title: Alamofire support HTTP ETAG mechanism
body: <p>I cannot understand if Alamofire support HTTP ETAG.</p>
  
  <p>I find this discussion <a href="https://github.com/Alamofire/AlamofireImage/issues/5" rel="nofollow noreferrer">https://github.com/Alamofire/AlamofireImage/issues/5</a></p>
  
  <p>and another thread on:</p>
  
  <p><a href="https://stackoverflow.com/questions/21659764/nsurlcache-and-etags">NSURLCache and ETags</a> </p>
  
  <p>Previously i use AFNETWORKING 1.x with Etag and i found this lines of code:</p>
  
  <pre><code>NSMutableURLRequest *mutableURLRequest = [self.request mutableCopy];
  if ([self.response respondsToSelector:@selector(allHeaderFields)] &amp;&amp; [[self.response allHeaderFields] valueForKey:@"ETag"]) {
      [mutableURLRequest setValue:[[self.response allHeaderFields] valueForKey:@"ETag"] forHTTPHeaderField:@"If-Range"];
  }
  </code></pre>
  
  <p>In AFHTTPRequestOperation.h (AFNETWORKING 1.x.x)</p>
  
  <p>I cannot understand if Etag automatically work with url cache policy:</p>
  
  <pre><code>NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:urlString]
                                                                 cachePolicy: NSURLRequestUseProtocolCachePolicy
                                                             timeoutInterval:60];
  </code></pre>
  
  <p>Or in another way..</p>
  
  <p>I'm just a little bit confused..</p>