Posting a web-form using TClientSocket. And how to use a web proxy-server

Problem/Question/Abstract:

Posting a web form using TClientSocket. This code snipset demonstrates posting directly and thru a web proxy-server. The result returned by the server is put into a string variable (FResult).

Answer:

{
Copyright (c) 1999 by E.J.Molendijk

This is a code snipset showing you how to
post a form to a webserver. Look at the comments
in the source for more details.

Connect the following events to your ClientSocket:
procedure T...Form.ClientSocket1Write;
procedure T...Form.ClientSocket1Read;
procedure T...Form.ClientSocket1Disconnect;
procedure T...Form.ClientSocket1Error;

It also shows how to route the transmission
thru a web proxy-server.

This is the format used to send to the webserver:
Normal: 'POST ' + PostAddr + 'HTTP/1.0' + HTTP_Data + Content
PROXY:  'POST http://' Webserver + PostAddr + 'HTTP/1.0' + HTTP_Data + Content
}

const
  WebServer = 'www.somehost.com';
  WebPort = 80;
  PostAddr = '/cgi-bin/form';

  { Proxy stuff is only needed if you use a proxy: }
  ProxyServer = 'proxy.somewhere.com';
  ProxyPort = 3128;

  // Some data needed in the post heading
  HTTP_Data =
    'Content-Type: application/x-www-form-urlencoded'#10 +
    'User-Agent: Delphi/5.0 ()'#10 + { Yes! Promote Delphi 5! }
  'Host: somewhere.com'#10 +
    'Connection: Keep-Alive'#10;

type
  T...Form = class(TForm)
    ...
    private
    { Private declarations }
    HTTP_POST: string;
    FContent: string;
    FResult: string; // This will hold the server responce
  public
    { Public declarations }
  end;

  { This functions does some url-encoding on St }
  { Eg.   'John Smith' => 'John+Smith'  }

function HTTPTran(St: string): string;
var
  i: Integer;
begin
  Result := '';
  for i := 1 to length(St) do
    if St[i] in ['a'..'z', 'A'..'Z', '0', '1'..'9'] then
      Result := Result + St[i]
    else if St[i] = ' ' then
      Result := Result + '+'
    else
      Result := Result + '%' + IntToHex(Byte(St[i]), 2);
end;

procedure T...Form.ClientSocket1Write(Sender: TObject;
  Socket: TCustomWinSocket);
begin
  // Post the data
  Socket.SendText(HTTP_POST + FContent);
end;

procedure T...Form.ClientSocket1Read(Sender: TObject;
  Socket: TCustomWinSocket);
begin
  // Incoming result data
  FResult := FResult + Socket.ReceiveText;
end;

procedure T...Form.ClientSocket1Disconnect(Sender: TObject;
  Socket: TCustomWinSocket);
begin
  // YOU CAN PROCESS FResult HERE //
end;

procedure T...Form.ClientSocket1Error(Sender: TObject;
  Socket: TCustomWinSocket; ErrorEvent: TErrorEvent;
  var ErrorCode: Integer);
begin
  ErrorCode := 0; // Ignore Errors
end;

{
And here is the routine you can call to post your form data.
}

procedure T...Form.PostTheForm;
begin
  // Clear result
  FResult := '';

  // You can enter whatever fields you want
  // These are some examples:
  FContent :=
    'Name=' + HTTPTran('John Smith') + '&' +
    'Address=' + HTTPTran('1 Waystreet') + '&' +
    'Email=' + HTTPTran('jsmith@somewhere.com') + '&' +
    'B1=Submit' +
    #10;

  // Calculate the contents length
  FContent :=
    'Content-Length: ' + IntToStr(Length(FContent)) + #10 + #10 + FContent;

  {-- Start proxy ---}
  { uncomment this code if you are using a proxy
  ClientSocket1.Host := ProxyServer;
  ClientSocket1.Port := ProxyPort;
  HTTP_POST := 'POST http://'+WebServer+PostAddr+' HTTP/1.0'#10;
  {--- End proxy ---}

  {--- Start normal connection --- }
  { remove this code if you are using a proxy }
  ClientSocket1.Host := WebServer;
  ClientSocket1.Port := WebPort;
  HTTP_POST := 'POST ' + PostAddr + ' HTTP/1.0'#10;
  {--- End normal ---}

  // Concat the header
  HTTP_Post := HTTP_Post + HTTP_Data;

  // Try to open connection
  ClientSocket1.Open;
end;