DBUS入门与C编程

2023-05-16

https://blog.csdn.net/weixin_45566765/article/details/125028296

一、D-Bus简介

1. D-Bus是什么

D-Bus最主要的用途是在 Linux 桌面环境为进程提供通信，同时能将 Linux 桌面环境和 Linux 内核事件作为消息传递到进程。D-Bus(其中D原先是代表桌面“Desktop” 的意思)，即：用于桌面操作系统的通信总线。

D-Bus的主要概念为总线，注册后的进程可通过总线接收或传递消息，进程也可注册后等待内核事件响应，例如等待网络状态的转变或者计算机发出关机指令。

D-Bus是为Linux系统开发的进程间通信（IPC）和远程过程调用（RPC）机制，使用统一的通信协议来代替现有的各种IPC解决方案。D-Bus允许系统级进程（如：打印机和硬件驱动服务）和普通用户进程进行通信。

2. D-Bus特性

D-Bus使用一个快速的二进制消息传递协议，D-Bus协议的低延迟和低消耗特点适用于同一台机器的通信。D-Bus的规范目前由freedesktop.org项目定义，可供所有团体使用。

D-Bus不和低层的IPC直接竞争，比如sockets，shared memory或message queues。低层IPC有自己的特点，和D-Bus并不冲突。

与其他重量级的进程间通信技术不同，D-Bus是非事务的。D-Bus使用了状态以及连接的概念，比UDP等底层消息传输协议更“聪明”。但另一方面，D-Bus传送的是离散消息，与TCP协议将数据看做“流”有所不同。D-Bus支持点对点的消息传递以及广播/订阅式的通信。

总结如下：

1、D-BUS的协议是低延迟而且低开销的，设计小巧且高效，以便最小化传送时间。从设计上避免往返交互并允许异步操作。
2、协议是二进制的，而不是文本，排除序列化过程。
3、考虑了字节序问题。
4、易用性：按照消息而不是字节流来工作，并且自动地处理了许多困难的IPC问题，并且D-Bus库以可以封装的方式来设计，开发者可以使用框架里存在的对象/类型系统，而不用学习一种新的专用于IPC的对象/类型系统。
5、请求时启动服务以及安全策略。
6、支持多语言（C/C++/Java/C#/Python/Ruby），多平台(Linux/windows/maemo)。
7、采用C语言，而不是C++。 H、由于基本上不用于internet上的IPC，因此对本地IPC进行了特别优化。
8、提供服务注册，理论上可以进行无限扩展。
9、支持广播类型的通信。
10、带有异常处理的通用远程调用接口；

二、D-Bus架构

1. 结构层次

D-Bus进程间通信主要有三层架构：
1.底层接口层：主要是通过libdbus这个函数库，给予系统使用DBus的能力。

2.总线层：主要Message bus daemon这个总线守护进程提供的，在Linux系统启动时运行，负责进程间的消息路由和传递，其中包括Linux内核和Linux桌面环境的消息传递。总线守护进程可同时与多个应用程序相连，并能把来自一个应用程序的消息路由到0或者多个其他程序。

3.应用封装层：通过一系列基于特定应用程序框架将DBus的底层接口封装成友好的Wrapper库，供不同开发人员使用。比如libdbus-glib, libdbus-python.

2.系统总线和会话总线

在一台机器上总线守护有多个实例(instance)。这些总线之间都是相互独立的。
在这里插入图片描述

一个持久的系统总线（system bus）

它在引导时就会启动。这个总线由操作系统和后台进程使用，安全性非常好，以使得任意的应用程序不能欺骗系统事件。它是桌面会话和操作系统的通信，这里操作系统一般而言包括内核和系统守护进程。这种通道的最常用的方面就是发送系统消息，比如：插入一个新的存储设备；有新的网络连接；等等。
还将有很多会话总线（session buses）‘
普通进程创建，可同时存在多条。会话总线属于某个进程私有，它用于进程间传递消息。

三、D-Bus编程基础知识

1.address地址

使用d-bus的应用程序既可以是server也可以是client，server监听到来的连接，client连接到 server，一旦连接建立，消息就可以流转。点对点通信时就是一个 server 和一个 client；如果使用dbus daemon，所有的应用程序都是client，bus daemon 是server，daemon监听所有的连接，应用程序初始化连接到daemon。

dbus地址指明server将要监听的地方，client将要连接的地方，例如，地址：unix:path=/tmp/abcdef表明 server将在/tmp/abcdef路径下监听unix域的socket，client也将连接到这个socket。一个地址也可以指明是 TCP/IP的socket，或者是其他的。

当使用bus daemon时，libdbus会从环境变量中（DBUS_SESSION_BUS_ADDRESS）自动认识“会话daemon”的地址。如果是系统 daemon，它会检查指定的socket路径获得地址，也可以使用环境变量（DBUS_SESSION_BUS_ADDRESS）进行设定。

2. bus name 总线名字

当一个应用连接到 bus daemon，daemon 立即会分配一个名字给这个连接，称为 Unique Connection Name，这个唯一标识的名字以冒号 “:” 开头，例如 :1.2，这个名字在 daemon 的整个生命周期是唯一的。

但是这种名字总是临时分配，无法确定的，也难以记忆，因此应用可以要求有另外一个公共名 well-known name 来对应这个唯一标识，就像我们使用域名来映射 IP地址一样。例如可以使用 org.fmddlmyy.Test 来映射 :1.2。这样我们就可以使用公共名连接到 DBus 服务。

3. 原生对象和对象路径

d-bus 的底层接口是没有这些对象的概念的，它提供的是一种叫对象路径（object path），用于让高层接口绑定到各个对象中去，允许远端应用程序指向它们。object path就像是一个文件路径，可以叫做 /org/kde/kspread/sheets/3/cells/4/5 等。

4. 接口 Interface

接口是一组方法和信号，每一个对象支持一个或者多个接口，接口定义一个对象实体的类型。 D-Bus使用简单的命名空间字符串来表示接口，例如 org.freedesktop.Introspectable。

5. Methods 和 Signals

每一个对象有两类成员：方法和信号：

方法就是一个函数，具有有输入和输出；
信号会被广播，感兴趣的对象可以处理这个信号，同时信号中也可以带有相关的数据。

在 D-BUS 中有四种类型的消息：

1、方法调用（method call） # 在对象上执行一个方法
2、方法返回（method return） # 返回方法执行的结果
3、信号（signal） # 调用方法产生的异常
4、错误（error）# 通知指定的信号发生了，可以想象成“事件”。

要执行D-BUS对象的方法，您需要向对象发送一个方法调用消息。它将完成一些处理（就是执行了对象中的Method，Method是可以带有输入参数的）并返回，返回消息或者错误消息。信号的不同之处在于它们不返回任何内容：既没有“信号返回”消息，也没有任何类型的错误消息。

6. 总结：方法所需要的参数

要在指定的对象中调用指定的方法，需要知道的参数如下：
Address -> [Bus Name] -> Path -> Interface -> Method

bus name是可选的，除非是希望把消息送到特定的应用中才需要。interface也是可选的，有一些历史原因，DCOP不需要指定接口，因为DCOP在同一个对象中禁止同名的方法。

四、D-Bus运行环境

1. 运行环境安装

# 安装依赖
sudo apt-get install dbus
sudo apt-get install libgtk2.0-dev
sudo apt-get install libdbus-glib-1-dev
# 安装 D-Feet
sudo apt-get install d-feet

  
  
  
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同时下载一个简单的 DBus 程序：链接，运行方法：

tar -zxvf hello-dbus3-0.1.tar.gz

# 编译
cd hello-dbus3-0.1/
./autogen.sh
./configure
make

# 运行
cd src
./example-service

运行 d-feet，打开 Session bus，找到 “org.fmddlmyy.Test” 连接名，这个链接就是我们刚刚运行的一个D-Bus程序：

在这里插入图片描述

在右侧展开栏我们会发现 org.fmddlmyy.Test.Basic 下有一个 Add 方法，我们点击它，输入 1，2，点击执行，可以看到给我们返回了结果：

在这里插入图片描述

通过上面的操作我们通过 d-feet 发起了一次 d-bus 请求。

2. dbus-send以及dbus-monitor

dbus提供了两个小工具：dbus-send和dbus-monitor。我们可以用dbus-send发送消息。用dbus-monitor监视总线上流动的消息。让我们通过dbus-send发送消息来调用前面的Add方法，这时dbus-send充当了应用程序B。用dbus-monitor观察调用过程中的消息

保持上面的example-server运行，新建两个窗口一个运行dubs-monitor一个运行如下命令

dbus-send --session --type=method_call --print-reply --dest=org.fmddlmyy.Test /TestObj org.fmddlmyy.Test.Basic.Add int32:100 int32:999

 
 
 
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dbus-send的详细用法可以参阅手册。调用远程方法的一般形式是

$ dbus-send [--system | --session] --type=method_call --print-reply --dest=连接名 对象路径 接口名.方法名 参数类型:参数值 参数类型:参数值

   
   
   
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dbus-send支持的参数类型包括：string, int32, uint32, double, byte, boolea

dubs-monitor窗口返回的消息如下：

# 1、向 D-Bus Damon 发送Hello建立连接
method call time=1653831830.713656 sender=:1.97 -> destination=org.freedesktop.DBus serial=1 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=Hello
method return time=1653831830.713685 sender=org.freedesktop.DBus -> destination=:1.97 serial=1 reply_serial=1
   string ":1.97"
# 2、广播全局，指定名称的拥有者发生了变化 
signal time=1653831830.713696 sender=org.freedesktop.DBus -> destination=(null destination) serial=10 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=NameOwnerChanged
   string ":1.97"  # 名字
   string ""       # 拥有者原始名字
   string ":1.97"  # 拥有者现在名字
# 3、通知应用获得了指定名称的拥有权
signal time=1653831830.713712 sender=org.freedesktop.DBus -> destination=:1.97 serial=2 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=NameAcquired
   string ":1.97"
# 4、调用 Add 方法  
method call time=1653831830.714160 sender=:1.97 -> destination=org.fmddlmyy.Test serial=2 path=/TestObj; interface=org.fmddlmyy.Test.Basic; member=Add
   int32 123
   int32 456
# 5、Add 方法返回结果
method return time=1653831830.714310 sender=:1.95 -> destination=:1.97 serial=7 reply_serial=2
   int32 579
# 6、通知应用失去了指定名称的拥有权
signal time=1653831830.715690 sender=org.freedesktop.DBus -> destination=:1.97 serial=6 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=NameLost
   string ":1.97"
# 7、广播全局，指定名称的拥有者发生了变化
signal time=1653831830.715717 sender=org.freedesktop.DBus -> destination=(null destination) serial=11 path=/org/freedesktop/DBus; interface=org.freedesktop.DBus; member=NameOwnerChanged
   string ":1.97"
   string ":1.97"
   string ""

 
 
 
 
 
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上述一次完整的 d-bus 通信的流程

3.Dbus通信流程总结

(1) 方法调用的一般流程：

1.使用不同语言绑定的dbus高层接口，都提供了一些代理对象，调用其他进程里面的远端对象就像是在本地进程中的调用一样。应用调用代理上的方法，代理将构造一个方法调用消息给远端的进程。
2.在DBUS的底层接口中，应用需要自己构造方法调用消息（method call message），而不能使用代理。
3.方法调用消息里面的内容有：目的进程的bus name，方法的名字，方法的参数，目的进程的对象路径，以及可选的接口名称。
4.方法调用消息是发送到bus daemon中的。
5.bus daemon查找目标的bus name，如果找到，就把这个方法发送到该进程中，否则，daemon会产生错误消息，作为应答消息给发送进程。
6. 目标进程解开消息，在dbus底层接口中，会立即调用方法，然后发送方法的应答消息给daemon。在dbus高层接口中，会先检测对象路径，接口，方法名称，然后把它转换成对应的对象（如GObject，QT中的QObject等）的方法，然后再将应答结果转换成应答消息发给daemon。
7.bus daemon接受到应答消息，将把应答消息直接发给发出调用消息的进程。
8.应答消息中可以包容很多返回值，也可以标识一个错误发生，当使用绑定时，应答消息将转换为代理对象的返回值，或者进入异常

(2) 信号的一般流程：

1.当使用dbus底层接口时，信号需要应用自己创建和发送到daemon，使用dbus高层接口时，可以使用相关对象进行发送，如Glib里面提供的信号触发机制。
2.信号包含的内容有：信号的接口名称，信号名称，发送进程的bus name，以及其他参数。
3.任何进程都可以依据”match rules”注册相关的信号，daemon有一张注册的列表。
4.daemon检测信号，决定哪些进程对这个信号感兴趣，然后把信号发送给这些进程。
5.每个进程收到信号后，如果是使用了dbus高层接口，可以选择触发代理对象上的信号。如果是dbus底层接口，需要检查发送者名称和信号名称，然后决定怎么做。

五、DBUS编程

1. 通用代码介绍

（1）连接代码

首先，客户端必须要连接上 Dbus，一般来说，系统中会有一个 System Bus 和一个 Session Bus。其次，你需要在 Dbus 中注册一个名字，用于标识自己。为了简单起见，这里先不考虑重名的情况：

DBusError err;
DBusConnection* conn;
int ret;
// initialise the errors
dbus_error_init(&err);

// connect to the bus
conn = dbus_bus_get(DBUS_BUS_SESSION, &err);
if (dbus_error_is_set(&err)) {
fprintf(stderr, “Connection Error (%s)\n”, err.message);
dbus_error_free(&err);
}
if (NULL == conn) {
exit(1);
}
// request a name on the bus
ret = dbus_bus_request_name(conn, “test.method.server”,
DBUS_NAME_FLAG_REPLACE_EXISTING
, &err);
if (dbus_error_is_set(&err)) {
fprintf(stderr, “Name Error (%s)\n”, err.message);
dbus_error_free(&err);
}
if (DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER != ret) {
exit(1);
}

一般来说，连接上 Dbus 和注册一个名称，应该是在程序最开始运行的时候就会进行的操作。

当然，在程序结束的时候，需要关闭掉与 Dbus 的连接。使用下面的函数：

dbus_connection_close(conn);

 
 
 
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(2) 发送信号（Sending Signal）

信号是一种广播的消息，你可以简单的发出一个信号，这样，所有连接在 DBus 总线上并注册了接受对应信号的进程，都会收到这个信号。

为了发出一个信号，需要的只是创建一个 DBusMessage 对象来代表信号，然后追加上一些需要发出的参数，就可以发向总线了。

发完之后还需要释放掉 Message。如果内存不足的话，这下面不少函数都会返回 false，所以一般情况下你都需要处理这些情况的返回值。

dbus_uint32_t serial = 0; // unique number to associate replies with requests
DBusMessage* msg;
DBusMessageIter args;

// create a signal and check for errors
msg = dbus_message_new_signal(“/test/signal/Object”, // object name of the signal
“test.signal.Type”, // interface name of the signal
“Test”); // name of the signal
if (NULL == msg)
{
fprintf(stderr, “Message Null\n”);
exit(1);
}

// append arguments onto signal
dbus_message_iter_init_append(msg, &args);
if (!dbus_message_iter_append_basic(&args, DBUS_TYPE_STRING, &sigvalue)) {
fprintf(stderr, “Out Of Memory!\n”);
exit(1);
}

// send the message and flush the connection
if (!dbus_connection_send(conn, msg, &serial)) {
fprintf(stderr, “Out Of Memory!\n”);
exit(1);
}
dbus_connection_flush(conn);

// free the message
dbus_message_unref(msg);

(3) 调用方法(Call a Methond)

调用一个远程方法（remote method）与发送一个信号（sending a signal）是很类似的。需要创建一个 DBusMessage，然后通过注册在 DBus 上的名称指定发送的对象，追加相应的参数，但调用方法分为两种，一种是阻塞式的，另一种则可以异步调用。异步调用的时候会得到一个 DBusMessage* 的返回，从这个 DBusMessage 中可以获取一些返回的参数。

调用方法1

DBusMessage* msg;
DBusMessageIter args;
DBusPendingCall* pending;

msg = dbus_message_new_method_call(“test.method.server”, // target for the method call
“/test/method/Object”, // object to call on
“test.method.Type”, // interface to call on
“Method”); // method name
if (NULL == msg) {
fprintf(stderr, “Message Null\n”);
exit(1);
}

// append arguments
dbus_message_iter_init_append(msg, &args);
if (!dbus_message_iter_append_basic(&args, DBUS_TYPE_STRING, &param)) {
fprintf(stderr, “Out Of Memory!\n”);
exit(1);
}

// send message and get a handle for a reply
if (!dbus_connection_send_with_reply (conn, msg, &pending, -1)) { // -1 is default timeout
fprintf(stderr, “Out Of Memory!\n”);
exit(1);
}
if (NULL == pending) {
fprintf(stderr, “Pending Call Null\n”);
exit(1);
}
dbus_connection_flush(conn);

// free message
dbus_message_unref(msg);

调用方法2

bool stat;
dbus_uint32_t level;

// block until we receive a reply
dbus_pending_call_block(pending);

// get the reply message
msg = dbus_pending_call_steal_reply(pending);
if (NULL == msg) {
fprintf(stderr, “Reply Null\n”);
exit(1);
}
// free the pending message handle
dbus_pending_call_unref(pending);

// read the parameters
if (!dbus_message_iter_init(msg, &args))
fprintf(stderr, “Message has no arguments!\n”);
else if (DBUS_TYPE_BOOLEAN != dbus_message_iter_get_arg_type(&args))
fprintf(stderr, “Argument is not boolean!\n”);
else
dbus_message_iter_get_basic(&args, &stat);

if (!dbus_message_iter_next(&args))
fprintf(stderr, “Message has too few arguments!\n”);
else if (DBUS_TYPE_UINT32 != dbus_message_iter_get_arg_type(&args))
fprintf(stderr, “Argument is not int!\n”);
else
dbus_message_iter_get_basic(&args, &level);

printf(“Got Reply: %d, %d\n”, stat, level);

// free reply and close connection
dbus_message_unref(msg);

(4) 接收消息（Receiving a Signal）

接下来的两种操作是从总线读取消息并处理这些消息。

要接收一个消息，你首先需要告诉 DBus 你对什么样的消息感兴趣：

// add a rule for which messages we want to see
dbus_bus_add_match(conn,
                   "type='signal',interface='test.signal.Type'",
                   &err); // see signals from the given interface
dbus_connection_flush(conn);
if (dbus_error_is_set(&err)) {
    fprintf(stderr, "Match Error (%s)\n", err.message);
    exit(1);
}

 
 
 
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然后，进程就可以在一个循环中等待这类消息的发生了：

/ loop listening for signals being emmitted
while (true) {
<span class="token comment">// non blocking read of the next available message</span>
<span class="token function">dbus_connection_read_write</span><span class="token punctuation">(</span>conn<span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
msg <span class="token operator">=</span> <span class="token function">dbus_connection_pop_message</span><span class="token punctuation">(</span>conn<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token comment">// loop again if we haven't read a message</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token constant">NULL</span> <span class="token operator">==</span> msg<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
    <span class="token function">sleep</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">continue</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token comment">// check if the message is a signal from the correct interface and with the correct name</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">dbus_message_is_signal</span><span class="token punctuation">(</span>msg<span class="token punctuation">,</span> <span class="token string">"test.signal.Type"</span><span class="token punctuation">,</span> <span class="token string">"Test"</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
    <span class="token comment">// read the parameters</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">dbus_message_iter_init</span><span class="token punctuation">(</span>msg<span class="token punctuation">,</span> <span class="token operator">&amp;</span>args<span class="token punctuation">)</span><span class="token punctuation">)</span>
        <span class="token function">fprintf</span><span class="token punctuation">(</span><span class="token constant">stderr</span><span class="token punctuation">,</span> <span class="token string">"Message has no arguments!\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span>DBUS_TYPE_STRING <span class="token operator">!=</span> <span class="token function">dbus_message_iter_get_arg_type</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>args<span class="token punctuation">)</span><span class="token punctuation">)</span>
        <span class="token function">fprintf</span><span class="token punctuation">(</span><span class="token constant">stderr</span><span class="token punctuation">,</span> <span class="token string">"Argument is not string!\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">else</span> <span class="token punctuation">{<!-- --></span>
        <span class="token function">dbus_message_iter_get_basic</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>args<span class="token punctuation">,</span> <span class="token operator">&amp;</span>sigvalue<span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"Got Signal with value %s\n"</span><span class="token punctuation">,</span> sigvalue<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

<span class="token comment">// free the message</span>
<span class="token function">dbus_message_unref</span><span class="token punctuation">(</span>msg<span class="token punctuation">)</span><span class="token punctuation">;</span>

}

(5) 提供被远程调用的方法（Exposing a Method to be called）

在(3) 调用方法(Call a Methond)中，我们看到了调用一个远程方法，这节就是告诉我们怎么样提供一个方法让别的应用程序调用。用下面的程序，就可以把方法关联在那些提供给外部的方法上，并解析出相应的参数，最后构建一个消息返回给调用方法的应用程序。

远程调用的方法1

// loop, testing for new messages
while (true) {
    // non blocking read of the next available message
    dbus_connection_read_write(conn, 0);
    msg = dbus_connection_pop_message(conn);
<span class="token comment">// loop again if we haven't got a message</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token constant">NULL</span> <span class="token operator">==</span> msg<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
    <span class="token function">sleep</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">continue</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token comment">// check this is a method call for the right interface and method</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">dbus_message_is_method_call</span><span class="token punctuation">(</span>msg<span class="token punctuation">,</span> <span class="token string">"test.method.Type"</span><span class="token punctuation">,</span> <span class="token string">"Method"</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
    <span class="token function">reply_to_method_call</span><span class="token punctuation">(</span>msg<span class="token punctuation">,</span> conn<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token comment">// free the message</span>
<span class="token function">dbus_message_unref</span><span class="token punctuation">(</span>msg<span class="token punctuation">)</span><span class="token punctuation">;</span>

}

远程调用方法2：

void reply_to_method_call(DBusMessage* msg, DBusConnection* conn)
{
    DBusMessage* reply;
    DBusMessageIter args;
    DBusConnection* conn;
    bool stat = true;
    dbus_uint32_t level = 21614;
    dbus_uint32_t serial = 0;
    char* param = "";
<span class="token comment">// read the arguments</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">dbus_message_iter_init</span><span class="token punctuation">(</span>msg<span class="token punctuation">,</span> <span class="token operator">&amp;</span>args<span class="token punctuation">)</span><span class="token punctuation">)</span>
    <span class="token function">fprintf</span><span class="token punctuation">(</span><span class="token constant">stderr</span><span class="token punctuation">,</span> <span class="token string">"Message has no arguments!\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span>DBUS_TYPE_STRING <span class="token operator">!=</span> <span class="token function">dbus_message_iter_get_arg_type</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>args<span class="token punctuation">)</span><span class="token punctuation">)</span>
    <span class="token function">fprintf</span><span class="token punctuation">(</span><span class="token constant">stderr</span><span class="token punctuation">,</span> <span class="token string">"Argument is not string!\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">else</span>
    <span class="token function">dbus_message_iter_get_basic</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>args<span class="token punctuation">,</span> <span class="token operator">&amp;</span>param<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"Method called with %s\n"</span><span class="token punctuation">,</span> param<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token comment">// create a reply from the message</span>
reply <span class="token operator">=</span> <span class="token function">dbus_message_new_method_return</span><span class="token punctuation">(</span>msg<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token comment">// add the arguments to the reply</span>
<span class="token function">dbus_message_iter_init_append</span><span class="token punctuation">(</span>reply<span class="token punctuation">,</span> <span class="token operator">&amp;</span>args<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">dbus_message_iter_append_basic</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>args<span class="token punctuation">,</span> DBUS_TYPE_BOOLEAN<span class="token punctuation">,</span> <span class="token operator">&amp;</span>stat<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
    <span class="token function">fprintf</span><span class="token punctuation">(</span><span class="token constant">stderr</span><span class="token punctuation">,</span> <span class="token string">"Out Of Memory!\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token function">exit</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">dbus_message_iter_append_basic</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>args<span class="token punctuation">,</span> DBUS_TYPE_UINT32<span class="token punctuation">,</span> <span class="token operator">&amp;</span>level<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
    <span class="token function">fprintf</span><span class="token punctuation">(</span><span class="token constant">stderr</span><span class="token punctuation">,</span> <span class="token string">"Out Of Memory!\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token function">exit</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token comment">// send the reply &amp;&amp; flush the connection</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">dbus_connection_send</span><span class="token punctuation">(</span>conn<span class="token punctuation">,</span> reply<span class="token punctuation">,</span> <span class="token operator">&amp;</span>serial<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
    <span class="token function">fprintf</span><span class="token punctuation">(</span><span class="token constant">stderr</span><span class="token punctuation">,</span> <span class="token string">"Out Of Memory!\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token function">exit</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token function">dbus_connection_flush</span><span class="token punctuation">(</span>conn<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token comment">// free the reply</span>
<span class="token function">dbus_message_unref</span><span class="token punctuation">(</span>reply<span class="token punctuation">)</span><span class="token punctuation">;</span>

}

2. 实例代码

(1) 客户端代码

client.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <dbus/dbus.h>

DBusConnection init_bus()
{
DBusConnection connection;
DBusError err;
int ret;

<span class="token function">dbus_error_init</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>err<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token comment">//连接到dbus,建立一个连接，称为对象</span>
connection <span class="token operator">=</span> <span class="token function">dbus_bus_get</span><span class="token punctuation">(</span>DBUS_BUS_SESSION<span class="token punctuation">,</span> <span class="token operator">&amp;</span>err<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token function">dbus_error_is_set</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>err<span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token punctuation">{<!-- --></span>
	<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"connection error: :%s -- %s\n"</span><span class="token punctuation">,</span> err<span class="token punctuation">.</span>name<span class="token punctuation">,</span> err<span class="token punctuation">.</span>message<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token function">dbus_error_free</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>err<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token keyword">return</span> <span class="token constant">NULL</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
    <span class="token comment">//为这个对象分配一个名字</span>
ret <span class="token operator">=</span> <span class="token function">dbus_bus_request_name</span><span class="token punctuation">(</span>connection<span class="token punctuation">,</span> <span class="token string">"hello.world.client"</span><span class="token punctuation">,</span> DBUS_NAME_FLAG_REPLACE_EXISTING<span class="token punctuation">,</span> <span class="token operator">&amp;</span>err<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token function">dbus_error_is_set</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>err<span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token punctuation">{<!-- --></span>
	<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"Name error: %s -- %s\n"</span><span class="token punctuation">,</span> err<span class="token punctuation">.</span>name<span class="token punctuation">,</span> err<span class="token punctuation">.</span>message<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token function">dbus_error_free</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>err<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token keyword">return</span> <span class="token constant">NULL</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">if</span><span class="token punctuation">(</span>ret <span class="token operator">!=</span> DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER<span class="token punctuation">)</span>
	<span class="token keyword">return</span> <span class="token constant">NULL</span><span class="token punctuation">;</span>

<span class="token keyword">return</span> connection<span class="token punctuation">;</span>

}

void send_signal(DBusConnection connection)
{
DBusMessage msg;
DBusMessageIter arg;
char *str = “hello world!”;

<span class="token comment">//创建一个signal对象</span>
<span class="token comment">//param1: path （这个逻辑来说，可以是任何字符串，只要符合规则即可）</span>
<span class="token comment">//param2: interface (一样)</span>
<span class="token comment">//param3: 信号方法名（必须与服务端名匹配）</span>
<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token punctuation">(</span>msg <span class="token operator">=</span> <span class="token function">dbus_message_new_signal</span><span class="token punctuation">(</span><span class="token string">"/hello"</span><span class="token punctuation">,</span> <span class="token string">"aa.bb.cc"</span><span class="token punctuation">,</span> <span class="token string">"alarm_test"</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token constant">NULL</span><span class="token punctuation">)</span>
<span class="token punctuation">{<!-- --></span>
	<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"message is NULL\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token keyword">return</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

#if 0
　//这个看需求添加，一般来说，信号是一种单向广播，加上这一句变单向单播
//param2: bus_name
if(!dbus_message_set_destination(msg, “hello.world.service”))
{
printf(“memory error\n”);
}
#endif

<span class="token comment">//添加参数的一些接口</span>
<span class="token function">dbus_message_iter_init_append</span><span class="token punctuation">(</span>msg<span class="token punctuation">,</span> <span class="token operator">&amp;</span>arg<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token function">dbus_message_iter_append_basic</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>arg<span class="token punctuation">,</span> DBUS_TYPE_STRING<span class="token punctuation">,</span> <span class="token operator">&amp;</span>str<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//入队</span>
<span class="token function">dbus_connection_send</span><span class="token punctuation">(</span>connection<span class="token punctuation">,</span> msg<span class="token punctuation">,</span> <span class="token constant">NULL</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//发送</span>
<span class="token function">dbus_connection_flush</span><span class="token punctuation">(</span>connection<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//释放内存</span>
<span class="token function">dbus_message_unref</span><span class="token punctuation">(</span>msg<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token keyword">return</span><span class="token punctuation">;</span>

}

void send_method_call(DBusConnection connection)
{
DBusMessage msg;
DBusMessageIter arg;
DBusPendingCall *pending;
int a = 100;
int b = 99;
int sum;

msg <span class="token operator">=</span> <span class="token function">dbus_message_new_method_call</span><span class="token punctuation">(</span><span class="token string">"hello.world.service"</span><span class="token punctuation">,</span> <span class="token string">"/hello/world"</span><span class="token punctuation">,</span><span class="token string">"hello.world"</span><span class="token punctuation">,</span> <span class="token string">"add"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span><span class="token punctuation">(</span>msg <span class="token operator">==</span> <span class="token constant">NULL</span><span class="token punctuation">)</span>
<span class="token punctuation">{<!-- --></span>
	<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"no memory\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token keyword">return</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token function">dbus_message_iter_init_append</span><span class="token punctuation">(</span>msg<span class="token punctuation">,</span> <span class="token operator">&amp;</span>arg<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">dbus_message_iter_append_basic</span> <span class="token punctuation">(</span><span class="token operator">&amp;</span>arg<span class="token punctuation">,</span> DBUS_TYPE_INT32<span class="token punctuation">,</span><span class="token operator">&amp;</span>a<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">{<!-- --></span>
    	<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"no memory!"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    	<span class="token function">dbus_message_unref</span><span class="token punctuation">(</span>msg<span class="token punctuation">)</span><span class="token punctuation">;</span>
    	<span class="token keyword">return</span><span class="token punctuation">;</span>
	<span class="token punctuation">}</span>
<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">dbus_message_iter_append_basic</span> <span class="token punctuation">(</span><span class="token operator">&amp;</span>arg<span class="token punctuation">,</span> DBUS_TYPE_INT32<span class="token punctuation">,</span><span class="token operator">&amp;</span>b<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">{<!-- --></span>
    	<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"no memory!"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    	<span class="token function">dbus_message_unref</span><span class="token punctuation">(</span>msg<span class="token punctuation">)</span><span class="token punctuation">;</span>
    	<span class="token keyword">return</span><span class="token punctuation">;</span>
	<span class="token punctuation">}</span>

<span class="token comment">//入队message,等待回复</span>
<span class="token comment">//param1: 连接描述符</span>
<span class="token comment">//param2:　message</span>
<span class="token comment">//param3: 相当于一个回调的一个描述符，为了获了返回的消息</span>
<span class="token comment">//param4:　超时间．　-１代表无限</span>
<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">dbus_connection_send_with_reply</span> <span class="token punctuation">(</span>connection<span class="token punctuation">,</span> msg<span class="token punctuation">,</span> <span class="token operator">&amp;</span>pending<span class="token punctuation">,</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">{<!-- --></span>
    <span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"no memeory!"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token function">dbus_message_unref</span><span class="token punctuation">(</span>msg<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">return</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token keyword">if</span><span class="token punctuation">(</span>pending <span class="token operator">==</span> <span class="token constant">NULL</span><span class="token punctuation">)</span><span class="token punctuation">{<!-- --></span>
    <span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"Pending is NULL, may be disconnect...\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token function">dbus_message_unref</span><span class="token punctuation">(</span>msg<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">return</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token comment">//send</span>
<span class="token function">dbus_connection_flush</span><span class="token punctuation">(</span>connection<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token function">dbus_message_unref</span><span class="token punctuation">(</span>msg<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token comment">//阻塞，直到接收到一个响应．</span>
<span class="token function">dbus_pending_call_block</span> <span class="token punctuation">(</span>pending<span class="token punctuation">)</span><span class="token punctuation">;</span>
msg <span class="token operator">=</span> <span class="token function">dbus_pending_call_steal_reply</span> <span class="token punctuation">(</span>pending<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>msg <span class="token operator">==</span> <span class="token constant">NULL</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
	<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"reply is null. error\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token keyword">return</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token comment">//释放pending内存 </span>
<span class="token function">dbus_pending_call_unref</span><span class="token punctuation">(</span>pending<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//解析参数</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">dbus_message_iter_init</span><span class="token punctuation">(</span>msg<span class="token punctuation">,</span> <span class="token operator">&amp;</span>arg<span class="token punctuation">)</span><span class="token punctuation">)</span>
    <span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"no argument, error\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token function">dbus_message_iter_get_arg_type</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>arg<span class="token punctuation">)</span> <span class="token operator">!=</span> DBUS_TYPE_INT32<span class="token punctuation">)</span>
<span class="token punctuation">{<!-- --></span>
	<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"paramter type error\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token function">dbus_message_iter_get_basic</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>arg<span class="token punctuation">,</span> <span class="token operator">&amp;</span>sum<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">" a(%d) + b(%d) = %d\n"</span><span class="token punctuation">,</span>a<span class="token punctuation">,</span> b<span class="token punctuation">,</span> sum<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token function">dbus_message_unref</span><span class="token punctuation">(</span>msg<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token keyword">return</span><span class="token punctuation">;</span>

}

int main(int argc, char argv)
{
DBusConnection *connection;

connection <span class="token operator">=</span> <span class="token function">init_bus</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span><span class="token punctuation">(</span>connection <span class="token operator">==</span> <span class="token constant">NULL</span><span class="token punctuation">)</span>
<span class="token punctuation">{<!-- --></span>
	<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"connect to bus failed...\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token keyword">return</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
    <span class="token comment">//发送一个信号及一个方法调用</span>
<span class="token function">send_signal</span><span class="token punctuation">(</span>connection<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token function">send_method_call</span><span class="token punctuation">(</span>connection<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token keyword">return</span> <span class="token number">0</span><span class="token punctuation">;</span>

}

(2) 服务端代码

service.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dbus/dbus.h>
#include <unistd.h>

DBusConnection init_bus()
{
DBusConnection connection;
DBusError err;
int ret = 0;

<span class="token function">dbus_error_init</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>err<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token comment">//与session dbus 建立连接</span>
<span class="token comment">//param1：bus type = {DBUS_BUS_SESSION, DBUS_BUS_SYSTEM} 一个系统dbus, 一个普通用户dbus</span>
<span class="token comment">//param2：错误信息，包括错误名与错误信息．</span>
connection <span class="token operator">=</span> <span class="token function">dbus_bus_get</span><span class="token punctuation">(</span>DBUS_BUS_SESSION<span class="token punctuation">,</span> <span class="token operator">&amp;</span>err<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token function">dbus_error_is_set</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>err<span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token punctuation">{<!-- --></span>
	<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"Connection Error: %s--%s\n"</span><span class="token punctuation">,</span> err<span class="token punctuation">.</span>name<span class="token punctuation">,</span> err<span class="token punctuation">.</span>message<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token function">dbus_error_free</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>err<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token keyword">return</span> <span class="token constant">NULL</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token comment">//为连接设置一个bus name: bus_name;</span>
<span class="token comment">//param 1: 连接描述符</span>
<span class="token comment">//param 2: 请求bus要分配的bus name(逻辑上讲，bus name可以是任何字符串，只要符合命名规则)</span>
<span class="token comment">//param 3:　flags ={DBUS_NAME_FLAG_REPLACE_EXISTING, </span>
<span class="token comment">//					DBUS_NAME_FLAG_ALLOW_REPLACEMENT,</span>
<span class="token comment">//					DBUS_NAME_FLAG_DO_NOT_QUEUE</span>
<span class="token comment">//					 }</span>
<span class="token comment">//param 4: err info</span>
ret <span class="token operator">=</span> <span class="token function">dbus_bus_request_name</span><span class="token punctuation">(</span>connection<span class="token punctuation">,</span> <span class="token string">"hello.world.service"</span><span class="token punctuation">,</span> DBUS_NAME_FLAG_REPLACE_EXISTING<span class="token punctuation">,</span> <span class="token operator">&amp;</span>err<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token function">dbus_error_is_set</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>err<span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token punctuation">{<!-- --></span> <span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"Name Error: %s--%s\n"</span><span class="token punctuation">,</span> err<span class="token punctuation">.</span>name<span class="token punctuation">,</span> err<span class="token punctuation">.</span>message<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token function">dbus_error_free</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>err<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token keyword">return</span> <span class="token constant">NULL</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token keyword">if</span><span class="token punctuation">(</span>ret <span class="token operator">!=</span> DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER<span class="token punctuation">)</span>
	<span class="token keyword">return</span> <span class="token constant">NULL</span><span class="token punctuation">;</span>

<span class="token comment">//注册感兴趣的signal: 来自接口dbus.test.signal.sender</span>
<span class="token comment">//param1: 连接描述符</span>
<span class="token comment">//param2: match rule　（常用的类型：　sender=</span>
<span class="token comment">//									interface=</span>
<span class="token comment">//									type=</span>
<span class="token comment">//									member= ）</span>
<span class="token comment">//param3: err info</span>
<span class="token comment">//只设置一个type = signal,表示所有信号都接受．也可以加上接口，发送者bus_name</span>
<span class="token function">dbus_bus_add_match</span><span class="token punctuation">(</span>connection<span class="token punctuation">,</span> <span class="token string">"type='signal'"</span><span class="token punctuation">,</span> <span class="token operator">&amp;</span>err<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//阻塞，直到消息发送成功．</span>
<span class="token function">dbus_connection_flush</span><span class="token punctuation">(</span>connection<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token function">dbus_error_is_set</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>err<span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token punctuation">{<!-- --></span>
	<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"add Match Error %s--%s\n"</span><span class="token punctuation">,</span> err<span class="token punctuation">.</span>name<span class="token punctuation">,</span> err<span class="token punctuation">.</span>message<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token function">dbus_error_free</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>err<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token keyword">return</span> connection<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">return</span> connection<span class="token punctuation">;</span>

}

void handle_message(DBusConnection connection)
{
DBusMessage msg;
DBusMessageIter arg;
char *str;

<span class="token keyword">while</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span>
<span class="token punctuation">{<!-- --></span>
	<span class="token comment">//param1: 连接描述符</span>
	<span class="token comment">//param2: 超时时间，　-1无限超时时间</span>
	<span class="token function">dbus_connection_read_write</span><span class="token punctuation">(</span>connection<span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token comment">//从队列中取出一条消息</span>
	msg <span class="token operator">=</span> <span class="token function">dbus_connection_pop_message</span><span class="token punctuation">(</span>connection<span class="token punctuation">)</span><span class="token punctuation">;</span> 
	<span class="token keyword">if</span><span class="token punctuation">(</span>msg <span class="token operator">==</span> <span class="token constant">NULL</span><span class="token punctuation">)</span>
	<span class="token punctuation">{<!-- --></span>
		<span class="token function">sleep</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token keyword">continue</span><span class="token punctuation">;</span>
	<span class="token punctuation">}</span>
	<span class="token comment">//这里应该过滤path，暂且不做</span>
	<span class="token comment">//打印出消息对象路径</span>
	<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"path: %s\n"</span><span class="token punctuation">,</span> <span class="token function">dbus_message_get_path</span> <span class="token punctuation">(</span>msg<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token comment">//param1: message</span>
	<span class="token comment">//param2: interface 这个名字必须与发送那个接口一样．才能处理</span>
	<span class="token comment">//param3: singal name 方法名也必须一样．</span>
	<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token function">dbus_message_is_signal</span><span class="token punctuation">(</span>msg<span class="token punctuation">,</span> <span class="token string">"aa.bb.cc"</span><span class="token punctuation">,</span> <span class="token string">"alarm_test"</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
	<span class="token punctuation">{<!-- --></span>
		<span class="token comment">//解析message 参数，０为无参数．</span>
		<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">dbus_message_iter_init</span><span class="token punctuation">(</span>msg<span class="token punctuation">,</span> <span class="token operator">&amp;</span>arg<span class="token punctuation">)</span><span class="token punctuation">)</span>
		<span class="token punctuation">{<!-- --></span>
			<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"no argument\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token punctuation">}</span>
		<span class="token comment">//获取第一个参数类型</span>
		<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token function">dbus_message_iter_get_arg_type</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>arg<span class="token punctuation">)</span> <span class="token operator">!=</span> DBUS_TYPE_INVALID<span class="token punctuation">)</span>
		<span class="token punctuation">{<!-- --></span>
			<span class="token comment">//获取参数的值</span>
			<span class="token function">dbus_message_iter_get_basic</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>arg<span class="token punctuation">,</span><span class="token operator">&amp;</span>str<span class="token punctuation">)</span><span class="token punctuation">;</span>
			<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"recv param --: %s\n"</span><span class="token punctuation">,</span> str<span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token punctuation">}</span>
		
	<span class="token punctuation">}</span>
	<span class="token keyword">else</span> <span class="token keyword">if</span><span class="token punctuation">(</span><span class="token function">dbus_message_is_method_call</span><span class="token punctuation">(</span>msg<span class="token punctuation">,</span> <span class="token string">"hello.world"</span><span class="token punctuation">,</span> <span class="token string">"add"</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
	<span class="token punctuation">{<!-- --></span><span class="token comment">//处理 add　远程调用．</span>
		DBusMessage <span class="token operator">*</span>rp<span class="token punctuation">;</span>
		DBusMessageIter r_arg<span class="token punctuation">;</span>
		<span class="token keyword">int</span> a <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
		<span class="token keyword">int</span> b <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
		<span class="token keyword">int</span> sum <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
		<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"service: add  function\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

		<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">dbus_message_iter_init</span><span class="token punctuation">(</span>msg<span class="token punctuation">,</span> <span class="token operator">&amp;</span>arg<span class="token punctuation">)</span><span class="token punctuation">)</span>
		<span class="token punctuation">{<!-- --></span>
			<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"no argument!\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
			<span class="token keyword">goto</span> out<span class="token punctuation">;</span>
		<span class="token punctuation">}</span>
		<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token function">dbus_message_iter_get_arg_type</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>arg<span class="token punctuation">)</span> <span class="token operator">!=</span> DBUS_TYPE_INT32<span class="token punctuation">)</span>
		<span class="token punctuation">{<!-- --></span>
			<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"argument error\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
			<span class="token keyword">goto</span> out<span class="token punctuation">;</span>
		<span class="token punctuation">}</span>
		<span class="token function">dbus_message_iter_get_basic</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>arg<span class="token punctuation">,</span> <span class="token operator">&amp;</span>a<span class="token punctuation">)</span><span class="token punctuation">;</span>

		<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">dbus_message_iter_next</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>arg<span class="token punctuation">)</span><span class="token punctuation">)</span>
		<span class="token punctuation">{<!-- --></span>
			<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"too few argument!\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
			<span class="token keyword">goto</span> out<span class="token punctuation">;</span>
		<span class="token punctuation">}</span>
		<span class="token comment">//check argument type....</span>
		<span class="token function">dbus_message_iter_get_basic</span><span class="token punctuation">(</span><span class="token operator">&amp;</span>arg<span class="token punctuation">,</span> <span class="token operator">&amp;</span>b<span class="token punctuation">)</span><span class="token punctuation">;</span>
		sum <span class="token operator">=</span> a <span class="token operator">+</span> b<span class="token punctuation">;</span>

out:
//new 一个回应对象
rp = dbus_message_new_method_return(msg);
dbus_message_iter_init_append(rp, &r_arg);
if(!dbus_message_iter_append_basic(&r_arg, DBUS_TYPE_INT32, &sum))
{
printf(“no memory!!\n”);
return;
}

		<span class="token comment">//param3: 这个跟消息序列有关</span>
		<span class="token keyword">if</span><span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">dbus_connection_send</span><span class="token punctuation">(</span>connection<span class="token punctuation">,</span> rp<span class="token punctuation">,</span> <span class="token constant">NULL</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
		<span class="token punctuation">{<!-- --></span>
			<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"no memory!!\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
			<span class="token keyword">return</span><span class="token punctuation">;</span>
		<span class="token punctuation">}</span>
		<span class="token function">dbus_connection_flush</span><span class="token punctuation">(</span>connection<span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token function">dbus_message_unref</span><span class="token punctuation">(</span>rp<span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token punctuation">}</span>
	<span class="token comment">//释放空间</span>
	<span class="token function">dbus_message_unref</span><span class="token punctuation">(</span>msg<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token comment">//dbus_bus_remove_match();</span>

}

int main(int argc, char argv)
{
int ret = 0;
DBusConnection *connection;

connection <span class="token operator">=</span> <span class="token function">init_bus</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span><span class="token punctuation">(</span>connection <span class="token operator">==</span> <span class="token constant">NULL</span><span class="token punctuation">)</span>
<span class="token punctuation">{<!-- --></span>
	<span class="token function">printf</span><span class="token punctuation">(</span><span class="token string">"connect the dbus failed...\n"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token keyword">return</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token function">handle_message</span><span class="token punctuation">(</span>connection<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token keyword">return</span> <span class="token number">0</span><span class="token punctuation">;</span>

}

(3)执行结果

客户端

在这里插入图片描述

服务端

在这里插入图片描述

参考博客：
D-Bus 学习
DBUS基础知识（非常全面）
DBus 入门与应用－－ DBus 的 C 编程接口
dbus 简单编程（二）

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DBUS入门与C编程

一、D-Bus简介

1. D-Bus是什么

2. D-Bus特性

二、D-Bus架构

1. 结构层次

2.系统总线和会话总线

三、D-Bus编程基础知识

1.address地址

2. bus name 总线名字

3. 原生对象和对象路径

4. 接口 Interface

5. Methods 和 Signals

6. 总结：方法所需要的参数

四、D-Bus运行环境

1. 运行环境安装

2. dbus-send以及dbus-monitor

3.Dbus通信流程总结

(1) 方法调用的一般流程：

(2) 信号的一般流程：

五、DBUS编程

1. 通用代码介绍

（1）连接代码

(2) 发送信号（Sending Signal）

(3) 调用方法(Call a Methond)

调用方法1

调用方法2

(4) 接收消息（Receiving a Signal）

(5) 提供被远程调用的方法（Exposing a Method to be called）

远程调用的方法1

远程调用方法2：

2. 实例代码

(1) 客户端代码

(2) 服务端代码

(3)执行结果

客户端

服务端

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