Fixed automatic guessing of Content-Type in downloadHandler (rstudio#…

…3393)

* Set default downloadHandler contentType to NULL.

The change from %OR% to %||% broke automatic guessing of content type
since `NA %||% ...` evaluates to `NA`. Setting the default contentType
to NULL restores the previous behavior of automatically setting the
content type based on the file extension.

* Updated NEWS.md: downloadHandler contentType fix.

* Update NEWS.md

Co-authored-by: Winston Chang <[email protected]>
Co-authored-by: Barret Schloerke <[email protected]>

NEWS.md

@@ -29,6 +29,8 @@ shiny development
 
 * Fixed a bug where updating an input value without a corresponding Input binding element did not trigger a JavaScript `shiny:inputchanged` event. Now, if no Input binding element is found, the `shiny:inputchanged` event is triggered on `window.document`. (#3584)
 
+* Restored the previous behavior of automatically guessing the `Content-Type` header for `downloadHandler` functions when no explicit `contentType` argument is supplied. (#3393)
+
 shiny 1.7.1
 ===========
 

R/shinywrappers.R

@@ -778,9 +778,9 @@ renderUI <- function(expr, env = parent.frame(), quoted = FALSE,
 #'   function.)
 #' @param contentType A string of the download's
 #'   [content type](https://en.wikipedia.org/wiki/Internet_media_type), for
-#'   example `"text/csv"` or `"image/png"`. If `NULL` or
-#'   `NA`, the content type will be guessed based on the filename
-#'   extension, or `application/octet-stream` if the extension is unknown.
+#'   example `"text/csv"` or `"image/png"`. If `NULL`, the content type 
+#'   will be guessed based on the filename extension, or 
+#'   `application/octet-stream` if the extension is unknown.
 #' @param outputArgs A list of arguments to be passed through to the implicit
 #'   call to [downloadButton()] when `downloadHandler` is used
 #'   in an interactive R Markdown document.
@@ -810,7 +810,7 @@ renderUI <- function(expr, env = parent.frame(), quoted = FALSE,
 #' shinyApp(ui, server)
 #' }
 #' @export
-downloadHandler <- function(filename, content, contentType=NA, outputArgs=list()) {
+downloadHandler <- function(filename, content, contentType=NULL, outputArgs=list()) {
   renderFunc <- function(shinysession, name, ...) {
     shinysession$registerDownload(name, filename, contentType, content)
   }