How to know server reply in iPhone?

Question

 - (IBAction)  uploadImage   {  
    /*
     turning the image into a NSData object  
     getting the image back out of the UIImageView  
     setting the quality to 100  
     */  
      NSData *imageData = UIImageJPEGRepresentation(image.image, 100);  
      // setting up the URL to post to  
    NSString *urlString = @"http://uploadhere.com/photos/iphone.php";

    // setting up the request object now
    NSMutableURLRequest *request = [[[NSMutableURLRequest alloc] init] autorelease];
    [request setURL:[NSURL URLWithString:urlString]];
    [request setHTTPMethod:@"POST"];

    /*
     add some header info now
     we always need a boundary when we post a file
     also we need to set the content type

     You might want to generate a random boundary.. this is just the same 
     as my output from wireshark on a valid html post
     */
    NSString *boundary = [NSString stringWithString:@"---------------------------14737809831466499882746641449"];
    NSString *contentType = [NSString stringWithFormat:@"multipart/form-data; boundary=%@",boundary];
    [request addValue:contentType forHTTPHeaderField: @"Content-Type"];

    /*
     now lets create the body of the post
     */
    NSMutableData *body = [NSMutableData data];
    [body appendData:[[NSString stringWithFormat:@"\r\n--%@\r\n",boundary] dataUsingEncoding:NSUTF8StringEncoding]];    
    [body appendData:[[NSString stringWithString:@"Content-Disposition: form-data; name=\"q\"\r\n\r\n"] dataUsingEncoding:NSUTF8StringEncoding]];
    [body appendData:[[NSString stringWithString:@"Content-Type: application/octet-stream\r\n\r\n"] dataUsingEncoding:NSUTF8StringEncoding]];
    [body appendData:[NSData dataWithData:imageData]];
    [body appendData:[[NSString stringWithFormat:@"\r\n--%@--\r\n",boundary] dataUsingEncoding:NSUTF8StringEncoding]];
    NSLog(@"here1");
    // setting the body of the post to the reqeust
    [request setHTTPBody:body];
    NSLog(@"here2");
    // now lets make the connection to the web
    NSData *returnData = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
    returnString = [[NSString alloc] initWithData:returnData encoding:NSUTF8StringEncoding];
    NSLog(@"here3");
    //NSLog(returnString);
    //picText = rowZero.pickerLabel.text;
    NSLog(@"here4");
    rowZero.path       = returnString;
    //NSLog(rowZero.path);


}

In the connection with web section, this is happening.

I am using this code to upload image on server. However, in this NSLog(@"%@", returnData) is giving me the value but NSLog(@"%@", returnString) is returning null value. I mean how would I know that my image is being uploaded on the server or not?