Need function for retrying a request

[hadley]

• Fixed number of tries
• Exponential back off
• Built-in randomness

[hadley]

@craigcitro if you're doing PRs, any interest in doing one for this?

[hadley]

Here's a first stab at it:

#' @inheritParams GET
#' @inheritParams POST
#' @param times Number of times to retry
#' @param pause_base,pause_cap This method uses exponential back-off of with
#'   full jitter (\url{}) - this means that each request will randomly wait
#'   between 0 and \code{pause_base * 2 ^ attempt} seconds, up to a maximum of 
#'   \code{pause_cap} seconds.
retry <- function(verb, url = NULL, config = list(), ...,
                  body = NULL, encode = c("multipart", "form", "json", "raw"),
                  times = 3, pause_base = 1, pause_cap = 60,
                  handle = NULL) {
  stopifnot(is.numeric(times), length(times) == 1L)

  hu <- handle_url(handle, url, ...)
  req <- request_build(verb, hu$url, body_config(body, match.arg(encode)), config, ...)
  resp <- request_perform(req, hu$handle$handle)

  i <- 1
  while (i <= .times && http_error(resp)) {
    resp <- request_perform(req, hu$handle$handle)

    backoff_full_jitter(i, pause_base, pause_cap)
    i <- i + 1
  }

  resp
}

backoff_full_jitter <- function(i, pause_base = 1, pause_cap = 60, quiet = FALSE) {
  stopifnot(is.integer(pause_base), length(pause_base) == 1L)
  stopifnot(is.integer(pause_cap), length(pause_cap) == 1L)

  length <- ceiling(runif(min(pause_cap, pause_base * 2 ^ i)))
  if (!quiet) {
    message("Retrying in ", length, " seconds")
  }
  Sys.sleep(length)
}

I'm using the technique from https://www.awsarchitectureblog.com/2015/03/backoff.html.

@craigcitro do you have any thoughts on the base and cap pauses?