Client to get a file from any Web Server (Lesson 6)

In this demo we are building a client application that will be able to receive any file it request from a site, all of this with the Client components from RealThinClient.
Basically we are going to:

  • Create a new Delphi project and add some controls
  • Define events to process our request.
  • Compile and run our project.

1. Start a new Project in Delphi

New Project

New Project

Set name of Form1 to fmMain.

Form Name Property

Form Name Property

3. Set the KeyPress property of your form to True

We will be catching the Enter key in any field so, when it is pressed, the system will start to search for the specified Server Address and File Name.

Key Preview Property

Key Preview Property

2. Put some controls in your form

Put a Label control

  • Set Caption to Server Address:

Put a TextEdit control

  • Set Name = edServerAddress
  • Set Text = www.realthinclient.net

Put another Label control.

  • Set Caption = File:

Put another TextEdit control

  • Set Name = edFileName
  • Set Text = /

Put one Memo control on your form

  • Set Name = mmResult
  • Set Scrollbars = ssBoth

This is how our form should look with the controls placed in it:

Form Finished

Form Finished

3. Put some RTC controls in your form.

From the RTC Client tab, put one RtcHttpClient on your main form:

RtcHttpClient Control Properties

RtcHttpClient Control Properties

For RtcHttpClient1:

  • Set MultiThreaded = True
  • Set ReconnectOn.ConnectLost = True
  • Set ServerAddr = www.realthinclient.net
  • Set ServerPort = 80
  • Set UseProxy = True

From the RTC Client tab, put one RtcDataRequest on your form:

RtcDataRequest Control

RtcDataRequest Control

For RtcDataRequest1:

  • Set Client = RtcHttpClient1
  • Set AutoRepost = 2
  • Set AutoSyncEvents = True

4. Define the OnBeginRequest event for RtcDataRequest control.

For RtcDataRequest1, define the OnBeginRequest event:

procedure TfmMain.RtcDataRequest1BeginRequest(Sender: TRtcConnection);
begin
  with Sender as TRtcDataClient do
  begin
  // (1)
  if Copy(Request.FileName, 1, 1) <> '/' then
    Request.FileName := '/' + Trim(Request.FileName);
  edFileName.Text := Request.FileName;
  // (2)
  if Request.Host = '' then
    if Trim(edServerAddress.Text) <> '' then
    begin
      ServerAddr := edServerAddress.Text;
      Request.Host := ServerAddr;
    end;
  mmResult.Lines.Clear;
  mmResult.Lines.Add('Requesting "' + Request.FileName + ' From ' + ServerAddr + '".');
  // (3)
  WriteHeader;
  end;
end;

What are we doing?

  1. We check that our request starts with /. If we make some change on the file name we reflect this change to the edFileName TextEdit control.
  2. Then, we define the HOST header
  3. After we have the HOST header defined, we send it out.

5. Define the OnDataReceived event for RtcDataRequest control

For RtcDataRequest1, define the OnDataReceived event:

procedure TfmMain.RtcDataRequest1DataReceived(Sender: TRtcConnection);
begin
  with Sender as TRtcDataClient do
  begin
    if Response.Started then
    begin
      // (1)
      with mmResult do
      begin
        Lines.Add('   Status Code: ' + IntToStr(Response.StatusCode));
        Lines.Add('   Status Text: ' + Response.StatusText);
        Lines.Add('   ALL Headers:');
        Lines.Add(Response.HeaderText);
        Lines.Add('Content Length:');
        Lines.Add(IntToStr(Response.ContentLength));
        Lines.Add('  Content Body:');
        Lines.Add('START >');
      end;
      // (2)
      mmResult.Text := mmResult.Text + Read;
      if Response.Done then
      begin
        // (3)
        mmResult.Lines.Add('> END');
        Request.Host := '';
        RtcHttpClient1.Disconnect;
      end;
    end;
  end;
end;

What are we doing?

  1. We execute the Header info display on Memo Control one time per request, when we start receiving the response.
  2. Depending on the content size, the line that show the content of the requested file could be executed several times.
  3. When we have received all the content of the requested file, we print the >END tag and clear the Host name. Last, we disconnect our RtcHttpClient connection.

7. Define the OnKeyPress event for your form.

For fmMain, define the OnKeyPress event:

procedure TfmMain.FormKeyPress(Sender: TObject; var Key: Char);
begin
  if Key = #13 then
  begin
    //(1)
    edServerAddress.Text := Trim(edServerAddress.Text);
    if Copy(edServerAddress.Text, Length(edServerAddress.Text), 1) = '/' then
      edServerAddress.Text := Copy(edServerAddress.Text, 1,
        Length(edServerAddress.Text) -1);
    RtcHttpClient1.ServerAddr := edServerAddress.Text;
    //(2)
    with RtcDataRequest1 do
    begin
      Request.Method := 'GET';
      Request.FileName := edFileName.Text;
      edServerAddress.SelectAll;
      edFileName.SelectAll;
      Post;
    end;
    //(3)
    Key := #0;
    //(4)
    RtcHttpClient1.Connect();
  end;
end;

What are we doing?

  1. We check the Server Address TextEdit control so we make a few validations on it. We could use regular expressions to do this job, but this is out of the scope of this demo.
  2. Configure our TRtcDataRequest. We are not making validations on the FileName, those are done whe the Request is started at the OnBeginRequest event.
  3. No Beep.
  4. Start the connection. We already set our ServerAddr property for our RtcHttpClient control, so now, we start our connection to that server.

20. Connect to the internet, then Compile and Run the project.

If every thing is ok, you should see your form ready to process your requests.

Project Running

Project Running

In this example, content is received piece-by-piece and filled into the Memo field (mmResult) by adding the text Read to Memo’s text and special care had to be taken to avoid clearing the memo in the middle of receiving.
You can access response header information in different ways:

  • All headers as text using Response.HeaderText;
  • Each header variable separately by using Response['variable-name'];
  • Most header information specially prepared for easier access (Response.ContentLength, Response.Query, Response.Cookie, etc). The same rules apply to request info (Request.HeaderText, Request['variable'], Request.ContentLength, etc).

Even though Response.ContentLength could be undefined (zero) if Server only supports HTTP/1.0 (server will end the response with a disconnect), you can always use the Response.ContentIn property to check how much of the response content has already arrived. This will increment for each package received, even if you do not call Read.

Other interesting events when receiving data are the OnResponseDone and OnConnectLost events. OnResponseDone event will be triggered after the last OnDataReceived event (after all data has been received), while the OnConnectLost event gets called in case your connection drops after executing the OnBeginRequest event, but before you received the complete response in the OnDataReceived event.

To store received data in a stream, you can open the stream from the OnDataReceived event when Response.Started, append (to the stream) everything you Read from the OnDataReceived event and close the stream from OnResponseDone and OnConnectLost events.

Files in this post.

One thought on “Client to get a file from any Web Server (Lesson 6)

  1. Job Espejel

    Thanks for this demo

    In step 4 there is an error in the code
    then name of the memo component es mmResult but in the code your’re using memo1

    best regards

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