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A simple package cache

Source: R/package-cache.R
package_cache.Rd

This is an R6 class that implements a concurrency safe package cache.

Details

By default these fields are included for every package:

  • fullpath Full package path.

  • path Package path, within the repository.

  • package Package name.

  • url URL it was downloaded from.

  • etag ETag for the last download, from the given URL.

  • sha256 SHA256 hash of the file.

Additional fields can be added as needed.

For a simple API to a session-wide instance of this class, see pkg_cache_summary() and the other functions listed there.

Usage

pc <- package_cache$new(path = NULL)

pc$list()
pc$find(..., .list = NULL)
pc$copy_to(..., .list = NULL)
pc$add(file, path, sha256 = shasum256(file), ..., .list = NULL)
pc$add_url(url, path, ..., .list = NULL, on_progress = NULL,
  http_headers = NULL)
pc$async_add_url(url, path, ..., .list = NULL, on_progress = NULL,
  http_headers = NULL)
pc$copy_or_add(target, urls, path, sha256 = NULL, ..., .list = NULL,
               on_progress = NULL, http_headers = NULL)
pc$async_copy_or_add(target, urls, path, ..., sha256 = NULL, ...,
               .list = NULL, on_progress = NULL, http_headers = NULL)
pc$update_or_add(target, urls, path, ..., .list = NULL,
               on_progress = NULL, http_headers = NULL)
pc$async_update_or_add(target, urls, path, ..., .list = NULL,
               on_progress = NULL, http_headers = NULL)
pc$delete(..., .list = NULL)

Arguments

  • path: For package_cache$new() the location of the cache. For other functions the location of the file inside the cache.

  • ...: Extra attributes to search for. They have to be named.

  • .list: Extra attributes to search for, they have to in a named list.

  • file: Path to the file to add.

  • url: URL attribute. This is used to update the file, if requested.

  • sha256: SHA256 hash of the file.

  • on_progress: Callback to create progress bar. Passed to internal function http_get().

  • target: Path to copy the (first) to hit to.

  • urls: Character vector or URLs to try to download the file from.

  • http_headers: HTTP headers to add to all HTTP queries.

Details

package_cache$new() attaches to the cache at path. (By default a platform dependent user level cache directory.) If the cache does not exists, it creates it.

pc$list() lists all files in the cache, returns a data frame with all the default columns, and potentially extra columns as well.

pc$find() list all files that match the specified criteria (fullpath, path, package, etc.). Custom columns can be searched for as well.

pc$copy_to() will copy the first matching file from the cache to target. It returns the data frame of all matching records, invisibly. If no file matches, it returns an empty (zero-row) data frame.

pc$add() adds a file to the cache.

pc$add_url() downloads a file and adds it to the cache.

pc$async_add_url() is the same, but it is asynchronous.

pc$copy_or_add() works like pc$copy_to(), but if the file is not in the cache, it tries to download it from one of the specified URLs first.

pc$async_copy_or_add() is the same, but asynchronous.

pc$update_or_add() is like pc$copy_to_add(), but if the file is in the cache it tries to update it from the urls, using the stored ETag to avoid unnecessary downloads.

pc$async_update_or_add() is the same, but it is asynchronous.

pc$delete() deletes the file(s) from the cache.

Examples


## Although package_cache usually stores packages, it may store
## arbitrary files, that can be search by metadata
pc <- package_cache$new(path = tempfile())
pc$list()
#> [1] fullpath path     package  url      etag     sha256  
#> <0 rows> (or 0-length row.names)

cat("foo\n", file = f1 <- tempfile())
cat("bar\n", file = f2 <- tempfile())
pc$add(f1, "/f1")
#>                               fullpath path package url etag
#> 1 /tmp/Rtmpwkkjty/file16935431efa1//f1  /f1      NA  NA   NA
#>                                                             sha256
#> 1 b5bb9d8014a0f9b1d61e21e796d78dccdf1352f23cd32812f4850b878ae4944c
pc$add(f2, "/f2")
#>                               fullpath path package url etag
#> 2 /tmp/Rtmpwkkjty/file16935431efa1//f2  /f2      NA  NA   NA
#>                                                             sha256
#> 2 7d865e959b2466918c9863afca942d0fb89d7c9ac0c99bafc3749504ded97730
pc$list()
#>                               fullpath path package url etag
#> 1 /tmp/Rtmpwkkjty/file16935431efa1//f1  /f1      NA  NA   NA
#> 2 /tmp/Rtmpwkkjty/file16935431efa1//f2  /f2      NA  NA   NA
#>                                                             sha256
#> 1 b5bb9d8014a0f9b1d61e21e796d78dccdf1352f23cd32812f4850b878ae4944c
#> 2 7d865e959b2466918c9863afca942d0fb89d7c9ac0c99bafc3749504ded97730
pc$find(path = "/f1")
#>                               fullpath path package url etag
#> 1 /tmp/Rtmpwkkjty/file16935431efa1//f1  /f1      NA  NA   NA
#>                                                             sha256
#> 1 b5bb9d8014a0f9b1d61e21e796d78dccdf1352f23cd32812f4850b878ae4944c
pc$copy_to(target = f3 <- tempfile(), path = "/f1")
#>                               fullpath path package url etag
#> 1 /tmp/Rtmpwkkjty/file16935431efa1//f1  /f1      NA  NA   NA
#>                                                             sha256
#> 1 b5bb9d8014a0f9b1d61e21e796d78dccdf1352f23cd32812f4850b878ae4944c
readLines(f3)
#> [1] "foo"