QMP server - Connection Refused bug.

[fredyshox]

Describe the bug
Related to pull request that I'm currently working on #113

UTM/Managers/UTMVirtualMachine.m

Lines 239 to 255 in c7ddf50

	[_qemu_system startWithCompletion:^(BOOL success, NSString *msg){
	if (!success) {
	[self errorTriggered:msg];
	}
	dispatch_semaphore_signal(self->_qemu_exit_sema);
	}];
	int tries = kMaxConnectionTries;
	do {
	[NSThread sleepForTimeInterval:0.1f];
	if ([_spice_connection connect]) {
	break;
	}
	} while (tries-- > 0);
	if (tries == 0) {
	[self errorTriggered:NSLocalizedString(@"Failed to connect to display server.", @"UTMVirtualMachine")];
	}
	[self->_qemu connect];

When the code between _qemu_system startWithCompletion: and _qemu connect, executes quickly enough (in my case serial console connection don't take much time), UTMJSONStream will fail to connect with Connection Refused error, because it is happening before qemu manages to start QMP server. In my code I duct taped it using NSThread sleep, but it's not perfect solution 😄.

Possible solution
One possible solution is to design reconnection mechanism in UTMJSONStream.

UTM/Managers/UTMJSONStream.m

Lines 53 to 70 in c7ddf50

	- (void)connect {
	CFReadStreamRef readStream;
	CFWriteStreamRef writeStream;
	CFStreamCreatePairWithSocketToHost(kCFAllocatorDefault, (__bridge CFStringRef)self.host, self.port, &readStream, &writeStream);
	@synchronized (self) {
	_inputStream = CFBridgingRelease(readStream);
	_outputStream = CFBridgingRelease(writeStream);
	_data = [NSMutableData data];
	_parsedBytes = 0;
	_open_curly_count = -1;
	[_inputStream setDelegate:self];
	[_inputStream scheduleInRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
	[_inputStream open];
	[_outputStream setDelegate:self];
	[_outputStream scheduleInRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
	[_outputStream open];
	}
	}

• Specify number of trials in connect
• Retry _inputStream/_outputStream open, after receiving NSStreamEventErrorOccurred and Connection refused NSError until number of trials is exceeded or NSStreamEventOpenCompleted is received.

[osy]

Thanks this may also be the issue in #130

[osy]

Apple's API really sucks here. Why can't they return an error immediately if the connection fails? The code becomes real messy if we have to implement some state to track "are we retrying connection".