R: Retry a request until it succeeds.

RETRY {httr}

R Documentation

Retry a request until it succeeds.

Description

Safely retry a request until it succeeds, as defined by the terminate_on parameter, which by default means a response for which http_error() is FALSE. Will also retry on error conditions raised by the underlying curl code, but if the last retry still raises one, RETRY will raise it again with stop(). It is designed to be kind to the server: after each failure randomly waits up to twice as long. (Technically it uses exponential backoff with jitter, using the approach outlined in https://www.awsarchitectureblog.com/2015/03/backoff.html.) If the server returns status code 429 and specifies a retry-after value, that value will be used instead, unless it's smaller than pause_min.

Usage

RETRY(verb, url = NULL, config = list(), ..., body = NULL,
  encode = c("multipart", "form", "json", "raw"), times = 3,
  pause_base = 1, pause_cap = 60, pause_min = 1, handle = NULL,
  quiet = FALSE, terminate_on = NULL)

Arguments

`verb`	Name of verb to use.
`url`	the url of the page to retrieve
`config`	Additional configuration settings such as http authentication (`authenticate`), additional headers (`add_headers`), cookies (`set_cookies`) etc. See `config` for full details and list of helpers.
`...`	Further named parameters, such as `query`, `path`, etc, passed on to `modify_url`. Unnamed parameters will be combined with `config`.
`body`	One of the following: `FALSE`: No body. This is typically not used with `POST`, `PUT`, or `PATCH`, but can be useful if you need to send a bodyless request (like `GET`) with `VERB()`. `NULL`: An empty body `""`: A length 0 body `upload_file("path/")`: The contents of a file. The mime type will be guessed from the extension, or can be supplied explicitly as the second argument to `upload_file()` A character or raw vector: sent as is in body. Use `content_type` to tell the server what sort of data you are sending. A named list: See details for encode.
`encode`	If the body is a named list, how should it be encoded? Can be one of form (application/x-www-form-urlencoded), multipart, (multipart/form-data), or json (application/json). For "multipart", list elements can be strings or objects created by `upload_file`. For "form", elements are coerced to strings and escaped, use `I()` to prevent double-escaping. For "json", parameters are automatically "unboxed" (i.e. length 1 vectors are converted to scalars). To preserve a length 1 vector as a vector, wrap in `I()`. For "raw", either a character or raw vector. You'll need to make sure to set the `content_type()` yourself.
`times`	Maximum number of requests to attempt.
`pause_base, pause_cap`	This method uses exponential back-off with full jitter - this means that each request will randomly wait between 0 and `pause_base * 2 ^ attempt` seconds, up to a maximum of `pause_cap` seconds.
`pause_min`	Minimum time to wait in the backoff; generally only necessary if you need pauses less than one second (which may not be kind to the server, use with caution!).
`handle`	The handle to use with this request. If not supplied, will be retrieved and reused from the `handle_pool` based on the scheme, hostname and port of the url. By default httr requests to the same scheme/host/port combo. This substantially reduces connection time, and ensures that cookies are maintained over multiple requests to the same host. See `handle_pool` for more details.
`quiet`	If `FALSE`, will print a message displaying how long until the next request.
`terminate_on`	Optional vector of numeric HTTP status codes that if found on the response will terminate the retry process. If `NULL`, will keep retrying while `http_error()` is `TRUE` for the response.

Value

The last response. Note that if the request doesn't succeed after times times this will be a failed request, i.e. you still need to use stop_for_status().

Examples

# Succeeds straight away
RETRY("GET", "http://httpbin.org/status/200")
# Never succeeds
RETRY("GET", "http://httpbin.org/status/500")

# Invalid hostname generates curl error condition and is retried but eventually
# raises an error condition.
RETRY("GET", "http://invalidhostname/")

[Package httr version 1.3.1 Index]