HelperFunction.R

# function that downloads files from the web and verifies their checksum. 
# If file already exists in working directory, will use local copy.
load.web.file <- function(
    url, md5sum, outfile, zipfile = F) {
  # check if local file exists
  if (file.exists(outfile)) {
    # verify checksum
    realsum <- tools::md5sum(outfile)[[1]]
    if (realsum != md5sum) stop(sprintf("Local file %s has wrong checksum: %s", outfile, realsum))
    # do not delete wrong file, it was already here before
    
  } else {
    if(zipfile){
      # download file
      temp <- tempfile()
      download.file(url,temp)
      unzip(zipfile = temp, files = outfile, exdir = ".")
    } else {
      # download file
      download.file(url, outfile)
    }
    # verify checksum
    realsum <- tools::md5sum(outfile)[[1]]
    if (realsum != md5sum) { 
      # delete wrong file
      unlink(outfile)
      stop(sprintf("Remote file %s has wrong checksum: %s", url, realsum))
    }
  }
}