B.6 WWW Page Retrieval: Using the HTTP Agent
The example program in this section demonstrates how to fetch a World Wide Web (WWW) page using the HTTP agent class.
HTTP is the native protocol of the WWW. It is a stateless client-server protocol: the client requests a document from the server using its Universal Resource Locator (URL), the server transmits the document to the client, and then the server shuts down the connection.
An HTTP URL has the following format:
http://<hostname>[:<port>]/[<path>]
where:
<hostname> is the host name (or IP address) of the server;
<port> is the port number for the server, which defaults to 80;
<path> is the path to the document. An empty path returns the root document.
B.6.1 Code and Explanation
Here is a portion of code followed by comments explaining key lines.
RWCString urlpath;
// ... construct urlpath
RWURL url(urlpath);
cout << "connecting to '" << url.host() << "'..." << endl; // 1
RWIHttpAgent httpAgent(url_.host(), RWIHttpVersion_1_0()); // 2
RWSocketPortal portal = httpAgent.get(urlpath); // 3
RWPortalIStream strm(portal); // 4
RWCString packet;
while (1) {
packet.readLine(strm); // 5
if (packet.isNull()) break;
cout << packet << "\n";
}
| //1 | Reports the HTTP server information to standard output. Note that an HTTP URL is stored in url, which is an instance of the Internet Protocols package's RWURL convenience class. This class encapsulates the parsing and component management of URL information. Here, the host() method of RWURL returns the host portion of the URL. |
| //2 | Constructs an RWIHttpAgent object that connects to an HTTP/1.0 compliant server. |
| //3 | Executes the get() method to retrieve the indented document, and redeems the RWSocketPortal from the returned RWIOUResult. Note that this function call may block. |
| //4 | Builds an input stream from the socket portal. |
| //5 | Reads the document's data from the socket portal. |
B.6.2 Further Discussion
The RWURL class is provided in the Internet Protocols package as a convenience class. It recognizes some popular URL schemes and parses out their various parts via its methods. See the entry for class RWURL in the Internet Protocols Module Reference Guide for further information.
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