Question

I have an application that speaks to a server on a regular basis using HTTP POST. I am trying to make the connection as failsafe as possible, so the application will not try to send a thing if it does not have a working data connection. How can I detect a connection loss during the middle of a NSURLConnection? The timeout does not work without a minimum time of 240, so that is out of the question. I could use an NSTimer, but it still hangs because the NSURLConnection seems to take up the main thread not allowing any changes. Some sort of delgate maybe?

My code is as follows:

-(NSData*) postData: (NSString*) strData //it's gotta know what to post, nawmean?
{    
    //postString is the STRING TO BE POSTED
    NSString *postString;

    //this is the string to send
    postString = @"data=";
    postString = [postString stringByAppendingString:strData]; 

    NSURL *url = [NSURL URLWithString:@"MYSERVERURLHERE"];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    NSString *msgLength = [NSString stringWithFormat:@"%d", [postString length]];

    //setting prarameters of the POST connection
    [request setHTTPMethod:@"POST"];
    [request addValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
    [request addValue:msgLength forHTTPHeaderField:@"Content-Length"];
    [request addValue:@"en-US" forHTTPHeaderField:@"Content-Language"];
    [request setHTTPBody:[postString dataUsingEncoding:NSUTF8StringEncoding]];
    //[request setTimeoutInterval:10.0];

    NSLog(@"%@",postString);

    NSURLResponse *response;
    NSError *error;

    NSLog(@"Starting the send!");
    //this sends the information away. everybody wave!
    NSData *urlData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];

    NSLog(@"Just finished receiving!");

    if (urlData == nil)
    {
         if (&error)
         {
         NSLog(@"ERROR");
         NSString *errorString = [NSString stringWithFormat:@"ERROR"];
         urlData = [errorString dataUsingEncoding:NSUTF8StringEncoding];
         }
    }

    return urlData;
}

Answer 1

Sure your main thread is blocked when using sendSynchronousRequest:. That is very bad practice for if the user loses the internet connection, the UI will be completely out of order. Apple writes in the documentation:

Important: Because this call can potentially take several minutes to
fail (particularly when using a cellular network in iOS), you should
never call this function from the main thread of a GUI application.

I strongly advise to use the asynchronous methods connectionWithRequest:delegate:. You can easily catch the interruption in connection:didFailWithError:.

Believe me, it’s not that hard, but well worth the effort.