Serving Dynamic Content¶
Previous: Serving Static Content
This example will show how to dynamically generate the contents of a web page.
First, the ever-exciting library and module definitions. In addition to common-dylan and http-server we need streams for writing data to the response and date so we can show something dynamic happening:
define library web60-dynamic-content
use common-dylan;
use io, import: { streams };
use http-common;
use http-server;
use system, import: { date };
end;
define module web60-dynamic-content
use common-dylan;
use date, import: { as-iso8601-string, current-date };
use http-common;
use http-server;
use streams, import: { write };
end;
A web page is a resource mapped to a URL inside the web server. To create a resource we subclass <resource>:
define class <clock-page> (<resource>) end;
To make our resource do something we define a method on respond. (If we only wanted to implement the GET request method we could define a method on respond-to-get instead.)
define method respond (page :: <clock-page>, #key)
let stream = current-response();
set-header(stream, "Content-Type", "text/html");
let date = as-iso8601-string(current-date());
write(stream, concatenate("<html><body>", date, "</body></html>"));
end;
current-response returns the active <response> object. To send data back to the client we write to the current response.
let server = make(<http-server>,
listeners: list("0.0.0.0:8888"));
add-resource(server, "/", make(<clock-page>));
start-server(server);
In the previous example we already saw how to create and start a server, so the new bit here is using add-resource to map a URL to a <resource>. The first argument to add-resource is the URL router. (In Routes terminology it would be a “mapper”.) For convenience, an <http-server> is a kind of router so we can add resources directly to the server. In a future example, I will show how to do more complex URL routing, which will explain the reason for the mysterious #key in the respond definition above.
Here’s the complete code:
---- File: library.dylan ----
Module: dylan-user
define library web60-dynamic-content
use common-dylan;
use io, import: { streams };
use http-common;
use http-server;
use system, import: { date };
end;
define module web60-dynamic-content
use common-dylan;
use date, import: { as-iso8601-string, current-date };
use http-common;
use http-server;
use streams, import: { write };
end;
---- File: main.dylan ----
Module: web60-dynamic-content
define class <clock-page> (<resource>)
end;
define method respond (page :: <clock-page>, #key)
let stream = current-response();
set-header(stream, "Content-Type", "text/html");
let date = as-iso8601-string(current-date());
write(stream, concatenate("<html><body>", date, "</body></html>"));
end;
let server = make(<http-server>,
listeners: list("0.0.0.0:8888"));
add-resource(server, "/", make(<clock-page>));
start-server(server);