Downloading Part of a Document

SourcePro : Internet Protocols Module User’s Guide : PART II Packages of the Internet Protocols Module : The HTTP Package : Advanced Topics : Downloading Part of a Document

When a download is interrupted before it is complete, your application needs to be able to retrieve only the part of the document that was not received. The HTTP/1.1 specification and the SourcePro HTTP classes enable you to do this through the HTTP Range header. Example 14 uses a simple GET request to retrieve the first 500 bytes of a document.

Example 14 – Retrieving part of a document with RWHttpClient

RWHttpClient client = RWHttpSocketClient::make();

// initialize, and connect the client…

RWHttpRangeHeader rangeHeader(0, 499); // 1

RWHttpHeaderList headerlist;

headerlist.addHeader(rangeHeader); // 2

RWHttpRequest request(RWHttpRequest::Get, "/", headerlist); // 3

client.submit(request);

// retrieve reply from the server

//1 Constructs an RWHttpRangeHeader that specifies the byte range to retrieved. In this case, it is the first 500 bytes of the document.

//2 Adds the Range header to the header list.

//3 Includes the Range header in the request object.

RWHttpAgent also enables you to retrieve a portion of a document. Example 15 shows how the previous example is implemented using RWHttpAgent.

Example 15 – Retrieving part of a document with RWHttpAgent

RWHttpAgent agent;

RWTIOUResult<RWHttpReply> replyIOU;

replyIOU = agent.executeGetRange("http://www.perforce.com/",

0, 499);

For more information about partial downloads, see the ResumableDownload sample program distributed with the product.

NOTE: 	Sample programs are located in the examples directory created for your installation. For more information, see Installing and Building Your SourcePro Products and Building Your Applications.