本文主要是介绍dbus介绍与例子，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
D-bus是一个进程间通信的工具，优点不在这里赘述。
网上很多关于dbus的帖子都是基于dbus-glib或者QT D-bus的，直接使用dbus的教程比较少。也难怪，因为连D-bus的官网都说："If you use this low-level API directly, you're signing up for some pain."
但实际上，直接使用D-bus也没有想象中难。本文将对直接使用D-bus做一个介绍。
本文参考了其他一些网站的帖子或者介绍
官网：http://www.freedesktop.org/wiki/Software/dbus/
经典例子：http://www.matthew.ath.cx/articles/dbus
不错的帖子：http://blog.csdn.net/flowingflying/article/details/4527634
一、概念介绍
这里虽然说是概念介绍，其实只是我个人对D-bus的一个理解，不一定完整准确。
１．首先，D-bus可以分成三部分来看，
（１）dbus-daemon，一个dbus的后台守护程序，用于多个应用之间消息的转发；
（２）libdbus.so，dbus的功能接口，当你的程序需要使用dbus时，其实就是调用libdbus.so里面的接口；
（３）高层封装，如dbus-glib和QT D-bus，这些其实都对D-bus的再封装，让你使用起来更方便。
从D-bus官网下载到源码，其实只包含上面所说的１和２两部分，libdbus.so里面的接口也就是官网说的low-level API。
２．关于address、bus name、path。。。。
D-bus里面提到了一些概念，刚开始不太好理解，这些概念也很容易混淆。这些概念的权威解释可以看这里。
首先，运行一个dbus-daemon就是创建了一条通信的总线Bus。当一个application连接到这条Bus上面时，就产生了Connection。
每个application里面会有不同的Object。这里Object的概念，可以简单地理解为C++里面一个类的实例。从D-bus的概念上说，通信双方是Object，不是application，一个application是可以包含很多个Object的。
而一个Object里面又会有不同的Interface，这个Interface我把它理解为Object里面的一个类的成员。这些Interface其实是通信方式的集合。
这里又牵扯出来一个通信方式，D-bus里面支持的通信方式有两种，一种叫signal，一种叫method。signal简单地讲，其实就是广播，就是一对多的通信方式，可以从app1向其他所有的app发消息，但其他的app是不会对signal进行回复的。method则是一对一的通信，一问一答。这种方式有点像远程调用，app1调用app2的method并传递参数给这个method，获取到这个method返回的结果。
上面把D-bus通信里面的几个重要元素都介绍了一下，大概的关系是这样的：
几个重要的元素之间的关系都画出来了，那么在程序里面怎么去标识这些元素呢？这里又提出来了一些名词address、bus name、path、Interface name。
（１）address是用来标识dbus-daemon的。当一个dbus-daemon运行以后，其他的app该怎么连接到这个dbus-daemon，靠的就是address。address的格式要求像这样：unix:path=/var/run/dbus/system_bus_socket。
（２）bus name是用来标识application的。当一个app1连接上dbus-daemon以后，相当于有了一个Connection，但其他的app2、app3怎么找到app1，靠的就是bus name。这个bus name标识了app1的Connection，也就相当于标识了app1。bus name由两种，一种是已冒号开头的唯一标识，像:34-907这样；另一种是通用的标识，是方便人看的，像com.mycompany.TextEditor。
（３）path用于标识Object。当app1的Object1要跟app2的Object2通信时，Object1要和Object2通信时，就要告诉dbus-daemon，Object2的path。path的格式像这样，/com/mycompany/TextFileManager，已“/”开头。
（４）每个Interface都会有自己的名字，也就是interface name，我们通过这个interface name就可以找到这个interface。interface name像这样org.freedesktop.Hal.Manager
（５）Signal和Method也有自己的名字，这个名字没什么特别的格式要求，随便改个名字就可以了。
官网上对这些标识列了一个表，如下：
| A... | is identified by a(n)... | which looks like... | and is chosen by... |
| Bus | address | unix:path=/var/run/dbus/system_bus_socket | system configuration |
| Connection | bus name | :34-907 (unique) or com.mycompany.TextEditor (well-known) | D-Bus (unique) or the owning program (well-known) |
| Object | path | /com/mycompany/TextFileManager | the owning program |
| Interface | interface name | org.freedesktop.Hal.Manager | the owning program |
| Member | member name | ListNames | the owning program |
二、例子
我在Matthew Johnson和恺风的例子基础上做了修改，如下：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <dbus/dbus.h>/** listen, wait a call or a signal*/
#define DBUS_SENDER_BUS_NAME "com.ty3219.sender_app"#define DBUS_RECEIVER_BUS_NAME "com.ty3219.receiver_app"
#define DBUS_RECEIVER_PATH "/com/ty3219/object"
#define DBUS_RECEIVER_INTERFACE "com.ty3219.interface"
#define DBUS_RECEIVER_SIGNAL "signal"
#define DBUS_RECEIVER_METHOD "method"#define DBUS_RECEIVER_SIGNAL_RULE "type='signal',interface='%s'"
#define DBUS_RECEIVER_REPLY_STR "i am %d, get a message"#define MODE_SIGNAL 1
#define MODE_METHOD 2#define DBUS_CLIENT_PID_FILE "/tmp/dbus-client.pid"/**** @param msg* @param conn*/
void reply_method_call(DBusMessage *msg, DBusConnection *conn)
{DBusMessage *reply;DBusMessageIter reply_arg;DBusMessageIter msg_arg;dbus_uint32_t serial = 0;pid_t pid;char reply_str[128];void *__value;char *__value_str;int __value_int;int ret;pid = getpid();//创建返回消息replyreply = dbus_message_new_method_return(msg);if (!reply){printf("Out of Memory!\n");return;}//在返回消息中填入参数。snprintf(reply_str, sizeof(reply_str), DBUS_RECEIVER_REPLY_STR, pid);__value_str = reply_str;__value = &__value_str;dbus_message_iter_init_append(reply, &reply_arg);if (!dbus_message_iter_append_basic(&reply_arg, DBUS_TYPE_STRING, __value)){printf("Out of Memory!\n");goto out;}//从msg中读取参数，根据传入参数增加返回参数if (!dbus_message_iter_init(msg, &msg_arg)){printf("Message has NO Argument\n");goto out;}do{int ret = dbus_message_iter_get_arg_type(&msg_arg);if (DBUS_TYPE_STRING == ret){dbus_message_iter_get_basic(&msg_arg, &__value_str);printf("I am %d, get Method Argument STRING: %s\n", pid,__value_str);__value = &__value_str;if (!dbus_message_iter_append_basic(&reply_arg,DBUS_TYPE_STRING, __value)){printf("Out of Memory!\n");goto out;}}else if (DBUS_TYPE_INT32 == ret){dbus_message_iter_get_basic(&msg_arg, &__value_int);printf("I am %d, get Method Argument INT32: %d\n", pid,__value_int);__value_int++;__value = &__value_int;if (!dbus_message_iter_append_basic(&reply_arg,DBUS_TYPE_INT32, __value)){printf("Out of Memory!\n");goto out;}}else{printf("Argument Type ERROR\n");}} while (dbus_message_iter_next(&msg_arg));//发送返回消息if (!dbus_connection_send(conn, reply, &serial)){printf("Out of Memory\n");goto out;}dbus_connection_flush(conn);
out:dbus_message_unref(reply);
}/* 监听D-Bus消息，我们在上次的例子中进行修改 */
void dbus_receive(void)
{DBusMessage *msg;DBusMessageIter arg;DBusConnection *connection;DBusError err;pid_t pid;char name[64];char rule[128];const char *path;void *__value;char *__value_str;int __value_int;int ret;pid = getpid();dbus_error_init(&err);//创建于session D-Bus的连接connection = dbus_bus_get(DBUS_BUS_SESSION, &err);if (!connection){if (dbus_error_is_set(&err))printf("Connection Error %s\n", err.message);goto out;}//设置一个BUS nameif (0 == access(DBUS_CLIENT_PID_FILE, F_OK))snprintf(name, sizeof(name), "%s%d", DBUS_RECEIVER_BUS_NAME, pid);elsesnprintf(name, sizeof(name), "%s", DBUS_RECEIVER_BUS_NAME);printf("i am a receiver, PID = %d, name = %s\n", pid, name);ret = dbus_bus_request_name(connection, name,DBUS_NAME_FLAG_REPLACE_EXISTING, &err);if (ret != DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER){if (dbus_error_is_set(&err))printf("Name Error %s\n", err.message);goto out;}//要求监听某个signal：来自接口test.signal.Type的信号snprintf(rule, sizeof(rule), DBUS_RECEIVER_SIGNAL_RULE, DBUS_RECEIVER_INTERFACE);dbus_bus_add_match(connection, rule, &err);dbus_connection_flush(connection);if (dbus_error_is_set(&err)){printf("Match Error %s\n", err.message);goto out;}while (1){dbus_connection_read_write(connection, 0);msg = dbus_connection_pop_message(connection);if (msg == NULL){sleep(1);continue;}path = dbus_message_get_path(msg);if (strcmp(path, DBUS_RECEIVER_PATH)){printf("Wrong PATH: %s\n", path);goto next;}printf("Get a Message\n");if (dbus_message_is_signal(msg, DBUS_RECEIVER_INTERFACE, DBUS_RECEIVER_SIGNAL)){printf("Someone Send me a Signal\n");if (!dbus_message_iter_init(msg, &arg)){printf("Message Has no Argument\n");goto next;}ret = dbus_message_iter_get_arg_type(&arg);if (DBUS_TYPE_STRING == ret){dbus_message_iter_get_basic(&arg, &__value_str);printf("I am %d, Got Signal with STRING: %s\n",pid, __value_str);}else if (DBUS_TYPE_INT32 == ret){dbus_message_iter_get_basic(&arg, &__value_int);printf("I am %d, Got Signal with INT32: %d\n",pid, __value_int);}else{printf("Argument Type ERROR\n");goto next;}}else if (dbus_message_is_method_call(msg, DBUS_RECEIVER_INTERFACE, DBUS_RECEIVER_METHOD)){printf("Someone Call My Method\n");reply_method_call(msg, connection);}else{printf("NOT a Signal OR a Method\n");}
next:dbus_message_unref(msg);}out:dbus_error_free(&err);
}/** call a method*/
static void dbus_send(int mode, char *type, void *value)
{DBusConnection *connection;DBusError err;DBusMessage *msg;DBusMessageIter arg;DBusPendingCall *pending;dbus_uint32_t serial;int __type;void *__value;char *__value_str;int __value_int;pid_t pid;int ret;pid = getpid();//Step 1: connecting session bus/* initialise the erroes */dbus_error_init(&err);/* Connect to Bus*/connection = dbus_bus_get(DBUS_BUS_SESSION, &err);if (!connection){if (dbus_error_is_set(&err))printf("Connection Err : %s\n", err.message);goto out1;}//step 2: 设置BUS name，也即连接的名字。ret = dbus_bus_request_name(connection, DBUS_SENDER_BUS_NAME,DBUS_NAME_FLAG_REPLACE_EXISTING, &err);if (ret != DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER){if (dbus_error_is_set(&err))printf("Name Err : %s\n", err.message);goto out1;}if (!strcasecmp(type, "STRING")){__type = DBUS_TYPE_STRING;__value_str = value;__value = &__value_str;}else if (!strcasecmp(type, "INT32")){__type = DBUS_TYPE_INT32;__value_int = atoi(value);__value = &__value_int;}else{printf("Wrong Argument Type\n");goto out1;}if (mode == MODE_METHOD){printf("Call app[bus_name]=%s, object[path]=%s, interface=%s, method=%s\n",DBUS_RECEIVER_BUS_NAME, DBUS_RECEIVER_PATH,DBUS_RECEIVER_INTERFACE, DBUS_RECEIVER_METHOD);//针对目的地地址，创建一个method call消息。//Constructs a new message to invoke a method on a remote object.msg = dbus_message_new_method_call(DBUS_RECEIVER_BUS_NAME, DBUS_RECEIVER_PATH,DBUS_RECEIVER_INTERFACE, DBUS_RECEIVER_METHOD);if (msg == NULL){printf("Message NULL");goto out1;}dbus_message_iter_init_append(msg, &arg);if (!dbus_message_iter_append_basic(&arg, __type, __value)){printf("Out of Memory!");goto out2;}//发送消息并获得reply的handle 。Queues a message to send, as with dbus_connection_send() , but also returns a DBusPendingCall used to receive a reply to the message.if (!dbus_connection_send_with_reply(connection, msg, &pending, -1)){printf("Out of Memory!");goto out2;}if (pending == NULL){printf("Pending Call NULL: connection is disconnected ");goto out2;}dbus_connection_flush(connection);dbus_message_unref(msg);//waiting a reply，在发送的时候，已经获取了method reply的handle，类型为DBusPendingCall。// block until we receive a reply， Block until the pending call is completed.dbus_pending_call_block(pending);// get the reply message，Gets the reply, or returns NULL if none has been received yet.msg = dbus_pending_call_steal_reply(pending);if (msg == NULL){printf("Reply Null\n");goto out1;}// free the pending message handledbus_pending_call_unref(pending);// read the Argumentsif (!dbus_message_iter_init(msg, &arg)){printf("Message has no Argument!\n");goto out2;}do{int ret = dbus_message_iter_get_arg_type(&arg);if (DBUS_TYPE_STRING == ret){dbus_message_iter_get_basic(&arg, &__value_str);printf("I am %d, get Method return STRING: %s\n", pid,__value_str);}else if (DBUS_TYPE_INT32 == ret){dbus_message_iter_get_basic(&arg, &__value_int);printf("I am %d, get Method return INT32: %d\n", pid,__value_int);}else{printf("Argument Type ERROR\n");}} while (dbus_message_iter_next(&arg));printf("NO More Argument\n");}else if (mode == MODE_SIGNAL){printf("Signal to object[path]=%s, interface=%s, signal=%s\n",DBUS_RECEIVER_PATH, DBUS_RECEIVER_INTERFACE, DBUS_RECEIVER_SIGNAL);//步骤3:发送一个信号//根据图，我们给出这个信号的路径（即可以指向对象），接口，以及信号名，创建一个Messagemsg = dbus_message_new_signal(DBUS_RECEIVER_PATH,DBUS_RECEIVER_INTERFACE, DBUS_RECEIVER_SIGNAL);if (!msg){printf("Message NULL\n");goto out1;}dbus_message_iter_init_append(msg, &arg);if (!dbus_message_iter_append_basic(&arg, __type, __value)){printf("Out of Memory!");goto out2;}//将信号从连接中发送if (!dbus_connection_send(connection, msg, &serial)){printf("Out of Memory!\n");goto out2;}dbus_connection_flush(connection);printf("Signal Send\n");}out2:dbus_message_unref(msg);
out1:dbus_error_free(&err);
}static void usage(void)
{
#define USAGE "usage: ./dbus-client [send | receive] <param>\n" \"\treceive -- listen, wait a signal or a method call\n" \"\t\tif you want to test signal broadcast, run two receiver like this:\n" \"\t\trm -f /tmp/dbus-client.pid\n" \"\t\t./dbus-client receive &\n" \"\t\techo > /tmp/dbus-client.pid\n" \"\t\t./dbus-client receive &\n" \"\tsend [mode] [type] [value] -- send a signal or call a method\n" \"\t\tmode -- SIGNAL | METHOD\n" \"\t\ttype -- STRING | INT32\n" \"\t\tvalue -- string or number\n" \"\t\texample:\n" \"\t\t./dbus-client send SIGNAL STRING hello\n" \"\t\t./dbus-client send METHOD INT32 99\n" \"\n"printf(USAGE);
}int main(int argc, char *argv[])
{if (argc < 2){usage();return -1;}if (!strcmp(argv[1], "receive")){dbus_receive();}else if (!strcmp(argv[1], "send")){if (argc < 5){usage();}else{if (!strcasecmp(argv[2], "SIGNAL"))dbus_send(MODE_SIGNAL, argv[3], argv[4]);else if (!strcasecmp(argv[2], "METHOD"))dbus_send(MODE_METHOD, argv[3], argv[4]);elseusage();}}else{usage();}return 0;
}三、运行
想要运行上面的例子，还需要一些步骤。
（１）运行dbus-daemon
dbus-daemon的运行需要一个配置文件，这个配置文件稍微有点复杂，这里提供一个最简单的，无任何权限检查的例子debug-allow-all.conf
<!-- Bus that listens on a debug pipe and doesn't create any restrictions --><!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN""http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
<busconfig><type>session</type><listen>unix:tmpdir=/tmp</listen><standard_session_servicedirs /><policy context="default"><!-- Allow everything to be sent --><allow send_destination="*" eavesdrop="true"/><!-- Allow everything to be received --><allow eavesdrop="true"/><!-- Allow anyone to own anything --><allow own="*"/><allow user="*"/></policy></busconfig>执行下面的命令
./dbus-daemon --config-file=/path/to/debug-allow-all.conf --fork --print-addressunix:path=/tmp/dbus-UXeqD3TJHE,guid=88e7712c8a5775ab4599725500000051
其实这个就是dbus-daemon的地址，我们需要把这个地址设置到环境变量里面，当你运行app的时候，libdbus.so就会读取这个环境变量，然后连接到这个dbus-daemon上。
设置环境变量
export DBUS_SESSION_BUS_ADDRESS=unix:path=/tmp/dbus-UXeqD3TJHE,guid=88e7712c8a5775ab4599725500000051（２）这个时候你就可以运行上面例子编译出来的程序
./dbus-app作为接收方时运行
./dbus-app receive &作为发送方时，发送signal
./dbus-app send SIGNAL STRING hello作为发送方时，调用method
/dbus-app send METHOD INT32 30 至此，一个dbus的例子就可以运行起来了，想详细了解这个例子需要自己去看例子的源码。
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