Delphi - Download a File with Progress using Synapse - http

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