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module Content


Content provides access to the content server of the Rascal terminal for viewing interactive HTML output.


import Content;

data Content

Content wraps the HTTP Request/Response API to support interactive visualization types on the terminal ((RascalShell)).

data Content  
= content(str id, Response (Request) callback, str title=id, int viewColumn=1)
| content(Response response, str title="*static content*", int viewColumn=1)

Values wrapped in a Content wrapper will be displayed by interactive Rascal applications such as the IDE, the REPL terminal and the documentation pages.

For example, a piece of html can be displayed directly like such:

rascal>html("\<a href=\"\"\>Rascal homepage\</a\>")


In its most general form, Content is an HTTP(s) webserver callback, such that you might deliver any kind of content, based on any kind of request. If you produce a Content value which processes requests dynamically, subsequent interaction from the web browser will be processed as well. So using the Content wrapper you can start an interactive user experience in the browser directly from the REPL.

Content values stay plugged into the application server that is hidden in the REPL environment until they have not been used for at least 30 minutes. If you want the same interaction back after 30 minutes of non-usage, you have to produce another Content value on the commandline.

When you are happy with the interaction, or you want a permanent visualization which is not garbage collected after 30 minutes, you can consider wrapping the same callback in a webserver using the serve function.

function html

Directly serve a static html page

Content html(str html)

function file

Directly serve the contents of a file

Content file(loc src)

function plainText

Directly serve the contents of a string as plain text

Content plainText(str text)

alias Body

value (type[value] expected)

data Request

Request values represent what a browser is asking for, most importantly the URL path.

data Request (map[str, str] headers = (), map[str, str] parameters = (), map[str,str] uploads = ()) 
= get (str path)
| put (str path, Body content)
| post(str path, Body content)
| delete(str path)
| head(str path)

A request value also contains the full HTTP headers, the URL parameters as a map[str,str] and possibly uploaded content, also coded as a map[str,str]. From the constructor type, put or get you can see what kind of HTTP request it was.


  • Note that put and post have not been implemented yet in the REPL server.

data Response

A response encodes what is send back from the server to the browser client.

data Response  
= response(Status status, str mimeType, map[str,str] header, str content)
| fileResponse(loc file, str mimeType, map[str,str] header)
| jsonResponse(Status status, map[str,str] header, value val, str dateTimeFormat = "yyyy-MM-dd\'T\'HH:mm:ss\'Z\'")

The three kinds of responses, encode either content that is already a str, some file which is streamed directly from its source location or a jsonResponse which involves a handy, automatic, encoding of Rascal values into json values.

function response

Utility to quickly render a string as HTML content

Response response(str content, map[str,str] header = ())

function response

Utility to quickly report an HTTP error with a user-defined message

Response response(Status status, str explanation, map[str,str] header = ())

function plain

Utility to quickly make a plaintext response.

Response plain(str text)

function response

Utility to serve a file from any source location.

Response response(loc f, map[str,str] header = ())

function response

Utility to quickly serve any rascal value as a json text. This comes in handy for asynchronous HTTP requests from Javascript.

default  Response response(value val, map[str,str] header = ())

data Status

Encoding of HTTP status

data Status  
= ok()
| created()
| accepted()
| noContent()
| partialContent()
| redirect()
| notModified()
| badRequest()
| unauthorized()
| forbidden()
| notFound()
| rangeNotSatisfiable()
| internalError()