lisp/retry.lisp @ 05ef9c8cbeeb

(eval-when (:compile-toplevel :load-toplevel :execute)
  (ql:quickload
    '(:adopt :iterate :external-program :parse-number :alexandria :with-user-abort)
    :silent t))

(defpackage :retry
  (:use :cl :iterate)
  (:export :toplevel :*ui*))

(in-package :retry)

;;;; Configuration ------------------------------------------------------------
(defparameter *version* "0.0.1")


;;;; Functionality ------------------------------------------------------------
(defun backoff-immediate ()
  (lambda (try) (declare (ignore try))))

(defun backoff-constant (seconds)
  (lambda (try)
    (declare (ignore try))
    (sleep seconds)))

(defun backoff-exponential (seconds)
  (lambda (try)
    (sleep (* try seconds))))

(defun retry (command &key backoff tries)
  (iterate
    (with (program . args) = command)
    (for try :from 1)
    (for (values nil code) =
         (external-program:run program args :input t :output t :error t))
    (finding code :such-that #'zerop :on-failure 1)
    (while (or (null tries) (< try tries)))
    (when backoff
      (funcall backoff try))))


;;;; Run ----------------------------------------------------------------------
(defun run (arguments options)
  (retry (let ((shell (gethash 'shell options)))
           (if shell
             `("sh" "-c" ,shell)
             arguments))
         :tries (gethash 'tries options)
         :backoff (gethash 'backoff options)))


;;;; User Interface -----------------------------------------------------------
(adopt:define-string *help*
  "retry runs another command, retrying it if it returns a non-zero exit code.~@
   ~@
   Options are available for configuring the number of retries and how long ~
   to wait before retrying.  If the command eventually succeeds, retry will ~
   return an exit code of 0, otherwise it will return an exit code of 1.")

(adopt:define-string *help-command*
  "By default, any non-option arguments to retry will designate the command ~
   to be run.  If the command itself has options, you'll need to use -- to tell ~
   retry which options belong to the command, e.g.:~@
   ~@
   ~:
    retry --backoff 5 -- ping -c 1 -w 1 example.com~@
   ~@
   You can use the --shell option to specify the command to run as a single ~
   string, which can be handy if you need to redirect its output:~@
   ~@
   ~:
    retry -t5 -b1 --shell 'curl -Lsf stevelosh.com | grep -q Hello'")

(defparameter *examples*
  '(("Retry flashing a cheap EEPROM a few times before giving up:"
     . "retry --tries 3 -- minipro -p AT28C256 -w rom.bin")
    ("Try to curl a healthcheck endpoint with exponential backoff:"
     . "retry --backoff 1 --tries 5 --shell \"curl -Lsf 'http://example.com/healthcheck/' >/dev/null\"")))


(defparameter *option-shell*
  (adopt:make-option 'shell
    :help "Execute `sh -c \"$CMD\"`, instead of passing the command as separate arguments to retry."
    :long "shell"
    :short #\s
    :parameter "CMD"
    :reduce #'adopt:last))

(defparameter *option-no-shell*
  (adopt:make-option 'no-shell
    :result-key 'shell
    :help "Execute the non-option arguments to retry as the command (the default)."
    :long "no-shell"
    :short #\S
    :reduce (constantly nil)))

(defparameter *option-immediate*
  (adopt:make-option 'immediate
    :result-key 'backoff
    :help "Retry the command immediately on failure (the default)."
    :long "immediate"
    :short #\i
    :reduce (constantly (backoff-immediate))))

(defparameter *option-wait*
  (adopt:make-option 'wait
    :result-key 'backoff
    :help "Wait N seconds before retrying a failed command."
    :long "wait"
    :short #\w
    :parameter "N"
    :key (alexandria:compose #'backoff-constant #'parse-number:parse-number)
    :reduce #'adopt:last))

(defparameter *option-backoff*
  (adopt:make-option 'backoff
    :result-key 'backoff
    :help "Backoff (N * try) seconds before retrying a failed command."
    :long "backoff"
    :short #\b
    :parameter "N"
    :key (alexandria:compose #'backoff-exponential #'parse-number:parse-number)
    :reduce #'adopt:last))

(defparameter *option-tries*
  (adopt:make-option 'tries
    :help "Maximum number of tries to attempt."
    :long "tries"
    :short #\t
    :parameter "N"
    :initial-value nil
    :key #'parse-integer
    :reduce #'adopt:last))

(defparameter *option-try-forever*
  (adopt:make-option 'try-forever
    :result-key 'tries
    :help "Try forever (the default)."
    :long "try-forever"
    :short #\T
    :reduce (constantly nil)))

(defparameter *option-help*
  (adopt:make-option 'help
    :help "Display help and exit."
    :long "help"
    :short #\h
    :reduce (constantly t)))

(defparameter *option-version*
  (adopt:make-option 'version
    :help "Display version information and exit."
    :long "version"
    :reduce (constantly t)))


(defparameter *ui*
  (adopt:make-interface
    :name "retry"
    :usage "[OPTIONS] -- COMMAND [ARG...]"
    :summary "retry running a command"
    :help *help*
    :examples *examples*
    :contents (list
                (adopt:make-group
                  'tries
                  :title "Number of Tries"
                  :options (list
                             *option-tries*
                             *option-try-forever*))

                (adopt:make-group
                  'backoff-policy
                  :title "Backoff Policy"
                  :options (list
                             *option-immediate*
                             *option-wait*
                             *option-backoff*))

                (adopt:make-group
                  'command
                  :title "Specifying a Command"
                  :help *help-command*
                  :options (list
                             *option-shell*
                             *option-no-shell*))

                *option-help*
                *option-version*)))



(defun parse-options-or-exit (ui)
  (handler-case (adopt:parse-options ui)
    (error (c) (adopt:print-error-and-exit c))))


(defun toplevel ()
  #+sbcl (sb-ext:disable-debugger)
  (handler-case
      (with-user-abort:with-user-abort
        (multiple-value-bind (arguments options)
            (parse-options-or-exit *ui*)
          (cond
            ((gethash 'help options) (adopt:print-help-and-exit *ui*))
            ((gethash 'version options) (write-line *version*) (adopt:exit))
            (t (adopt:exit (run arguments options))))))
    (with-user-abort:user-abort () (adopt:exit 130))))