D-Bus學習(六) Method的收發小例子
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我們繼續學習D-Bus,參考http://dbus.freedesktop.org/doc/dbus/libdbus-tutorial.html,相關的API介面reference參考http://dbus.freedesktop.org/doc/dbus/api/html/modules.html
監聽Method call訊息,並返回Method reply訊息
Method的監聽和signal的監聽的處理時一樣,但是訊號是不需要答覆,而Method需要。在下面的例子中,我們將學習如何在訊息中加入多個引數(在D-Bus學習(四)中,我們加入了一個引數)的情況。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dbus/dbus-glib.h>
#include <dbus/dbus.h>
#include <unistd.h>
/*讀取訊息的引數,並且返回兩個引數,一個是bool值stat,一個是整數level*/
void reply_to_method_call(DBusMessage * msg, DBusConnection * conn){
DBusMessage * reply;
DBusMessageIter arg;
char * param = NULL;
dbus_bool_t stat = TRUE;
dbus_uint32_t level = 2010;
dbus_uint32_t serial = 0;
//從msg中讀取引數,這個在上一次學習中學過
if(!dbus_message_iter_init(msg,&arg))
printf("Message has no args/n");
else if(dbus_message_iter_get_arg_type(&arg) != DBUS_TYPE_STRING)
printf("Arg is not string!/n");
else
dbus_message_iter_get_basic(&arg,& param);
if(param == NULL) return;
//建立返回訊息reply
reply = dbus_message_new_method_return(msg);
//在返回訊息中填入兩個引數,和訊號加入引數的方式是一樣的。這次我們將加入兩個引數。
dbus_message_iter_init_append(reply,&arg);
if(!dbus_message_iter_append_basic(&arg,DBUS_TYPE_BOOLEAN,&stat)){
printf("Out of Memory!/n");
exit(1);
}
if(!dbus_message_iter_append_basic(&arg,DBUS_TYPE_UINT32,&level)){
printf("Out of Memory!/n");
exit(1);
}
//傳送返回訊息
if( !dbus_connection_send(conn, reply, &serial)){
printf("Out of Memory/n");
exit(1);
}
dbus_connection_flush(conn);
dbus_message_unref(reply);
}
/* 監聽D-Bus訊息,我們在上次的例子中進行修改 */
void listen_dbus()
{
DBusMessage * msg;
DBusMessageIter arg;
DBusConnection * connection;
DBusError err;
int ret;
char * sigvalue;
dbus_error_init(&err);
//創建於session D-Bus的連線
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;
//設定一個BUS name:test.wei.dest
ret = dbus_bus_request_name(connection,"test.wei.dest",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;
//要求監聽某個singal:來自介面test.signal.Type的訊號
dbus_bus_add_match(connection,"type='signal',interface='test.signal.Type'",&err);
dbus_connection_flush(connection);
if(dbus_error_is_set(&err)){
fprintf(stderr,"Match Error %s/n",err.message);
dbus_error_free(&err);
}
while(true){
dbus_connection_read_write(connection,0);
msg = dbus_connection_pop_message(connection);
if(msg == NULL){
sleep(1);
continue;
}
if(dbus_message_is_signal(msg,"test.signal.Type","Test")){
if(!dbus_message_iter_init(msg,&arg))
fprintf(stderr,"Message Has no Param");
else if(dbus_message_iter_get_arg_type(&arg) != DBUS_TYPE_STRING)
g_printerr("Param is not string");
else
dbus_message_iter_get_basic(&arg,&sigvalue);
}else if(dbus_message_is_method_call(msg,"test.method.Type","Method")){
//我們這裡面先比較了介面名字和方法名字,實際上應當現比較路徑
if(strcmp(dbus_message_get_path(msg),"/test/method/Object") == NULL)
reply_to_method_call(msg, connection);
}
dbus_message_unref(msg);
}
}
int main( int argc , char ** argv){
listen_dbus();
return 0;
}
傳送Method call訊息,並等待Method reply訊息
下面的例子在上次學習訊號傳送的例子上進行修改。如下:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dbus/dbus-glib.h>
#include <dbus/dbus.h>
#include <unistd.h>
//建立與session D-Bus daemo的連線,並設定連線的名字,相關的程式碼已經多次使用過了
DBusConnection * connect_dbus(){
DBusError err;
DBusConnection * connection;
int ret;
//Step 1: connecting session bus
/* 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 NULL;
//step 2: 設定BUS name,也即連線的名字。
ret = dbus_bus_request_name(connection,"test.wei.source",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 NULL;
return connection;
}
void send_a_method_call(DBusConnection * connection,char * param)
{
DBusError err;
DBusMessage * msg;
DBusMessageIter arg;
DBusPendingCall * pending;
dbus_bool_t * stat;
dbus_uint32_t * level;
dbus_error_init(&err);
//針對目的地地址,請參考圖,建立一個method call訊息。Constructs a new message to invoke a method on a remote object.
msg = dbus_message_new_method_call("test.wei.dest","/test/method/Object","test.method.Type","Method");
if(msg == NULL){
g_printerr("Message NULL");
return;
}
//為訊息新增引數。Append arguments
dbus_message_iter_init_append(msg, &arg);
if(!dbus_message_iter_append_basic(&arg, DBUS_TYPE_STRING,¶m)){
g_printerr("Out of Memory!");
exit(1);
}
//傳送訊息並獲得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)){
g_printerr("Out of Memory!");
exit(1);
}
if(pending == NULL){
g_printerr("Pending Call NULL: connection is disconnected ");
dbus_message_unref(msg);
return;
}
dbus_connection_flush(connection);
dbus_message_unref(msg);
//waiting a reply,在傳送的時候,已經獲取了method reply的handle,型別為DBusPendingCall。
// block until we recieve 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) {
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, &arg))
fprintf(stderr, "Message has no arguments!/n");
else if ( dbus_message_iter_get_arg_type(&arg) != DBUS_TYPE_BOOLEAN)
fprintf(stderr, "Argument is not boolean!/n");
else
dbus_message_iter_get_basic(&arg, &stat);
if (!dbus_message_iter_next(&arg))
fprintf(stderr, "Message has too few arguments!/n");
else if ( dbus_message_iter_get_arg_type(&arg) != DBUS_TYPE_UINT32 )
fprintf(stderr, "Argument is not int!/n");
else
dbus_message_iter_get_basic(&arg, &level);
printf("Got Reply: %d, %d/n", stat, level);
dbus_message_unref(msg);
}
int main( int argc , char ** argv){
DBusConnection * connection;
connection = connect_dbus();
if(connection == NULL)
return -1;
send_a_method_call(connection,"Hello, D-Bus");
return 0;
}
相關連結: 我的D-Bus相關文章