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;; disfluid, implementation of the Solid specification
;; Copyright (C) 2020, 2021 Vivien Kraus
;; This program is free software: you can redistribute it and/or modify
;; it under the terms of the GNU Affero General Public License as
;; published by the Free Software Foundation, either version 3 of the
;; License, or (at your option) any later version.
;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;; GNU Affero General Public License for more details.
;; You should have received a copy of the GNU Affero General Public License
;; along with this program. If not, see <https://www.gnu.org/licenses/>.
(define-module (webid-oidc cache)
#:use-module ((webid-oidc stubs) #:prefix stubs:)
#:use-module ((webid-oidc parameters) #:prefix p:)
#:use-module (web client)
#:use-module (web request)
#:use-module (web response)
#:use-module (web uri)
#:use-module (ice-9 ftw)
#:use-module (ice-9 receive)
#:use-module (ice-9 optargs)
#:use-module (srfi srfi-19)
#:use-module (rnrs bytevectors)
#:export
(
clean-cache
add
read
varies?
valid?
revalidate
with-cache
))
;; The cache follows the recommendations of
;; https://developer.mozilla.org/en-US/docs/Web/HTTP/Caching
;; In a directory, we dump files, indexed by the hash of the URI, and
;; containing the request, response and response body.
;; We keep only one version of the resource, even with varying
;; headers. If the cache validation fails due to varying headers, we
;; simply drop the old variant and replace it with the new. For things
;; like user agents or accepted language or encoding, you’re not
;; likely to alternate quickly between two values anyway.
;; We’re not very concerned by the cache growing. We provide a cleanup
;; function that will kill a few percents of the cached entries at
;; random, and that you should call with a cron job regularly. It will
;; sometimes drop valid cached entries, but life goes on. By default,
;; each cache update has a 5% chance to trigger the elimination of 5%
;; of the cache.
;; There is a global lock file at the root of the cache, which serves
;; for region locking. Do not remove it!
(define (web-cache-dir)
(string-append (p:cache-home) "/web-cache/"))
(define (file-name uri)
(when (string? uri)
(set! uri (string->uri uri)))
(string-append (web-cache-dir)
(stubs:hash 'SHA-256 (uri->string uri))))
(define (lock-file-name)
(string-append (web-cache-dir) ".lock"))
(define (event? percents)
(<= (* (random:uniform) 100)
percents))
(define* (clean-cache
#:key
(percents 5))
(define lock-file (lock-file-name))
(define (survives?)
(not (event? percents)))
(define (enter? name stat result)
#t)
(define (leaf name stat result)
(unless (or (string-suffix? ".lock" name)
(survives?))
(unless
(false-if-exception
(begin
(format (current-error-port) "Dropping cache item ~a.~%" name)
(stubs:atomically-update-file
name
lock-file
(lambda (whatever)
#f))))
(format (current-error-port) "Could not clean file ~a.~%" name)))
result)
(define (down name stat result) result)
(define (up name stat result) result)
(define (skip name stat result) result)
(define (error name stat errno result)
(format (current-error-port) "While cleaning the cache: ~a: ~a~%"
name (strerror errno))
result)
(file-system-fold enter? leaf down up skip error 0
(web-cache-dir)))
(define (maybe-clean-cache
pc-happen
pc-cleaned)
(when (event? pc-happen)
(clean-cache #:percents pc-cleaned)))
(define (remove-uncacheable-headers response)
(let ((headers (response-headers response)))
(let ((filtered
(filter
(lambda (h)
(case (car h)
((connection keep-alive transfer-encoding)
#f)
(else #t)))
headers)))
(build-response
#:code (response-code response)
#:reason-phrase (response-reason-phrase response)
#:headers filtered
#:port #f))))
(define (add request response response-body)
;; Don’t store it if there’s a cache-control no-store
(unless
(let ((cc (response-cache-control response '())))
(assq-ref cc 'no-store))
(set! response (remove-uncacheable-headers response))
(let ((final-file-name (file-name (request-uri request)))
(lock-file (lock-file-name)))
(maybe-clean-cache 5 5)
(stubs:atomically-update-file
final-file-name
lock-file
(lambda (port)
(write-request request port)
(let ((file-response
(write-response response port)))
(when (string? response-body)
(set! response-body (string->utf8 response-body)))
(when response-body
(write-response-body file-response response-body))
#t))))))
(define (read uri)
(let ((final-file-name (file-name uri)))
(catch 'system-error
(lambda ()
(call-with-input-file final-file-name
(lambda (port)
(let ((request (read-request port)))
(let ((response (read-response port)))
(values request response (read-response-body response)))))))
(lambda error
(format (current-error-port) "Cache miss for ~a: ~s~%"
(uri->string uri)
error)
(values #f #f #f)))))
(define (varies-header? request-a request-b header)
(let ((a (assq-ref (request-headers request-a) header))
(b (assq-ref (request-headers request-b) header)))
(not (equal? a b))))
(define (varies-any-header? request-a request-b headers)
(and (not (null? headers))
(or (varies-header? request-a request-b (car headers))
(varies-any-header? request-a request-b (cdr headers)))))
(define (varies? request-a request-b response)
(let ((vary (response-vary response)))
(or (eq? vary '*)
(varies-any-header? request-a request-b vary))))
(define (valid? response)
;; current-date is a thunk parameter
(let* ((current-date ((p:current-date)))
(current-time (time-second (date->time-utc current-date))))
(let ((cc (response-cache-control response #f))
(date (time-second (date->time-utc (response-date response current-date))))
(last-modified
(let ((as-date (response-last-modified response)))
(and as-date
(time-second (date->time-utc as-date))))))
(if cc
;; Use cache-control
(let ((cc-no-cache (assq-ref cc 'no-cache))
(cc-no-store (assq-ref cc 'no-store))
(cc-max-age
(or (assq-ref cc 'max-age)
;; Heuristic freshness
(and last-modified
(/ (- date last-modified) 10)))))
(and (not cc-no-cache)
(not cc-no-store)
cc-max-age
(>= (+ date cc-max-age) current-time)))
;; Use expires
(let ((exp
(let ((as-date (response-expires response)))
(and as-date
(time-second (date->time-utc as-date))))))
(and exp
(>= exp current-time)))))))
(define* (revalidate uri response body
#:key
(headers '())
(http-get http-get))
(define (keep-header? h)
(case (car h)
((if-none-match if-unmodified-since) #f)
(else #t)))
(let ((etag (response-etag response)))
(if etag
(receive (new-response new-response-body)
(http-get uri
#:headers
(acons 'if-none-match (list etag)
(filter keep-header? headers)))
(if (eqv? (response-code new-response) 304)
(values
(build-response
#:headers
(append
(response-headers new-response)
(filter
(lambda (h)
(case (car h)
((cache-control content-location date etag expires vary)
;; These are overriden by new-response
#f)
(else #t)))
(response-headers response))))
body)
(values new-response new-response-body)))
(http-get uri #:headers headers))))
(define* (with-cache #:key (http-get http-get))
(lambda* (uri #:key (headers '()))
(when (string? uri)
(set! uri (string->uri uri)))
(let ((request (build-request uri #:headers headers)))
(receive (stored-request stored-response body) (read uri)
(if stored-response
(let ((valid (valid? stored-response))
(invariant (not (varies? request stored-request stored-response))))
(unless invariant
(format (current-error-port) "Cache entry for ~a varies.\n" (uri->string uri)))
(if (and valid invariant)
(values stored-response body)
(receive (final-response final-body)
(revalidate uri stored-response body
#:headers headers
#:http-get http-get)
(add request final-response final-body)
(values final-response final-body))))
(receive (final-response final-body)
(http-get uri #:headers headers)
(add request final-response final-body)
(values final-response final-body)))))))
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