Here is a weird thing, I create two sockets and bind them to the exactly same address(INADDR_ANY) and port.
When SO_REUSEADDR is set to both socket, the second bind will fail with error EADDRINUSE.
When SO_REUSEPORT is set to both socket, all bind call will succeed, but only the first socket could receive data, the socket which bind later will never receive any data.
I'm currently working on iOS 10, and I believe it works differently on Android.
Anyone has seen the same problem? Is this an iOS intended behavior? How could I receive data for the second socket without release the first one?
With a simple demo I can confirm that this is intended behavior of iOS(and similar BSD based systems) , and Linux/Android will behave oppositely.
Related
I am sure there is little % of iOS developers who haven't used Reachability, directly or via some framework like Alamofire.
What I am interested what it actually does? The best guess I can make is that given host it opens sockets and then listens for said host. But what network protocol does it use, is it simple UDP (it is not http as far as I can observe), where it periodically sends packages to said host and awaits answer?
Reachability sends no packets at all. It doesn't even tell you that a host is actually reachable. It just tells you that if you made a network request, then the system has an active network interface that it would try to use. That's all. There's no promise those packets would arrive (let alone that you'd get a response), just that iOS would try to send them.
Reachability really only has a couple of uses (and most of the time shouldn't be used). It is useful if "no network is available" would cause you to modify your user interface, or to tell you that it might be a good time to re-try a previously failed connection. (Since iOS 12, you should really use NWPathMonitor for this. I don't know any good uses for Reachability since iOS 12.)
The only way that you can know that a request will actually succeed is to try to send it and see if you get a response. That's why it is not recommended that you test Reachability before sending requests. Just send the request and deal with the errors if they come, since it is always possible to have an error, even if Reachability said you could connect.
I have a navigation application that works with both CoreLocation (Backgrounding mode Location updates) as well as GPS data provided over a UDP connection from an external sensor.
I've noticed that when I background the app the socket goes down (which likely makes sense).
What is the procedure to keep the socket open in backgorunding?
Idea
I thought perhaps to register as a VoIP app - would keep the socket open but it looks like that works differently now.
The documentation suggest implementing setKeepAliveTimeout:handler: but this appears to be deprecated.
I'm not sure exactly how to proceed. Any ideas? The best I can come up with is a hack to have my location-update handler run a check on the socket so see if there is new data - but I'm assume there is a legitimate way to do this.
When the phone goes in stand-by all the UDP socket are closed and only TCP connection can be used. Yes probably with VOIP app you can use the UDP but in that case your app will be reject because your don't use a real VOIP service. I had the same problem ... In my case, even if the phone is in background, I want to send UDP message to a domotic system but is not possible.
I've searched the web extensively but haven't found a good answer to this.
Im writing a socket based application in C++ using posix sockets on iOS/Android.
When switching from wifi->3g, SOMETIMES the socket goes dead without giving any errors when reading/writing.
I can use the reachability API on iOS (and similar on android) to detect when the network switches.
I am destroying/recreating the socket when this occurs. The problem is if the socket is alive, the server will receive the signal when I close the socket. If the server receives the close signal, it will assume the client disconnected intentionally and notify others about this, which is not what I want. If the socket is dead, the server doesn't receive this signal and everything is OK.
How do other people handle this scenario? I really don't want to use a timeout to detect this.
Why does it only sometimes die too? And how can I tell the socket is actually dead?
Just to close this issue, this is the approach I'm taking.
When switching networks, I'm sending a ping-and-reconnect packet to the server, AND creating a new socket.
Which ever responds first, I close the other connection.
Required a bit of server side changes to handle this correctly too
I am trying to write an iOS application that connects to an OBD-II Interface over WiFi (specifically the OBDLink MX WiFi Scan Tool). I have written some basic socket code taken and I am able to open a socket to 192.168.0.10:35000. I receive the NSStreamEventOpenCompleted for both input and output streams.
The first event that fires shortly after is the NSStreamEventHasBytesAvailable. I attempt to read the stream, but the length comes back 0. My question is what is the flow of execution for communicating with these devices? I have tried to issue an ATZ\r command, but nothing is happening (no stream events are firing).
How do I know if if I am connected and the OBD-II interface is ready?
The usual command terminator is ˋ\r\nˋ, so first try sending ˋATZˋ with this command. Only send, after you have received the HasSpace notification from the ˋNSOutputStreamˋ.
Another alternative to communicate with this device would be this Car Diagnostics API, access to the API can be found on
https://github.com/HellaVentures/Car-Diagnostic-API
is sending a message to the device which is connected via TCP Socket and calculate the time it takes to reply is the right approach?
The most common implementation for checking networking latency is based on ICMP packages and is called ping.
There is a nice and easy sample available from Apple.
Please note that even though the sample is provided for OSX, it should build and work fine on iOS as well.
Here are some additions I just found: splinter.com.au/how-to-ping-a-server-in-objective-c-iphone
I would go with ping as that way you would not have to build the "echoing" part yourself, that part is done by the remote system/network-stack.