httr (version 1.2.1)

RETRY: Retry a request until it succeeds.

Description

Safely retry a request until it succeeds (returns an HTTP status code below 400). 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.)

Usage

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

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.

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.

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

# NOT RUN {
# Succeeds straight away
RETRY("GET", "http://httpbin.org/status/200")
# Never succeeds
RETRY("GET", "http://httpbin.org/status/500")
# }