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Download a file and check it

Source: R/download.R
download_file.Rd

Downloads to a temporary name next to the destination and moves the file into place only once it has been received and checked, so that an interrupted run leaves no truncated file that a later run would take for a complete one.

  • download_file() applies any check;

  • download_pdf() checks the PDF signature, since some links return a web page (error or landing page) with status 200;

  • is_pdf_file() is that check.

Usage

download_file(
  url,
  dest,
  pause = getOption("politecollect.delay", 2),
  check = NULL,
  check_failure = "file failed the check",
  ...
)

download_pdf(url, dest, pause = getOption("politecollect.delay", 2), ...)

is_pdf_file(path)

Arguments

url

Character. The URL.

dest

Character. Destination path; its folder is created if needed.

pause

Numeric. Minimum seconds between two requests to this site.

check

Function of a file path returning TRUE or FALSE, or NULL.

check_failure

Character. Reason recorded when the check fails.

...

Other arguments of polite_request().

path

Character. A file on disk.

Value

download_file() and download_pdf(): TRUE if the file was saved, FALSE otherwise; last_failure() then gives the reason. An existing file is replaced only by a file that passed the check. is_pdf_file(): TRUE or FALSE.

See also

Other downloads: queue_downloads()

Examples

f <- tempfile(fileext = ".pdf")
writeLines("<html>not found</html>", f)
is_pdf_file(f)
#> [1] FALSE

if (FALSE) { # \dontrun{
options(politecollect.user_agent = "my_project (me@example.org)")
if (!download_pdf("https://www.bis.org/review/r240101a.pdf", "r240101a.pdf")) {
  last_failure()
}
} # }