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!

I presume the number of bytes read or written. If the content isn't text, you should be able to access the headers returned off of your GET request and look for "content length" as in "Content-Length: 3495" and get your total file size. Unfortunately, I've never used Synapse so I can't offer any more guidance than that. — Glenn1234, May 02 '13 at 21:28
Hi @Glenn1234, thank you. I will try to get more information about how to get header of GET. — Guybrush, May 02 '13 at 21:47
Well, I gave up trying to do this with Synapse. I am using Indy again, it is much more easy to do this. Thank you anyway! — Guybrush, May 03 '13 at 15:28

score 2 · Accepted Answer · answered Sep 10 '15 at 17:08

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

Delphi - Download a File with Progress using Synapse

1 Answers1