check if an URL exists without opening it

[Peter Hansen]

David wrote:
> 
> Thanks for your answer.
> But how GetRight or Gozilla work or Download Accelarator plus ?
> 
> It seems to me that they check the existence before beginning the download.

They probably don't.  They might, however, do an HTTP HEAD request
instead of the GET request that is used for the download itself.
That retrieves only the header portion (for HTML files anyway) and
not the whole file.

-Peter