Asynchronous HTTP HEAD request

An async HTTP deferred object is also an event emitter, see http_get() for details, and also event_emitter.

http_head(
  url,
  headers = character(),
  file = NULL,
  options = list(),
  on_progress = NULL
)

Arguments

url

URL to connect to.

headers

HTTP headers to send.

file

If not NULL, it must be a string, specifying a file. The body of the response is written to this file.

options

Options to set on the handle. Passed to curl::handle_setopt().

on_progress

Progress handler function. It is only used if the response body is written to a file. See details below.

Value

Deferred object.

See also

Other asyncronous HTTP calls: http_get(), http_setopt()

Examples

# \donttest{
afun <- async(function() {
  dx <- http_head("https://eu.httpbin.org/status/200")$
    then(function(x) x$status_code)
})
synchronise(afun())
#> [1] 200

# Check a list of URLs in parallel
afun <- function(urls) {
  when_all(.list = lapply(urls, http_head))$
    then(function(x) lapply(x, "[[", "status_code"))
}
urls <- c("https://google.com", "https://eu.httpbin.org")
synchronise(afun(urls))
#> [[1]]
#> [1] 200
#> 
#> [[2]]
#> [1] 200
#> 
# }