response.lisp

;;;;
;;;; Copyright (c) 2008, 2015 Zachary Beane, All Rights Reserved
;;;;
;;;; Redistribution and use in source and binary forms, with or without
;;;; modification, are permitted provided that the following conditions
;;;; are met:
;;;;
;;;;   * Redistributions of source code must retain the above copyright
;;;;     notice, this list of conditions and the following disclaimer.
;;;;
;;;;   * Redistributions in binary form must reproduce the above
;;;;     copyright notice, this list of conditions and the following
;;;;     disclaimer in the documentation and/or other materials
;;;;     provided with the distribution.
;;;;
;;;; THIS SOFTWARE IS PROVIDED BY THE AUTHOR 'AS IS' AND ANY EXPRESSED
;;;; OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
;;;; WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
;;;; ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
;;;; DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
;;;; DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
;;;; GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
;;;; INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
;;;; WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
;;;; NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
;;;; SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
;;;;
;;;; response.lisp

(in-package #:zs3)


(defvar *response-element-classes*
  (make-hash-table :test 'equal))

(defun set-element-class (element-name class)
  (setf (gethash element-name *response-element-classes*) class))

(defclass response ()
  ((request
    :initarg :request
    :accessor request)
   (body
    :initarg :body
    :accessor body)
   (http-code
    :initarg :http-code
    :accessor http-code)
   (http-phrase
    :initarg :http-phrase
    :accessor http-phrase)
   (http-headers
    :initarg :http-headers
    :accessor http-headers))
  (:default-initargs
   :request nil
   :body nil
   :http-code 999
   :http-phrase "<uninitialized>"
   :http-headers nil))


(defmethod print-object ((response response) stream)
  (print-unreadable-object (response stream :type t :identity t)
    (format stream "~D ~S" (http-code response) (http-phrase response))))

(defgeneric xml-string (response)
  (:method (response)
    (flexi-streams:octets-to-string (body response) :external-format :utf-8)))

(defgeneric response-specialized-class (name)
  (:method (name)
    (gethash name *response-element-classes*)))

(defgeneric specialized-initialize (object source)
  (:method (object (source t))
    object))

(defgeneric content-length (response)
  (:method (response)
    (parse-integer (drakma:header-value :content-length (http-headers response)))))

(defgeneric specialize-response (response)
  (:method ((response response))
    (cond ((or (null (body response))
               (and (not (streamp (body response)))
                    (zerop (length (body response)))))
           (when (<= 500 (http-code response) 599)
              (change-class response 'amazon-error)
              (specialized-initialize response nil))
           response)
          (t
           (let* ((source (xml-source (body response)))
                  (type (xml-document-element source))
                  (class (response-specialized-class type)))
             (when class
               (change-class response class)
               (specialized-initialize response source))
             response)))))


(defun close-keep-alive ()
  (when *keep-alive-stream*
    (ignore-errors (close *keep-alive-stream*))
    (setq *keep-alive-stream* nil)))


(defun request-response (request &key
                         body-stream
                         keep-stream
                         (handler 'specialize-response))
  (setf (endpoint request) (redirected-endpoint (endpoint request)
                                                (bucket request)))
  (ensure-amz-header request "date"
                     (iso8601-basic-timestamp-string (date request)))
  (multiple-value-bind (body code headers uri stream must-close phrase)
      (send request :want-stream body-stream
                    :stream *keep-alive-stream*)
    (declare (ignore uri))
    (let ((response
           (make-instance 'response
                          :request request
                          :body body
                          :http-code code
                          :http-phrase phrase
                          :http-headers headers)))
      (if (and keep-stream (not must-close))
          (progn
            (when *use-keep-alive*
              (unless (eq *keep-alive-stream* stream)
                (close-keep-alive)
                (setq *keep-alive-stream* stream)))
            (funcall handler response))
          (with-open-stream (stream stream)
            (declare (ignorable stream))
            (setq *keep-alive-stream* nil)
            (funcall handler response))))))

(defvar *backoff* (cons 3 100)
  "Used as the default value of :BACKOFF when submitting a request.
   The value should be a cons of two numbers: how many times to try
   before giving up, and how long to wait (in ms) before trying for
   the second time. Each subsequent attempt will double that time.")

(defun submit-request (request
                       &key body-stream
                         (keep-stream *use-keep-alive*)
                         (handler 'specialize-response))
  ;; The original endpoint has to be stashed so it can be updated as
  ;; needed by AuthorizationHeaderMalformed responses after being
  ;; clobbered in the request by TemporaryRedirect responses.
  (let* ((original-endpoint (endpoint request))
         (backoff *backoff*)
         (tries (car backoff))
         (delay (/ (cdr backoff) 1000)))
    (loop
      (handler-case
          (let ((response (request-response request
                                            :keep-stream keep-stream
                                            :body-stream body-stream
                                            :handler handler)))
            (maybe-signal-error response)
            (setf (request response) request)
            (return response))
        (temporary-redirect (condition)
          (setf (endpoint request)
                (request-error-endpoint condition)))
        (authorization-header-malformed (condition)
          (let ((region (request-error-region condition)))
            (setf (redirection-data original-endpoint (bucket request))
                  (list (endpoint request)
                        region))
            (setf (region request) region)))
        (permanent-redirect (condition)
          ;; Remember the new endpoint long-term
          (let ((new-endpoint (request-error-endpoint condition))
                (new-region (cdr (assoc :x-amz-bucket-region
                                        (http-headers (request-error-response condition))))))
            (setf (redirection-data (endpoint request)
                                    (bucket request))
                  (list new-endpoint (or new-region (region request))))
            (setf (endpoint request) new-endpoint)
            (when new-region
              (setf (region request) new-region))))
        (internal-error (e)
          ;; Per the S3 docs, InternalErrors should be retried. Up to
          ;; a point.
          (close-keep-alive)
          (when (minusp (decf tries))
            ;; We've exceeded our failure allowance. Resignal.
            (error e))
          (sleep delay)
          (incf delay delay))
        (error (e)
          ;; Ensure that we don't reuse the stream, it may be the source of
          ;; our error.  Then resignal.
          (close-keep-alive)
          (error e))))))