Download from SourceForge/fr

...
    uses httpsend {a Synapse unit}
    ...
    function DownloadHTTPStream(URL: string; Buffer: TStream): boolean;
      // Download file; retry if necessary.
    const
      MaxRetries = 3;
    var
      RetryAttempt: integer;
      HTTPGetResult: boolean;
    begin
      Result:=false;
      RetryAttempt := 1;
      HTTPGetResult := False;
      while ((HTTPGetResult = False) and (RetryAttempt < MaxRetries)) do
      begin
        HTTPGetResult := HttpGetBinary(URL, Buffer);
        //Application.ProcessMessages;
        Sleep(100 * RetryAttempt);
        RetryAttempt := RetryAttempt + 1;
      end;
      if HTTPGetResult = False then
        raise Exception.Create('Cannot load document from remote server');
      Buffer.Position := 0;
      if Buffer.Size = 0 then
        raise Exception.Create('Downloaded document is empty.');
      Result := True;
    end;
    
    function SFDirectLinkURL(URL: string; Document: TMemoryStream): string;
    {
    Transform this part of the body:
    <noscript>
    <meta http-equiv="refresh" content="5; url=http://downloads.sourceforge.net/project/base64decoder/base64decoder/version%202.0/b64util.zip?r=&amp;ts=1329648745&amp;use_mirror=kent">
    </noscript>
    into a valid URL:
    http://downloads.sourceforge.net/project/base64decoder/base64decoder/version%202.0/b64util.zip?r=&amp;ts=1329648745&amp;use_mirror=kent
    }
    const
      Refresh='<meta http-equiv="refresh"';
      URLMarker='url=';
    var
      Counter: integer;
      HTMLBody: TStringList;
      RefreshStart: integer;
      URLStart: integer;
    begin
      HTMLBody:=TStringList.Create;
      try
        HTMLBody.LoadFromStream(Document);
        for Counter:=0 to HTMLBody.Count-1 do
        begin
          // This line should be between noscript tags and give the direct download locations:
          RefreshStart:=Ansipos(Refresh, HTMLBody[Counter]);
          if RefreshStart>0 then
          begin
            URLStart:=AnsiPos(URLMarker, HTMLBody[Counter])+Length(URLMarker);
            if URLStart>RefreshStart then
            begin
              // Look for closing "
              URL:=Copy(HTMLBody[Counter],
                URLStart,
                PosEx('"',HTMLBody[Counter],URLStart+1)-URLStart);
              infoln('debug: new url after sf noscript:');
              infoln(URL);
              break;
            end;
          end;
        end;
      finally
        HTMLBody.Free;
      end;
      result:=URL;
    end;
    
    function SourceForgeURL(URL: string): string;
    // Detects sourceforge download and tries to deal with
    // redirection, and extracting direct download link.
    // Thanks to
    // Ocye: http://lazarus.freepascal.org/index.php/topic,13425.msg70575.html#msg70575
    const
      SFProjectPart = '//sourceforge.net/projects/';
      SFFilesPart = '/files/';
      SFDownloadPart ='/download';
    var
      HTTPSender: THTTPSend;
      i, j: integer;
      FoundCorrectURL: boolean;
      SFDirectory: string; //Sourceforge directory
      SFDirectoryBegin: integer;
      SFFileBegin: integer;
      SFFilename: string; //Sourceforge name of file
      SFProject: string;
      SFProjectBegin: integer;
    begin
      // Detect SourceForge download; e.g. from URL
      //          1         2         3         4         5         6         7         8         9
      // 1234557890123456789012345578901234567890123455789012345678901234557890123456789012345578901234567890
      // http://sourceforge.net/projects/base64decoder/files/base64decoder/version%202.0/b64util.zip/download
      //                                 ^^^project^^^       ^^^directory............^^^ ^^^file^^^
      FoundCorrectURL:=true; //Assume not a SF download
      i:=Pos(SFProjectPart, URL);
      if i>0 then
      begin
        // Possibly found project; now extract project, directory and filename parts.
        SFProjectBegin:=i+Length(SFProjectPart);
        j := PosEx(SFFilesPart, URL, SFProjectBegin);
        if (j>0) then
        begin
          SFProject:=Copy(URL, SFProjectBegin, j-SFProjectBegin);
          SFDirectoryBegin:=PosEx(SFFilesPart, URL, SFProjectBegin)+Length(SFFilesPart);
          if SFDirectoryBegin>0 then
          begin
            // Find file
            // URL might have trailing arguments... so: search for first
            // /download coming up from the right, but it should be after
            // /files/
            i:=RPos(SFDownloadPart, URL);
            // Now look for previous / so we can make out the file
            // This might perhaps be the trailing / in /files/
            SFFileBegin:=RPosEx('/',URL,i-1)+1;
    
            if SFFileBegin>0 then
            begin
              SFFilename:=Copy(URL,SFFileBegin, i-SFFileBegin);
              //Include trailing /
              SFDirectory:=Copy(URL, SFDirectoryBegin, SFFileBegin-SFDirectoryBegin);
              FoundCorrectURL:=false;
            end;
          end;
        end;
      end;
    
      if not FoundCorrectURL then
      begin
        try
          // Rewrite URL if needed for Sourceforge download redirection
          // Detect direct link in HTML body and get URL from that
          HTTPSender := THTTPSend.Create;
          //Who knows, this might help:
          HTTPSender.UserAgent:='curl/7.21.0 (i686-pc-linux-gnu) libcurl/7.21.0 OpenSSL/0.9.8o zlib/1.2.3.4 libidn/1.18';
          while not FoundCorrectURL do
          begin
            HTTPSender.HTTPMethod('GET', URL);
            infoln('debug: headers:');
            infoln(HTTPSender.Headers.Text);
            case HTTPSender.Resultcode of
              301, 302, 307:
                begin
                  for i := 0 to HTTPSender.Headers.Count - 1 do
                    if (Pos('Location: ', HTTPSender.Headers.Strings[i]) > 0) or
                      (Pos('location: ', HTTPSender.Headers.Strings[i]) > 0) then
                    begin
                      j := Pos('use_mirror=', HTTPSender.Headers.Strings[i]);
                      if j > 0 then
                        URL :=
                          'http://' + RightStr(HTTPSender.Headers.Strings[i],
                          length(HTTPSender.Headers.Strings[i]) - j - 10) +
                          '.dl.sourceforge.net/project/' +
                          SFProject + '/' + SFDirectory + SFFilename
                      else
                        URL:=StringReplace(
                          HTTPSender.Headers.Strings[i], 'Location: ', '', []);
                      HTTPSender.Clear;//httpsend
                      FoundCorrectURL:=true;
                      break; //out of rewriting loop
                  end;
                end;
              100..200:
                begin
                  //Assume a sourceforge timer/direct link page
                  URL:=SFDirectLinkURL(URL, HTTPSender.Document); //Find out
                  FoundCorrectURL:=true; //We're done by now
                end;
              500: raise Exception.Create('No internet connection available');
                //Internal Server Error ('+aURL+')');
              else
                raise Exception.Create('Download failed with error code ' +
                  IntToStr(HTTPSender.ResultCode) + ' (' + HTTPSender.ResultString + ')');
            end;//case
          end;//while
          infoln('debug: resulting url after sf redir: *' + URL + '*');
        finally
          HTTPSender.Free;
        end;
      end;
      result:=URL;
    end;

...
    function DownloadHTTP(URL, TargetFile: string): boolean;
    // Download file; retry if necessary.
    // Deals with SourceForge download links
    var
      Buffer: TMemoryStream;
    begin
      result:=false;
      URL:=SourceForgeURL(URL); //Deal with sourceforge URLs
      try
        Buffer := TMemoryStream.Create;
        DownloadHTTPStream(URL, Buffer);
        Buffer.SaveToFile(TargetFile);
        result:=true;
      finally
        FreeAndNil(Buffer);
      end;
    end;