Added ability to check if a blob exists (#34)

* Added ability to check if a blob exists

* Fixing Rd file

* Fixing Rd file

NAMESPACE

@@ -99,6 +99,7 @@ export(break_lease)
 export(call_azcopy)
 export(call_storage_endpoint)
 export(change_lease)
+export(check_blob)
 export(copy_url_to_blob)
 export(copy_url_to_storage)
 export(create_adls_dir)

R/blob_client_funcs.R

@@ -215,7 +215,7 @@ delete_blob_container.blob_endpoint <- function(endpoint, name, confirm=TRUE, le
 
 #' Operations on a blob container or blob
 #'
-#' Upload, download, or delete a blob; list blobs in a container.
+#' Upload, download, or delete a blob; list blobs in a container; check blob availability.
 #'
 #' @param container A blob container object.
 #' @param blob A string naming a blob.
@@ -242,7 +242,7 @@ delete_blob_container.blob_endpoint <- function(endpoint, name, confirm=TRUE, le
 #' `upload_blob` and `download_blob` can display a progress bar to track the file transfer. You can control whether to display this with `options(azure_storage_progress_bar=TRUE|FALSE)`; the default is TRUE.
 #'
 #' @return
-#' For `list_blobs`, details on the blobs in the container. For `download_blob`, if `dest=NULL`, the contents of the downloaded blob as a raw vector.
+#' For `list_blobs`, details on the blobs in the container. For `download_blob`, if `dest=NULL`, the contents of the downloaded blob as a raw vector. For `check_blob` a flag whether the blob exists.
 #'
 #' @seealso
 #' [blob_container], [az_storage], [storage_download], [call_azcopy]
@@ -419,4 +419,14 @@ delete_blob <- function(container, blob, confirm=TRUE)
     invisible(do_container_op(container, blob, http_verb="DELETE"))
 }
 
-
+#' @rdname blob
+#' @export
+check_blob <- function(container, blob)
+{
+    res <- do_container_op(container, blob, headers = list(), http_verb = "HEAD", http_status_handler = "pass")
+    if (httr::status_code(res) == 404L) {
+        return(FALSE)
+    }
+    httr::stop_for_status(res, storage_error_message(res))
+    return(TRUE)
+}

man/blob.Rd

@@ -5,6 +5,7 @@
 \alias{upload_blob}
 \alias{multiupload_blob}
 \alias{download_blob}
+\alias{check_blob}
 \alias{multidownload_blob}
 \alias{delete_blob}
 \alias{copy_url_to_blob}
@@ -30,6 +31,8 @@ multidownload_blob(container, src, dest, recursive = FALSE,
 
 delete_blob(container, blob, confirm = TRUE)
 
+check_blob(container, blob)
+
 copy_url_to_blob(container, src, dest, lease = NULL, async = FALSE)
 
 multicopy_url_to_blob(container, src, dest, lease = NULL,
@@ -67,10 +70,10 @@ multicopy_url_to_blob(container, src, dest, lease = NULL,
 \item{async}{For \code{copy_url_to_blob} and \code{multicopy_url_to_blob}, whether the copy operation should be asynchronous (proceed in the background).}
 }
 \value{
-For \code{list_blobs}, details on the blobs in the container. For \code{download_blob}, if \code{dest=NULL}, the contents of the downloaded blob as a raw vector.
+For \code{list_blobs}, details on the blobs in the container. For \code{download_blob}, if \code{dest=NULL}, the contents of the downloaded blob as a raw vector. For \code{check_blob} a flag whether the blob exists.
 }
 \description{
-Upload, download, or delete a blob; list blobs in a container.
+Upload, download, or delete a blob; list blobs in a container; check blob availability.
 }
 \details{
 \code{upload_blob} and \code{download_blob} are the workhorse file transfer functions for blobs. They each take as inputs a \emph{single} filename as the source for uploading/downloading, and a single filename as the destination. Alternatively, for uploading, \code{src} can be a \link{textConnection} or \link{rawConnection} object; and for downloading, \code{dest} can be NULL or a \code{rawConnection} object. If \code{dest} is NULL, the downloaded data is returned as a raw vector, and if a raw connection, it will be placed into the connection. See the examples below.

tests/testthat/test02_blob.R

@@ -134,6 +134,10 @@ test_that("Blob client interface works",
     iris3 <- as.data.frame(jsonlite::fromJSON(con))
     expect_identical(iris, iris3)
 
+    # check blob
+    expect_false(check_blob(cont, "nonexisting.blob"))
+    expect_true(check_blob(cont, "iris.json"))
+
     # ways of deleting a container
     delete_blob_container(cont, confirm=FALSE)
     delete_blob_container(bl, "newcontainer2", confirm=FALSE)