Glib之dbus簡單demo

1.安裝所需庫 

# sudo apt install libdbus-glib-1-dev libdbus-1-dev libglib2.0-dev

2.send_signal.c 

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

int send_a_signal( char * sigvalue)
{
  DBusError err;
  DBusConnection * connection;
  DBusMessage * msg;
  DBusMessageIter arg;
  dbus_uint32_t  serial = 0;
  int ret;

  //步驟1:建立與D-Bus後臺的連接
  /* initialise the erroes */
  dbus_error_init(&err);
  /* Connect to Bus*/
  connection = dbus_bus_get(DBUS_BUS_SESSION , &err );
  if(dbus_error_is_set(&err)){
    fprintf(stderr,"Connection Err : %s\n",err.message);
    dbus_error_free(&err);
  }
  if(connection == NULL)
    return -1;

  //步驟2:給連接名分配一個well-known的名字作爲Bus name，這個步驟不是必須的，可以用if 0來註釋着一段代碼，我們可以用這個名字來檢查，是否已經開啓了這個應用的另外的進程。
#if 1
  ret = dbus_bus_request_name(connection,"test.singal.source1",DBUS_NAME_FLAG_REPLACE_EXISTING,&err );
  if(dbus_error_is_set(&err)){
    fprintf(stderr,"Name Err : %s\n",err.message);
    dbus_error_free(&err);
  }
  if(ret != DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER)
    return -1;
#endif

  //步驟3:發送一個信號
  //根據圖，我們給出這個信號的路徑（即可以指向對象），接口，以及信號名，創建一個Message
  if((msg = dbus_message_new_signal ("/test/signal/Object","test.signal.Type1","Test")) == NULL){
    fprintf(stderr,"Message NULL\n");
    return -1;
  }
  //給這個信號（messge）具體的內容
  dbus_message_iter_init_append (msg,&arg);
  if(!dbus_message_iter_append_basic (&arg,DBUS_TYPE_STRING,&sigvalue)){
    fprintf(stderr,"Out Of Memory!\n");
    return -1;
  }

  //步驟4: 將信號從連接中發送
  if( !dbus_connection_send (connection,msg,&serial)){
    fprintf(stderr,"Out of Memory!\n");
    return -1;
  }
  dbus_connection_flush (connection);
  printf("Signal Send\n");

  while(1);
  //步驟5: 釋放相關的分配的內存。
  dbus_message_unref(msg );
  return 0;
}


int main( int argc , char ** argv){
  send_a_signal("Hello,world!");
  return 0;
}

3.receive_signal.c 

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

void listen_signal()
{
  DBusMessage * msg;
  DBusMessageIter arg;
  DBusConnection * connection;
  DBusError err;
  int ret;
  char * sigvalue;

  //步驟1:建立與D-Bus後臺的連接
  dbus_error_init(&err);
  connection = 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(connection == NULL)
    return;

  //步驟2:給連接名分配一個可記憶名字test.singal.dest作爲Bus name，這個步驟不是必須的,但推薦這樣處理
  ret = dbus_bus_request_name(connection,"test.singal.dest1",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(ret != DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER)
    return;

  //步驟3:通知D-Bus daemon，希望監聽來行接口test.signal.Type的信號
  dbus_bus_add_match(connection,"type='signal',interface='test.signal.Type'",&err);

  //步驟3:通知D-Bus daemon，希望監聽來行接口test.signal.Type的信號
  dbus_bus_add_match(connection,"type='signal',interface='test.signal.Type1'",&err);
  //實際需要發送東西給daemon來通知希望監聽的內容，所以需要flush
  dbus_connection_flush(connection);
  if(dbus_error_is_set(&err)){
    fprintf(stderr,"Match Error %s\n",err.message);
    dbus_error_free(&err);
  }

  //步驟4:在循環中監聽，每隔開1秒，就去試圖自己的連接中獲取這個信號。這裏給出的是中連接中獲取任何消息的方式，所以獲取後去檢查一下這個消息是否我們期望的信號，並獲取內容。我們也可以通過這個方式來獲取method call消息。
  while(1){
    //dbus_connection_flush(connection);
    dbus_connection_read_write(connection,0);
    msg = dbus_connection_pop_message (connection);
    if(msg == NULL){
      sleep(1);
      continue;
    }
    printf("listen signal\n");
    if(dbus_message_is_signal(msg,"test.signal.Type","Test") ){
      if(!dbus_message_iter_init(msg,&arg) ) {
	fprintf(stderr,"Message Has no Param");
	printf("Message Has no Param\n");
      } else if(dbus_message_iter_get_arg_type(&arg) != DBUS_TYPE_STRING)
	printf("Param is not string");
      else
	dbus_message_iter_get_basic(&arg,&sigvalue);
      printf("test.signal.Type     ====Got Singal with value : %s\n",sigvalue);
    }

    if(dbus_message_is_signal(msg,"test.signal.Type1","Test") ){
      if(!dbus_message_iter_init(msg,&arg) ) {
	fprintf(stderr,"Message Has no Param");
	printf("Message Has no Param\n");
      } else if(dbus_message_iter_get_arg_type(&arg) != DBUS_TYPE_STRING)
	printf("Param is not string");
      else
	dbus_message_iter_get_basic(&arg,&sigvalue);
      printf("test.signal.Type1  ++++Got Singal with value : %s\n",sigvalue);
    }
    dbus_message_unref(msg);
  }//End of while

}

int main( int argc , char ** argv){
  listen_signal();
  return 0;
}

4.Makefile 

#gcc send_signal.c `pkg-config --cflags --libs glib-2.0 gthread-2.0 dbus-1 dbus-glib-1`
CC = gcc
CC_FLAGS = $(shell pkg-config --cflags glib-2.0 gthread-2.0 dbus-1 dbus-glib-1)
CC_FLAGS += -std=c99 -g
LD_FLAGS = $(shell pkg-config --libs glib-2.0 gthread-2.0 dbus-1 dbus-glib-1)

all:send receive
send:send_signal.o
	$(CC) -o $@ $+ $(LD_FLAGS)
send_signal.o:send_signal.c
	$(CC) $(CC_FLAGS) -c -o $@ $<

receive:receive_signal.o
	$(CC) -o $@ $+ $(LD_FLAGS)
receive_signal.o:receive_signal.c
	$(CC) $(CC_FLAGS) -c -o $@ $<

clean:
	rm send_signal.o send receive_signal.o receive