/resource.lisp

(in-package #:ws)

;;; resource stuff
;;;
;;;  name ("/foo", etc)
;;;
;;;  accept function
;;;    args = resource name, headers, client host/port
;;;    return
;;;      reject connection
;;;      abort connection?
;;;      ? for accepted

;; fixme: make this per-server, so we can run different servers on
;; different ports?
;; fixme: add support for more complex matching than just exact match
(defparameter *resources* (make-hash-table :test 'equal)
  "hash mapping resource name to (list of handler instance, origin
 validation function, ?)")

(defun register-global-resource (name resource-handler origin-validation-fn)
  "Registers a resource instance where NAME is a path string like
'/swank', resource-handler is an instance of WS-RESOURCE, and
ORIGIN-VALIDATION-FN is a function that takes an origin string as
input and returns T if that origin is allowed to access this
resource."
  (setf (gethash name *resources*)
        (list resource-handler origin-validation-fn)))

(defun find-global-resource (name)
  "Returns the resource registered via REGISTER-GLOBAL-RESOURCE with name NAME."
  (first (gethash name *resources*)))

(defun unregister-global-resource (name)
  "Removes the resource registered via REGISTER-GLOBAL-RESOURCE with name NAME."
  (remhash name *resources*))

(defun valid-resource-p (server resource)
  "Returns non-nil if there is a handler registered for the resource
of the given name (a string)."
  (declare (type string resource)
           (ignore server))
  (when resource
    (gethash resource *resources*)))

;; functions for checking origins...
(defun any-origin (o) (declare (ignore o)) t)

(defun origin-prefix (&rest prefixes)
  "Returns a function that checks whether a given path matches any of
the prefixes passed as arguments."
  (lambda (o)
    (loop :for p :in prefixes
          :for m = (mismatch o p)
          :when (or (not m) (= m (length p)))
          :return t)))

(defun origin-exact (&rest origins)
  "Returns a function that checks whether a given path matches any of
the origins passed as arguments exactly."
  ;; fixme: probably should use something better than a linear search
  (lambda (o)
    (member o origins :test #'string=)))

(defgeneric resource-read-queue (resource)
  (:documentation "The concurrent mailbox used to pass messages
  between the server thread and resource thread."))

(defclass ws-resource ()
  ((read-queue :initform (make-mailbox) :reader resource-read-queue))
  (:documentation "A server may have many resources, each associated
  with a particular resource path (like /echo or /chat).  An single
  instance of a resource handles all requests on the server for that
  particular url, with the help of RUN-RESOURCE-LISTENER,
  RESOURCE-RECEIVED-FRAME, and RESOURCE-CLIENT-DISCONNECTED."))

(defgeneric resource-accept-connection (res resource-name headers client)
  (:documentation "Decides whether to accept a connection and returns
values to process the connection further. Defaults to accepting all
connections and using the default mailbox and origin, so most resources
shouldn't need to define a method.

Passed values
    - RES is the instance of ws-resource
    - RESOURCE-NAME is the resource name requested by the client (string)
    - HEADERS is the hash table of headers from the client
    - client is the instance of client

Returns values
    1. NIL if the connection should be rejected, or non-nil otherwise
    2. Concurrent mailbox in which to place messages received from the
       client, or NIL for default
    3. origin from which to claim this resource is responding, or NIL
       for default.
    4. handshake-resource or NIL for default
    5. protocol or NIL for default

Most of the time this function will just return true for the first
value to accept the connection, and nil for the other values.

Note that the connection is not fully established yet, so this
function should not try to send anything to the client, see
resource-client-connected for that.

This function may be called from a different thread than most resource
functions, so methods should be careful about accessing shared data, and
should avoid blocking for extended periods.
"))

(defgeneric resource-client-disconnected (resource client)
  (:documentation "Called when a client disconnected from a WebSockets resource."))

(defgeneric resource-client-connected (resource client)
  (:documentation "Called when a client finishes connecting to a
WebSockets resource, and data can be sent to the client.

Methods can return :reject to immediately close the connection and
ignore any already received data from this client."))

#++
(defgeneric resource-received-frame (resource client message)
  ;;; not used for the moment, since newer ws spec combine 'frame's into
  ;;; 'message's, which might be binary or text...
  ;;; may add this back later as an interface to processing per frame
  ;;; instead of per message?
  (:documentation "Called when a client sent a frame to a WebSockets resource."))
(defgeneric resource-received-text (resource client message)
  (:documentation "Called when a client sent a text message to a WebSockets resource."))

(defgeneric resource-received-binary (resource client message)
  (:documentation "Called when a client sent a binary message to a WebSockets resource."))

(defgeneric resource-received-custom-message (resource message)
  (:documentation "Called on the resource listener thread when a
  client is passed an arbitrary message via
  SEND-CUSTOM-MESSAGE-TO-RESOURCE. "))

(defgeneric send-custom-message-to-resource (resource message)
  (:documentation "Thread-safe way to pass a message to the resource
  listener.  Any message passed with this function will result in
  RESOURCE-RECEIVED-CUSTOM-MESSAGE being called on the resource thread
  with the second argument of this function."))

(defmethod resource-accept-connection (res resource-name headers client)
  (declare (ignore res resource-name headers client))
  t)

(defmethod resource-client-connected (res client)
  (declare (ignore res client))
  nil)

(defmethod send-custom-message-to-resource (resource message)
  (mailbox-send-message (resource-read-queue resource)
                        (list message  :custom)))

(defclass funcall-custom-message ()
  ((function :initarg :function :initform nil :reader message-function))
  (:documentation "A type of so-called 'custom message' used to call a
  function on the main resource thread."))

(defmethod resource-received-custom-message (resource (message funcall-custom-message))
  (declare (ignore resource))
  (funcall (message-function message)))

(defgeneric call-on-resource-thread (resource fn)
  (:documentation "Funcalls FN on the resource thread of RESOURCE."))

(defmethod call-on-resource-thread (resource fn)
  (send-custom-message-to-resource
   resource (make-instance 'funcall-custom-message :function fn)))

(defun disconnect-client (client)
  (when (client-resource client)
    (resource-client-disconnected (client-resource client) client)
    (setf (client-resource client) nil)))

(defun run-resource-listener (resource)
  "Runs a resource listener in its own thread indefinitely, calling
RESOURCE-CLIENT-DISCONNECTED and RESOURCE-RECEIVED-FRAME as appropriate."
  (macrolet
      ((restarts (&body body)
         `(handler-bind
              ((error
                 (lambda (c)
                   (cond
                     (*debug-on-resource-errors*
                      (invoke-debugger c))
                     (t
                      (lg "resource handler error ~s, dropping client~%" c)
                      (invoke-restart 'drop-client))))))
            (restart-case
                (progn ,@body)
              (drop-client ()
                (unless (client-connection-rejected client)
                  (ignore-errors (disconnect-client client)))
                ;; none of the defined status codes in draft 14 seem right for
                ;; 'server error'
                (ignore-errors (write-to-client-close client :code nil))
                (setf (client-connection-rejected client) t))
              (drop-message () #|| do nothing ||#)))))
    (loop :for (client data) = (mailbox-receive-message (slot-value resource 'read-queue))
          ;; fixme should probably call some generic function with all
          ;; the remaining messages
          :while (not (eql data :close-resource))
          :do
          (cond
            ((eql data :custom)
             ;; here we use the client place to store the custom message
             (handler-bind
                 ((error
                    (lambda (c)
                      (cond
                        (*debug-on-resource-errors*
                         (invoke-debugger c))
                        (t
                         (lg "resource handler error ~s in custom, ignoring~%" c)
                         (invoke-restart 'continue))))))
              (let ((message client))
                (restart-case
                    (resource-received-custom-message resource message)
                  (continue () :report "Continue"  )))))
            ((and client (client-connection-rejected client))
             #|| ignore any further queued data from this client ||#)
            ((eql data :connect)
             (restarts
              (when (eq :reject (resource-client-connected resource client))
                (setf (client-connection-rejected client) t)
                (write-to-client-close client))))
            ((eql data :eof)
             (restarts
              (disconnect-client client))
             (write-to-client-close client))
            ((eql data :dropped)
             (restarts
              (disconnect-client client))
             (write-to-client-close client))
            ((eql data :close-resource)
             (restarts
              (disconnect-client client)))
            ((eql data :flow-control)
             (%write-to-client client :enable-read))
            ((symbolp data)
             (error "Unknown symbol in read-queue of resource: ~S " data))
            ((consp data)
             (restarts
              (if (eq (car data) :text)
                  (resource-received-text resource client (cadr data))
                  (resource-received-binary resource client (cadr data)))))
            (t
             (error "got unknown data in run-resource-listener?"))))))

(defun kill-resource-listener (resource)
  "Terminates a RUN-RESOURCE-LISTENER from another thread."
  (mailbox-send-message (resource-read-queue resource)
                        '(nil :close-resource)))