Delphi - Download a File with Progress using Synapse

Question

I have been using Synapse for some time now, to send e-mails mainly. Today I am creating a simple installer, and trying to download the application exe file through HTTP. The file is about 9 MB in size, so I´d like to add a progress status to user, but I do not understand the examples I found. Here is what I got so far:

type
  THookSocketStatus = Procedure(Sender: TObject; Reason: THookSocketReason; const Value: String) of Object;
  CallBack = class
    Class Procedure Status(Sender: TObject; Reason: THookSocketReason; const Value: String);
  end;


Class Procedure CallBack.Status(Sender: TObject; Reason: THookSocketReason; const Value: String);
var
  V: String;
Begin
  V := GetEnumName(TypeInfo(THookSocketReason), Integer(Reason)) + ' ' + Value;
  Form1.mem1.Lines.Add(V);
  application.ProcessMessages;
end;

procedure TForm1.btn1Click(Sender: TObject);
var
  HTTP: THTTPSend;
  MSTM: TMemoryStream;
begin
  Screen.Cursor := crHourGlass;
  HTTP := THTTPSend.Create;
  MSTM := TMemoryStream.Create;
  Try
    Try
      HTTP.Sock.OnStatus := CallBack.Status;
      If HTTP.HTTPMethod('GET', edt1.Text) Then
      Begin
        MSTM.Seek(0, soFromBeginning);
        MSTM.CopyFrom(HTTP.Document, 0);
        MSTM.SaveToFile(ExtractFilePath(Application.ExeName) + 'test.exe');
      end;
    Except
    end;
  Finally
    MSTM.Free;
    HTTP.Free;
    Screen.Cursor := crDefault;
  end;
end;

In this simple test I got this result:

HR_SocketClose
HR_ResolvingBegin www.website.com:80
HR_ResolvingEnd 176.102.295.18:80
HR_SocketCreate IPv4
HR_Connect www.website.com:80
HR_WriteCount 158
HR_CanRead
HR_ReadCount 288
HR_CanRead
HR_ReadCount 8192
HR_ReadCount 8192
HR_ReadCount 8192
HR_ReadCount 6720
HR_CanRead
HR_ReadCount 3299
.
.
.
HR_ReadCount 8192
HR_ReadCount 8192
HR_ReadCount 7828
HR_SocketClose
HR_SocketClose

Please, what means WriteCount and ReadCount? How can I get total file size to set the progress bar before start the download?

Thank you guys!

Answer 1

I had the same problem and found a solution by extending the code above. The file length was available as suggested above by using the Header information.

Here is my code:

unit uhttpdownloader;


{$mode Delphi}{$H+}

interface

uses
  Classes, SysUtils, httpsend, blcksock, typinfo;

//Interface for notifications about the progress
type
  IProgress = interface
    procedure ProgressNotification(Text: String; CurrentProgress : integer; MaxProgress : integer);
  end;

type
  { THttpDownloader }

  THttpDownloader = class
  public
    function DownloadHTTP(URL, TargetFile: string; ProgressMonitor : IProgress): Boolean;
  private
    Bytes : Integer;
    MaxBytes : Integer;
    HTTPSender: THTTPSend;
    ProgressMonitor : IProgress;
    procedure Status(Sender: TObject; Reason: THookSocketReason; const Value: String);
    function GetSizeFromHeader(Header: String):integer;
  end;

implementation

function THttpDownloader.DownloadHTTP(URL, TargetFile: string; ProgressMonitor : IProgress): Boolean;
var
  HTTPGetResult: Boolean;
begin
  Result := False;
  Bytes:= 0;
  MaxBytes:= -1;
  Self.ProgressMonitor:= ProgressMonitor;

  HTTPSender := THTTPSend.Create;
  try
    //add callback function for status updates
    HTTPSender.Sock.OnStatus:= Status;
    HTTPGetResult := HTTPSender.HTTPMethod('GET', URL);
    if (HTTPSender.ResultCode >= 100) and (HTTPSender.ResultCode<=299) then begin
      HTTPSender.Document.SaveToFile(TargetFile);
      Result := True;
    end;
  finally
    HTTPSender.Free;
  end;
end;

//Callback function for status events
procedure THttpDownloader.Status(Sender: TObject; Reason: THookSocketReason; const Value: String);
var
  V, currentHeader: String;
  i: integer;
begin
  //try to get filesize from headers
  if (MaxBytes = -1) then
  begin
    for i:= 0 to HTTPSender.Headers.Count - 1 do
    begin
      currentHeader:= HTTPSender.Headers[i];
      MaxBytes:= GetSizeFromHeader(currentHeader);
      if MaxBytes <> -1 then break;
    end;
  end;

  V := GetEnumName(TypeInfo(THookSocketReason), Integer(Reason)) + ' ' + Value;

  //HR_ReadCount contains the number of bytes since the last event
  if Reason = THookSocketReason.HR_ReadCount then
  begin
    Bytes:= Bytes + StrToInt(Value);
    ProgressMonitor.ProgressNotification(V, Bytes, MaxBytes);
  end;
end;

function THttpDownloader.GetSizeFromHeader(Header: String): integer;
var
  item : TStringList;
begin
  //the download size is contained in the header (e.g.: Content-Length: 3737722)
  Result:= -1;

  if Pos('Content-Length:', Header) <> 0 then
  begin
    item:= TStringList.Create();
    item.Delimiter:= ':';
    item.StrictDelimiter:=true;
    item.DelimitedText:=Header;
    if item.Count = 2 then
    begin
      Result:= StrToInt(Trim(item[1]));
    end;
  end;
end;
end.

The complete source code and example can be downloaded here as well: http://andydunkel.net/lazarus/delphi/2015/09/09/lazarus_synapse_progress.html

Andy