windows/svc/mgr: add Mgr.ListServices

Add API to list services installed on the system.

Fixes golang/go#20596

Change-Id: Ifa2f20ef15ccb962bd21d03788ce931dd45f2630
Reviewed-on: https://go-review.googlesource.com/45711
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

windows/svc/mgr/mgr.go

@@ -14,6 +14,7 @@ package mgr
 import (
 	"syscall"
 	"unicode/utf16"
+	"unsafe"
 
 	"golang.org/x/sys/windows"
 )
@@ -119,3 +120,43 @@ func (m *Mgr) OpenService(name string) (*Service, error) {
 	}
 	return &Service{Name: name, Handle: h}, nil
 }
+
+// ListServices enumerates services in the specified
+// service control manager database m.
+// If the caller does not have the SERVICE_QUERY_STATUS
+// access right to a service, the service is silently
+// omitted from the list of services returned.
+func (m *Mgr) ListServices() ([]string, error) {
+	var err error
+	var bytesNeeded, servicesReturned uint32
+	var buf []byte
+	for {
+		var p *byte
+		if len(buf) > 0 {
+			p = &buf[0]
+		}
+		err = windows.EnumServicesStatusEx(m.Handle, windows.SC_ENUM_PROCESS_INFO,
+			windows.SERVICE_WIN32, windows.SERVICE_STATE_ALL,
+			p, uint32(len(buf)), &bytesNeeded, &servicesReturned, nil, nil)
+		if err == nil {
+			break
+		}
+		if err != syscall.ERROR_MORE_DATA {
+			return nil, err
+		}
+		if bytesNeeded <= uint32(len(buf)) {
+			return nil, err
+		}
+		buf = make([]byte, bytesNeeded)
+	}
+	if servicesReturned == 0 {
+		return nil, nil
+	}
+	services := (*[1 << 20]windows.ENUM_SERVICE_STATUS_PROCESS)(unsafe.Pointer(&buf[0]))[:servicesReturned]
+	var names []string
+	for _, s := range services {
+		name := syscall.UTF16ToString((*[1 << 20]uint16)(unsafe.Pointer(s.ServiceName))[:])
+		names = append(names, name)
+	}
+	return names, nil
+}

windows/svc/mgr/mgr_test.go

@@ -150,5 +150,20 @@ func TestMyService(t *testing.T) {
 
 	testConfig(t, s, c)
 
+	svcnames, err := m.ListServices()
+	if err != nil {
+		t.Fatalf("ListServices failed: %v", err)
+	}
+	var myserviceIsInstalled bool
+	for _, sn := range svcnames {
+		if sn == name {
+			myserviceIsInstalled = true
+			break
+		}
+	}
+	if !myserviceIsInstalled {
+		t.Errorf("ListServices failed to find %q service", name)
+	}
+
 	remove(t, s)
 }

windows/svc/mgr/service.go

@@ -15,8 +15,6 @@ import (
 
 // TODO(brainman): Use EnumDependentServices to enumerate dependent services.
 
-// TODO(brainman): Use EnumServicesStatus to enumerate services in the specified service control manager database.
-
 // Service is used to access Windows service.
 type Service struct {
 	Name   string