GNU R package that allows package users to download and cache optional data files in a local directory.
Allow Users of Your Package to Download and Manage Optional Package Data
This package allows you to give users of your package an easy way to download and manage optional data for your package. The data can be hosted on your webserver or any location accessible via HTTP(S) over the internet, and will be stored locally in a permanent directory called a package file cache. Checking of MD5 sums is supported, and re-downloading only ever occurs if MD5 sums mismatch if they are available.
The pkgfilecache package is on CRAN, so you can simply:
install.packages("pkgfilecache")When package authors want to ship data for their package, they will quickly hit the package size limit on CRAN (which is 5 MB as of September 2019). The solution is to host the data elsewhere and download it on demand when the user requests it, then store it for future use. This is what pkgfilecache allows you to do. You can put your files onto a web server of your choice, take the MD5 sums, and have pkgfilecache download them locally. Files are automatically compared with the local package cache direcory, and only missing files or files with incorrect MD5 checksums will be downloaded. Users can then access the data in a convenient way, similar to accessing files shipped in inst/extdata via system.file. They can also erase the data if it is no longer needed.
The intended way of using pkgfilecache is to not call the download function in your package code, but have it as part of your API that the user can decide to call if they want to download the optional data. However, you are of course free to call the download function in your unit test code, which will only be run by developers or continuous integration systems.
You specify a list of optional data files, and package users can download them with a single command from within GNU R. For each file, you provide:
- a full URL to the file, hosted on some public web server
- the MD5 checksum of the file (optional, but highly recommended)
- a local filename, under which the file can be retrieved from the package cache
Users can then access the file by the local filename. See the documentation for details.
See the vignette for more detailed examples!
pkg_info = pkgfilecache::get_pkg_info("yourpackage"); # to identify the cache dir
### Specify your optional data:
# 1) How the files should be called in the local package file cache
local_filenames = c("file1.txt", "file2.txt");
# 2) Where they can be downloaded
urls = c("https://your.server/yourpackage/large_file1.txt", "https://your.server/yourpackage/large_file2.txt");
# 3) Optional, but highly recommended: MD5 checksums for the files.
md5sums = c("35261471bcd198583c3805ee2a543b1f", "85ffec2e6efb476f1ee1e3e7fddd86de");
# Now use the package cache to get the files. Will only download if needed (file missing or MD5 mismatch):
cfiles = pkgfilecache::ensure_files_available(pkg_info, local_filenames, urls, md5sums=md5sums);
# Great, now let's access a file:
local_file_full_path = pkgfilecache::get_filepath(pkg_info, "file1.txt", mustWork=TRUE);Full documentation is built-in, and can be accessed from within R in the usual ways. A vignette is also included:
library("pkgfilecache")
browseVignettes("pkgfilecache")You can also read the pkgfilecache vignette online at CRAN.
Unit tests can be run locally using devtools::check(), and CI is running on Travis for Linux and AppVeyor for Windows:
It is not allowed to store data in the user directory on CRAN servers, not even temporarily. So please do not use this package to download data into the user directory in unit tests on CRAN. You can use testthat::skip_on_cran() at the top of test functions that require/download external data from running on CRAN. You should test on your CI provider instead, and limit CRAN unit tests to those with data that can be generated in the test code.
MIT
- I haven't tried it myself, but according to this article in the R journal, drat hosting of data could be an option.
- For BioConductor, there is BiocFileCache, but it's not gonna help you for CRAN.