download.pas

procedure Download;
var
  ms: TFileStream; // where to store file
  fSize: integer; // total size of download file
  fSectionSize: longint; // size of the packet to get
  sPos: int64; // range start position
  ePos: int64; // range stop position
  url: String; // URL to download
  LocalFileName: String; // filename to save as
  HTTP: TIdHTTP; // HTTP object
  idx: integer; // index counter for getting packets
begin
  HTTP := TIdHTTP.Create(nil);
  url := 'http://car-partbidmate.com/cmw/cmw_qaupgrade_86_82_0.exe';
  LocalFileName := 'cmw_qaupgrade_86_82_0.exe';
  HTTP.Head(url); // calls the URL to grab the initial file size
  ms := TFileStream.Create(LocalFileName, fmCreate or fmOpsenReadWrite);
  ms.Position := 0;
  fSize := HTTP.Response.ContentLength;
  fSectionSize := fSize div (1024 * 1024);
  // preset our range
  sPos := 0;
  ePos := 1024 * 1024 - 1;
  for idx := 1 to fSectionSize + 1 do
  begin
    with HTTP.Request.Ranges.Add do // add our range
    begin
      StartPos := sPos;
      endpos := ePos;
    end;
    if idx = fSectionSize then // if LAST packet range
    begin
      sPos := ePos + 1;
      ePos := fSize - 1;
    end
    else
    begin // anything BUT the LAST packet range
      sPos := ePos + 1;
      ePos := sPos + (1024 * 1024) - 1;
    end;
    // call and get the next packet to the file stream
    HTTP.Get(url, ms);
    HTTP.Request.Ranges.Clear; // make sure we clear out the last range
  end;
  freeandnil(ms);
  freeandnil(HTTP);
end;

wiert [9:20 AM]
“for idx := 1 to fSectionSize + 1 do” versus “if idx = fSectionSize then // if LAST packet range”

wiert [9:21 AM]
rename fSectionSize into fPartialSecionCount
Get your casing correct: freeandnil -> FreeAndNul
FreeAndNil even

wiert [9:22 AM]
Get your variable naming conventions right to. Some have prefixes, some don’t, some start with lowercase, others don’t

wiert [9:24 AM]
And where is the “recovery” code?
Rename idx into fPartialSectionIndex
Then keep an fSucceededTransfers: IList {or TArray}, then for each succeeded fPartialSectionIndex set it to True. Repeat loop until all true while skipping the succeeded transfers (or too many retries).
Ensure the server has a sha256/sha512 hash for each file, then finally match hashes. Or maybe better: hashes for each section.
Download over https instead of http to prevent man-in-the-middle modifications.

wiert [9:34 AM]
The FreeAndNil need to be in a try-finally section.