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
Related
I'd like to find out if a Wi-Fi has internet connection or not. Sometimes our devices are connected with Wi-Fi, but the Wi-Fi doesn't have an internet connection.
NWPathMonitor or Connectivity thirdparty. I tried it, but it is not fool proof.
I know I can write a method to ping a server, but this is a very ineffective and costly affair.
Any ideas?
The only way to know for sure if a network has an Internet connection is to try and make a connection to the Internet. There is nothing on the device that you can query to get the answer.
Even if there were it would have to resort to polling/pinging since connectivity can change at any instant.
A WiFi connection can transition from no-Internet to Internet when the user completes a Hotspot login form. A WiFi connection can transition from Internet to no-Internet if the upstream Internet connection fails in some way. A WiFi connection may be connected to the Internet but not be able to communicate with the specific host your app needs due to a routing failure or some other issue.
For all of these reasons Apple actively discourages "pre flight" checks. Even if a check passes a network operation can still fail due to a change in network status that occurred a microsecond later. It is also unnecessary overhead as it is generally a safe assumption that most devices have some sort of Internet connection most of the time, particularly if the device is an iPhone.
You need to handle errors anyway. Just try the operation and see what happens. If there is no network connection it will fail pretty quickly.
If you want to provide more feedback to the user then you could begin actively checking Internet connectivity with exponential back off in response to a connection error.
That way your app isn't constantly "pinging".
You can also use the error to start a process that uses SCNetworkReachability to check connectivity for you. Rather than using that framework directly, particularly if you are writing in Swift, you might like to use something that wraps it and makes it more accessible like Ashley Mills' Reachability.swift
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.
I'm looking to build a pair of apps that work in a similar way to iTunes and the Remote app for iOS... Is there a framework for connecting iOS and MacOS over wifi?
Bluetooth is something I'd like to avoid and there's no need for a web service, I'm just looking to control my Mac app remotely from the phone.
Thanks in advance.
Id say the most ideal way to accomplish this is via the Bonjour protocol.
Here is a great article on the subject, http://mobileorchard.com/tutorial-networking-and-bonjour-on-iphone/.
Good thing with using Bonjour in iOS is it also works via Bluetooth.
Hope this helps !
here is an example project which exchange the data between iphone and iMAC with WiFi connectivity.
https://github.com/boobalaninfo/Bonjour-iOS-MAC-Apps
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 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 been reading about MQTT and I understand it uses TCP for network transport. So if I have a mobile app that will send subscribe request, I presume this will be an full-duplex connection so the client can be notified for incoming pushed data.
How then is this more battery and network efficient? I mean you still established an open TCP connection. Also how does it handle disconnection, does it auto-reconnect to the broker?
Taking into account my comment on the question, assuming you want to compare to HTTP Long polling these 2 links may help to answer your question:
https://www.ibm.com/developerworks/community/blogs/sowhatfordevs/entry/using_mqtt_protocol_advantages_over_http_in_mobile_application_development5?lang=en
http://stephendnicholas.com/archives/1217
TL;DR version:
The message sizes tend to be significantly smaller with MQTT vs HTTP (especially when you take into account all the http headers that get sent), this saves on network usage and in turn battery usage.
As for the reconnect side of things, the client libraries do not automatically reconnect but they do trigger a call back when the connection drops so you can handle reconnecting as required.