我正在编写一个需要可靠 UDP 的实时游戏，因此我选择使用 UDT（基于 UDP 的数据传输协议 - http://sourceforge.net/projects/udt/）。
客户端（在浏览器上）通过 CGI 脚本向我的服务器发送实时消息。问题是有一些消息正在丢失，我不知道为什么，因为服务器说它已成功将所有消息发送到相应的客户端，但有时客户端没有收到消息。
在我的调试文件中，我发现当客户端没有收到消息时，它的脚本说：
error in recv();
recv: Connection was broken.
我想获得一些关于服务器如何知道客户端是否收到消息的帮助；我应该从客户端发送 NACK 或其他东西吗？我认为 UDT 应该为我做到这一点。有人可以澄清这种情况吗？
我的代码的通信部分的相关部分如下所示，并带有一些注释：
服务器的相关代码：
//...
void send_msg_in(player cur, char* xml){
/*this function stores the current message, xml, in a queue if xml!=NULL, and sends the 1st message of the queue to the client*/
/*this function is called when the player connects with the entering xml=NULL to get the 1st message of the queue,
or with xml!=NULL when a new message arrives: in this case the message is stored in the queue, and then the message will be sent in the appropriate time, i.e. the messages are ordered.*/
char* msg_ptr=NULL;
if (xml!=NULL){ //add the message to a queue (FIFO), the cur.xml_msgs
msg_ptr=(char*) calloc(strlen(xml)+1, sizeof(char));
strcpy(msg_ptr, xml);
(*(cur.xml_msgs)).push(msg_ptr);
} //get the 1st message of the queue
if (!(*(cur.xml_msgs)).empty()){
xml=(*(cur.xml_msgs)).front();
}
if (cur.get_udt_socket_in()!=NULL){
UDTSOCKET cur_udt = *(cur.get_udt_socket_in());
// cout << "send_msg_in(), cur_udt: " << cur_udt << endl;
//send the "xml", i.e. the 1st message of the queue...
if (UDT::ERROR == UDT::send(cur_udt, xml, strlen(xml)+1, 0)){
UDT::close(cur_udt);
cur.set_udt_socket_in(NULL);
}
else{ //if no error this else is reached
cout << "TO client:\n" << xml << "\n"; /*if there is no error,
i.e. on success, the server prints the message that was sent.*/
// / \
// /_!_\
/*the problem is that
the messages that are lost don't appear on the client side,
but they appear here on the server! */
if (((string) xml).find("<ack.>")==string::npos){
UDT::close(cur_udt);
cur.set_udt_socket_in(NULL); //close the socket
}
(*(cur.xml_msgs)).pop();
}
}
}
//...
客户相关代码：
//...
#define MSGBUFSIZE 1024
char msgbuf[MSGBUFSIZE];
UDTSOCKET client;
ofstream myfile;
//...
main(int argc, char *argv[]){
//...
// connect to the server, implict bind
if (UDT::ERROR == UDT::connect(client, (sockaddr*)&serv_addr, sizeof(serv_addr))){
cout << "error in connect();" << endl;
return 0;
}
myfile.open("./log.txt", ios::app);
send(xml);
char* cur_xml;
do{
cur_xml = receive(); //wait for an ACK or a new message...
myfile << cur_xml << endl << endl; // / \
/* /_!_\ the lost messages don't appear on the website
neither on this log file.*/
} while (((string) cur_xml).find("<ack.>")!=string::npos);
cout << cur_xml << endl;
myfile.close();
UDT::close(client);
return 0;
}
char* receive(){
if (UDT::ERROR == UDT::recv(client, msgbuf, MSGBUFSIZE, 0)){
// / \
/* /_!_\ when a message is not well received
this code is usually reached, and an error is printed.*/
cout << "error in recv();" << endl;
myfile << "error in recv();" << endl;
myfile << "recv: " << UDT::getlasterror().getErrorMessage() << endl << endl;
return 0;
}
return msgbuf;
}
void* send(string xml){
if (UDT::ERROR == UDT::send(client, xml.c_str(), strlen(xml.c_str())+1, 0)){
cout << "error in send();" << endl;
myfile << "error in send();" << endl;
myfile << "send: " << UDT::getlasterror().getErrorMessage() << endl << endl;
return 0;
}
}
感谢您的任何帮助！
PS。在找到链接http://udt.sourceforge.net/udt4/doc/opt.htm后，我尝试增加 close() 的逗留时间，将以下内容添加到服务器的代码中：
struct linger l;
l.l_onoff = 1;
l.l_linger = ...; //a huge value in seconds...
UDT::setsockopt(*udt_socket_ptr, 0, UDT_LINGER, &l, sizeof(l));
但问题还是一样...
聚苯乙烯。服务器端通信的其他部分是：（注意：对我来说，它们并不那么相关）
main(int argc, char *argv[]){
char msgbuf[MSGBUFSIZE];
UDTSOCKET serv = UDT::socket(AF_INET, SOCK_STREAM, 0);
sockaddr_in my_addr;
my_addr.sin_family = AF_INET;
my_addr.sin_port = htons(PORT);
my_addr.sin_addr.s_addr = INADDR_ANY;
memset(&(my_addr.sin_zero), '\0', sizeof(my_addr.sin_zero));
if (UDT::ERROR == UDT::bind(serv, (sockaddr*)&my_addr, sizeof(my_addr))){
cout << "error in bind();";
return 0;
}
UDT::listen(serv, 1);
int namelen;
sockaddr_in their_addr;
while (true){
UDTSOCKET recver = UDT::accept(serv, (sockaddr*)&their_addr, &namelen);
if (UDT::ERROR == UDT::recv(recver, msgbuf, MSGBUFSIZE, 0)){
//this recv() function is called only once for each aqccept(), because the clients call CGI scripts via a browser, they need to call a new CGI script with a new UDT socket for each request (this in in agreement to the clients' code presented before).
cout << "error in recv();" << endl;
}
char* player_xml = (char*) &msgbuf;
cur_result = process_request((char*) &msgbuf, &recver, verbose); //ACK
}
}
struct result process_request(char* xml, UDTSOCKET* udt_socket_ptr, bool verbose){
//parse the XML...
//...
player* cur_ptr = get_player(me); //searches in a vector of player, according to the string "me" of the XML parsing.
UDTSOCKET* udt_ptr = (UDTSOCKET*) calloc(1, sizeof(UDTSOCKET));
memcpy(udt_ptr, udt_socket_ptr, sizeof(UDTSOCKET));
if (cur_ptr==NULL){
//register the player:
player* this_player = (player*) calloc(1, sizeof(player));
//...
}
}
else if (strcmp(request_type.c_str(), "info_waitformsg")==0){
if (udt_ptr!=NULL){
cur_ptr->set_udt_socket_in(udt_ptr);
if (!(*(cur_ptr->xml_msgs)).empty()){
send_msg_in(*cur_ptr, NULL, true);
}
}
}
else{ //messages that get instant response from the server.
if (udt_ptr!=NULL){
cur_ptr->set_udt_socket_out(udt_ptr);
}
if (strcmp(request_type.c_str(), "info_chat")==0){
info_chat cur_info;
to_object(&cur_info, me, request_type, msg_ptr); //convert the XML string values to a struct
process_chat_msg(cur_info, xml);
}
/* else if (...){ //other types of messages...
}*/
}
}
void process_chat_msg(info_chat cur_info, char* xml_in){
player* player_ptr=get_player(cur_info.me);
if (player_ptr){
int i=search_in_matches(matches, cur_info.match_ID);
if (i>=0){
match* cur_match=matches[i];
vector<player*> players_in = cur_match->followers;
int n=players_in.size();
for (int i=0; i<n; i++){
if (players_in[i]!=msg_owner){
send_msg_in(*(players_in[i]), xml, flag);
}
}
}
}
}