Ajax: Support binary data (including FormData)

Two changes have been applied:
* prefilters are now applied before data is converted to a string;
  this allows prefilters to disable such a conversion
* a prefilter for binary data is added; it disables data conversion
  for non-string non-plain-object `data`; for `FormData` bodies, it
  removes manually-set `Content-Type` header - this is required
  as browsers need to append their own boundary to the header

Ref gh-4150
Closes gh-5197

1 files changed, 17 insertions, 0 deletions

diff --git a/src/ajax/binary.js b/src/ajax/binary.js
new file mode 100644
index 000000000..e96661da7
--- /dev/null
+++ b/src/ajax/binary.js
@@ -0,0 +1,17 @@
+import jQuery from "../core.js";
+
+import "../ajax.js";
+
+jQuery.ajaxPrefilter( function( s ) {
+
+	// Binary data needs to be passed to XHR as-is without stringification.
+	if ( typeof s.data !== "string" && !jQuery.isPlainObject( s.data ) ) {
+		s.processData = false;
+	}
+
+	// `Content-Type` for requests with `FormData` bodies needs to be set
+	// by the browser as it needs to append the `boundary` it generated.
+	if ( s.data instanceof window.FormData ) {
+		s.contentType = false;
+	}
+} );