The Clever Component team has put together an article designed to demonstrate how one can use Delphi to transfer files between the client and server using the HTTP protocol.
In this article we will discuss the automation of the upload process via HTTP protocol by the POST method using the components from Clever Internet Suite.
A lot of web-software companies have to establish the tight links with their clients by using not only email and forums. Often there is the task to transmit data from the client to the server where the initiative belongs to the client.
The traditional ways to solve this problem, such as send data via email attach or by FTP, cannot be applied in particular cases. The email has the problems of low efficiency and difficulties when sorting. The write-accessed FTP resources are the problem too, because of the security requirements and the probability of getting spam.
If you want to get more control on the process or perform some actions on the received information then using the upload via HTTP protocol by the POST method will solve the above problems simultaneously.

The data-transfer method via HTTP protocol is intended to have two key facilities which support the contacts between the server and the client:
- Client-side engine
- Server-side engine, in the most cases it is ASP script or CGI application.
The responsibilities of the client are to build and send the server the message which contains some headers with information about the resource being downloaded, the resource itself and probably, different additional data. The server should be able to accept and process this message. Depending on your desire, the accepting facility may just save it locally to the server, forward it into other server, check for viruses and so on - the resource is fully under your control!
Next, let's take a look at these facilities in details.
Client-side engine
In the simplest case, the facility which transfers data may be an ordinary client script. Its main purpose is to build the POST command, find the information being sent and specify the resource accepted this data. It's easy to say that in HTML:
<BODY>
...
<p><b><i>Enter File Name and press the Upload button</i></b></p>
<TABLE border=0>
<TBODY>
<TR>
<FORM action="clHTTPUpload.asp" method="post" enctype="multipart/form-data">
<TD align=left><INPUT type="submit" value="Upload File"></TD>
<TD align=left><INPUT type="file" name="FileName"></TD>
</FORM>
</TD>
</TR>
</TBODY>
</TABLE>
...
</BODY>
How you can see from the above example, the form we created organizes the POST method with multipart/form-data type. It means now you shouldn't worry any longer - your browser will care about any headers and their contents itself.
For more information on URL-encoding and the format of a Form POST request, see section 8.2 in RFC 1866, which you can find here: http://www.w3.org/Protocols/HTTP/Object_Headers.html,
http://www.w3.org/Protocols/rfc1341/7_2_Multipart.html and many others.
In case of automation the downloading process by using the POST method we have to build such headers and send them to the server ourselves.
Let's use the abilities of the TclUploader from the Clever Internet Suite library. It can be done in a few simple steps:
- Create a new Delphi project
- Place the TclUploader component on the form and setup its URL property (if you need you can setup the UserName and Password properties as well)
- Setup the headers of the component
- To use headers you should activate them by setting the UseHTTPHeaders property to TRUE
- Implement the call the Start function of the component to initiate the uploading process
All additional settings can be skipped in order to this article be brief.

Headers Setup
In many cases, the server does not respond appropriately if a Content-Type is not specified.
Therefore in our case the header may look like this:
-----------------------------7d23542a1a12c2
Content-Disposition: form-data; name="FileName"; filename="C:\test.txt"
Content-Type: text/asp
here places content of the C:\test.txt file
-----------------------------7d21fa22012ca--
As it can be seen from the above example, it is convenient to split the header into some parts:
- The first determines the Content-Type field, the file name and other parameters.
- The second is the data being uploaded itself.
- The third signs the end of the resource.
In that way, we set the Header Item Content Type for the first and the third parts as ctTextData, and the second has ctFileName.
To setup headers the TclUploader component has the design-time editor.

The contents of each header element can be edited within the second page of the component-editor.

Also, it is easy to create the Header Item in runtime. To make the creation process more simple, the headers collection class, TclHTTPHeaders, has a number of the special functions. By using them you can build different header structures as easy and fast as in design-time.
procedure TMainForm.FillHeaders(const AFileName: string);
begin
clUploader.HTTPHeaders.AddTextData('-----------------------------7d23542a1a12c2');
clUploader.HTTPHeaders.AddTextData('Content-Disposition: form-data; name="FileName"; filename="' + AFileName + '"');
clUploader.HTTPHeaders.AddTextData('Content-Type: text/asp');
clUploader.HTTPHeaders.AddFileName(AFileName);
clUploader.HTTPHeaders.AddTextData('-----------------------------7d21fa22012ca--');
end;
To initiate the uploading process you have to call the Start method of the TclUploader component.
procedure TMainForm.btnUploadClick(Sender: TObject);
var
filename: string;
begin
memResponse.Clear();
filename := edtFileName.Text;
FillHeaders(filename);
end;
As the result of the upload the server may return the answer which can consists of the custom text or other data defined by the developers of the accepting facility. To get the server's answer you just need to read the ServerResponse property of the component.
procedure TMainForm.clUploaderStatusChanged(Sender: TObject; Status: TclProcessStatus);
begin
if (Status <> psProcess) then
begin
memResponse.Lines.AddStrings(clUploader.ServerResponse);
end;
end;
Due to the fact that we use the HTTPSendRequestEx function from the WinInet library the uploading process can be given a progress indicator. To do it, let's just write a handler of the OnDataItemProceed event.
procedure TMainForm.clUploaderDataItemProceed(Sender: TObject;
ResourceInfo: TclResourceInfo; AStateItem: TclResourceStateItem; CurrentData: PChar;
CurrentDataSize: Integer);
begin
Caption := Format('%s %d bytes proceed', [edtFileName.Text, AStateItem.ResourceState.BytesProceed]);
end;
Starting at this moment, the client-side is fully functional. The example can be downloaded here: httppostclient.zip for Delphi and httppostclient_bcb.zip for C++ Builder.
Next, we'll take a look at the server-side accepting facility.
Server-side engine
The server facility isn't a big difficulty at all and in the very first approach it can be written as ASP server script.
To work well, the script should accept the incoming data. We use the server Request and Response objects to accept data and send results back to the client. You can retrieve the values of the form elements by using the Forms property of the Request object and by using the BinaryRead method to get raw binary data.
Notice, there is one interesting moment - if you use the BinaryRead method, you cannot use the Forms property simultaneously, and vice-versa. So, if you want to post other form data along with your file, you'll have to dig it out of the posted data by hand.
The headers parser can be developed in many ways. The widest method is using the special written ActiveX component. ASP server script just transfers binary data to this object.
Easier to say in Java Script:
<%@Language = "JScript"%>
<%
try
{
var Binary;
Binary = Request.BinaryRead(Request.TotalBytes);
var fso = new ActiveXObject("HTTPPost.clHTTPPost");
fso.AcceptData(Binary);
Response.Write(Request.TotalBytes);
Response.Write("<br/>");
Response.Write("File uploaded");
}
catch(e)
{
Response.Write(e.message);
}
%>
The implementation of the ActiveX component is easy and may look like as following:
IclHTTPPost = interface(IDispatch)
['{1DFF5FE4-F803-4DB6-A007-7AA4728624D3}']
procedure AcceptData(Data: OleVariant); safecall;
end;
procedure TclHTTPPost.AcceptData(Data: OleVariant);
var
str: TStream;
p: Pointer;
begin
str := TFileStream.Create('c:\Temp\SampleData.txt', fmCreate);
try
p := VarArrayLock(Data);
str.Write(p, SizeOf(BYTE) * (VarArrayHighBound(Data, 1) - VarArrayLowBound(Data, 1) + 1));
finally
VarArrayUnlock(Data);
str.Free();
end;
end;
To make this sample, we created the ActiveX Library in Delphi and added a new Automation Object named clHTTPPost.
The sources of the server-side can be downloaded here: httppostserver.zip for Delphi and httppostserver_bcb.zip for C++ Builder.
The server-side facility is done now. You may write the complete header parsing in ASP script itself. This way can be more convenient some time, because it avoids the ActiveX registration. To read more about this technique see the Upload Files with HTML Forms and Pure ASP article in MSDN library.
Anyway, you have to be sure for the save operation to work, your IIS anonymous user account, usually IUSR_machinename, must have write access to the directory you want to save the files in. And, obviously, the full urlpath to the accepting script must be specified in the URL property of the TclUploader component.
In conclusion we would like to notice that the given method of data sending have some benefits in comparing to the Web Form Post request, when using the certified authorization. The point is that while authorizing an HTML form resends the built headers and if the server requests certificate, all headers will be sent twice within the certificate information.
This process doesn't occur if you use Clever Uploader because it uses both HTTPSendRequest and HTTPSendRequestEx from the WinInet library. Such method allows you to keep the traffic low when transferring a lot of data.
If you want you may not use the UI at all and this allows you to automate the sending process which can be easy scheduled later.
Sergey S,
Clever Components Team.
| DISCLAIMER: The content provided in this article is not warranted or guaranteed by Developer Shed, Inc. The content provided is intended for entertainment and/or educational purposes in order to introduce to the reader key ideas, concepts, and/or product reviews. As such it is incumbent upon the reader to employ real-world tactics for security and implementation of best practices. We are not liable for any negative consequences that may result from implementing any information covered in our articles or tutorials. If this is a hardware review, it is not recommended to open and/or modify your hardware. |
More Delphi-Kylix Articles
More By Clever Components
developerWorks - FREE Tools! |
Join us for this on demand webcast to learn about developing complex systems more quickly and efficiently. We'll cover market drivers for developing, governing and reusing systems software assets and how you can develop system software assets with Rational Asset Manager. FREE! Go There Now!
|
|
|
|
Visit IBM developerWorks to download a free trial of the Rational Host Access Transformation Services (HATS) Toolkit. The HATS toolkit provides a set of plug-ins for the IBM Rational Software Delivery Platform to help you easily extend your legacy applications. HATS makes your 3270 and 5250 applications available as HTML through the most popular Web browsers, while converting your host screens to a Web look and feel and it also enables you to develop new Web, portal, and rich-client applications. FREE! Go There Now!
|
|
|
|
Manage, govern, and share services across your organization by using WebSphere Service Registry and Repository. Follow the hands-on exercises to learn how to navigate the Web interface to publish, find, reuse, and update services. FREE! Go There Now!
|
|
|
|
Listen to this webcast to get an overview of Info 2.0 and a technical demo of how to quickly build an enterprise mashup. IBM's Info 2.0 technology leverages emerging Web 2.0 technologies such as mashups, feeds, AJAX, and JSON in order to simplify assembly of information using feeds and services. Come learn about the technical elements of Info 2.0 including the Feed Generation framework, Mashup Engine, and mashup assembly components. Learn how to pull information from databases, departmental information, and the Web to create mashups critical to your company’s success. We will also discuss best practices to help you get started. FREE! Go There Now!
|
|
|
|
This Fall, IBM Rational talks to you directly through a special teleconference series giving you access to the best minds in IBM Rational - product experts and market thought leaders who will answer your questions during these pre-scheduled telephone conference calls. Register today! FREE! Go There Now!
|
|
|
|
Join this Rational Talks to You teleconference on December 11 at 1:00 pm ET to get tips on building your own plugins with Rational Method Composer. Get your questions answered! FREE! Go There Now!
|
|
|
|
Get a free trial download of IBM Lotus Forms V3.0 (formerly Workplace Forms), which provides a zero-footprint eForms solution to help you automate and move forms-based business processes off the desktop and onto the Web. With Lotus Forms, you can extend applications beyond the firewall by creating a single electronic form document ready for use in both thick and Web 2.0 thin client format. FREE! Go There Now!
|
|
|
|
Visit IBM developerWorks to try the IBM SOA Sandbox for process. The SOA Sandbox for process focuses on providing a trial environment with the necessary tooling and components required to gain a better understanding of business processes and how to best improve existing business processes to derive value quickly. FREE! Go There Now!
|
|
|
|
Attend this launch webcast with Scott Hebner, Vice President of IBM Rational Marketing and Strategy, where he will overview Rational’s new offerings and programs to help customers accelerate software innovation on System z. He will discuss how these solutions help organizations extend their core business processes toward modern architectures such as SOA and web technologies to deliver business improvements that stand the test of time. FREE! Go There Now!
|
|
|
|
With IBM Rational Systems Development Solution, you can deliver products faster with higher quality. Within this kit, Read the “Model Driven Systems Development” white paper to see how to improve product quality and communication. Then check out the rest of the e-Kit to learn more about important topics that can affect the success of any software project through customer examples, tutorials, informative Webcasts, and best practices for designing, building and managing systems. From start to finish, at every stage in your projects, Rational Systems Development Solution can help your company reach its full potential. FREE! Go There Now!
|
|
|
|
All FREE IBM® developerWorks Tools! |