Dbus是個很龐雜的東西，不管它多麼複雜，有一些東西總是最基本的，就和我們下圍棋一樣，有些東西我們叫定式。我不知道Dbus裏面究竟是怎麼樣實現的，儘管我下載了它全部的源碼，但現在時間不允許我去閱讀它。我現在只想做一個蹩腳的棋手，我僅想知道它的接口都有哪些，我怎麼用它。下面這些是我從Dbus的官方主頁上down來的東西，都是在官方網站有的，覺得我的表述太羅嗦就直接上官方網站好啦。
文字的東西是4種基本應用的流程，也是對着樣例程序翻譯的，官方網站提供的源碼我貼在後面了。
1、建立服務的流程：建立1個Dbus連接之後，爲這個Dbus連 接起名，這個名字將會成爲我們在後續進行遠程調用的時候的服務名，然後我們進入監聽循環。在循環中，我們從總線上取出消息，並通過比對消息中的方法接口名 和方法名，如果一致，那麼我們跳轉到相應的處理中去。在相應的處理中，我們會從消息中取出遠程調用的參數。並且建立起回傳結果的通路。回傳動作本身等同於 一次不需要等待結果的遠程調用。
2、發送信號的流程：建立一個Dbus連接之後，爲這個Dbus連接起名，建立一個發送信號的通道，注意，在建立通道的函數中，需要我們填寫該信號的接口名和信號名。然後我們把信號對應的相關參數壓進去。然後就可以啓動發送了
3、進行一次遠程調用的流程：建立好Dbus連接之後，爲這Dbus連 接命名，申請一個遠程調用通道，注意，在申請遠程調用通道的時候，需要填寫服務器名，本次調用的接口名，和本次調用名（方法名）。壓入本次調用的參數，實 際上是申請了一個首地址，我們就是把我們真正要傳的參數，往這個首地址裏面送（送完之後一般都會判斷是否內存越界了）。然後就是啓動發送調用並釋放發送相 關的消息結構。這個啓動函數中帶有一個句柄。我們馬上會阻塞等待這個句柄給我們帶回總線上回傳的消息。當這個句柄回傳消息之後，我們從消息結構中分離出參 數。用Dbus提供的函數 提取參數的類型和參數。也就達成了我們進行本次遠程調用的目的了。
4、信號接收流程：建立一個Dbus連接之後，爲這個Dbus連接起名，爲我們將要進行的消息循環添加匹配條件（就是通過信號名和信號接口名來進行匹配控制的）。我們進入等待循環後，只需要對信號名，信號接口名進行判斷就可以分別處理各種信號了。在各個處理分支上。我們可以分離出消息中的參數。對參數類型進行判斷和其他的處理。
/*
* Example low-level D-Bus code.
* Written by Matthew Johnson <[email protected]>
*
* 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, ¶m)) {
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, ¶m);
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;
}
轉自weiercn的博客