Listen for printer changes and refresh the printers list when it happ…

…ens (#361)

* Listen for printer changes and refresh the printers list when such happen.

This reduces the delay after new printer is added until it shows up
as a printer avaiable for printing in Goolge Cloud Print on Windows.

Timer based refreshes still need to happen due to other sources of
printers eg Privet etc.

* Adjust the code to the commited version of golang.org/x/sys/windows/svc.

gcp-windows-connector/gcp-windows-connector.go

@@ -171,6 +171,16 @@ func (service *service) Execute(args []string, r <-chan svc.ChangeRequest, s cha
 	}
 	defer pm.Quit()
 
+	statusHandle := svc.StatusHandle()
+	if statusHandle != 0 {
+		err = ws.StartPrinterNotifications(statusHandle)
+		if err != nil {
+			log.Error(err)
+		} else {
+			log.Info("Successfully registered for device notifications.")
+		}
+	}
+
 	if config.CloudPrintingEnable {
 		if config.LocalPrintingEnable {
 			log.Infof("Ready to rock as proxy '%s' and in local mode", config.ProxyName)
@@ -198,6 +208,15 @@ func (service *service) Execute(args []string, r <-chan svc.ChangeRequest, s cha
 
 			return false, 0
 
+		case svc.DeviceEvent:
+			log.Infof("Printers change notification received %d.", request.EventType)
+			// Delay the action to let the OS finish the process or we might
+			// not see the new printer. Even if we miss it eventually the timed updates
+			// will pick it up.
+			time.AfterFunc(time.Second*5, func() {
+				pm.SyncPrinters(false)
+			})
+
 		default:
 			log.Errorf("Received unsupported service command from service control manager: %d", request.Cmd)
 		}

lib/printer.go

@@ -239,7 +239,7 @@ func FilterBlacklistPrinters(printers []Printer, list map[string]interface{}) []
 
 func FilterWhitelistPrinters(printers []Printer, list map[string]interface{}) []Printer {
 	if len(list) == 0 {
-		return printers; // Empty whitelist means don't use whitelist
+		return printers // Empty whitelist means don't use whitelist
 	}
 
 	return filterPrinters(printers, list, true)

lib/printer_test.go

@@ -9,22 +9,22 @@ https://developers.google.com/open-source/licenses/bsd
 package lib
 
 import (
-	"testing"
 	"reflect"
+	"testing"
 )
 
 func TestFilterBlacklistPrinters(t *testing.T) {
-	printers := []Printer {
+	printers := []Printer{
 		{Name: "Stay1"},
 		{Name: "Go1"},
 		{Name: "Go2"},
 		{Name: "Stay2"},
 	}
-	blacklist := map[string]interface{} {
+	blacklist := map[string]interface{}{
 		"Go1": "",
 		"Go2": "",
 	}
-	correctFilteredPrinters := []Printer {
+	correctFilteredPrinters := []Printer{
 		{Name: "Stay1"},
 		{Name: "Stay2"},
 	}
@@ -37,17 +37,17 @@ func TestFilterBlacklistPrinters(t *testing.T) {
 }
 
 func TestFilterWhitelistPrinters(t *testing.T) {
-	printers := []Printer {
+	printers := []Printer{
 		{Name: "Stay1"},
 		{Name: "Go1"},
 		{Name: "Go2"},
 		{Name: "Stay2"},
 	}
-	whitelist := map[string]interface{} {
+	whitelist := map[string]interface{}{
 		"Stay1": "",
 		"Stay2": "",
 	}
-	correctFilteredPrinters := []Printer {
+	correctFilteredPrinters := []Printer{
 		{Name: "Stay1"},
 		{Name: "Stay2"},
 	}

manager/printermanager.go

@@ -105,7 +105,7 @@ func NewPrinterManager(native NativePrintSystem, gcp *gcp.GoogleCloudPrint, priv
 	// Sync once before returning, to make sure things are working.
 	// Ignore privet updates this first time because Privet always starts
 	// with zero printers.
-	if err = pm.syncPrinters(true); err != nil {
+	if err = pm.SyncPrinters(true); err != nil {
 		return nil, err
 	}
 
@@ -146,7 +146,7 @@ func (pm *PrinterManager) syncPrintersPeriodically(interval time.Duration) {
 		for {
 			select {
 			case <-t.C:
-				if err := pm.syncPrinters(false); err != nil {
+				if err := pm.SyncPrinters(false); err != nil {
 					log.Error(err)
 				}
 				t.Reset(interval)
@@ -158,7 +158,7 @@ func (pm *PrinterManager) syncPrintersPeriodically(interval time.Duration) {
 	}()
 }
 
-func (pm *PrinterManager) syncPrinters(ignorePrivet bool) error {
+func (pm *PrinterManager) SyncPrinters(ignorePrivet bool) error {
 	log.Info("Synchronizing printers, stand by")
 
 	// Get current snapshot of native printers.
@@ -442,7 +442,7 @@ func (pm *PrinterManager) printJob(nativePrinterName, filename, title, user, job
 	}
 }
 
-func (pm *PrinterManager)releaseJob(printerName string, nativeJobID uint32, jobID string) {
+func (pm *PrinterManager) releaseJob(printerName string, nativeJobID uint32, jobID string) {
 	if err := pm.native.ReleaseJob(printerName, nativeJobID); err != nil {
 		log.ErrorJob(jobID, err)
 	}

winspool/win32.go

@@ -15,33 +15,37 @@ import (
 	"strings"
 	"syscall"
 	"unsafe"
+
+	"golang.org/x/sys/windows"
 )
 
 var (
 	gdi32    = syscall.MustLoadDLL("gdi32.dll")
 	kernel32 = syscall.MustLoadDLL("kernel32.dll")
 	ntoskrnl = syscall.MustLoadDLL("ntoskrnl.exe")
 	winspool = syscall.MustLoadDLL("winspool.drv")
-
-	abortDocProc           = gdi32.MustFindProc("AbortDoc")
-	closePrinterProc       = winspool.MustFindProc("ClosePrinter")
-	createDCProc           = gdi32.MustFindProc("CreateDCW")
-	deleteDCProc           = gdi32.MustFindProc("DeleteDC")
-	deviceCapabilitiesProc = winspool.MustFindProc("DeviceCapabilitiesW")
-	documentPropertiesProc = winspool.MustFindProc("DocumentPropertiesW")
-	endDocProc             = gdi32.MustFindProc("EndDoc")
-	endPageProc            = gdi32.MustFindProc("EndPage")
-	enumPrintersProc       = winspool.MustFindProc("EnumPrintersW")
-	getDeviceCapsProc      = gdi32.MustFindProc("GetDeviceCaps")
-	getJobProc             = winspool.MustFindProc("GetJobW")
-	openPrinterProc        = winspool.MustFindProc("OpenPrinterW")
-	resetDCProc            = gdi32.MustFindProc("ResetDCW")
-	rtlGetVersionProc      = ntoskrnl.MustFindProc("RtlGetVersion")
-	setGraphicsModeProc    = gdi32.MustFindProc("SetGraphicsMode")
-	setJobProc             = winspool.MustFindProc("SetJobW")
-	setWorldTransformProc  = gdi32.MustFindProc("SetWorldTransform")
-	startDocProc           = gdi32.MustFindProc("StartDocW")
-	startPageProc          = gdi32.MustFindProc("StartPage")
+	user32   = syscall.MustLoadDLL("user32.dll")
+
+	abortDocProc                   = gdi32.MustFindProc("AbortDoc")
+	closePrinterProc               = winspool.MustFindProc("ClosePrinter")
+	createDCProc                   = gdi32.MustFindProc("CreateDCW")
+	deleteDCProc                   = gdi32.MustFindProc("DeleteDC")
+	deviceCapabilitiesProc         = winspool.MustFindProc("DeviceCapabilitiesW")
+	documentPropertiesProc         = winspool.MustFindProc("DocumentPropertiesW")
+	endDocProc                     = gdi32.MustFindProc("EndDoc")
+	endPageProc                    = gdi32.MustFindProc("EndPage")
+	enumPrintersProc               = winspool.MustFindProc("EnumPrintersW")
+	getDeviceCapsProc              = gdi32.MustFindProc("GetDeviceCaps")
+	getJobProc                     = winspool.MustFindProc("GetJobW")
+	openPrinterProc                = winspool.MustFindProc("OpenPrinterW")
+	resetDCProc                    = gdi32.MustFindProc("ResetDCW")
+	rtlGetVersionProc              = ntoskrnl.MustFindProc("RtlGetVersion")
+	setGraphicsModeProc            = gdi32.MustFindProc("SetGraphicsMode")
+	setJobProc                     = winspool.MustFindProc("SetJobW")
+	setWorldTransformProc          = gdi32.MustFindProc("SetWorldTransform")
+	startDocProc                   = gdi32.MustFindProc("StartDocW")
+	startPageProc                  = gdi32.MustFindProc("StartPage")
+	registerDeviceNotificationProc = user32.MustFindProc("RegisterDeviceNotificationW")
 )
 
 // System error codes.
@@ -798,8 +802,8 @@ func (hPrinter HANDLE) SetJobUserName(jobID int32, userName string) error {
 		return err
 	}
 
-	ji1.pUserName = pUserName;
-	ji1.position = 0; // To prevent a possible access denied error (0 is JOB_POSITION_UNSPECIFIED)
+	ji1.pUserName = pUserName
+	ji1.position = 0 // To prevent a possible access denied error (0 is JOB_POSITION_UNSPECIFIED)
 	err = hPrinter.SetJobInfo1(jobID, ji1)
 	if err != nil {
 		return err
@@ -1196,3 +1200,49 @@ func GetWindowsVersion() string {
 
 	return version
 }
+
+type GUID struct {
+	Data1 uint32
+	Data2 uint16
+	Data3 uint16
+	Data4 [8]byte
+}
+
+var PRINTERS_DEVICE_CLASS = GUID{
+	0x4d36e979,
+	0xe325,
+	0x11ce,
+	[8]byte{0xbf, 0xc1, 0x08, 0x00, 0x2b, 0xe1, 0x03, 0x18},
+}
+
+type DevBroadcastDevinterface struct {
+	dwSize       uint32
+	dwDeviceType uint32
+	dwReserved   uint32
+	classGuid    GUID
+	szName       uint16
+}
+
+const (
+	DEVICE_NOTIFY_SERVICE_HANDLE        = 1
+	DEVICE_NOTIFY_ALL_INTERFACE_CLASSES = 4
+
+	DBT_DEVTYP_DEVICEINTERFACE = 5
+)
+
+func RegisterDeviceNotification(handle windows.Handle) error {
+
+	var notificationFilter DevBroadcastDevinterface
+	notificationFilter.dwSize = uint32(unsafe.Sizeof(notificationFilter))
+	notificationFilter.dwDeviceType = DBT_DEVTYP_DEVICEINTERFACE
+	notificationFilter.dwReserved = 0
+	// BUG(pastarmovj): This class is ignored for now. Figure out what the right GUID is.
+	notificationFilter.classGuid = PRINTERS_DEVICE_CLASS
+	notificationFilter.szName = 0
+
+	r1, _, err := registerDeviceNotificationProc.Call(uintptr(handle), uintptr(unsafe.Pointer(&notificationFilter)), DEVICE_NOTIFY_SERVICE_HANDLE|DEVICE_NOTIFY_ALL_INTERFACE_CLASSES)
+	if r1 == 0 {
+		return err
+	}
+	return nil
+}

winspool/winspool.go

@@ -18,6 +18,7 @@ import (
 
 	"github.com/google/cloud-print-connector/cdd"
 	"github.com/google/cloud-print-connector/lib"
+	"golang.org/x/sys/windows"
 )
 
 // winspoolPDS represents capabilities that WinSpool always provides.
@@ -918,6 +919,11 @@ func (ws *WinSpool) ReleaseJob(printerName string, jobID uint32) error {
 	return nil
 }
 
+func (ws *WinSpool) StartPrinterNotifications(handle windows.Handle) error {
+	err := RegisterDeviceNotification(handle)
+	return err
+}
+
 // The following functions are not relevant to Windows printing, but are required by the NativePrintSystem interface.
 
 func (ws *WinSpool) RemoveCachedPPD(printerName string) {}