gistfile1.m

- (CFHTTPMessageRef)createHeadMessage
{
    NSURL* url = self.request.URL;
    CFHTTPMessageRef request = CFHTTPMessageCreateRequest(NULL, (CFStringRef)@"HEAD", (__bridge CFURLRef)url, kCFHTTPVersion1_1);
    return request;
}

- (NSDictionary *)responseHeaders:(CFHTTPMessageRef)request
{
    CFReadStreamRef requestStream = CFReadStreamCreateForHTTPRequest(NULL, request);
    CFReadStreamOpen(requestStream);
    NSMutableData* responseBytes = [NSMutableData data];
    CFIndex numBytesRead = 0;
    
    do
    {
        UInt8 buf[1024];
        numBytesRead = CFReadStreamRead(requestStream, buf, sizeof(buf));
        
        if(numBytesRead > 0)
            [responseBytes appendBytes:buf length:numBytesRead];
    }
    while(numBytesRead > 0);
    
    CFHTTPMessageRef response = (CFHTTPMessageRef)CFReadStreamCopyProperty(requestStream, kCFStreamPropertyHTTPResponseHeader);
    CFHTTPMessageSetBody(response, (__bridge CFDataRef)responseBytes);
    CFReadStreamClose(requestStream);
    CFRelease(requestStream);
    NSDictionary* responseHeaders = CFBridgingRelease(CFHTTPMessageCopyAllHeaderFields(response));
    CFRelease(response);
    
    return responseHeaders;
}

- (void)_doesLoacalCacheNeedUpdate
{
    if (!_cachedResponse)
    {
        // If we don't have some cached data, we need an update!
        [self _startLoadingConnection];
    }
    else
    {
        CFHTTPMessageRef request = [self createHeadMessage];
        NSDictionary* responseHeaders = [self responseHeaders:request];
        CFRelease(request);
        
        [self _compareFreshHeaders:responseHeaders
                  withCacheHeaders:self.cachedResponse.response.allHeaderFields];
    }
}