NSMutableURLRequest's addValue does not work?

Question

This is for iOS:

I am trying to resume a file download from a previously interrupted connection. To do so, I simply use the HTTP header's range field to set the starting point of the download request as such:

NSMutableURLRequest *urlRequest = [NSMutableURLRequest requestWithURL:[NSURL URLWithString: url]];


// Find out if file already exists.
if([[NSFileManager defaultManager] fileExistsAtPath:filename])
{
    NSError *error;
    unsigned long long currentSize =[[[NSFileManager defaultManager]  attributesOfItemAtPath:filename error:&error] fileSize];

    NSLog(@"File exists, size:%llu",currentSize);

    // If the file was not completly downloaded -> resume download
    [urlRequest addValue:[NSString stringWithFormat:@"bytes=%llu-",currentSize] forHTTPHeaderField:@"Range"];

    //[urlRequest setValue:[NSString stringWithFormat:@"%llu-",currentSize] forHTTPHeaderField:@"range"];


}

As you can see in the src above, I also tried using setValue. In both cases, it seems the "Range" field is added but is not working. The file is always sent from byte offset 0. When I do a NSLog(@"%@", [urlRequest allHTTPHeaderFields]), I get the range value being set but it still doesn't seem to work:

Doing a NSLog(@"%@", [urlRequest allHTTPHeaderFields]) displays: {Range = "bytes=13207107-"; } or, in the case of the commented out setValue code: {Range = "13207107-";}.

I thought maybe the HTTP server does not support range but the IT guy assured me it does...

Does anyone see any problem in the code above? Is there an easy way to test if a web server does support the range field?

Thanks!

Answer 1

I'd test the server independently of your app. The format of the request seems correct. The easiest way to tell is to use curl which is shipped with OSX:

curl -sv -H 'Range: bytes=100-500' http://www.google.com/intl/en_com/images/srpr/logo3w.png > /dev/null

If you don't see Content-Range in the response header and the appropriate Content-Length header (401 in this case), you'll know the server is at fault.