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Diffstat (limited to 'src/scm/webid-oidc/cache.scm')
-rw-r--r-- | src/scm/webid-oidc/cache.scm | 281 |
1 files changed, 281 insertions, 0 deletions
diff --git a/src/scm/webid-oidc/cache.scm b/src/scm/webid-oidc/cache.scm new file mode 100644 index 0000000..9d9da0f --- /dev/null +++ b/src/scm/webid-oidc/cache.scm @@ -0,0 +1,281 @@ +(define-module (webid-oidc cache) + #:use-module ((webid-oidc stubs) #:prefix stubs:) + #: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)) + +;; 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 (default-cache-dir) + (let ((xdg-cache-home + (or (getenv "XDG_CACHE_HOME") + (format #f "~a/.cache")))) + (format #f "~a/webid-oidc" xdg-cache-home))) + +(define (web-cache-dir dir) + (when (thunk? dir) + (set! dir (dir))) + (string-append dir + "/web-cache/")) + +(define (file-name uri dir) + (when (string? uri) + (set! uri (string->uri uri))) + (string-append (web-cache-dir dir) + (stubs:hash 'SHA-256 (uri->string uri)))) + +(define (lock-file-name dir) + (string-append (web-cache-dir dir) ".lock")) + +(define (event? percents) + (<= (* (random:uniform) 100) + percents)) + +(define*-public (clean-cache + #:key + (percents 5) + (dir default-cache-dir)) + (define lock-file (lock-file-name dir)) + (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 dir))) + +(define (maybe-clean-cache + pc-happen + pc-cleaned + dir) + (when (event? pc-happen) + (clean-cache #:percents pc-cleaned #:dir dir))) + +(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*-public (add request response response-body + #:key (dir default-cache-dir)) + ;; 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) dir)) + (lock-file (lock-file-name dir))) + (maybe-clean-cache 5 5 dir) + (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 (the-current-time) + (time-utc->date + (current-time))) + +(define*-public (read uri + #:key + (dir default-cache-dir)) + (let ((final-file-name (file-name uri dir))) + (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-public (varies? request-a request-b response) + (let ((vary (response-vary response))) + (or (eq? vary '*) + (varies-any-header? request-a request-b vary)))) + +(define*-public (valid? response + #:key + (current-time the-current-time)) + (when (thunk? current-time) + (set! current-time (current-time))) + (when (integer? current-time) + (set! current-time + (make-time time-utc 0 current-time))) + (when (time? current-time) + (set! current-time (time-utc->date current-time))) + (set! current-time + (date->time-utc current-time)) + (set! current-time + (time-second current-time)) + (let ((cc (response-cache-control response #f)) + (date (response-date response + (time-utc->date + (make-time time-utc 0 current-time)))) + (last-modified (response-last-modified response))) + (set! date (date->time-utc date)) + (set! date (time-second date)) + (when last-modified + (set! last-modified (date->time-utc last-modified)) + (set! last-modified (time-second last-modified))) + (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 (response-expires response))) + (when exp + (set! exp (date->time-utc exp)) + (set! exp (time-second exp))) + (and exp + (>= exp current-time)))))) + +(define*-public (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*-public (with-cache + #:key + (current-time the-current-time) + (http-get http-get) + (dir default-cache-dir)) + (lambda* (uri #:key (headers '())) + (when (string? uri) + (set! uri (string->uri uri))) + (let ((dir (if (thunk? dir) (dir) dir)) + (request (build-request uri #:headers headers))) + (receive (stored-request stored-response body) + (read uri #:dir dir) + (if stored-response + (let ((valid (valid? stored-response #:current-time the-current-time)) + (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 #:dir dir) + (values final-response final-body)))) + (receive (final-response final-body) + (http-get uri #:headers headers) + (add request final-response final-body #:dir dir) + (values final-response final-body))))))) |