I have an C application that receives commands/info from a client application on localhost but needs to send data to the client on another IP address. Does someone have any previeous kind of experience of doing such a thing? From what i've read You cannot redirect an TCP connection?
Thanks
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I have a problem in this question, please anyone can guide me
Communication between client and server in C ubantu:
Client will send message and address of another client to server and server will forward that message to that client. Other client will reply to server in a same format and server will forward that message to specified client.
I have to use fork command in this Question.
How I will send address to server and message together?
I don't think you should use fork in this case. You can keep an array containing your client's sockets with a unique ID, which can be the address, and forward the message you receive from a client to the one with the ID specified in the original message. The select() system call can be useful when monitoring an array of file descriptors.
I'm implementing in c a sort of FTP protocol.
I' ve a server running.
I start the client, connect to the server, and then send a GET file.txt request.
The client parse the command, see it's a GET command and starts a server socket.
The server recieves the command, and starts the data connection with the client and start sending file.txt on this connection.
When the server sent the file, it closes the client socket (Data).
When i want to GET another file, the port is already in use. How can i prevent this? Should i keep the data-connection open for all the command-connection session? In this case, how can my client know when the file is over?
Thanks
When a socket is closed, it enters the TIME WAIT state (see here for the possible TCP states) and no other socket can be bound to the same address/port pair until the socket leaves TIME WAIT and is in the CLOSED state.
You can go around this by setting the SO_REUSEADDR socket option, that will allow two sockets to be bound to the same address if one of the sockets is in the TIME WAIT state.
you need to open socket for transfer each time as the server will close it when transfer finish.
you will know that the file is downloaded/uploaded by reading response from FTP Server for status code (226 or 250) - check List of FTP server return codes:
https://en.wikipedia.org/wiki/List_of_FTP_server_return_codes
In my project, I use apache-commons-net,
just keep the command connection alive with heartbeat command,
and enter local passive mode every time to do file tranfer.
The principle is same for your situation, I suggest send
EPSV
command before GETTING a file.txt.
refer: https://commons.apache.org/proper/commons-net/
I have strange problem with multicast server/client application. I wrote simple server and client udp multicast application in C and I tested it using two laptops and one wireless router.Server is connected with the ethernet cable to the wrt54gl linksys router with 192.168.1.101 IP address. Client with IP 192.168.1.105 address is connected to the router via wireless interface. They can ping each other. Server is sending UDP packets using sendto function and client is receiving them using recvfrom function. When I run my server I can see sent udp packet in wireshark destined for multicast group with IP address 226.1.1.1 but on client side I don't receive those packets and also I can't see them in wireshark. I'm pretty sure that code is properly written. Do you have experience with multicast to advice me?
Thank you
Am just beginner of this socket programming ...
i tried to make a UDP client_server program using SOCK_RAW .I can send message from the server part.But in client part am getting garbage values. And the receiving message packet size also different.Can U help me to do this client server program using SOCK_RAW.
I tried this client -server with eth0 & eht1,i tried to send 1 packet from eth0 to eth1 sending side is showing "OK" message.. but received data is garbage..
before i done normal client server program using UDP protocol.I got correct output from normal udp client server .When i tried with SOCK_ROW its showing error in sending part.
Make your life simpler and use SOCK_DGRAM - Kernel will take care of datagram headers, you only need to provide valid IP address and data. It is user's responsibility to append (before transmitting) and parse (upon reception) UDP headers using SOCK_RAW.
Most likely you are seeing IP and UDP headers and calling them "garbage". That is what SOCK_ROW does. You should parse and skip protocol headers if you want to get to your message content while using SOCK_ROW.
I'm new to this forum (at least at asking questions), so please be patient. I'm trying to write simple client-server applications to communicate using datagram (UDP) sockets, with C and Windows.
The scenario is very simple, I want to be able to send/receive data from a machine in some local network (behind a GATEWAY/NAT) to some host having public IP. I can send the data, but it seems impossible to receive any data back, because the remote server can't see the client's local IP.
I don't want the user to perform manual port forwarding on the GATEWAY, and I also don't want to use UPnP because of security issues (though it also should be enabled by the user).
I think it is possible because applications like Skype or Browsers can do it, but how ?
Are there some automatically forwarded ports or things like that ? I'm exhausted of searching the web ... PLEASE HELP !
For UDP connections, most home NAT gateways will automatically create a temporary reverse mapping for each outbound packet.
Consider a scenario where your client is running on the internal machine with IP address 192.168.4.5, sending a UDP packet from port 65000 to the external address 64.34.119.12:6789, via a gateway with external IP address 192.0.43.10. When the gateway sees your internal client send a UDP packet from 192.168.4.5:65000 to the external address, it will NAT it to an external address and port, like 192.0.43.10:5500. Your server will see a packet with a source address of 192.0.43.10:5500 and destination address 64.34.119.12:6789. The router also sets up a reverse mapping, so that if it sees a packet arrive on the external interface with a source of 64.34.119.12:6789 and a destination of 192.0.43.10:5500, it will redirect it back to 192.168.4.5:65000. This mapping typically times out after a short while.
This means that in simple cases, all you need to do is:
On the client, use the same port to send to the server and listen for responses;
On the server, respond to the client at the address and port that the client's packet was receieved from, using the same server port that recieved the packet;
Have the client send the initial packet in the conversation;
Don't leave the "connection" idle for more than a few minutes at a time.