dbus 例程

/*
* Example low-level D-Bus code.
* Written by Matthew Johnson <dbus@matthew.ath.cx>
*
* This code has been released into the Public Domain.
* You may do whatever you like with it.
*/
#include <dbus/dbus.h>
#include <stdbool.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

/**
* Connect to the DBUS bus and send a broadcast signal
*/
void sendsignal(char* sigvalue)
{
   DBusMessage* msg;
   DBusMessageIter args;
   DBusConnection* conn;
   DBusError err;
   int ret;
   dbus_uint32_t serial = 0;

   printf("Sending signal with value %s\n", sigvalue);

   // initialise the error value
   dbus_error_init(&err);

   // connect to the DBUS system bus, and check for errors
   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); 
   }

   // register our name on the bus, and check for errors
   ret = dbus_bus_request_name(conn, "test.signal.source", 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);
   }

   // create a signal & 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);
   
   printf("Signal Sent\n");
   
   // free the message 
   dbus_message_unref(msg);
}

/**
* Call a method on a remote object
*/
void query(char* param) 
{
   DBusMessage* msg;
   DBusMessageIter args;
   DBusConnection* conn;
   DBusError err;
   DBusPendingCall* pending;
   int ret;
   bool stat;
   dbus_uint32_t level;

   printf("Calling remote method with %s\n", param);

   // initialiset the errors
   dbus_error_init(&err);

   // connect to the system bus and check for errors
   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 our name on the bus
   ret = dbus_bus_request_name(conn, "test.method.caller", 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);
   }

   // create a new method call and check for errors
   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);
   
   printf("Request Sent\n");
   
   // free message
   dbus_message_unref(msg);
   
   // block until we recieve 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 
   dbus_message_unref(msg);   
}


void reply_to_method_call(DBusMessage* msg, DBusConnection* conn)
{
   DBusMessage* reply;
   DBusMessageIter args;
   bool stat = true;
   dbus_uint32_t level = 21614;
   dbus_uint32_t serial = 0;
   char* param = "";

   // read the arguments
   if (!dbus_message_iter_init(msg, &args))
      fprintf(stderr, "Message has no arguments!\n"); 
   else if (DBUS_TYPE_STRING != dbus_message_iter_get_arg_type(&args)) 
      fprintf(stderr, "Argument is not string!\n"); 
   else 
      dbus_message_iter_get_basic(&args, &param);

   printf("Method called with %s\n", param);

   // create a reply from the message
   reply = dbus_message_new_method_return(msg);

   // add the arguments to the reply
   dbus_message_iter_init_append(reply, &args);
   if (!dbus_message_iter_append_basic(&args, DBUS_TYPE_BOOLEAN, &stat)) { 
      fprintf(stderr, "Out Of Memory!\n"); 
      exit(1);
   }
   if (!dbus_message_iter_append_basic(&args, DBUS_TYPE_UINT32, &level)) { 
      fprintf(stderr, "Out Of Memory!\n"); 
      exit(1);
   }

   // send the reply && flush the connection
   if (!dbus_connection_send(conn, reply, &serial)) {
      fprintf(stderr, "Out Of Memory!\n"); 
      exit(1);
   }
   dbus_connection_flush(conn);

   // free the reply
   dbus_message_unref(reply);
}



/**
* Server that exposes a method call and waits for it to be called
*/
void listen() 
{
   DBusMessage* msg;
   DBusMessage* reply;
   DBusMessageIter args;
   DBusConnection* conn;
   DBusError err;
   int ret;
   char* param;

   printf("Listening for method calls\n");

   // initialise the error
   dbus_error_init(&err);
   
   // connect to the bus and check for errors
   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) {
      fprintf(stderr, "Connection Null\n"); 
      exit(1); 
   }
   
   // request our name on the bus and check for errors
   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) { 
      fprintf(stderr, "Not Primary Owner (%d)\n", ret);
      exit(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);

      // loop again if we haven't got a message
      if (NULL == msg) { 
         sleep(1); 
         continue; 
      }
      
      // check this is a method call for the right interface & method
      if (dbus_message_is_method_call(msg, "test.method.Type", "Method")) 
         reply_to_method_call(msg, conn);

      // free the message
      dbus_message_unref(msg);
   }
}



/**
* Listens for signals on the bus
*/
void receive()
{
   DBusMessage* msg;
   DBusMessageIter args;
   DBusConnection* conn;
   DBusError err;
   int ret;
   char* sigvalue;

   printf("Listening for signals\n");

   // initialise the errors
   dbus_error_init(&err);
   
   // connect to the bus and check for errors
   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 our name on the bus and check for errors
   ret = dbus_bus_request_name(conn, "test.signal.sink", 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);
   }

   // 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); 
   }
   printf("Match rule sent\n");

   // loop listening for signals being emmitted
   while (true) {

      // non blocking read of the next available message
      dbus_connection_read_write(conn, 0);
      msg = dbus_connection_pop_message(conn);

      // loop again if we haven't read a message
      if (NULL == msg) { 
         sleep(1);
         continue;
      }

      // check if the message is a signal from the correct interface and with the correct name
      if (dbus_message_is_signal(msg, "test.signal.Type", "Test")) {
         
         // read the parameters
         if (!dbus_message_iter_init(msg, &args))
            fprintf(stderr, "Message Has No Parameters\n");
         else if (DBUS_TYPE_STRING != dbus_message_iter_get_arg_type(&args)) 
            fprintf(stderr, "Argument is not string!\n"); 
         else
            dbus_message_iter_get_basic(&args, &sigvalue);
         
         printf("Got Signal with value %s\n", sigvalue);
      }

      // free the message
      dbus_message_unref(msg);
   }
}



int main(int argc, char** argv)
{
   if (2 > argc) {
      printf ("Syntax: dbus-example [send|receive|listen|query] [<param>]\n");
      return 1;
   }
   char* param = "no param";
   if (3 >= argc && NULL != argv[2]) param = argv[2];
   if (0 == strcmp(argv[1], "send"))
      sendsignal(param);
   else if (0 == strcmp(argv[1], "receive"))
      receive();
   else if (0 == strcmp(argv[1], "listen"))
      listen();
   else if (0 == strcmp(argv[1], "query"))
      query(param);
   else {
      printf ("Syntax: dbus-example [send|receive|listen|query] [<param>]\n");
      return 1;
   }
   return 0;
} 



编译
----------------------------------------------------------
错误1:
$ gcc test.c
test.c:8:23: 错误： dbus/dbus.h：No such file or directory
......
$ 
错误提示，dbus库的头文件位置不正确(如果已经安装了dbus的话)
$ sudo updatedb
$ sudo locate dbus.h (查看dbus.h的所在位置)
/usr/local/include/dbus-1.0/dbus/dbus.h
/usr/include/dbus-1.0/dbus/dbus.h
看来dbus.h的存放位置的确不正确，这可能是由于dbus-1.0的安装位置有问题，没关系，调整一下dbus的头文件位置就可以了(调整方法如下):
root@zxl:/usr/include# ln -sf dbus-1.0/dbus 


错误2:
$ gcc test.c
在包含自 test.c：8 的文件中:
/usr/include/dbus/dbus.h:29:33: 错误： dbus/dbus-arch-deps.h：No such file or directory
......

依然有头文件无法正确定位的问题，从错误提示来看，该文件应该在/usr/include/dbus/目录下，可是进入该目录查看竟然没有，那就在整个系统中查找该文件。
root@zxl:/usr/include/dbus# locate dbus-arch-deps.h
/usr/local/lib/dbus-1.0/include/dbus/dbus-arch-deps.h
/usr/lib/dbus-1.0/include/dbus/dbus-arch-deps.h
将该文件复制到/usr/include/dbus目录下



错误3:
$ gcc test.c
......
test.c:(.text+0xbb6): undefined reference to `dbus_message_iter_get_basic'
test.c:(.text+0xbd4): undefined reference to `dbus_message_unref'
collect2: ld 返回 1

需要连接动态库dbus
$ cd /usr/lib
$ ls *dbus*
libdbus-1.a   libdbus-1.so.3      libdbus-glib-1.so
libdbus-1.la libdbus-1.so.3.2.0 libdbus-glib-1.so.2
libdbus-1.so libdbus-glib-1.a    libdbus-glib-1.so.2.1.0

$ gcc test.c -l dbus-1 -o dbus


执行(用普通用户身份执行)
----------------------------------------------------------
$ ./dbus receive
Listening for signals
Match rule sent
Got Signal with value luoling


$ ./dbus send luoling    (再开一个标签)
Sending signal with value luoling
Signal Sent