To put it simply: How do I connect to my friends that live a few blocks away? (I have just started to learn how to make multiplayer games)
All the tutorials I've seen just say "we'll connect to local host for now" and then never come back to it.
Do I need to just change the server_ip to something specific or do I need to completely redo the networking?
Will my IPv4 work as server_ip for this?
Here is some of my code:
// o_client - Create Event
#macro PORT 45000
server_ip = "127.0.0.1"
socket = network_create_socket(network_socket_tcp);
connect = network_connect(socket, server_ip, PORT);
// o_server - Create Event
server = network_create_server(network_socket_tcp, PORT, MAX_CLIENTS);
Thanks!
I Got it to work!
The problem was you need to set server_ip to your router's ip adress (google what is my ip) and you need to set a port forwarding rule (type ipconfig in command prompt type default gateway into a web browser and set the port to send to my devices ip (ipconfig > IPv4))
Related
I'm new in work with interprocess communication. I need you help and clear explanation. I have 2 applications. One of them is a service and one is a client. I've used QT/C++ to write them. When they are working on the one local PC - all is good. But I need to separate them.
So, I have a service on the PC with IP 192.30.82.101.
I connect it to bus using next code:
QDBusConnection connection = QDBusConnection::sessionBus();
connection.registerObject("/my/service/MyService", mySvc);
connection.registerService("my.service.MyService");
Also I have a client on the another PC with IP 192.30.82.40.
I connect my client using the next code:
QDBusServiceWatcher serviceWatcher = new QDBusServiceWatcher();
serviceWatcher->setConnection(QDBusConnection::sessionBus());
serviceWatcher->addWatchedService("my.service.MyService");
.....
myServiceProxy = new local::MyService("my.service.MyService",
"/my/service/MyService", QDBusConnection::sessionBus(), this);
I need to connect my client on the PC with IP 192.30.82.40 to the service on the PC 192.30.82.101. I don't know how to do this. I've found a few topics on the forum but I still don't understand what to do.
So, what I have found:
On the PC where is my service I have to add additional lines to /etc/dbus-1/session.conf:
<listen>tcp:host=<host>,port=<port></listen>
<listen>unix:tmpdir=/tmp</listen>
<auth>ANONYMOUS</auth>
<allow_anonymous/>
Here I have a question: Which IP address I have to use here (server or client)? Which port is used for DBUS (is it default port or how I can check it)? I have tried to set an IP address of my client PC, my service PC and different ports, and port 0, but I've got an error: Failed to bind socket "172.30.82.40:0": Cannot assign requested address.
On the client side I have to set DBUS_SESSION_BUS_ADDRESS with the same address: export DBUS_SESSION_BUS_ADDRESS=tcp:host=<host>,port=<port>.
I've tried to do this with different ports, with 0 port, because this means - use any free port. But I cannot start bus daemon with any port+IP configuration.
Also I've tried to connect client QDBusServiceWatcher to bus using the next code:
serviceWatcher->setConnection(QDBusConnection::connectToBus("tcp:host=<host>,port=<port>", "session"));
It was not successful.
I have no idea how to connect them to each other.
Can anybody, please, explain me how it should be, how does it work?
I want to clearly understanding how does it work?
I will be very grateful for any help. I hope for your kindness.
UPDATE
I have found how to connect my client to DBus bus via TCP:
On the PC where is my service I have to add additional lines to /etc/dbus-1/session.conf:
<listen>tcp:host=localhost,bind=*,port=6667,family=ipv4</listen>
<listen>unix:tmpdir=/tmp</listen>
<auth>ANONYMOUS</auth>
<allow_anonymous/>
Here we should add PORT. We can find it in dbus config file.
On the client side I have to set DBUS_SESSION_BUS_ADDRESS with corresponding address (IP of PC where is service):
export DBUS_SESSION_BUS_ADDRESS=tcp:host=192.50.88.10,port=6667,family=ipv4.
Thats all. We can check it just started dbus-monitor.
But now I have another issue: how to connect my client to my service?
I need to do something more to connect to my service.
I guess that this is something like:
QDBusConnection::connectToBus("tcp:host=<host>,port=<port>","connectionName");
I've tried to connect with any random name, but this is not correct.
So, my question is - where I can get correct connection name?
Correct answer to my question is:
On the PC where is one application add additional lines to
/etc/dbus-1/session.conf:
<listen>tcp:host=localhost,bind=*,port=6667,family=ipv4</listen>
<listen>unix:tmpdir=/tmp</listen>
<auth>ANONYMOUS</auth>
<allow_anonymous/>
Correct port you can find in dbus config file.
On the client side It's needed to set DBUS_SESSION_BUS_ADDRESS with
corresponding address (IP of PC where is service):
export DBUS_SESSION_BUS_ADDRESS=tcp:host=192.50.88.10,port=6667,family=ipv4.
To connect to session where is alive your remote app use the next
connection string:
DBusConnection::connectToBus("tcp:host=192.50.88.10,port=6667", "qt_default_session_bus"));
How to know session name? I've added log in my service:
qDebug() << "Connection name: " << connection.name();
Then started app, copy printed name and set it in my client.
Now it works!
I can run my Qt DBus test by connecting to the session bus:
QDBusConnection connection = QDBusConnection::sessionBus();
connection.registerService(...)
....
TestserviceInterface testserviceInterface( .... , connection, &a);
But can I connect to this DBus from a different computer. I know I can do something like this:
connection = QDBusConnection::connectToPeer("tcp:host=127.0.0.1,port=45000", Testservice::ServiceName);
But how would I obtain the port? Whatever I have tried, there seems to be no connection. Or am I at the wrong path here and need to us Peer 2 Peer DBus instead of the session bus?
I am almost sure the service name is correct, as I can see it qdbusviewer. When I use dbus-monitor the output does not mean a lot to me, I cannot see any port, etc.
Any idea how I would be able to connect from another computer?
PS: I am aware that there is something like gabriel for tunnelling via SSH (http://gabriel.sourceforge.net/howto.html). This is not what I am up to, I am looking for a "direct connection".
Session bus daemon usually listens unix socket /var/run/dbus/system_bus_socket ( check your /usr/local/etc/dbus-1/session.conf config ) which means that you can't access it remotely via tcp. Start some kind of port forwarding on computer where bus daemon is running (using socat for example) or configure it to listen tcp.
You can use SSH to create a tunnel for DBus.
ssh -nNT -L ./dbus_on_local:/var/run/dbus/system_bus_socket user#remote
Explanation
This will create a local "file" (unix domain socket) dbus_on_local that you can connect to.
I have to write a server which have to accept clients on ports that they have specified.
Example : A wants to connect on port 1337, so server listen on port 1337. B on 1992 so server listen on 1992, etc...
I don't know how to handle this.
Should I make a system like :
- All clients connects on the same port : XXXX ;
- The client's 1st packet specify the port he wants ;
- The server binds / listens / accepts on the new port ;
- The server answers the client that it's OK ;
- The client stops connecting on port XXXX and start connecting on the new port.
I don't know if this kind of system is good, but I can't figure out how else to do it.
Thank you, Florian
You'll want some kind of master process or central table that keeps the room to port mappings. You'll need clients to either connect to the master process or to some kind of "entry room" to get connected in the first place. Then, when they move from room to room, just look up the port they need to connect to, and refer them to the next port. All the central information can be kept in a database, if desired.
You'll need to have at least one standard port open for clients to connect to if they're to communicate their requests about other ports. It doesn't have to be obviously open, it can just quietly accept UDP packets for instance, as some ssh hiding systems do. It can also work with TCP if you're willing to produce some kind of response that the new port is bound and ready.
In any case, listening on multiple ports is not especially tricky if you have the right framework. libevent is an example of how you might get started.
It does seem odd that you'd have a standard port open as well as an unknown number of dynamic ports, though. When do you close these down? Do they time-out eventually? Is the listen call only short-term by nature?
TCP standard has "simultaneous open" feature.
The implication of the feature, client trying to connect to local port, when the port is from ephemeral range, can occasionally connect to itself (see here).
So client think it's connected to server, while it actually connected to itself. From other side, server can not open its server port, since it's occupied/stolen by client.
I'm using RHEL 5.3 and my clients constantly tries to connect to local server.
Eventually client connects to itself.
I want to prevent the situation. I see two possible solutions to the problem:
Don't use ephemeral ports for server ports.
Agree ephemeral port range and configure it on your machines (see ephemeral range)
Check connect() as somebody propose here.
What do you thinks?
How do you handle the issue?
P.S. 1
Except of the solution, which I obviously looking for,
I'd like you to share your real life experience with the problem.
When I found the cause of the problem, I was "astonished" on my work place people are not familiar with it. Polling server by connecting it periodically is IMHO common practice,
so how it's that the problem is not commonly known.
When I stumbled into this I was flabbergasted. I could figure out that the outgoing
port number accidentally matches the incoming port number, but not why the TCP
handshake (SYN SYN-ACK ACK) would succeed (ask yourself: who is sending the ACK if
there is nobody doing a listen() and accept()???)
Both Linux and FreeBSD show this behavior.
Anyway, one solution is to stay out of the high range of port numbers for servers.
I noticed that Darwin side-steps this issue by not allowing the outgoing port
to be the same as the destination port. They must have been bitten by this as well...
An easy way to show this effect is as follows:
while true
do
telnet 127.0.0.1 50000
done
And wait for a minute or so and you will be chatting with yourself...
Trying 127.0.0.1...
telnet: Unable to connect to remote host: Connection refused
Trying 127.0.0.1...
telnet: Unable to connect to remote host: Connection refused
Trying 127.0.0.1...
telnet: Unable to connect to remote host: Connection refused
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
hello?
hello?
Anyway, it makes good job interview material.
Bind the client socket to port 0 (system assigns), check the system assigned port, if it matches the local server port you already know the server is down and and can skip connect().
For server you need to bind() socket to port. Once addr:port pair had socket bound, it will no longer be used for implicit binding in connect().
No problem, no trouble.
Note that this solution is theoretical and I have not tested it on my own. I've not experienced it before (or did not realize) and hopefully I won't experience it anymore.
I'm assuming that you cannot edit neither the client source code nor the server source. Additionally I'm assuming the real problem is the server which cannot start.
Launch the server with a starter application. If the target port that the server will bind is being used by any process, create an RST (reset packet) by using raw sockets.
The post below briefly describes what an RST packet is (taken from http://forum.soft32.com/linux/killing-socket-connection-cmdline-ftopict473059.html)
You have to look at a "raw socket" packet generator.
And you have to be superuser.
You probably need a network sniffer as well.
http://en.wikipedia.org/wiki/Raw_socket
http://kerneltrap.org/node/3072 - TCP RST attacks
http://search.cpan.org/dist/Net-RawIP/lib/Net/RawIP.pm - a Perl module
http://mixter.void.ru/rawip.html - raw IP in C
In the C version, you want a TH_RST packet.
RST is designed to handle the following case.
A and B establish a connection.
B reboots, and forgets about this.
A sends a packet to B to port X from port Y.
B sends a RST packet back, saying "what are you talking about? I don't
have a connection with you. Please close this connection down."
So you have to know/fake the IP address of B, and know both ports X
and Y. One of the ports will be the well known port number. The other
you have to find out. I thnk you also need to know the sequence
number.
Typically people do this with a sniffer. You could use a switch with a
packet mirroring function, or run a sniffer on either host A or B.
As a note, Comcast did this to disable P2P traffic.
http://www.eff.org/wp/packet-forgery-isps-report-comcast-affair
In our case we don't need to use a sniffer since we know the information below:
So you have to know/fake the IP address of B, and know both ports X
and Y
X = Y and B's IP address is localhost
Tutorial on http://mixter.void.ru/rawip.html describes how to use Raw Sockets.
NOTE that any other process on the system might also steal our target port from ephemeral pool. (e.g. Mozilla Firefox) This solution will not work on this type of connections since X != Y B's IP address is not localhost but something like 192.168.1.43 on eth0. In this case you might use netstat to retrieve X, Y and B's IP address and then create a RST packet accordingly.
Hmm, that is an odd problem. If you have a client / server on the same machine and it will always be on the same machine perhaps shared memory or a Unix domain socket or some other form of IPC is a better choice.
Other options would be to run the server on a fixed port and the client on a fixed source port. Say, the server runs on 5000 and the client runs on 5001. You do have the issue of binding to either of these if something else is bound to them.
You could run the server on an even port number and force the client to an odd port number. Pick a random number in the ephemeral range, OR it with 1, and then call bind() with that. If bind() fails with EADDRINUSE then pick a different odd port number and try again.
This option isn't actually implemented in most TCPs. Do you have an actual problem?
That's an interesting issue! If you're mostly concerned that your server is running, you could always implement a heartbeat mechanism in the server itself to report status to another process. Or you could write a script to check and see if your server process is running.
If you're concerned more about the actual connection to the server being available, I'd suggest moving your client to a different machine. This way you can verify that your server at least has some network connectivity.
In my opinion, this is a bug in the TCP spec; listening sockets shouldn't be able to send unsolicited SYNs, and receiving a SYN (rather than a SYN+ACK) after you've sent one should be illegal and result in a reset, which would quickly let the client close the unluckily-chosen local port. But nobody asked for my opinion ;)
As you say, the obvious answer is not to listen in the ephemeral port range. Another solution, if you know you'll be connecting to a local machine, is to design your protocol so that the server sends the first message, and have a short timeout on the client side for receiving that message.
The actual problem you are having seems to be that while the server is down, something else can use the ephemeral port you expect for your server as the source port for an outgoing connection. The detail of how that happens is separate to the actual problem, and it can happen in ways other than the way you describe.
The solution to that problem is to set SO_REUSEADDR on the socket. That will let you create a server on a port that has a current outgoing connection.
If you really care about that port number, you can use operating specific methods to stop it being allocated as an ephemeral port.
I have a C++ Program listening for incoming socket connections on port 2222.
I have an Adobe AIR/Flex application that attempts to connect to it, when I click a button.
When I Connect To My Socket Over My Intranet, My C++ program hears and accepts the incoming socket connection and Everything Works Fine:
var Sock:Socket=new Socket("192.168.1.100",2222);
But When I Try To Connect Using My Real IP, I Get Error #2031:
var Sock:Socket=new Socket("76.18.24.118",2222);
Both programs are running on my laptop computer. I am behind a router, but have configured that router with port forwarding so that port 2222 maps to my laptop.
What Am I Missing? I am very new to this, so perhaps I'm missing something obvious to you smarties.
What does the error code mean (see your docs for socket)
Are you sure the receiving server process is alive?
The traditional starting point is Beej's guide
Port forwarding does not mean that you can use an external IP address, your laptop is still on the private 192.168 network. What it means is that when someone tries to connect on 78.18.24.118:2222 the router converts the IP address to 192.168.1.100:2222. This effectively allows you to run a server inside your network but allows an outside client to connect to you.
Look up DNAT for more information.