Windows下，dbus的hello world

      dbus的是一个低延迟，低开销，高可用性的IPC机制。通过dbus的daemon，可以实现进程间通信和函数调用。Windows下，dbus的开发库可以去这里（http://code.google.com/p/dbus-windows-installer/downloads/list）下载，在VS设置头文件和lib库的路径即可。若是要编写其Hello World，自然包含客户端和服务端两部分。下面的Hello World代码包含了发送消息和函数调用两部分，分别描述之。

      1) 信号

假设客户端发送消息，服务端接收。客户端发送消息的流程如下：
1.创建于dbus daemon的会话连接。
2.创建消息，若有消息参数，附加之（这个一般都有）
3.通过连接发送消息。

   1: int main (int argc, char *argv[])

   2: {

   3:     DBusError dberr;

   4:     DBusConnection *dbconn;

   5:     DBusMessage *dbmsg;

   6:     char *text;

   7:  

   8:     // 初始话错误信息的结构体

   9:     dbus_error_init (&dberr);

  10:     

  11:     // 创建会话连接

  12:     dbconn = dbus_bus_get (DBUS_BUS_SESSION, &dberr);  

  13:     if (dbus_error_is_set (&dberr)) {

  14:         fprintf (stderr, "getting session bus failed: %s/n", dberr.message);

  15:         dbus_error_free (&dberr);

  16:         return EXIT_FAILURE;

  17:     }

  18:  

  19:     // 创建消息

  20:     dbmsg = dbus_message_new_signal ("/com/wiley/test",

  21:                                      "com.wiley.test",

  22:                                      "TestSignal");

  23:     if (!dbmsg) {

  24:         fprintf (stderr, "Could not create a new signal/n");

  25:         return EXIT_FAILURE;

  26:     }

  27:  

  28:     // 消息中，附加文本

  29:     text = "Hello World";

  30:     if (!dbus_message_append_args (

  31:         dbmsg, DBUS_TYPE_STRING, &text, DBUS_TYPE_INVALID)) {

  32:         fprintf(stderr, "Out Of Memory!/n"); 

  33:         return EXIT_FAILURE;

  34:     }

  35:  

  36:     // 发送消息

  37:     if (!dbus_connection_send (dbconn, dbmsg, NULL)) {

  38:         fprintf(stderr, "Out Of Memory!/n"); 

  39:         return EXIT_FAILURE;

  40:     }

  41:     dbus_connection_flush(dbconn);

  42:  

  43:     printf ("Sending signal to D-Bus/n");

  44:  

  45:     // 释放消息

  46:     dbus_message_unref (dbmsg);

  47:  

  48:     // 释放会话连接

  49:     dbus_connection_unref (dbconn);

  50:  

  51:     return EXIT_SUCCESS;

  52: }

服务端接收消息的流程如下：
1.创建于dbus daemon的会话连接。
2.为本次连接设置名称，客户端可以通过此名称进行通信
3.设置消息对应的回调函数
4.添加消息匹配规则
5.进入处理消息的循环

   1: static DBusHandlerResult

   2: filter_func (DBusConnection *connection,

   3:              DBusMessage *message,

   4:              void *user_data)

   5: {

   6:     dbus_bool_t handled = FALSE;

   7:     char *signal_text = NULL;

   8:  

   9:     // 若为指定信号

  10:     if (dbus_message_is_signal (message, "com.wiley.test", "TestSignal")) {

  11:         DBusError dberr;

  12:         // 初始化错误结构体

  13:         dbus_error_init (&dberr);

  14:         // 获取消息的参数

  15:         dbus_message_get_args (message, &dberr, DBUS_TYPE_STRING, &signal_text, DBUS_TYPE_INVALID);

  16:         if (dbus_error_is_set (&dberr)) {

  17:             fprintf (stderr, "Error getting message args: %s", dberr.message);

  18:             dbus_error_free (&dberr);

  19:         } else {

  20:             printf ("Received TestSignal with value of: '%s'/n", signal_text);

  21:             // 标识本消息已处理

  22:             handled = TRUE;

  23:         }

  24:     }

  25:     // 返回值决定该消息是否处理

  26:     return (handled ? DBUS_HANDLER_RESULT_HANDLED : DBUS_HANDLER_RESULT_NOT_YET_HANDLED);

  27: }

  28:  

  29:  

  30: int main (int argc, char *argv[])

  31: {

  32:     DBusError dberr;

  33:     DBusConnection *dbconn;

  34:  

  35:     // 初始话错误信息的结构体

  36:     dbus_error_init (&dberr);

  37:     

  38:     // 创建会话

  39:     dbconn = dbus_bus_get (DBUS_BUS_SESSION, &dberr);

  40:     if (dbus_error_is_set (&dberr)) {

  41:         fprintf (stderr, "getting session bus failed: %s/n", dberr.message);

  42:         dbus_error_free (&dberr);

  43:         return EXIT_FAILURE;

  44:     }

  45:  

  46:     // 向daemon追加了一条路由到该应用程序入口

  47:     dbus_bus_request_name (dbconn, "com.wiley.test",

  48:                            DBUS_NAME_FLAG_REPLACE_EXISTING, &dberr);

  49:     if (dbus_error_is_set (&dberr)) {

  50:         fprintf (stderr, "requesting name failed: %s/n", dberr.message);

  51:         dbus_error_free (&dberr);

  52:         return EXIT_FAILURE;

  53:     }

  54:  

  55:     // 设置处理消息的函数

  56:     if (!dbus_connection_add_filter (dbconn, filter_func, NULL, NULL)) {

  57:         return EXIT_FAILURE;

  58:     }

  59:  

  60:     // 添加消息匹配规则

  61:     dbus_bus_add_match (dbconn,

  62:                         "type='signal',interface='com.wiley.test'",

  63:                         &dberr);

  64:     if (dbus_error_is_set (&dberr)) {

  65:         fprintf (stderr, "Could not match: %s", dberr.message);

  66:         dbus_error_free (&dberr);

  67:         return EXIT_FAILURE;

  68:     }

  69:  

  70:     // 分派消息的Loop

  71:     while (dbus_connection_read_write_dispatch (dbconn, -1))

  72:         ; /* empty loop body */

  73:  

  74:     return EXIT_SUCCESS;

  75: }

      2) 跨进程调用

跨进程调用中，客户端和服务端的流程差不多，假设客户端跨进程调用服务端函数。
客户端

   1: int main (int argc, char *argv[])

   2: {

   3:     DBusMessage* msg;

   4:     DBusMessageIter args;

   5:     DBusConnection* conn;

   6:     DBusError err;

   7:     DBusPendingCall* pending;

   8:     char* param = "no param";

   9:     int ret;

  10:     dbus_bool_t stat = FALSE;

  11:     dbus_uint32_t level = 0;

  12:  

  13:     printf("Calling remote method with %s/n", param);

  14:  

  15:     // 初始化错误

  16:     dbus_error_init(&err);

  17:  

  18:     // 获取会话连接

  19:     conn = dbus_bus_get(DBUS_BUS_SESSION, &err);

  20:     if (dbus_error_is_set(&err)) { 

  21:         fprintf(stderr, "Connection Error (%s)/n", err.message); 

  22:         dbus_error_free(&err);

  23:     }

  24:     if (NULL == conn) { 

  25:         exit(1); 

  26:     }

  27:  

  28:     // 设置连接名称，若存在则替换

  29:     ret = dbus_bus_request_name(conn, "test.method.caller", DBUS_NAME_FLAG_REPLACE_EXISTING , &err);

  30:     if (dbus_error_is_set(&err)) { 

  31:         fprintf(stderr, "Name Error (%s)/n", err.message); 

  32:         dbus_error_free(&err);

  33:     }

  34:     if (DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER != ret) { 

  35:         exit(1);

  36:     }

  37:  

  38:     // 创建方法调用的消息

  39:     msg = dbus_message_new_method_call("com.test.dbus.server",    // target for the method call

  40:                                        "/test/method/Object",    // object to call on

  41:                                        "test.method.Interface", // interface to call on

  42:                                        "Method");                // method name

  43:     if (NULL == msg) { 

  44:         fprintf(stderr, "Message Null/n");

  45:         exit(1);

  46:     }

  47:  

  48:     // 附加参数

  49:     dbus_message_iter_init_append(msg, &args);

  50:     if (!dbus_message_iter_append_basic(&args, DBUS_TYPE_STRING, &param)) {

  51:         fprintf(stderr, "Out Of Memory!/n"); 

  52:         exit(1);

  53:     }

  54:  

  55:     // 发送消息（-1表示使用默认超时）

  56:     if (!dbus_connection_send_with_reply (conn, msg, &pending, -1)) {

  57:         fprintf(stderr, "Out Of Memory!/n"); 

  58:         exit(1);

  59:     }

  60:     if (NULL == pending) { 

  61:         fprintf(stderr, "Pending Call Null/n"); 

  62:         exit(1); 

  63:     }

  64:  

  65:     // 阻塞直到发送的消息队列为空

  66:     dbus_connection_flush(conn);

  67:  

  68:     printf("Request Sent/n");

  69:  

  70:     // 释放消息

  71:     dbus_message_unref(msg);

  72:  

  73:     // 阻塞至消息返回

  74:     dbus_pending_call_block(pending);

  75:  

  76:     // 获取返回消息

  77:     msg = dbus_pending_call_steal_reply(pending);

  78:     if (NULL == msg) {

  79:         fprintf(stderr, "Reply Null/n"); 

  80:         exit(1); 

  81:     }

  82:     

  83:     // 释放pending

  84:     dbus_pending_call_unref(pending);

  85:  

  86:     // 读取参数

  87:     if (!dbus_message_iter_init(msg, &args))

  88:         fprintf(stderr, "Message has no arguments!/n"); 

  89:     else if (DBUS_TYPE_BOOLEAN != dbus_message_iter_get_arg_type(&args)) 

  90:         fprintf(stderr, "Argument is not boolean!/n"); 

  91:     else

  92:         dbus_message_iter_get_basic(&args, &stat);

  93:  

  94:     if (!dbus_message_iter_next(&args))

  95:         fprintf(stderr, "Message has too few arguments!/n"); 

  96:     else if (DBUS_TYPE_UINT32 != dbus_message_iter_get_arg_type(&args)) 

  97:         fprintf(stderr, "Argument is not int!/n"); 

  98:     else

  99:         dbus_message_iter_get_basic(&args, &level);

 100:  

 101:     printf("Got Reply: %d, %d/n", stat, level);

 102:  

 103:     // 释放方法返回的消息

 104:     dbus_message_unref(msg);  

 105:  

 106:     return EXIT_SUCCESS;

 107: }

服务端

   1: static

   2: void reply_to_method_call(DBusMessage* msg, DBusConnection* conn)

   3: {

   4:     DBusMessage* reply;

   5:     DBusMessageIter args;

   6:     dbus_bool_t stat = TRUE;

   7:     dbus_uint32_t level = 21614;

   8:     dbus_uint32_t serial = 0;

   9:     char* param = "";

  10:  

  11:     // 读取参数

  12:     if (!dbus_message_iter_init(msg, &args)) // 获取参数

  13:         fprintf(stderr, "Message has no arguments!/n"); 

  14:     else if (DBUS_TYPE_STRING != dbus_message_iter_get_arg_type(&args)) // 参数类型不为字符串

  15:         fprintf(stderr, "Argument is not string!/n"); 

  16:     else { // 参数为字符串

  17:         dbus_message_iter_get_basic(&args, &param);

  18:     }

  19:  

  20:     printf("Method called with %s/n", param);

  21:  

  22:     // 创建返回类型的消息，对应于调用的消息

  23:     reply = dbus_message_new_method_return(msg);

  24:  

  25:     // 初始化返回的参数

  26:     dbus_message_iter_init_append(reply, &args);

  27:     if (!dbus_message_iter_append_basic(&args, DBUS_TYPE_BOOLEAN, &stat)) { // 附加基本类型的值到消息中

  28:         fprintf(stderr, "Out Of Memory!/n"); 

  29:         exit(1);

  30:     }

  31:     if (!dbus_message_iter_append_basic(&args, DBUS_TYPE_UINT32, &level)) { // 附加基本类型的值到消息中

  32:         fprintf(stderr, "Out Of Memory!/n"); 

  33:         exit(1);

  34:     }

  35:  

  36:     // 发送返回消息

  37:     if (!dbus_connection_send(conn, reply, &serial)) {

  38:         fprintf(stderr, "Out Of Memory!/n"); 

  39:         exit(1);

  40:     }

  41:     dbus_connection_flush(conn);

  42:  

  43:     // 释放方法返回的消息

  44:     dbus_message_unref(reply);

  45: }

  46:  

  47: int main (int argc, char *argv[])

  48: {

  49:     DBusError dberr;

  50:     DBusConnection * dbconn;

  51:     DBusMessage * msg;

  52:     int ret;

  53:  

  54:     // 初始话错误信息的结构体

  55:     dbus_error_init (&dberr);

  56:     // 创建会话

  57:     dbconn = dbus_bus_get (DBUS_BUS_SESSION, &dberr);

  58:     if (dbus_error_is_set (&dberr)) {

  59:         fprintf (stderr, "getting session bus failed: %s/n", dberr.message);

  60:         dbus_error_free (&dberr);

  61:         return EXIT_FAILURE;

  62:     }

  63:  

  64:     // 为本次连接设置名称，客户端可以通过此名称进行通信

  65:     ret = dbus_bus_request_name (dbconn, "com.test.dbus.server",

  66:                            DBUS_NAME_FLAG_REPLACE_EXISTING, &dberr);

  67:     if (dbus_error_is_set (&dberr)) {

  68:         fprintf (stderr, "requesting name failed: %s/n", dberr.message);

  69:         dbus_error_free (&dberr);

  70:         return EXIT_FAILURE;

  71:     }

  72:     if (DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER != ret) { 

  73:         fprintf(stderr, "Not Primary Owner (%d)/n", ret);

  74:         exit(1); 

  75:     }

  76:  

  77:     // 循环等待消息

  78:     while (true) {

  79:         // 非阻塞的获取下一个消息

  80:         // TODO: 如何阻塞？

  81:         dbus_connection_read_write(dbconn, 0);

  82:  

  83:         // 获取消息

  84:         msg = dbus_connection_pop_message(dbconn);

  85:         if (NULL == msg) { 

  86:             // sleep(1);

  87:             continue; 

  88:         }

  89:  

  90:         // 相应消息调用

  91:         if (dbus_message_is_method_call(msg, "test.method.Interface", "Method")) 

  92:             reply_to_method_call(msg, dbconn);

  93:  

  94:         // 释放引用

  95:         dbus_message_unref(msg);

  96:     }

  97:  

  98:     return EXIT_SUCCESS;

  99: }