windows/svc: add new package to help create and manage Windows services

Change-Id: I58bb446aaa387b31d8a9ff4217793a170b96a7e2
Reviewed-on: https://go-review.googlesource.com/9104
Reviewed-by: Rob Pike <r@golang.org>

windows/svc/mgr/config.go

@@ -0,0 +1,139 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build windows
+
+package mgr
+
+import (
+	"syscall"
+	"unicode/utf16"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+const (
+	// Service start types.
+	StartManual    = windows.SERVICE_DEMAND_START // the service must be started manually
+	StartAutomatic = windows.SERVICE_AUTO_START   // the service will start by itself whenever the computer reboots
+	StartDisabled  = windows.SERVICE_DISABLED     // the service cannot be started
+
+	// The severity of the error, and action taken,
+	// if this service fails to start.
+	ErrorCritical = windows.SERVICE_ERROR_CRITICAL
+	ErrorIgnore   = windows.SERVICE_ERROR_IGNORE
+	ErrorNormal   = windows.SERVICE_ERROR_NORMAL
+	ErrorSevere   = windows.SERVICE_ERROR_SEVERE
+)
+
+// TODO(brainman): Password is not returned by windows.QueryServiceConfig, not sure how to get it.
+
+type Config struct {
+	ServiceType      uint32
+	StartType        uint32
+	ErrorControl     uint32
+	BinaryPathName   string // fully qualified path to the service binary file, can also include arguments for an auto-start service
+	LoadOrderGroup   string
+	TagId            uint32
+	Dependencies     []string
+	ServiceStartName string // name of the account under which the service should run
+	DisplayName      string
+	Password         string
+	Description      string
+}
+
+func toString(p *uint16) string {
+	if p == nil {
+		return ""
+	}
+	return syscall.UTF16ToString((*[4096]uint16)(unsafe.Pointer(p))[:])
+}
+
+func toStringSlice(ps *uint16) []string {
+	if ps == nil {
+		return nil
+	}
+	r := make([]string, 0)
+	for from, i, p := 0, 0, (*[1 << 24]uint16)(unsafe.Pointer(ps)); true; i++ {
+		if p[i] == 0 {
+			// empty string marks the end
+			if i <= from {
+				break
+			}
+			r = append(r, string(utf16.Decode(p[from:i])))
+			from = i + 1
+		}
+	}
+	return r
+}
+
+// Config retrieves service s configuration paramteres.
+func (s *Service) Config() (Config, error) {
+	var p *windows.QUERY_SERVICE_CONFIG
+	n := uint32(1024)
+	for {
+		b := make([]byte, n)
+		p = (*windows.QUERY_SERVICE_CONFIG)(unsafe.Pointer(&b[0]))
+		err := windows.QueryServiceConfig(s.Handle, p, n, &n)
+		if err == nil {
+			break
+		}
+		if err.(syscall.Errno) != syscall.ERROR_INSUFFICIENT_BUFFER {
+			return Config{}, err
+		}
+		if n <= uint32(len(b)) {
+			return Config{}, err
+		}
+	}
+
+	var p2 *windows.SERVICE_DESCRIPTION
+	n = uint32(1024)
+	for {
+		b := make([]byte, n)
+		p2 = (*windows.SERVICE_DESCRIPTION)(unsafe.Pointer(&b[0]))
+		err := windows.QueryServiceConfig2(s.Handle,
+			windows.SERVICE_CONFIG_DESCRIPTION, &b[0], n, &n)
+		if err == nil {
+			break
+		}
+		if err.(syscall.Errno) != syscall.ERROR_INSUFFICIENT_BUFFER {
+			return Config{}, err
+		}
+		if n <= uint32(len(b)) {
+			return Config{}, err
+		}
+	}
+
+	return Config{
+		ServiceType:      p.ServiceType,
+		StartType:        p.StartType,
+		ErrorControl:     p.ErrorControl,
+		BinaryPathName:   toString(p.BinaryPathName),
+		LoadOrderGroup:   toString(p.LoadOrderGroup),
+		TagId:            p.TagId,
+		Dependencies:     toStringSlice(p.Dependencies),
+		ServiceStartName: toString(p.ServiceStartName),
+		DisplayName:      toString(p.DisplayName),
+		Description:      toString(p2.Description),
+	}, nil
+}
+
+func updateDescription(handle windows.Handle, desc string) error {
+	d := windows.SERVICE_DESCRIPTION{toPtr(desc)}
+	return windows.ChangeServiceConfig2(handle,
+		windows.SERVICE_CONFIG_DESCRIPTION, (*byte)(unsafe.Pointer(&d)))
+}
+
+// UpdateConfig updates service s configuration parameters.
+func (s *Service) UpdateConfig(c Config) error {
+	err := windows.ChangeServiceConfig(s.Handle, c.ServiceType, c.StartType,
+		c.ErrorControl, toPtr(c.BinaryPathName), toPtr(c.LoadOrderGroup),
+		nil, toStringBlock(c.Dependencies), toPtr(c.ServiceStartName),
+		toPtr(c.Password), toPtr(c.DisplayName))
+	if err != nil {
+		return err
+	}
+	return updateDescription(s.Handle, c.Description)
+}