[GitHub] [arrow] nealrichardson commented on a change in pull request #8058: ARROW-9854: [R] Support reading/writing data to/from S3

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nealrichardson commented on a change in pull request #8058:
URL: https://github.com/apache/arrow/pull/8058#discussion_r486656550



##########
File path: r/R/filesystem.R
##########
@@ -242,11 +242,31 @@ FileSystem <- R6Class("FileSystem", inherit = ArrowObject,
   )
 )
 FileSystem$from_uri <- function(uri) {
+  assert_that(is.string(uri))
   out <- fs___FileSystemFromUri(uri)
   out$fs <- shared_ptr(FileSystem, out$fs)$..dispatch()
   out
 }
 
+get_path_and_filesystem <- function(x, filesystem = NULL) {
+  # Wrapper around FileSystem$from_uri that handles local paths
+  # and an optional explicit filesystem
+  assert_that(is.string(x))
+  if (is_url(x)) {
+    if (!is.null(filesystem)) {
+      # Stop? Can't have URL (which yields a fs) and another fs

Review comment:
       What happens here is that `filesystem` will be ignored if `x` is a URL, i.e. we'll use the filesystem that `from_uri(x)` returns. So that should either Just Work if the filesystems happen to be the same, or you're right, it should error with some kind of File Not Found later. 




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