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Using Indy idHTTP to post binary and text (Views: 17112)


Problem/Question/Abstract:

Using Indy idHTTP to post binary and text

Answer:

This is a small example of using post to send data to web server. There is two different ways to do this operation.

Solve 1:

procedure TForm1.SendPostData;
const
  CRLF = #13#10;
var
  aStream: TMemoryStream;
  Params: TMemoryStream;
  S: string;
begin
  aStream := TMemoryStream.create;
  Params := TMemoryStream.Create;

  HTTP.Request.ContentType := 'multipart/form-data;
    boundary = - - - - - - - - - - - - - - - - - - - - - - - - - - - - -7
      cf87224d2020a';

  try
    S := '-----------------------------7cf87224d2020a' + CRLF +
      'Content-Disposition: form-data; name="file1"; filename="c:abc.txt"' +
      CRLF +
      'Content-Type: text/plain' + CRLF + CRLF +
      'file one content. Contant-Type can be application/octet-stream or if
    you want you can ask your OS fot the exact type
    .' + CRLF +
      '-----------------------------7cf87224d2020a' + CRLF +
      'Content-Disposition: form-data; name="sys_return_url2"' + CRLF + CRLF +
      'hello2' + CRLF +
      '-----------------------------7cf87224d2020a--';

    Params.Write(S[1], Length(S));

    with HTTP do
    begin
      try
        HTTP.Post('http://www.mydomain.com/postexampe.cgi', Params,
          aStream);
      except
        on E: Exception do
          showmessage('Error encountered during POST: ' + E.Message);
      end;
    end;
    aStream.WriteBuffer(#0' ', 1);
    showmessage(PChar(aStream.Memory));
  except
  end;
end;


Solve 2:

procedure TForm1.SendPostData;
var
  aStream: TMemoryStream;
  Params: TStringStream;
begin
  aStream := TMemoryStream.create;
  Params := TStringStream.create('');
  HTTP.Request.ContentType := 'application/x-www-form-urlencoded';

  try
    Params.WriteString(URLEncode('sys_return_url=' + 'helo1' + '&'));
    Params.WriteString(URLEncode('sys_return_url=' + 'helo2'));
    with HTTP do
    begin
      try
        HTTP.Post('http://www.mydomain.com/postexampe.cgi', Params,
          aStream);
      except
        on E: Exception do
          showmessage('Error encountered during POST: ' + E.Message);
      end;
    end;
    aStream.WriteBuffer(#0' ', 1);
    showmessage(PChar(aStream.Memory));
  except
  end;
end;

As you can see there is a difference in the way post stream is constructed and the ContentType. In the first example ContentType is "multipart/form-data; boundary=-----------------------------7cf87224d2020a" and this boundary is used to separate different parameters.

In the second example the ContentType is "application/x-www-form-urlencoded". In this case the paremeteras are passed in the form

ParamName=ParamValue&ParamName=ParamValue

Note that the Pramaeters in the second form must be URL encoded.

Where these two formats of post information are used?

The first one is used when you have binary data to post and the second one is when you are going to post only text fields.

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