+}
+
+func addProcesses([]Port) ([]Port, error) {
+	panic("unused on windows; needed to compile for now")
 }