I want to create a data streaming server, and I need a solution, cuz I can't understand what I should to use.
Okay, I have a central home server, which contains infos about temperature, light, motion sensors, music on my central home sound bus and more. And I want to create solution like:
Server continuously sends the data to the local network via port.
And at any time I have an opportunities to connect. For e.g. I connect to 192.168.1.2:1234 and immediately start to listening all information. I can do it from any clients and at the same time. And the server may not even know about connections. It only sends the data to the local network via port, and nothing more.
UPD:
I used TCP protocol to exchange the data between server and clients, but it wasn't a good solution, cuz it's not suit to my described idea.
Related
I'm trying to build instant messaging app. Clients will not only send messages but also often send audios. And I've decided to use websocket connection to communicate with clients. It is fast and allows to send binary data.
The main idea is to receive from client1 message and notify about it client2. But here's the thing. My app will be running on GAE. And what if client1's socket is opened on server1 and client2's is opened on server2. This servers don't know about each others clients.
I have one idea how to solve it, but I am sure it is shitty way. I am going to use some sort of communication between servers(for example JMS or open another websocket connection between servers, doesn't matter right now).
But it surely will lead to a disaster. I can't even imagine how often those servers will speak to each other. For each message server1 should notify server2, server2 should notify client2. But things become even worse when serverN comes into play.
Another way I see this to work is Firebase. But it restricts message size to 4KB. So I can't send audios via it. As a solution I can notify client about new audio and he goes to my server for it.
Hope I clearly explained the problem. Does anyone know how to solve it? Or maybe there are another ways to build such apps?
If you are building a messaging cluster and expect communicating clients to connect to different instances of the server then server-server communication is inevitable. Usually it's not a problem though.
First, if you don't use any load balancing your clients will connect to the same server 50% of time on average (in case of 2 servers).
Second, intra-datacenter links are fast and free in all known public clouds.
Third, you can often do something smart on the frontend to make sure two likely to communicate clients connect to the same server. For instance direct all clients from the same country to the same server using DNS load balancing.
The second part of the question is about passing large media files. It's a common best practice to send it out of band - store on the server and only pass the reference to it. Like someone suggested in the comment, save the audio on the server and just send a message like "audio is available, fetch it from here ...". You don't need to poll the server for that. Just fetch it once when the receiving client requests it.
In general, it seems like you are trying to reinvent the wheel. Just use something off the shelf.
Let all client get connected to multiple servers and each server keeps this metadata
A centralized system like zookeeper stores active servers details
When a client c1 sends a message to client c2:
the message is received by a server (say s1, we can add a load balancer to distribute incoming requests)
s1 will broadcast this information to all other servers to get which server the client c2 is connected to OR a better approach to use consistent hashing which decides which server the client can connect to & in this approach message broadcast is not required
the corresponding server responses to server s1 (say s2)
now s1 sends the message m to s2 and server s2 to client c2
Cons of the above approach:
Each server will have a connection with the n-1 servers, creating a mesh topology
Centralized system (zookeeper) becomes a single point of failures (which is solvable)
Apps like Whatsapp, G-Talk uses XMPP and TCP/IP.
The challenge: We have a number of clients in distributed outposts that I have to manage with a central server. As some clients are located in DMZ or behind proxies, they should be connecting to the server!
As I only have to deal with one client at a time, the server doesn't necessarily have to be able to handle multiple clients simultaniously, however, I would like to see a list of the clients that are trying to connect to the server. Plus, I would like to see more information about the clients than just the IP address, for example the geographic location and some information, if the client has some files in a specific directory that the central server is interested in. My question is, how I best do smth like that.
Sure, I could simply show every client trying to connect in a listbox and accept only the one that I want to connect with, but is that really the way to go? I doubt I can get more information about the client than it's IP address?
I was wondering, if this calls for UDP. The clients send UDP datagrams that just inform the server that they are alive and that they want to connect. On the server, I see all these clients listed with the data they sent. I can then select one client, send an answer/"connection request" with UDP so that this particular client will connect via TCP to the server?
Is that possible?
This sounds like using a hammer to crack a nut. Just have them all connect via TCP. Then you get their presence, their IP address, anything else they care to send you. Deal with them all at once. It's not hard.
This Morning I Booted my Computer and Had multiple applications needing an update. While I was waiting for the applications to update, a question came to mind which I thought I'd ask in here.
The question is How does each application known which internet data being retrieved is theirs?
The applications don't even care about it, they let the Kernel sort out that information.
When an application establishes a connection with a remote computer, the Kernel assigns that application a local port, which is a number among 0-65535. This port on the receiving end can either be requested by the application or the kernel will assign a random port. Generally there is only one application per port, however it is possible for multiple applications to receive the same data, though this is rare.
When a packet is received by the network interface, the kernel will sort the packet by its destination port. There will be a table in the kernel mapping ports to processes, and each application will receive the relevant data without caring about any other possible data that could be coming in the computer.
If you are a programmer, you can learn about all this stuff by reading about socket programming:
http://en.wikipedia.org/wiki/Network_socket
is a good place to start. You can also google "socket programming" with your preferred programming language to get an idea of how this is set up on the programming end.
I am creating a class which communicates with remote server. Currently my device (iPhone 4) is having connectivity via wifi and local network cellular. By default it uses wifi. It works fine in both the cases.
However when I switch from wifi to cell service, it hits error delegate. I want keep communication on going even when connectivity is changed.
Is it possible? How?
Thanks,
I don't expect it is possible. Having switched networks, you've probably also switched IP addresses. Connections are defined by the IP addresses of the end points (as well as protocol and protocol-specific data such as port numbers). So, you can't maintain a connection when the IP address changes. You must cleanup and dispose of the broken connection and open a new one.
If the high-level protocol you're using, such as FTP or HTTP, allows it, you can try resuming the data transfer at the point it was interrupted. For example, if downloading a file, you may be able to resume the download at the file position of the last data you received.
I have no experience with sockets nor multiplayer programming.
I need to code a multiplayer mode for a game I made in c++. It's a puzzle game but the game mode will not be turn-based, it's more like cooperative.
I decided to use UDP, so I've read some tutorials, and all the samples I find decribes how to create a client that sends data and a server that receives it.
My game will be played by two players, and both will send and receive data to/from the other.
Do I need to code a client and a server?
Should I use the same socket to send and receive?
Should I send and receive data in the same port?
Thanks, I'm kind of lost.
Read how the masters did it:
http://www.bluesnews.com/abrash/chap70.shtml
Read the code:
git clone git://quake.git.sourceforge.net/gitroot/quake/quake
Open one UDP socket and use sendto and recvfrom. The following file contains the functions for the network client.
quake/libs/net/nc/net_udp.c
UDP_OpenSocket calls socket (PF_INET, SOCK_DGRAM, IPPROTO_UDP)
NET_SendPacket calls sendto
NET_GetPacket calls recvfrom
Do I need to code a client and a server?
It depends. For a two player game, with both computers on the same LAN, or both on the open Internet, you could simply have the two computers send packets to each other directly.
On the other hand, if you want your game to work across the Internet, when one or both players are behind a NAT and/or firewall, then you have the problem that the NAT and/or firewall will probably filter out the other player's incoming UDP packets, unless the local player goes to the trouble of setting up port-forwarding in their firewall... something that many users are not willing (or able) to do. In that case, you might be better off running a public server that both clients can connect to, which forwards data from one client to another. (You might also consider using TCP instead of UDP in that case, at least as a fallback, since TCP streams are in general likely to have fewer issues with firewalls than UDP packets)
Should I use the same socket to send and receive?
Should I send and receive data in the same port?
You don't have to, but you might as well -- there's no downside to using just a single socket and a single port, and it will simplify your code a bit.
Note that this answer is all about using UDP sockets. If you change your mind to use TCP sockets, it will almost all be irrelevant.
Do I need to code a client and a server?
Since you've chosen to to use UDP (a fair choice if your data isn't really important and benefits more from lower latency than reliable communication), you don't have much of a choice here: a "server" is a piece of code for receiving packets from the network, and your "client" is for sending packets into the network. UDP doesn't provide any mechanism for the server to communicate to the client (unlike TCP which establishes a 2 way socket). In this case, if you want to have two way communication between your two hosts, they'll each need server and client code.
Now, you could choose to use UDP broadcasts, where both clients listen and send on the broadcast address (usually 192.168.1.255 for home networks, but it can be anything and is configurable). This is slightly more complex to code for, but it would eliminate the need for client/server configuration and may be seen as more plug 'n play for your users. However, note that this will not work over the Internet.
Alternatively, you can create a hybrid method where hosts are discovered by broadcasting and listening for broadcasts, but then once the hosts are chosen you use host to host unicast sockets. You could provide fallback to manually specify network settings (remote host/port for each) so that it can work over the Internet.
Finally, you could provide a true "server" role that all clients connect to. The server would then know which clients connected to it and would in turn try to connect back to them. This is a server at a higher level, not at the socket level. Both hosts still need to have packet sending (client) and receiving (server) code.
Should I use the same socket to send and receive?
Well, since you're using UDP, you don't really have a choice. UDP doesn't establish any kind of persistent connection that they can communicate back and forth over. See the above point for more details.
Should I send and receive data in the same port?
In light of the above question, your question may be better phrased "should each host listen on the same port?". I think that would certainly make your coding easier, but it doesn't have to. If you don't and you opt for the 3rd option of the first point, you'll need a "connect back to me on this port" datafield in the "client's" first message to the server.