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.
Related
I am trying to create a dart/flutter application that is capable of sending and receiving data with sockets over the internet (WAN), without an intermediary, peer-to-peer.
I may have managed to create this on the local network (LAN), through the wifi I can transfer data, but how to transfer data on the global network?
It seems to me that I need to open a port, but how can I do this on dart? Or is there another way.
Briefly - Chat between 2 directly connected users wherever they are.
I tried to connect to an external IP address, but it does not work, I searched and asked people, but they do not know.
Imagine there's relatively complex network infrastructure, from PC, then intelligent hub, then router, then area network switches, then internet, and then same chain of devices towards the server.
Imagine I make HTTP request from some local PC's IP address and some its local port, to the remote server's port 80 (HTTP). Under normal circumstances communication goes from connection request packet, through acknowledgments and requests, and then finally till the finalization and channel close. All intelligent network devices can see this communication, and act accordingly.
Now imagine the following situation: PC makes request from its IP address and some fixed source port, receives half of data, and then reboots. After reboot it again makes request from same IP address and same source port.
Question - which possible behavior it will cause at network devices involved? How are they going to handle previous session before PC reboots?
This is very open ended question, and I need your view onto the situation. It is caused by me having strange problems with embedded network device, which reuses port numbers after power-cycle. I plan to see what is going on on the network using Wireshark, but need direction where to look at. Thank you.
Edit: I am adding proxy server(s) into the chain (which can work higher level than layer-3).
I've read tons of questions about this all over the web, and can't seem to find a solid answer. If I have an iPhone that's running on cellular data and another iOS device on wifi (in two separate locations), is it possible for them to send data to each other directly without sending it first to a web server, then retrieving it? Are the only options sending and receiving from a server/Apple's iCloud? What if I knew the devices' ip addresses? Note that the iPhone has WiFi disabled.
I'm not looking to put this in the app store, it is for personal use. I know NSNotificationCenter isn't an option.
Using the gamekit framework you can send data between two iOS devices. It is easy to implement. Other than that I don't think there is any other way to send data between two iOS devices.
Actually, it IS possible. You may want to google for something called "UDP hole punching" or "TCP hole punching".
The main approach in short: Assuming you got something like a relay server, that is some server in the internet that is publicly addressable from every private LAN that is connected to the www. No you have your two clients A and B in (different) private LANs, with some Network address translation (NAT) going on, that want to establish a peer to peer connection.
First of all both will tell the server their IP address and the port they have in their own LAN. In the UDP or TCP packet, the server will find the public address and port of the device (or the NAT (router)). So the server knows the private and the public IP address as well as the ports.
If now A wants to communicate with B, it asks the server for help. The server will send a message to B that A wants to communicate with her telling her A's public and private IP and port. A gets back B's public and private information and port.
Now here is where the magic happens. Both clients now send packets out to establish a connection simultaneously to the private and public addresses of the other party and thus punching a whole in their NATs such that incoming connections will not be blocked. Even if one party's connection establishing packets will arrive before this whole is created, the other's packets will get through to such that a connection can be created.
Beware of some NATs that scan the data for IP addresses and translate them as well, but if you encrypt your data or change the appearance of the address (complement, ...) you will be fine.
Now the master question, how can the server communicate with one of the clients without an active connection. Well in this case you can use "connection reversal" and apple's "push notifications". Use the "push notifications" (pn) to tell a client behind a NAT that there is something of interest going on and that it should contact the server. Once it has done that the connection is active and can be used in the previous described fashion.
I hope this helps some people that get to this problem although the post is quite old!
You can only use direct IP address communications if the IP address are publicly reachable IP addresses accessible over the internet, and they are static (enough) so that they are not changing on you regularly as devices get assigned to addresses dynamically. In many (most) cases, that won't be true because your devices will be assigned their IP address dynamically and those addresses are frequently going to be self-assigned IP addresses that aren't publicly addressable.
As others have commented, using Apple-provided mechanisms like iCloud are probably the easiest options. If that's not something you'd like to entertain, there are probably ways to make use of a dynamic DNS service like DynDNS to manage the actual IP addresses of your devices. With something like that you might be able to use a direct IP connection between devices based on a named DNS lookup. You'd probably have to jump through some hoops to make that happen though and I'm not sure you'd want to go to that extent.
I think that Bluetooth would be a good option for you
I've spent a few days looking for different solutions, but the whole area is quite complicated, and I'm wondering if anybody knows of any project where I can simply transfer NSData or an NSString or some other simple file over wifi to another iPhone on the network?
Np. Use bonjour to search for devices. Then use CocoaAsyncSocket to send and receive data. It works like a charm.
Little info about AsyncSock:
GCDAsyncSocket and AsyncSocket are TCP/IP socket networking libraries.
Here are the key features available in both:
Native objective-c, fully self-contained in one class. No need to muck
around with sockets or streams. This class handles everything for you.
Full delegate support Errors, connections, read completions, write
completions, progress, and disconnections all result in a call to your
delegate method.
Queued non-blocking reads and writes, with optional timeouts. You tell
it what to read or write, and it handles everything for you. Queueing,
buffering, and searching for termination sequences within the stream -
all handled for you automatically.
Automatic socket acceptance. Spin up a server socket, tell it to
accept connections, and it will call you with new instances of itself
for each connection.
Support for TCP streams over IPv4 and IPv6. Automatically connect to
IPv4 or IPv6 hosts. Automatically accept incoming connections over
both IPv4 and IPv6 with a single instance of this class. No more
worrying about multiple sockets.
Support for TLS / SSL Secure your socket with ease using just a single
method call. Available for both client and server sockets.
I have been working on a local LAN service which uses a multicast port to coordinate several machines. Each machine listens on the multicast port for instructions, and when a certain instruction is received, will send messages directly to other machines.
In other words the multicast port is used to coordinate peer-to-peer UDP messaging.
In practice this works quite well but there is a lingering issue related to correctly setting up these peer-to-peer transmissions. Basically, each machine needs to announce on the multicast port its own IP address, so that other machines know where to send messages when they wish to start a P2P transmission.
I realize that in general the idea of identifying the local IP is not necessarily sensible, but I don't see any other way-- the local receiving IP must be announced one way or another. At least I am not working on the internet, so in general I won't need to worry about NATs, just need to identify the local LAN IP. (No more than 1 hop for the multicast packets is allowed.)
I wanted to, if possible, determine the IP passively, i.e., without sending any messages.
I have been using code that calls getifaddrs(), which returns a linked list of NICs on the machine, and I scan this list for non-zero IP addresses and choose the first one.
In general this has worked okay, but we have had issues where for example a machine with both a wired and wifi connection are active, it will identify the wrong one, and the only work-around we found was to turn off the wifi.
Now, I imagine that a more reliable solution would be to send a message to the multicast telling other machines to report back with the source address of the message; that might allow to identify which IP is actually visible to the other machines on the net. Alternatively maybe even just looking at the multicast loopback message would work.
What do you think, are there any passive solutions to identify which address to use? If not, what's the best active solution?
I'm using POSIX socket API from C. Must work on Linux, OS X, Windows. (For Windows I have been using GetAdapterAddresses().)
Your question about how to get the address so you can advertise it right is looking at it from the wrong side. It's a losing proposition to try to guess what your address is. Better for the other side to detect it itself.
When a listening machine receives a message, it is probably doing do using recvfrom(2). The fifth argument is a buffer into which the kernel will store the address of the peer, if the underlying protocol offers it. Since you are using IP/UDP, the buffer should get filled in with a sockaddr_in showing the IP address of the sender.
I'd use the address on the interface I use to send the announcement multicast message -- on the wired interface announce the wired address and on the wireless interface announce the wireless address.
When all the receivers live on the wired side, they will never see the message on the wireless network.
When there is a bridge between the wired and the wireless network, add a second step in discovery for round-trip time estimation, and include a unique host ID in the announcement packet, so multiple routes to the same host can be detected and the best one chosen.
Also, it may be a good idea to add a configuration option to limit the service to certain interfaces.