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Shiv Kumar

Hobbyist Filmmaker / Editor

Uploading Files using Indy (multipart/form-data)	0votes
January 01, 2008 12:16 PM	Views: 7978 Favorited: 0 Comments: 0

	Filed Under: Programming
Tags: Delphi, ISAPI

In this tutorial, I'll show you how you can use Indy to upload files to a Web Server (either an ISAPI or ASP) that can accept file uploads using the W3C specified multipart/form-data encoding type.

If you haven't already, take a look at the tutorial on my site called Multi-file upload with addtional form fields. The live demo app (server side) is the same app we will use in this tutorial as our test server.

In this tutorial and the project we build here, we'll use the server mentioned in the tutorial above as our test server. It's a good test that shows that the protocol used by the Indy built client application matches that of a regular browser. A kind of confirmation if you will.

To assist us in this task, I've built a simple class derived from a TMemoryStream that encapsulates the nitty-gritty of the multipart/form-data encoding protocol.

The class delaration of the TMsMultipartFormDataStream class.

  TMsMultiPartFormDataStream = class(TMemoryStream)
  private
    FBoundary: string;
    FRequestContentType: string;
    function GenerateUniqueBoundary: string;
  public
    procedure AddFormField(const FieldName, FieldValue: string);
    procedure AddFile(const FieldName, FileName, ContentType: string; FileData: TStream); overload;
    procedure AddFile(const FieldName, FileName, ContentType: string); overload;
    procedure PrepareStreamForDispatch;
    constructor Create;
    property Boundary: string read FBoundary;
    property RequestContentType: string read FRequestContentType;
  end;

This class allows for uploading multiple files along with multiple form fields. As you can see, the interface is very simple to understand and use. So I won't go into the details of each of them.

The most important point to remember is that once you've added the form fields, and files that you need, you must call the PrepareStreamForDispatch method before you send the stream.

Building the Application

This is a simple application that uses the test server found at the URL http://www.matlus.com/scripts/multifileupload.dll/upload. This is essentially the HTML form's action attribute if you were to use a browser or the AURL parameter of the IdHTTP component.

Show the GUI Interface of the Application

The Send button's OnClick event looks like this:

procedure TForm1.Button2Click(Sender: TObject);
var
  ResponseStream: TMemoryStream;
  MultiPartFormDataStream: TMsMultiPartFormDataStream;
begin
  MultiPartFormDataStream := TMsMultiPartFormDataStream.Create;
  ResponseStream := TMemoryStream.Create;
  try
    IdHttp1.Request.ContentType := MultiPartFormDataStream.RequestContentType;
    MultiPartFormDataStream.AddFormField('PersonName', edtPersonName.Text);
    MultiPartFormDataStream.AddFormField('Description', edtDescription.Text);
    MultiPartFormDataStream.AddFile(edtFile.Name, edtFile.Text, edtMIMEType.Text);
    { You must make sure you call this method *before* sending the stream }
    MultiPartFormDataStream.PrepareStreamForDispatch;
    MultiPartFormDataStream.Position := 0;
    IdHTTP1.Post(edtHost.Text, MultiPartFormDataStream, ResponseStream);
  finally
    MultiPartFormDataStream.Free;
    ResponseStream.Free;
  end;
end;

Testing

The application we build uses the test server mentioned earlier. Once you have used this application to upload a file, you can download the file using your browser using the URL http://www.matlus.com/scripts/multifileupload.dll/upload/filename. Be sure to include the file extension as well. In this way, you can confirm that the file you've just uploaded was uploaded without a hitch. For this code to work in your production environment, you need to be certain that the ISAPI or ASP etc. supports uploading files larger than 48K and the multipart/form-data ENC-TYPE W3c spec.