dbus实例讲解（三）：数据类型和dteeth

我想在freerunner（一个开源linux手机）上查看fso（openmoko的诸多软件版本之一）的dbus信息。但fso的 python没有gtk模块，跑不了d-feet。在上一讲我介绍了d-feet的基本思路：用 “org.freedesktop.DBus.ListNames”枚举消息总线上的连接，用 “org.freedesktop.DBus.Introspectable.Introspect” 从"/"开始遍历连接的对象树。上一讲我们手工查看了两个连接，那么我们能不能写一个程序自动遍历连接的对象树，输出指定连接的所有对象的所有接口的所有 方法和信号？

当然可以，为此我写了一个叫dteeth的python脚本。不过在介绍这个脚本前，让我们先看看dbus的数据类型。

1、dbus的数据类型

dbus用xml描述接口，例如：

<?xml version="1.0" encoding="UTF-8" ?>

<node name="/org/freesmartphone/GSM/Device">
  <interface name="org.freesmartphone.GSM.SMS">
    <method name="SendMessage">
       <arg name="number" type="s"/>
       <arg name="contents" type="s"/>
       <arg name="featuremap" type="a{sv}"/>
       <arg type="i" direction="out"/>
    </method>
    <signal name="IncomingMessage">
       <arg name="address" type="s"/>
       <arg name="contents" type="s"/>
       <arg name="features" type="a{sv}"/>
    </signal>
  </interface>
</node>

其实前两讲已经看过很多例子了。node就是接口中的对象，node可以包含node，构成对象树。 dbus的接口描述文件统一采用utf-8编码。我相信读者很容易理解这个接口描述文件。我只想解释一下描述参数数据类型的type域。 dbus的数据类型是由"s"或"a{sv}"这样的类型签名（Type Signatures）定义的。类型签名中可以使用以下标记：

a	ARRAY 数组
b	BOOLEAN 布尔值
d	DOUBLE IEEE 754双精度浮点数
g	SIGNATURE 类型签名
i	INT32 32位有符号整数
n	INT16 16位有符号整数
o	OBJECT_PATH 对象路径
q	UINT16 16位无符号整数
s	STRING 零结尾的UTF-8字符串
t	UINT64 64位无符号整数
u	UINT32 32位无符号整数
v	VARIANT 可以放任意数据类型的容器，数据中包含类型信息。例如glib中的GValue。
x	INT64 64位有符号整数
y	BYTE 8位无符号整数
()	定义结构时使用。例如"(i(ii))"
{}	定义键－值对时使用。例如"a{us}"

a表示数组，数组元素的类型由a后面的标记决定。例如：

• "as"是字符串数组。
• 数组"a(i(ii))"的元素是一个结构。用括号将成员的类型括起来就表示结构了，结构可以嵌套。
• 数组"a{sv}"的元素是一个键－值对。"{sv}"表示键类型是字符串，值类型是VARIANT。

在以后的例子中，我们会亲手实现上面这个xml描述的接口，包括服务器和客户程序。到时候，读者会对dbus的数据类型有更直观的认识。

2、dteeth

2.1、运行dteeth

可以从这里 下载dteeth的源代码。其中包含两个python脚本：dteeth.py和_introspect_parser.py。 dteeth.py是我写的。_introspect_parser.py是个开源模块，可以分析Introspect返回的xml数据。

dteeth用法如下：

$ ./dteeth.py -h
Usage: dteeth [--system] <name of a connection on the bus >

默认连接session总线，除非你加上--system。可以一次指定同一消息总线的多个连接。先在PC上试一试：

$ ./dteeth.py org.fmddlmyy.Test
org.fmddlmyy.Test
    /TestObj
        org.fmddlmyy.Test.Basic
            methods
                Add( in i arg0 , in i arg1 , out i ret )
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s data )
        org.freedesktop.DBus.Properties
            methods
                Set( in s interface , in s propname , in v value )
                GetAll( in s interface , out a{sv} props )
                Get( in s interface , in s propname , out v value )

我也在fso版本的freerunner手机上运行了一下，得到了org.freesmartphone.ogsmd的所有对象的所有的接口的所有方法和信号：

org.freesmartphone.ogsmd
    /org/freedesktop/Gypsy
        org.freedesktop.Gypsy.Time
            signals
                TimeChanged( i time )
            methods
                GetTime( out i )
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freedesktop.Gypsy.Device
            signals
                FixStatusChanged( i fixstatus )
                ConnectionStatusChanged( b constatus )
            methods
                GetConnectionStatus( out b )
                Stop( )
                Start( )
                GetFixStatus( out i )
        org.freedesktop.Gypsy.Course
            signals
                CourseChanged( i fields , i tstamp , d speed , d heading , d climb )
            methods
                GetCourse( out i , out i , out d , out d , out d )
        org.freedesktop.Gypsy.Position
            signals
                PositionChanged( i fields , i tstamp , d lat , d lon , d alt )
            methods
                GetPosition( out i , out i , out d , out d , out d )
        org.freedesktop.Gypsy.Accuracy
            signals
                AccuracyChanged( i fields , d pdop , d hdop , d vdop )
            methods
                GetAccuracy( out i , out d , out d , out d )
        org.freesmartphone.Resource
            methods
                Enable( )
                Disable( )
                Suspend( )
                Resume( )
        org.freedesktop.Gypsy.Satellite
            signals
                SatellitesChanged( a(ubuuu) satellites )
            methods
                GetSatellites( out a(ubuuu) )
        org.freesmartphone.GPS.UBX
            signals
                DebugPacket( s clid , i length , aa{sv} data )
            methods
                SendDebugPacket( in s clid , in i length , in aa{sv} data )
                GetDebugFilter( in s clid , out b )
                SetDebugFilter( in s clid , in b state )
        org.freedesktop.Gypsy.Server
            methods
                Create( in s device , out o )
                Shutdown( in o path )
    /org/freesmartphone/Device/Audio
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.Device.Audio
            signals
                SoundStatus( s name , s status , a{sv} properties )
                Scenario( s scenario , s reason )
            methods
                SetScenario( in s name )
                GetInfo( out s )
                GetAvailableScenarios( out as )
                PushScenario( in s name )
                GetScenario( out s )
                PullScenario( out s )
                StopSound( in s name )
                StopAllSounds( )
                PlaySound( in s name )
                StoreScenario( in s name )
    /org/freesmartphone/Device/Display/pcf50633_bl
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.Device.Display
            methods
                SetBrightness( in i brightness )
                GetName( out s )
                SetBacklightPower( in b power )
                GetBrightness( out i )
                GetBacklightPower( out b )
    /org/freesmartphone/Device/IdleNotifier/0
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.Device.IdleNotifier
            signals
                State( s state )
            methods
                SetState( in s state )
                GetState( out s )
                SetTimeout( in s state , in i timeout )
                GetTimeouts( out a{si} )
    /org/freesmartphone/Device/Info
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.Device.Info
            methods
                GetCpuInfo( out a{sv} )
    /org/freesmartphone/Device/Input
        org.freesmartphone.Device.Input
            signals
                Event( s name , s action , i seconds )
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
    /org/freesmartphone/Device/LED/gta02_aux_red
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.Device.LED
            methods
                SetBrightness( in i brightness )
                GetName( out s )
                SetBlinking( in i delay_on , in i delay_off )
    /org/freesmartphone/Device/LED/gta02_power_blue
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.Device.LED
            methods
                SetBrightness( in i brightness )
                GetName( out s )
                SetBlinking( in i delay_on , in i delay_off )
    /org/freesmartphone/Device/LED/gta02_power_orange
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.Device.LED
            methods
                SetBrightness( in i brightness )
                GetName( out s )
                SetBlinking( in i delay_on , in i delay_off )
    /org/freesmartphone/Device/LED/neo1973_vibrator
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.Device.LED
            methods
                SetBrightness( in i brightness )
                GetName( out s )
                SetBlinking( in i delay_on , in i delay_off )
    /org/freesmartphone/Device/PowerControl/Bluetooth
        org.freesmartphone.Device.PowerControl
            signals
                Power( s device , b power )
            methods
                Reset( )
                GetName( out s )
                SetPower( in b power )
                GetPower( out b )
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.Resource
            methods
                Resume( )
                Enable( )
                Disable( )
                Suspend( )
    /org/freesmartphone/Device/PowerControl/UsbHost
        org.freesmartphone.Device.PowerControl
            signals
                Power( s device , b power )
            methods
                Reset( )
                GetName( out s )
                SetPower( in b power )
                GetPower( out b )
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
    /org/freesmartphone/Device/PowerControl/WiFi
        org.freesmartphone.Device.PowerControl
            signals
                Power( s device , b power )
            methods
                Reset( )
                GetName( out s )
                SetPower( in b power )
                GetPower( out b )
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.Resource
            methods
                Resume( )
                Enable( )
                Disable( )
                Suspend( )
    /org/freesmartphone/Device/PowerSupply/apm
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.Device.PowerSupply
            methods
                GetName( out s )
                GetEnergyPercentage( out i )
                GetOnBattery( out b )
                GetInfo( out a{sv} )
    /org/freesmartphone/Device/PowerSupply/bat
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.Device.PowerSupply
            signals
                PowerStatus( s status )
                Capacity( i percent )
            methods
                GetEnergyPercentage( out i )
                GetInfo( out a{sv} )
                IsPresent( out b )
                GetName( out s )
                GetCapacity( out i )
                GetPowerStatus( out s )
    /org/freesmartphone/Device/RealTimeClock/rtc0
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.Device.RealTimeClock
            methods
                GetWakeupReason( out s )
                SetCurrentTime( in s t )
                Suspend( )
                GetWakeupTime( out s )
                GetName( out s )
                GetCurrentTime( out s )
                SetWakeupTime( in s t )
    /org/freesmartphone/Events
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.Events
            methods
                AddRule( in s rule_str )
                TriggerTest( in s name , in b value )
    /org/freesmartphone/Framework
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.Framework
            methods
                GetDebugLevel( in s logger , out s )
                GetDebugDestination( out s , out s )
                ListDebugLoggers( out as )
                ListObjectsInSubsystem( in s subsystem , out as )
                SetDebugDestination( in s category , in s destination )
                SetDebugLevel( in s logger , in s levelname )
                ListObjectsByInterface( in s interface , out ao )
                ListSubsystems( out as )
    /org/freesmartphone/GSM/Device
        org.freesmartphone.GSM.Call
            signals
                CallStatus( i index , s status , a{sv} properties )
            methods
                Activate( in i index )
                Emergency( in s number )
                SendDtmf( in s tones )
                ReleaseHeld( )
                HoldActive( )
                ReleaseAll( )
                Initiate( in s number , in s type_ , out i )
                ListCalls( out a(isa{sv}) )
                Transfer( in s number )
                Release( in i index )
                ActivateConference( in i index )
        org.freesmartphone.GSM.Debug
            methods
                DebugInjectString( in s channel , in s string )
                DebugCommand( in s command , out as )
                DebugEcho( in s echo , out s )
                DebugListChannels( out as )
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.GSM.Device
            methods
                CancelCommand( )
                GetInfo( out a{sv} )
                GetAntennaPower( out b )
                SetSimBuffersSms( in b sim_buffers_sms )
                GetFeatures( out a{sv} )
                SetAntennaPower( in b power )
                GetSimBuffersSms( out b )
        org.freesmartphone.GSM.SMS
            signals
                IncomingMessage( s address , s text , a{sv} features )
            methods
                SendMessage( in s number , in s contents , in a{sv} featuremap , out i )
        org.freesmartphone.GSM.SIM
            signals
                ReadyStatus( b status )
                MemoryFull( )
                AuthStatus( s status )
                IncomingStoredMessage( i index )
            methods
                RetrievePhonebook( in s category , out a(iss) )
                SendAuthCode( in s code )
                ChangeAuthCode( in s old_pin , in s new_pin )
                SendGenericSimCommand( in s command , out s )
                ListPhonebooks( out as )
                SetServiceCenterNumber( in s number )
                GetHomeZones( out a(siii) )
                RetrieveEntry( in s category , in i index , out s , out s )
                DeleteMessage( in i index )
                SendRestrictedSimCommand( in i command , in i fileid , in i p1 , in i p2 , in i p3 , in s data , out i , out i , out s )
                GetMessagebookInfo( out a{sv} )
                GetSimReady( out b )
                GetPhonebookInfo( in s category , out a{sv} )
                GetSimInfo( out a{sv} )
                SendStoredMessage( in i index , out i )
                SetAuthCodeRequired( in b required , in s pin )
                GetAuthStatus( out s )
                StoreMessage( in s number , in s contents , in a{sv} featuremap , out i )
                GetAuthCodeRequired( out b )
                RetrieveMessage( in i index , out s , out s , out s , out a{sv} )
                StoreEntry( in s category , in i index , in s name , in s number )
                Unlock( in s puk , in s new_pin )
                GetServiceCenterNumber( out s )
                RetrieveMessagebook( in s category , out a(isssa{sv}) )
                DeleteEntry( in s category , in i index )
        org.freesmartphone.GSM.Network
            signals
                Status( a{sv} status )
                SignalStrength( i strength )
                IncomingUssd( s mode , s message )
            methods
                EnableCallForwarding( in s reason , in s class_ , in s number , in i timeout )
                ListProviders( out a(isss) )
                GetCallForwarding( in s reason , out a{sv} )
                Unregister( )
                SetCallingIdentification( in s status )
                Register( )
                SendUssdRequest( in s request )
                DisableCallForwarding( in s reason , in s class_ )
                GetSignalStrength( out i )
                GetCallingIdentification( out s )
                RegisterWithProvider( in i operator_code )
                GetNetworkCountryCode( out s )
                GetStatus( out a{sv} )
        org.freesmartphone.Resource
            methods
                Enable( )
                Disable( )
                Suspend( )
                Resume( )
        org.freesmartphone.GSM.CB
            signals
                IncomingCellBroadcast( i channel , s data )
            methods
                GetCellBroadcastSubscriptions( out s )
                SetCellBroadcastSubscriptions( in s channels )
        org.freesmartphone.GSM.PDP
            signals
                ContextStatus( i index , s status , a{sv} properties )
            methods
                SetCurrentGprsClass( in s class_ )
                ActivateContext( in s apn , in s user , in s password )
                DeactivateContext( )
                ListAvailableGprsClasses( out as )
                GetContextStatus( out s )
                GetCurrentGprsClass( out s )
    /org/freesmartphone/GSM/Server
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.GSM.HZ
            signals
                HomeZoneStatus( s zone )
            methods
                GetHomeZoneStatus( out s )
                GetKnownHomeZones( out as )
    /org/freesmartphone/PIM/Contacts
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.PIM.Contacts
            methods
                Query( in a{sv} query , out s )
                Add( in a{sv} contact_data , out s )
                GetSingleContactSingleField( in a{sv} query , in s field_name , out s )
        org.freesmartphone.PIM.Contact
            methods
                GetContent( out a{sv} )
                GetMultipleFields( in s field_list , out a{sv} )
    /org/freesmartphone/PIM/Contacts/Queries
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.PIM.ContactQuery
            methods
                GetContactPath( out s )
                Skip( in i num_entries )
                Dispose( )
                GetResult( out a{sv} )
                GetResultCount( out i )
                Rewind( )
                GetMultipleResults( in i num_entries , out aa{sv} )
    /org/freesmartphone/PIM/Messages
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.PIM.Messages
            signals
                NewMessage( s message_URI )
            methods
                GetSingleMessageSingleField( in a{sv} query , in s field_name , out s )
                Query( in a{sv} query , out s )
                Add( in a{sv} message_data , out s )
                GetFolderURIFromName( in s folder_name , out s )
                GetFolderNames( out as )
        org.freesmartphone.PIM.Message
            methods
                GetContent( out a{sv} )
                MoveToFolder( in s new_folder_name )
                GetMultipleFields( in s field_list , out a{sv} )
    /org/freesmartphone/PIM/Messages/Folders
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.PIM.Messages
            signals
                NewMessage( s message_URI )
            methods
                GetSingleMessageSingleField( in a{sv} query , in s field_name , out s )
                Query( in a{sv} query , out s )
                Add( in a{sv} message_data , out s )
                GetFolderURIFromName( in s folder_name , out s )
                GetFolderNames( out as )
        org.freesmartphone.PIM.Message
            methods
                GetContent( out a{sv} )
                MoveToFolder( in s new_folder_name )
                GetMultipleFields( in s field_list , out a{sv} )
    /org/freesmartphone/PIM/Messages/Folders/0
        org.freesmartphone.PIM.MessageFolder
            signals
                MessageMoved( s message_uri , s new_folder_name )
            methods
                GetMessageCount( out i )
                GetMessageURIs( in i first_message_id , in i message_count , out as )
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
    /org/freesmartphone/PIM/Messages/Folders/1
        org.freesmartphone.PIM.MessageFolder
            signals
                MessageMoved( s message_uri , s new_folder_name )
            methods
                GetMessageCount( out i )
                GetMessageURIs( in i first_message_id , in i message_count , out as )
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
    /org/freesmartphone/PIM/Messages/Queries
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.PIM.MessageQuery
            methods
                Skip( in i num_entries )
                Dispose( )
                GetResult( out a{sv} )
                GetResultCount( out i )
                Rewind( )
                GetMultipleResults( in i num_entries , out a{ia{sv}} )
                GetMessageURI( out s )
    /org/freesmartphone/PIM/Sources
        org.freesmartphone.PIM.Sources
            methods
                GetEntryCount( out i )
                InitAllEntries( )
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.PIM.Source
            methods
                GetSupportedPIMDomains( out as )
                GetName( out s )
                GetStatus( out s )
    /org/freesmartphone/Phone
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.Phone
            signals
                Incoming( o call )
            methods
                InitProtocols( out as )
                CreateCall( in s number , in s protocol , in b force , out o )
    /org/freesmartphone/Preferences
        org.freesmartphone.Preferences
            methods
                GetProfiles( out as )
                GetService( in s name , out o )
                GetServices( out as )
                SetProfile( in s profile )
                GetProfile( out s )
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
    /org/freesmartphone/Preferences/rules
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.Preferences.Service
            signals
                Notify( s key , v value )
            methods
                GetType( in s key , out s )
                SetValue( in s key , in v value )
                GetKeys( out as )
                IsProfilable( in s key , out b )
                GetValue( in s key , out v )
    /org/freesmartphone/Time
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.Time
            signals
                Minute( i year , i mon , i day , i hour , i min , i sec , i wday , i yday , i isdst )
            methods
                GetLocalTime( in i seconds , out i , out i , out i , out i , out i , out i , out i , out i , out i )
    /org/freesmartphone/Time/Alarm
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )
        org.freesmartphone.Time.Alarm
            methods
                ClearAlarm( in s busname )
                SetAlarm( in s busname , in i timestamp )
    /org/freesmartphone/Usage
        org.freesmartphone.Usage
            signals
                ResourceAvailable( s resourcename , b state )
                ResourceChanged( s resourcename , b state , a{sv} attributes )
            methods
                ReleaseResource( in s resourcename )
                Suspend( )
                GetResourceState( in s resourcename , out b )
                SetResourcePolicy( in s resourcename , in s policy )
                GetResourcePolicy( in s resourcename , out s )
                GetResourceUsers( in s resourcename , out as )
                ListResources( out as )
                RegisterResource( in s resourcename , in o path )
                RequestResource( in s resourcename )
        org.freedesktop.DBus.Introspectable
            methods
                Introspect( out s )

2.2、源代码

下面是dteeth的源代码：

$ cat -n dteeth.py
     1  #!/usr/bin/env python
     2  # -*- coding: utf-8 -*-
     3
     4  import dbus
     5  import _introspect_parser
     6  import getopt, sys
     7
     8  MARGIN_WIDTH = 4
     9  ONE_MARGIN = ' ' * MARGIN_WIDTH
    10
    11  # signal是个元组，它有一个元素，是一个列表。列表的元素是signal的参数
    12  # 列表的每个元素都是字典。它有两个元素，键值分别是'type'和'name'
    13  def show_signal(name, signal, margin):
    14      print margin+name+'(',
    15      args = signal[0]
    16      for i, arg in enumerate(args):
    17          if i > 0:
    18              print ',',
    19          if arg['name']:
    20              print '%s %s' % (arg['type'], arg['name']),
    21          else:
    22              print '%s' % arg['type'],
    23      print  ')'
    24
    25  # method是个元组，它有两个元素，都是列表。前一个列表的元素是输入参数，后一个列表的元素是输出参数
    26  def show_method(name, method, margin):
    27      print margin+name+'(',
    28  # 输入参数
    29      args = method[0]
    30      in_num = len(args)
    31      out_num = len(method[1])
    32      for i, arg in enumerate(args):
    33          if i > 0:
    34              print ',',
    35          if arg['name']:
    36              print 'in %s %s' % (arg['type'], arg['name']),
    37          else:
    38              print 'in %s' % arg['type'],
    39  # 输出参数
    40      if (in_num > 0) and (out_num > 0) :
    41          print ',',
    42      args = method[1]
    43      for i, arg in enumerate(args):
    44          if i > 0:
    45              print ',',
    46          if arg['name']:
    47              print 'out %s %s' % (arg['type'], arg['name']),
    48          else:
    49              print 'out %s' % arg['type'],
    50      print  ')'
    51
    52  def show_property(name, property, margin):
    53      print margin+name
    54      print margin,
    55      print property
    56
    57  # interfaces是个字典，它有三个元素，键值分别是'signals'、'methods'和'properties'
    58  def show_iface(name, iface, margin):
    59      print margin + name
    60      margin += ONE_MARGIN
    61      signals=iface['signals']
    62      l = len(signals)
    63      if l > 0:
    64          print margin+'signals'
    65          for node in signals:
    66              show_signal(node, signals[node], margin+ONE_MARGIN)
    67
    68      methods=iface['methods']
    69      l = len(methods)
    70      if l > 0:
    71          print margin+'methods'
    72          for node in methods:
    73              show_method(node, methods[node], margin+ONE_MARGIN)
    74
    75      properties=iface['properties']
    76      l = len(properties)
    77      if l > 0:
    78          print margin+'properties'
    79          for node in properties:
    80              show_property(node, properties[node], margin+ONE_MARGIN)
    81
    82  def show_obj(bus, name, obj_name, margin):
    83      obj=bus.get_object(name, obj_name)
    84      iface=dbus.Interface(obj, 'org.freedesktop.DBus.Introspectable')
    85      xml=iface.Introspect();
    86      data = _introspect_parser.process_introspection_data(xml)
    87
    88      # data是个字典，它有两个元素，键值分别是'child_nodes'和'interfaces'
    89      if len(data['interfaces']) > 0:
    90          print margin + obj_name
    91
    92      for node in data['interfaces']:
    93          iface=data['interfaces'][node]
    94          show_iface(node, iface, margin+ONE_MARGIN)
    95
    96      for node in data['child_nodes']:
    97          if obj_name == '/':
    98              show_obj(bus, name, '/' + node, margin)
    99          else:
   100              show_obj(bus, name, obj_name + '/' + node, margin)
   101
   102  def show_connection(bus, name, margin):
   103      print margin + name
   104      show_obj(bus, name, '/', margin+ONE_MARGIN)
   105
   106  def usage():
   107      print "Usage: dteeth [--system] "
   108
   109  def main():
   110      try:
   111          opts, args = getopt.getopt(sys.argv[1:], "h", ["help", "system"])
   112      except getopt.GetoptError, err:
   113          # print help information and exit:
   114          print str(err) # will print something like "option -a not recognized"
   115          usage()
   116          sys.exit(2)
   117
   118      if len(args) == 0:
   119          usage()
   120          sys.exit(2)
   121
   122      use_system = False
   123      for o, a in opts:
   124          if o in ("-h", "--help"):
   125              usage()
   126              sys.exit()
   127          if o == "--system":
   128              use_system = True
   129          else:
   130              assert False, "unhandled option"
   131
   132      if use_system:
   133          bus=dbus.SystemBus()
   134      else:
   135          bus=dbus.SessionBus()
   136
   137      for arg in args:
   138          show_connection(bus, arg, "")
   139
   140  if __name__ == "__main__":
   141      main()

dteeth是我写的第一个超过10行的python脚本。对于熟悉python的读者，dteeth应该是很简单的。不过我还是简单解释一下dteeth的主要逻辑。

2.3、dteeth的主要逻辑

main函数分析命令行，对命令行上指定的每个连接调用show_connection函数。 show_connection在打印连接名后调用show_obj从根对象"/"开始遍历连接的对象树。

show_obj对输入对象调用Introspect方法，返回的xml数据交由_introspect_parser处理。 _introspect_parser会从xml数据中分出inerface和node。 show_obj对inerface调用show_iface显示。 show_obj对node会递归调用show_obj，实现对象树的遍历。

2.4、_introspect_parser的输出格式

_introspect_parser.process_introspection_data函数分析Introspect方法返回的xml数据。为了了解_introspect_parser的输出格式，我们可以写个小脚本：

$ cat ti.py
#!/usr/bin/env python
import dbus
import _introspect_parser
bus=dbus.SessionBus()
obj=bus.get_object('org.freesmartphone.ogsmd', '/org/freesmartphone/GSM/Device')
iface=dbus.Interface(obj, 'org.freedesktop.DBus.Introspectable')
xml=iface.Introspect();
data = _introspect_parser.process_introspection_data(xml)
print data

可以用这个脚本直接打印process_introspection_data返回的数据。下面是整理后的输出：

{
	'interfaces': 
	{
		u'org.freedesktop.DBus.Introspectable': 
		{
			'signals': {}, 
			'methods': 
			{
				u'Introspect': 
				(
					[], 
					[{'type': u's', 'name': u'data'}]
				)
			}, 
			'properties': {}
		}, 
		u'org.freedesktop.DBus.Properties': 
		{
			'signals': {}, 
			'methods': 
			{
				u'Set': 
				(
					[{'type': u's', 'name': u'interface'}, {'type': u's', 'name': u'propname'}, {'type': u'v', 'name': u'value'}], 
					[]
				), 
				u'GetAll': 
				(
					[{'type': u's', 'name': u'interface'}], 
					[{'type': u'a{sv}', 'name': u'props'}]
				), 
				u'Get': 
				(
					[{'type': u's', 'name': u'interface'}, {'type': u's', 'name': u'propname'}], 
					[{'type': u'v', 'name': u'value'}]
				)
			}, 
			'properties': {}
		}, 
		u'org.freesmartphone.GSM.SMS': 
		{
			'signals': 
			{
				u'IncomingMessage': 
				(
					[{'type': u's', 'name': None}, {'type': u's', 'name': None}, {'type': u'a{sv}', 'name': None}],
				)
			},
			'methods': 
			{
				u'SendMessage': 
				(
					[{'type': u's', 'name': u'number'}, {'type': u's', 'name': u'contents'}, {'type': u'a{sv}', 'name': u'featuremap'}], 
					[{'type': u'i', 'name': u'arg3'}]
				)
			},
			'properties': {}
		}
	}, 
	'child_nodes': []
}

所有字符串前面都有前缀u，表示这些字符串都是Unicode编码。在python中，字典用{}，元组用()，列表用[]。从括号我们就能看出数据格式。

我们看到process_introspection_data返回返回一个字典。这个字典有两个映射。一个映射的键值是"interfaces"，另一个映射的键值是"child_nodes"。

• 映射"child_nodes"的值是一个列表，列出所有子节点的名称。

• 映射"interfaces"的值还是一个字典。这个字典的每个映射的键值是一个接口名称。每个映射的值类型还是字典， 这个字典有3个映射，映射的键值分别是'signals'、'methods'和'properties'，映射的值类型都是字典。

  • 'signals'对应字典的每个键值是一个信号名称。每个映射的值类型是元组。这个元组只有一个元素，类型是列表， 即信号的参数列表。

    • 参数列表的元素类型是字典。这个字典有2个映射，映射的键值分别是'type'和'name'。'type'是参数类型，'name'是参数名称。 映射的值类型都是字符串。

  • 'methods'对应字典的每个键值是一个方法名称。每个映射的值类型是元组。这个元组有两个元素，类型是列表， 分别是方法的输入参数列表和输出参数列表。参数列表的元素类型和信号的参数列表相同。

  • 我看到'properties'映射都是空的，就没有研究。

3、python基础

简单介绍一下与dteeth有关的python语法。

3.1、代码块和缩进

python用缩进来区分语句所属的代码块，从类定义、函数到for、if的代码块都是用缩进来去区分的。没有缩进的代码块是脚本的主体代码。一个 脚本文件也被称作一个模块。不管模块被直接运行还是被其它模块导入，主体代码都会在载入时被执行。例如dteeth的主体代码只有两句：

   140  if __name__ == "__main__":
   141      main()

__xxx__这样的标志符通常是python的系统变量。如果模块被导入，__name__的值是模块的名字。如果模块被直接执行，__name__的值是"__main__"。我们通常在模块被直接执行时，调用主函数或模块的测试函数。

3.2、脚本文件格式

python脚本的起始行通常是：/p>

     1  #!/usr/bin/env python

env是一个可以修改环境变量并执行程序的工具，它可以自动在系统路径中搜索要执行的程序。 python脚本文件必须以0A为换行符，默认仅支持ASCII字符。如果要写中文注释（显然是不提倡的），可以在起始行后用以下语句将文件指定为utf-8编码：

     2  # -*- coding: utf-8 -*-

这时，文件必须被保存为没有BOM的utf-8编码文件。

3.3、列表、元组和字典

列表类似于C的数组，列表元素用[]包括。元组是不可变的列表，元组元素用()包括。元组的元素个数和类型在创建后就不能改变了。元组中基本类型的值是不能改变的，但如果元组的一个元素是列表，我们可以改变列表内容，即我们可以改变元组中可变元素的内容。例如：

>>> a=(1,2,['abc'])
>>> a[2]='def'
Traceback (most recent call last):
  File "", line 1, in 
TypeError: 'tuple' object does not support item assignment
>>> a[2][0]='def'
>>> a
(1, 2, ['def'])

字典是键-值对的集合，字典元素用{}包括。

4、结束语

本文介绍了一个叫作dteeth的python脚本。这个脚本逻辑很简单，读者可以根据需要修改或扩充。讲了这么多dbus，我们还没有接触C代码。下一讲，我们讨论dbus的C实例。