On this page:
page
embed/ url
lambda/ page
define/ page
current-request
binding-id/ c
binding-format/ c
get-binding
get-bindings

8 Page: Short-hand for Common Patterns

 (require web-server/page)

The Web Server provides a simple utility library for building Web applications that consistent mostly of send/suspend/dispatch-created pages and request handling.

Most Web applications rely heavily on send/suspend/dispatch and typically use the pattern:
  (send/suspend/dispatch
   (λ (my-embed/url)
     .... (my-embed/url other-page) ....))

(page e ...)
The page macro automates this by expanding (page e ...) to a usage of send/suspend/dispatch where the syntax parameter embed/url is bound to the argument of send/suspend/dispatch.

When used inside page syntactically, a rename transformer for the procedure embedding function; otherwise, a syntax error.

A simple example:
  (page
   (response/xexpr
    `(html
      (body
       (a ([href
            ,(embed/url
              (λ (req)
                "You clicked!"))])
          "Click me")))))

Similarly, many Web applications make use almost exclusively of functions that are arguments to embed/url and immediately invoke send/suspend/dispatch.

(lambda/page formals e ...)
(define/page (id . formals) e ...)
The lambda/page and define/page automate this by expanding to functions that accept a request as the first argument (followed by any arguments specified in formals) and immediately wrap their body in page. This functions also cooperate with get-binding by binding the request to the current-request parameter.

The binding interface of web-server/http is powerful, but subtle to use conveniently due to its protection against hostile clients.

(current-request)  request?
(current-request req)  void?
  req : request?
binding-id/c : contract?
binding-format/c : contract?
(get-binding id [req #:format format])
  (or/c false/c string? bytes? binding?)
  id : binding-id/c
  req : request? = (current-request)
  format : binding-format/c = 'string
(get-bindings id [req #:format format])
  (listof (or/c string? bytes? binding?))
  id : binding-id/c
  req : request? = (current-request)
  format : binding-format/c = 'string
The get-binding(s) interface attempts to resolve this by providing a powerful interface with convenient defaults.

get-binding extracts the first binding of a form input from a request, while get-bindings extracts them all.

They accept a form identifier (id) as either a byte string, a string, or a symbol. In each case, the user input is compared in a case-sensitive way with the form input.

They accept an optional request argument (req) that defaults to the value of the current-request parameter used by lambda/page and define/page.

Finally, they accept an optional keyword argument (format) that specifies the desired return format. The default, 'string, produces a UTF-8 string (or #f if the byte string cannot be converted to UTF-8.) The 'bytes format always produces the raw byte string. The 'file format produces the file upload content (or #f if the form input was not an uploaded file.) The 'binding format produces the binding object.