Download from SourceForge

From Free Pascal wiki

You can use the Synapse networking library to download files from SourceForge. Because SourceForge store files on multiple mirrors you have to deal with redirection.

...
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;

Then you can download file using standard method.

...
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;

See also