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dbus实例讲解(四下):使用dbus-glib

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4、复杂的数据类型

在dbus中怎样处理复杂的数据类型?第一个建议是尽量不要使用复杂的数据类型。但如果确实需要呢?有的网友建议用GArray作为容器,不管什么参数,在客户端都手工放入GArray,在服务器端再自己取出来。这确实是个思路,比较适合服务器和客户端都是自己开发的情况。还有一篇"How to pass a variant with dbus-glib" 介绍了怎样用GValue传递复杂的数据类型,读者可以参考。

下面看看在我们的例子中是怎样处理a{sv}参数的:

$ cat sms_features.h
#ifndef SMS_FEATURES_H
#define SMS_FEATURES_H

#include <glib-object.h>

GHashTable *sms_create_features(const char * alphabet, int csm_num, int csm_seq);

GType sms_get_features_type(void);

void sms_release_features(GHashTable *features);

void sms_show_features(GHashTable *features);

#endif

sms_features.h声明了几个函数。这个例子的服务器、客户端都会调用。以下是这些函数的实现:

$ cat -n sms_features.c
     1  #include "sms_features.h"
     2
     3  static void release_val(gpointer data)
     4  {
     5      GValue *val = (GValue *)data;
     6      g_value_unset(val);
     7      g_free(val);
     8  }
     9
    10  GHashTable *sms_create_features(const char * alphabet, int csm_num, int csm_seq)
    11  {
    12      GHashTable *hash;
    13      GValue *val;
    14
    15      hash = g_hash_table_new_full  (g_str_hash, NULL, NULL, release_val);
    16
    17      val = g_new0(GValue, 1);
    18      g_value_init (val, G_TYPE_STRING);
    19      g_value_set_string (val, alphabet);
    20      g_hash_table_insert(hash, "alphabet", val);
    21
    22      val = g_new0(GValue, 1);
    23      g_value_init (val, G_TYPE_INT);
    24      g_value_set_int (val, csm_num);
    25      g_hash_table_insert(hash, "csm_num", val);
    26
    27      val = g_new0(GValue, 1);
    28      g_value_init (val, G_TYPE_INT);
    29      g_value_set_int (val, csm_seq);
    30      g_hash_table_insert(hash, "csm_seq", val);
    31
    32      return hash;
    33  }
    34
    35  GType sms_get_features_type(void)
    36  {
    37      return dbus_g_type_get_map("GHashTable", G_TYPE_STRING, G_TYPE_VALUE);
    38  }
    39
    40  void sms_show_features(GHashTable *features)
    41  {
    42      GList *keys = g_hash_table_get_keys(features);
    43      gint len = g_list_length(keys);
    44      gint i;
    45
    46      for (i = 0; i < len; i++) {
    47          gchar  *key = g_list_nth_data(keys, i);
    48          GValue *val = g_hash_table_lookup(features, key);
    49
    50          g_print("%s=", key);
    51          switch (G_VALUE_TYPE(val)) {
    52          case G_TYPE_STRING:
    53              g_print("%s\n", g_value_get_string(val));
    54              break;
    55          case G_TYPE_INT:
    56              g_print("%d\n", g_value_get_int(val));
    57              break;
    58          default:
    59              g_print("Value is of unmanaged type!\n");
    60          }
    61      }
    62
    63      g_list_free(keys);
    64  }
    65
    66  void sms_release_features(GHashTable *features)
    67  {
    68      g_hash_table_destroy(features);
    69  }
    70

sms_get_features_type调用dbus_g_type_get_map创建a{sv}类型。服务器在创建信号时用到。客户端在调用方法和注册信号时都会用到。 sms_create_features调用g_hash_table_new_full创建哈希表,在创建的同时登记了值对象的清理函数。在sms_release_features调用g_hash_table_destroy销毁哈希表时,创建时登记的值对象清理函数会被调用。

5、客户端

5.1、代码

客户端程序如下:

$ cat -n smsc.c
     1  #include <dbus/dbus-glib.h>
     2  #include <stdio.h>
     3  #include <stdlib.h>
     4  #include <string.h>
     5  #include <glib/giochannel.h>
     6  #include "sms-marshal.h"
     7  #include "sms_features.h"
     8
     9  #define SMSC_DEBUG
    10
    11  static void lose (const char *str, ...)
    12  {
    13      va_list args;
    14      va_start (args, str);
    15      vfprintf (stderr, str, args);
    16      fputc ('\n', stderr);
    17      va_end (args);
    18      exit (1);
    19  }
    20
    21  static void lose_gerror (const char *prefix, GError *error)
    22  {
    23      if (error) {
    24          lose ("%s: %s", prefix, error->message);
    25      }
    26      else {
    27          lose ("%s", prefix);
    28      }
    29  }
    30
    31  static void incoming_message_handler (DBusGProxy *proxy, const char *address, const char *contents, GHashTable *features, gpointer user_data)
    32  {
    33      printf ("Received message with addree \"%s\" and it says: \n%s\n", address, contents);
    34      sms_show_features(features);
    35  }
    36
    37  static void send_message(DBusGProxy *remote_object)
    38  {
    39      GError *error = NULL;
    40      GHashTable *features;
    41      int ret;
    42
    43      features = sms_create_features ("gsm", 8, 2);
    44      printf("SendMessage ");
    45
    46      if (!dbus_g_proxy_call (remote_object, "SendMessage", &error,
    47          G_TYPE_STRING, "10987654321", G_TYPE_STRING, "hello world",
    48          sms_get_features_type(), features, G_TYPE_INVALID,
    49          G_TYPE_INT, &ret, G_TYPE_INVALID))
    50          lose_gerror ("Failed to complete SendMessage", error);
    51
    52      printf("return %d\n", ret);
    53      sms_release_features(features);
    54  }
    55
    56  static void shell_help(void)
    57  {
    58      printf( "\ts\tsend message\n"
    59          "\tq\tQuit\n"
    60          );
    61  }
    62
    63  #define STDIN_BUF_SIZE    1024
    64  static gboolean channel_cb(GIOChannel *source, GIOCondition condition, gpointer data)
    65  {
    66      int rc;
    67      char buf[STDIN_BUF_SIZE+1];
    68      DBusGProxy *remote_object = (DBusGProxy *)data;
    69
    70      if (condition != G_IO_IN) {
    71          return TRUE;
    72      }
    73
    74      /* we've received something on stdin.    */
    75      printf("# ");
    76      rc = fscanf(stdin, "%s", buf);
    77      if (rc <= 0) {
    78          printf("NULL\n");
    79          return TRUE;
    80      }
    81
    82      if (!strcmp(buf, "h")) {
    83          shell_help();
    84      } else if (!strcmp(buf, "?")) {
    85          shell_help();
    86      } else if (!strcmp(buf, "s")) {
    87          send_message(remote_object);
    88      } else if (!strcmp(buf, "q")) {
    89          exit(0);
    90      } else {
    91          printf("Unknown command `%s'\n", buf);
    92      }
    93      return TRUE;
    94  }
    95
    96  int main (int argc, char **argv)
    97  {
    98      DBusGConnection *bus;
    99      DBusGProxy *remote_object;
   100      GError *error = NULL;
   101      GMainLoop *mainloop;
   102      GIOChannel *chan;
   103      guint source;
   104      GType features_type;
   105
   106  #ifdef SMSC_DEBUG
   107      g_slice_set_config(G_SLICE_CONFIG_ALWAYS_MALLOC, TRUE);
   108  #endif
   109      g_type_init ();
   110      mainloop = g_main_loop_new (NULL, FALSE);
   111
   112      bus = dbus_g_bus_get (DBUS_BUS_SESSION, &error);
   113      if (!bus)
   114          lose_gerror ("Couldn't connect to session bus", error);
   115
   116      remote_object = dbus_g_proxy_new_for_name (bus, "org.freesmartphone.ogsmd",
   117          "/org/freesmartphone/GSM/Device",
   118          "org.freesmartphone.GSM.SMS");
   119      if (!remote_object)
   120          lose_gerror ("Failed to get name owner", NULL);
   121
   122      features_type = sms_get_features_type();
   123      dbus_g_object_register_marshaller (sms_marshal_VOID__STRING_STRING_BOXED, G_TYPE_NONE, G_TYPE_STRING, G_TYPE_STRING,
   124          features_type, G_TYPE_INVALID);
   125      dbus_g_proxy_add_signal (remote_object, "IncomingMessage", G_TYPE_STRING, G_TYPE_STRING, features_type, G_TYPE_INVALID);
   126      dbus_g_proxy_connect_signal (remote_object, "IncomingMessage", G_CALLBACK (incoming_message_handler), NULL, NULL);
   127
   128      chan = g_io_channel_unix_new(0);
   129      source = g_io_add_watch(chan, G_IO_IN, channel_cb, remote_object);
   130      g_main_loop_run (mainloop);
   131      exit (0);
   132  }

112行连接会话总线。116-118行在会话总线上获取连接"org.freesmartphone.ogsmd"的对象"/org/freesmartphone/GSM/Device" 的接口"org.freesmartphone.GSM.SMS"的接口代理对象。

123行调用dbus_g_object_register_marshaller向dbus-glib登记列集函数。 125行调用dbus_g_proxy_add_signal增加对信号IncomingMessage的监听。126行登记信号IncomingMessage的回调函数。 123行登记的还是我们用glib-genmarshal生成的函数sms_marshal_VOID__STRING_STRING_BOXED。 dbus-glib使用这个函数从signal消息中取出信号参数,传递给回调函数,即执行散集操作。这说明glib-genmarshal生成的列集函数既可以用于列集,也可以用于散集。

客户端程序同样用IO Channel接受用户输入。129行在登记回调函数时将指向接口代理对象的指针作为参数传入。回调函数channel_cb在用户键入's'命令后通过send_message函数调用org.freesmartphone.GSM.SMS接口对象的SendMessage方法。 107行的设置G_SLICE_CONFIG_ALWAYS_MALLOC同样是为了用valgrind检查内存泄漏。

5.2、执行

我们先运行 dbus-monitor,然后运行smss,再运行smsc。先在smsc中键入's'回车调用SendMessage方法。然后在smss中键入's'回车发送IncomingMessage信号。然后在smsc中键入'q'回车退出。最后在smss中键入'q'回车退出。

$ ./smss
service is running
number=10987654321
contents=hello world
csm_num=8
alphabet=gsm
csm_seq=2
h
#       s       send signal
        q       Quit
s
# q
$ ./smsc
h
#       s       send message
        q       Quit
s
# SendMessage return 11
Received message with addree "12345678901" and it says: 
hello signal!
csm_num=3
alphabet=ucs2
csm_seq=1
q

我们可以看到打印出来的信号和消息。对于同一件事情,不同的层次的观察者会看到不同的细节,下表是dbus-monitor看到的东西:

smss连接会话总线。会话总线发NameOwnerChanged信号,通知唯一名":1.21"被分配。 signal sender=org.freedesktop.DBus -> dest=(null destination) path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=NameOwnerChanged
string ":1.21"
string ""
string ":1.21"
smss向会话总线发送Hello取得自己的唯一名":1.21"。 method call sender=:1.21 -> dest=org.freedesktop.DBus path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=Hello
smss调用AddMatch要求接收会话总线的NameOwnerChanged信号。 method call sender=:1.21 -> dest=org.freedesktop.DBus path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
string "type='signal',sender='org.freedesktop.DBus',path='/org/freedesktop/DBus',interface='org.freedesktop.DBus',member='NameOwnerChanged'"
smss调用AddMatch要求接收会话总线发送的所有信号。 method call sender=:1.21 -> dest=org.freedesktop.DBus path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
string "type='signal',sender='org.freedesktop.DBus',path='/',interface='org.freedesktop.DBus'"
smss调用GetNameOwner获取连接"org.freedesktop.DBus"的唯一名。 method call sender=:1.21 -> dest=org.freedesktop.DBus path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=GetNameOwner
string "org.freedesktop.DBus"
会话总线发送NameOwnerChanged信号,通知唯一名为":1.21"的连接获得了公众名"org.freesmartphone.ogsmd"。 signal sender=org.freedesktop.DBus -> dest=(null destination) path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=NameOwnerChanged
string "org.freesmartphone.ogsmd"
string ""
string ":1.21"
smss请求公众名"org.freesmartphone.ogsmd"。分配公众名在前,请求公众名在后,应该是监控过程颠倒了消息次序。 method call sender=:1.21 -> dest=org.freedesktop.DBus path=/; interface=org.freedesktop.DBus; member=RequestName
string "org.freesmartphone.ogsmd"
uint32 0
smsc连接会话总线。会话总线发NameOwnerChanged信号,通知唯一名":1.22"被分配。 signal sender=org.freedesktop.DBus -> dest=(null destination) path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=NameOwnerChanged
string ":1.22"
string ""
string ":1.22"
smss向会话总线发送Hello取得自己的唯一名":1.22"。 method call sender=:1.22 -> dest=org.freedesktop.DBus path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=Hello
smsc调用AddMatch要求接收会话总线的NameOwnerChanged信号。 method call sender=:1.22 -> dest=org.freedesktop.DBus path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
string "type='signal',sender='org.freedesktop.DBus',path='/org/freedesktop/DBus',interface='org.freedesktop.DBus',member='NameOwnerChanged'"
smsc调用AddMatch要求接收连接'org.freesmartphone.ogsmd'中对象'/org/freesmartphone/GSM/Device'的'org.freesmartphone.GSM.SMS'接口的信号。 method call sender=:1.22 -> dest=org.freedesktop.DBus path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=AddMatch
string "type='signal',sender='org.freesmartphone.ogsmd',path='/org/freesmartphone/GSM/Device',interface='org.freesmartphone.GSM.SMS'"
smsc调用GetNameOwner获取连接"org.freesmartphone.ogsmd"的唯一名。 method call sender=:1.22 -> dest=org.freedesktop.DBus path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=GetNameOwner
string "org.freesmartphone.ogsmd"
smsc调用连接'org.freesmartphone.ogsmd'中对象'/org/freesmartphone/GSM/Device'的'org.freesmartphone.GSM.SMS'接口的SendMessage方法。 method call sender=:1.22 -> dest=org.freesmartphone.ogsmd path=/org/freesmartphone/GSM/Device; interface=org.freesmartphone.GSM.SMS; member=SendMessage
string "10987654321"
string "hello world"
array [
dict entry(
string "csm_seq"
variant int32 2
)
dict entry(
string "alphabet"
variant string "gsm"
)
dict entry(
string "csm_num"
variant int32 8
)
]
smss向smsc发送method return消息,返回SendMessage方法的输出参数。 method return sender=:1.21 -> dest=:1.22 reply_serial=5
int32 11
smss发送IncomingMessage信号。 signal sender=:1.21 -> dest=(null destination) path=/org/freesmartphone/GSM/Device; interface=org.freesmartphone.GSM.SMS; member=IncomingMessage
string "12345678901"
string "hello signal!"
array [
dict entry(
string "csm_seq"
variant int32 1
)
dict entry(
string "alphabet"
variant string "ucs2"
)
dict entry(
string "csm_num"
variant int32 3
)
]
会话总线通知连接":1.22",即smsc的连接已经切断。 signal sender=org.freedesktop.DBus -> dest=(null destination) path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=NameOwnerChanged
string ":1.22"
string ":1.22"
string ""
会话总线通知拥有公共名"org.freesmartphone.ogsmd"的连接已经切断。 signal sender=org.freedesktop.DBus -> dest=(null destination) path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=NameOwnerChanged
string "org.freesmartphone.ogsmd"
string ":1.21"
string ""
会话总线通知拥有唯一名":1.21"的连接已经切断。即smss已经终止。 signal sender=org.freedesktop.DBus -> dest=(null destination) path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=NameOwnerChanged
string ":1.21"
string ":1.21"
string ""

6、工程

我提供下载的文件要用make distcheck制作的,其中包含了一些自动生成的文件。执行./clean.sh可以删掉自动生成的文件,只留下我创建的文件:

$ find . -type f
./clean.sh
./Makefile.am
./autogen.sh
./src/gsm_sms.h
./src/Makefile.am
./src/sms-marshal.list
./src/smss.xml
./src/smss.c
./src/gsm_sms.c
./src/sms_features.h
./src/sms_features.c
./src/smsc.c
./configure.ac

前面已经介绍过所有的源文件。我们再看看工程文件:

$ cat autogen.sh
#! /bin/sh
touch `find .`
aclocal
autoconf
autoheader
touch NEWS README AUTHORS ChangeLog
automake --add-missing

$ cat Makefile.am
SUBDIRS = src
EXTRA_DIST = autogen.sh clean.sh

autogen.sh建立工程环境。在执行clean.sh后,执行autogen.sh重新生成configure等工程文件。其中的touch命令是为了防止文件有将来的时间戳。因为我在虚拟机中运行ubuntu,所以可能会出现这类问题。 Makefile.am将autogen.sh clean.sh也作为发布文件。最重要的工程文件是"configure.ac"和"src/Makefile.am"。

6.1、configure.ac

$ cat -n configure.ac
     1  AC_INIT()
     2  AM_INIT_AUTOMAKE(hello-dbus5, 0.1)
     3  AM_CONFIG_HEADER(config.h)
     4
     5  AC_PROG_CC
     6
     7
     8  # Dbus detection
     9  PKG_CHECK_MODULES(DBUS, dbus-1 >= 1.1, have_dbus=yes, have_dbus=no)
    10
    11  if test x$have_dbus = xno ; then
    12      AC_MSG_ERROR([DBus development libraries not found])
    13  fi
    14  AM_CONDITIONAL(HAVE_DBUS, test x$have_dbus = xyes)
    15
    16  AC_SUBST(DBUS_CFLAGS)
    17  AC_SUBST(DBUS_LIBS)
    18
    19
    20  # Glib detection
    21  PKG_CHECK_MODULES(DBUS_GLIB, gobject-2.0 >= 2.6, have_glib=yes, have_glib=no)
    22
    23  if test x$have_glib = xno ; then
    24      AC_MSG_ERROR([GLib development libraries not found])
    25  fi
    26
    27  AM_CONDITIONAL(HAVE_GLIB, test x$have_glib = xyes)
    28
    29  AC_SUBST(DBUS_GLIB_CFLAGS)
    30  AC_SUBST(DBUS_GLIB_LIBS)
    31
    32
    33  AC_OUTPUT([Makefile
    34             src/Makefile])

8-17行检查dbus库,它们会生成编译常数DBUS_CFLAGS和DBUS_LIBS。 20-30行检查dbus-glib库,它们会生成编译常数DBUS_GLIB_CFLAGS和DBUS_GLIB_LIBS。

6.2、src/Makefile.am

$ cat -n src/Makefile.am
     1  INCLUDES = \
     2          $(DBUS_CFLAGS)                          \
     3          $(DBUS_GLIB_CFLAGS)                     \
     4          -DDBUS_COMPILATION
     5
     6  LIBS = \
     7          $(DBUS_LIBS)                            \
     8          $(DBUS_GLIB_LIBS)                       \
     9          -ldbus-glib-1
    10
    11  # smss
    12  noinst_PROGRAMS = smss
    13
    14  BUILT_SOURCES = smss-glue.h sms-marshal.h sms-marshal.c
    15  smss_SOURCES = $(BUILT_SOURCES) smss.c gsm_sms.c sms_features.c
    16  noinst_HEADERS = gsm_sms.h sms_features.h
    17
    18
    19  smss-glue.h: smss.xml
    20          $(LIBTOOL) --mode=execute dbus-binding-tool --prefix=gsm_sms --mode=glib-server --output=smss-glue.h $(srcdir)/smss.xml
    21
    22  sms-marshal.h: sms-marshal.list
    23          $(LIBTOOL) --mode=execute glib-genmarshal --header sms-marshal.list --prefix=sms_marshal > sms-marshal.h
    24
    25  sms-marshal.c: sms-marshal.list
    26          $(LIBTOOL) --mode=execute glib-genmarshal --body sms-marshal.list --prefix=sms_marshal > sms-marshal.c
    27
    28  CLEANFILES = $(BUILT_SOURCES)
    29
    30  EXTRA_DIST = smss.xml sms-marshal.list
    31
    32  # smss
    33  noinst_PROGRAMS += smsc
    34  smsc_SOURCES= smsc.c sms-marshal.c sms_features.c

19-20行由接口描述文件smss.xml生成存根文件smss-glue.h。22-26行由列集接口定义生成包含列集函数的代码。

7、结束语

本文介绍了一个简单的dbus-glib的例子,包括服务器和客户端。第一讲中还有一个加法例子,如果你理解了本文的例子,那个例子就更简单了。 dbus-glib源代码中有两个例子:

  • example-service和example-client演示方法调用。这个例子的接口描述文件中有个参数类型写错了,将(us)写成(ss),运行时会出错。可能作者想演示一下接口定义与代码实现不一致的后果吧。读者可以从这里下载我修改过的代码。
  • example-signal-emitter和example-signal-recipient演示信号发射。这个例子中,example-signal-recipient调用example-signal-emitter的方法请求发送信号。实际上信号应该是来自服务器侧的信息。我将其改成在example-signal-emitter中敲键发送信号。读者可以从这里下载我修改过的代码。

好了,《dbus实例讲解》到此结束。其实我的所有文章只是希望能让这复杂的世界简单一点。

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