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A Clojure API for the AWS API

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;; Copyright (c) Cognitect, Inc.
;; All rights reserved.

(ns cognitect.aws.retry
  (:require [clojure.core.async :as a]))

(set! *warn-on-reflection* true)

(defn ^:skip-wiki with-retry
  "For internal use. Do not call directly.

  Calls req-fn, a *non-blocking* function that wraps some operation
  and returns a channel. When the response to req-fn is retriable?
  and backoff returns an int, waits backoff ms and retries, otherwise
  puts response on resp-chan."
  [req-fn resp-chan retriable? backoff]
  (a/go-loop [retries 0]
    (let [resp (a/! resp-chan resp))
        (a/>! resp-chan resp))))
  resp-chan)

(defn capped-exponential-backoff
  "Returns a function of the num-retries (so far), which returns the
  lesser of max-backoff and an exponentially increasing multiple of
  base, or nil when (>= num-retries max-retries).
  See with-retry to see how it is used.

  Alpha. Subject to change."
  [base max-backoff max-retries]
  (fn [num-retries]
    (when (< num-retries max-retries)
      (min max-backoff
           (* base (bit-shift-left 1 num-retries))))))

(def default-backoff
  "Returns (capped-exponential-backoff 100 20000 3).

  Alpha. Subject to change."
  (capped-exponential-backoff 100 20000 3))

(def default-retriable?
  "A fn of an http-response map which returns a truthy value
  if (:cognitect.anomalies/category http-response) is any of:
    - :cognitect.anomalies/busy
    - :cognitect.anomalies/interrupted
    - :cognitect.anomalies/unavailable

  Alpha. Subject to change."
  (comp #{:cognitect.anomalies/busy
          :cognitect.anomalies/interrupted
          :cognitect.anomalies/unavailable}
        :cognitect.anomalies/category))