Currently I use TIdHTTP in Delphi 11 to automatically download updates of my software. My installer is relatively big (about 100 MB) and the download takes a couple of minutes or even more.

Supposing I have the same installation file on different servers, is there a way to use all these servers to improve the download speed, something like Torrent does?

CodePudding user response：

Torrent works by downloading separate pieces of a file from multiple sources in parallel, and then putting the pieces together into the final file.

You can do that with TIdHTTP too, if all of the servers (or even just 1 server) support the HTTP Range request header. If so, then you can do the following:

1. Create a file on disk, and presize it to the total size of the final file.
2. For each piece of the file you want to download:
   • Create a TIdHTTP.
   • Create a TFileStream to the final file, requesting and sharing read/write access/rights, and then seek it to the desired start offset for the piece in the file.
   • Download the piece into the TFileStream, setting the TIdHTTP.Request.Range property to 'bytes=<start>-<end>', where start is the starting offset, and end is the ending offset, of the piece in the file.

Alternatively:

1. For each piece you want to download:
   • Create a TIdHTTP.
   • Create a TFileStream to a separate temp file, requesting write-only access and sharing no rights, and do not seek it.
   • Download the piece to the TFileStream, setting TIdHTTP.Request.Range as described above.
2. When all pieces are downloaded, create a new file on disk, and copy each piece, in order, to it.

So, for example, you could download the file in 1K chunks by downloading byte ranges 0-1023, 1024-2047, 2048-3071, and so on until the final chunk.