#' Upload an image to imgur.com

#'

#' This function uses the \pkg{httr} package to upload a image to

#' \url{https://imgur.com}, and parses the XML response to a list with

#' \pkg{xml2} which contains information about the image in the Imgur website.

#'

#' When the output format from \code{\link{knit}()} is HTML or Markdown, this

#' function can be used to upload local image files to Imgur, e.g. set the

#' package option \code{opts_knit$set(upload.fun = imgur_upload)}, so the output

#' document is completely self-contained, i.e. it does not need external image

#' files any more, and it is ready to be published online.

#' @param file Path to the image file to be uploaded.

#' @param key Client ID for Imgur. By default, this uses a client ID registered

#'   by Yihui Xie.

#' @return A character string of the link to the image; this string carries an

#'   attribute named \code{XML} which is a list converted from the response XML

#'   file; see Imgur API in the references.

#' @author Yihui Xie, adapted from the \pkg{imguR} package by Aaron Statham

#' @note Please register your own Imgur application to get your client ID; you

#'   can certainly use mine, but this ID is in the public domain so everyone has

#'   access to all images associated to it.

#' @references Imgur API version 3: \url{https://apidocs.imgur.com}; a demo:

#'   \url{https://yihui.org/knitr/demo/upload/}

#' @export

#' @examples \dontrun{

#' f = tempfile(fileext = '.png')

#' png(f); plot(rnorm(100), main = R.version.string); dev.off()

#'

#' res = imgur_upload(f)

#' res  # link to original URL of the image

#' attr(res, 'XML')  # all information

#' if (interactive()) browseURL(res)

#'

#' # to use your own key

#' opts_knit$set(upload.fun = function(file) imgur_upload(file, key = 'your imgur key'))

#' }

imgur_upload = function(file, key = '9f3460e67f308f6') {

  )

  # Breaking change in xml2 1.2.0

}