+(define string*
+ ;; Converts "string or #nil" coming from JSON to "string or #f".
+ (match-lambda
+ ((? string? str) str)
+ ((? null?) #f) ;Guile-JSON 3.x
+ ('null #f))) ;Guile-JSON 4.x
+
+(define %allow-request?
+ ;; Takes a URL and method (e.g., the 'http-get' procedure) and returns true
+ ;; to keep going. This can be used to disallow requests when
+ ;; 'request-rate-limit-reached?' returns true, for instance.
+ (make-parameter (const #t)))
+
+;; The time when the rate limit for "/origin/save" POST requests and that of
+;; other requests will be reset.
+;; See <https://archive.softwareheritage.org/api/#rate-limiting>.
+(define %save-rate-limit-reset-time 0)
+(define %general-rate-limit-reset-time 0)
+
+(define (request-rate-limit-reached? url method)
+ "Return true if the rate limit has been reached for URI."
+ (define uri
+ (string->uri url))
+
+ (define reset-time
+ (if (and (eq? method http-post*)
+ (string-prefix? "/api/1/origin/save/" (uri-path uri)))
+ %save-rate-limit-reset-time
+ %general-rate-limit-reset-time))
+
+ (< (car (gettimeofday)) reset-time))
+
+(define (update-rate-limit-reset-time! url method response)
+ "Update the rate limit reset time for URL and METHOD based on the headers in
+RESPONSE."
+ (let ((uri (string->uri url)))
+ (match (assq-ref (response-headers response) 'x-ratelimit-reset)
+ ((= string->number (? number? reset))
+ (if (and (eq? method http-post*)
+ (string-prefix? "/api/1/origin/save/" (uri-path uri)))
+ (set! %save-rate-limit-reset-time reset)
+ (set! %general-rate-limit-reset-time reset)))
+ (_
+ #f))))
+
+(define* (call url decode #:optional (method http-get*)