Issues with MonoTouch and CFStream API
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04-07-2021 - |
Вопрос
I am currently developing an application that needs to communicate with a MQTT server via a socket connection. As the System.Net.Sockets API tends to misbehave when switching from a WiFi network to a 3G network (and this happens quite a lot actually) I've decided to give the CFStream API a try. In doing so I've encountered several issues, as follows.
Creating a pair of streams with CreatePairWithSocketToHost
crashes the application as soon as I call Open() on either one of the streams.
CFStream.CreatePairWithSocketToHost(GetEndPoint(), out mReadStream, out mWriteStream);
mReadStream.EnableEvents(CFRunLoop.Current, CFRunLoop.CFDefaultRunLoopMode);
mWriteStream.EnableEvents(CFRunLoop.Current, CFRunLoop.CFDefaultRunLoopMode);
mReadStream.Open();
mWriteStream.Open();
The crash occurs regardless of whether I call EnableEvents()
or not. The exception is:
[ERROR] FATAL UNHANDLED EXCEPTION: MonoTouch.CoreFoundation.CFException: The operation couldn’t be completed. Cannot allocate memory
at MonoTouch.CoreFoundation.CFStream.CheckError () [0x0000f] in /Developer/MonoTouch/Source/monotouch/src/shared/CoreFoundation/CFStream.cs:236
at MonoTouch.CoreFoundation.CFStream.Open () [0x00040] in /Developer/MonoTouch/Source/monotouch/src/shared/CoreFoundation/CFStream.cs:248
at TestCfNework.RootViewController.TestCreatePairToHost () [0x00041] in /Users/adrian/Projects/TestCfNework/TestCfNework/RootViewController.cs:79
at TestCfNework.RootViewController.ViewDidLoad () [0x00000] in /Users/adrian/Projects/TestCfNework/TestCfNework/RootViewController.cs:24
at MonoTouch.UIKit.UIWindow.MakeKeyAndVisible () [0x00008] in /Developer/MonoTouch/Source/monotouch/src/UIKit/UIWindow.g.cs:124
at TestCfNework.AppDelegate.FinishedLaunching (MonoTouch.UIKit.UIApplication app, MonoTouch.Foundation.NSDictionary options) [0x0002e] in /Users/adrian/Projects/TestCfNework/TestCfNework/AppDelegate.cs:32
at MonoTouch.UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x0004c] in /Developer/MonoTouch/Source/monotouch/src/UIKit/UIApplication.cs:38
at TestCfNework.Application.Main (System.String[] args) [0x00000] in /Users/adrian/Projects/TestCfNework/TestCfNework/Main.cs:17
Creating a pair of streams with CreatePairWithSocket
by first creating and connecting a CFSocket
allows for Open()
to proceed without crashing, but CanAcceptBytesEvent
is never fired, CanAcceptBytes()
is always false and any write attempt fails with a timeout.
mSocket = new CFSocket(AddressFamily.InterNetwork,
SocketType.Stream,
ProtocolType.Tcp,
CFRunLoop.Current);
mSocket.ConnectEvent += delegate {
Console.WriteLine("Socket connected");
CFStream.CreatePairWithSocket(mSocket, out mReadStream, out mWriteStream);
mReadStream.EnableEvents(CFRunLoop.Current, CFRunLoop.CFDefaultRunLoopMode);
mWriteStream.EnableEvents(CFRunLoop.Current, CFRunLoop.CFDefaultRunLoopMode);
mReadStream.Open();
mWriteStream.Open();
mWriteStream.CanAcceptBytesEvent += delegate {
Console.WriteLine("Write stream can now accept data");
};
mWriteStream.ErrorEvent += delegate {
Console.WriteLine(mWriteStream.GetError());
};
};
mSocket.Connect(GetEndPoint(), 0);
Creating a pair of streams using CreatePairWithPeerSocketSignature
is the only one that actually produces a pair of streams that I can work with: opening does not crash and I am allowed to write to and read from respectively.
The API behaves this way both on the simulator and on the actual device. So, is this something I am doing wrong? Is it a MonoTouch issue? Is it a bug in the CFStream API itself?
MonoTouch version: 6.0.1. XCode version: 4.5.
Решение
I wrote most the CFNetwork code in MonoMac / MonoTouch, so I should hopefully be able to help you with this :-)
Your code looks ok to me. It works fine with MonoMac (stand-alone Cocoa application on the Mac), but I see the same problem with MonoTouch. Opening the read stream sometimes works, sometimes not, opening the write stream always fails.
CFStream.CreatePairWithSocketToHost()
calls CFStreamCreatePairWithSocketToCFHost()
.
After adding a new overloaded version:
public static void CreatePairWithSocketToHost (string host, int port,
out CFReadStream readStream,
out CFWriteStream writeStream)
which calls CFStreamCreatePairWithSocketToHost()
, this is now working fine.
I just had a look at this and found the problem, will have a fix for it shortly.
About your second problem, the CFSocket API is hitting the same code path internally, so it's also affected by this bug.
Другие советы
To wake up the 3G network, you want to use:
http://iosapi.xamarin.com/?link=T%3aMonoTouch.ObjCRuntime.Runtime%2fM%2fStartWWAN