ncurl Async

nano cURL - a minimalist http(s) client - async edition.

Usage

ncurl_aio(
  url,
  convert = TRUE,
  method = NULL,
  headers = NULL,
  data = NULL,
  response = NULL,
  timeout = NULL,
  tls = NULL
)

Arguments

url: the URL address.
convert: [default TRUE] logical value whether to attempt conversion of the received raw bytes to a character vector. Set to FALSE if downloading non-text data.
method: (optional) the HTTP method as a character string. Defaults to 'GET' if not specified, and could also be 'POST', 'PUT' etc.
headers: (optional) a named character vector specifying the HTTP request headers, for example:
c(Authorization = "Bearer APIKEY", "Content-Type" = "text/plain")
A non-character or non-named vector will be ignored.
data: (optional) request data to be submitted. Must be a character string or raw vector, and other objects are ignored. If a character vector, only the first element is taken. When supplying binary data, the appropriate 'Content-Type' header should be set to specify the binary format.
response: (optional) a character vector specifying the response headers to return e.g. c("date", "server"). These are case-insensitive and will return NULL if not present. Specify TRUE to return all response headers. A non-character vector will be ignored (other than TRUE).
timeout: (optional) integer value in milliseconds after which the transaction times out if not yet complete.
tls: (optional) applicable to secure HTTPS sites only, a client TLS Configuration object created by tls_config(). If missing or NULL, certificates are not validated.

Value

An 'ncurlAio' (object of class 'ncurlAio' and 'recvAio') (invisibly). The following elements may be accessed:

$status - integer HTTP repsonse status code (200 - OK). Use status_code() for a translation of the meaning.
$headers - named list of response headers (all headers if response = TRUE, or those specified in response, or NULL otherwise). If the status code is within the 300 range, i.e. a redirect, the response header 'Location' is automatically appended to return the redirect address.
$data - the response body, as a character string if convert = TRUE (may be further parsed as html, json, xml etc. as required), or a raw byte vector if FALSE (use writeBin() to save as a file).

Promises

'ncurlAio' may be used anywhere that accepts a 'promise' from the promises package through the included as.promise method.

The promises created are completely event-driven and non-polling.

If a status code of 200 (OK) is returned then the promise is resolved with the reponse body, otherwise it is rejected with a translation of the status code or 'errorValue' as the case may be.

Public Internet HTTPS

When making HTTPS requests over the public internet, you should supply a TLS configuration to validate server certificates. See tls_config() for details.

Examples

nc <- ncurl_aio(
  "https://postman-echo.com/get",
  response = c("date", "server"),
  timeout = 2000L
)
call_aio(nc)
nc$status
#> [1] 200
nc$headers
#> $date
#> [1] "Wed, 11 Feb 2026 20:07:17 GMT"
#> 
#> $server
#> [1] "cloudflare"
#> 
nc$data
#> [1] "{\"args\":{},\"headers\":{\"host\":\"postman-echo.com\",\"accept-encoding\":\"gzip, br\",\"x-forwarded-proto\":\"https\"},\"url\":\"https://postman-echo.com/get\"}"

if (FALSE) { # interactive() && requireNamespace("promises", quietly = TRUE)
library(promises)
p <- as.promise(nc)
print(p)

p2 <- ncurl_aio("https://postman-echo.com/get") %>%
  then(function(x) cat(x$data))
is.promise(p2)
}