From e0d941156900a6bff7c098c8ea7290528e468cf8 Mon Sep 17 00:00:00 2001
From: Andrei Fangli <andrei_fangli@outlook.com>
Date: Mon, 26 Nov 2018 19:00:41 +0200
Subject: [PATCH] Ajax: Fix getResponseHeader(key) for IE11

- getResponseHeader(key) combines all header values for the provided key into a
single result where values are concatenated by ', '. This does not happen for
IE11 since multiple values for the same header are returned on separate lines.
This makes the function only return the last value of the header for IE11.
- Updated ajax headers test to better cover Object.prototype collisions

Close gh-4173
Fixes gh-3403
---
 src/ajax.js                   | 8 +++++---
 test/data/mock.php            | 3 +++
 test/middleware-mockserver.js | 5 ++++-
 test/unit/ajax.js             | 5 ++++-
 4 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/src/ajax.js b/src/ajax.js
index aec26830a2..4cbefabaaf 100644
--- a/src/ajax.js
+++ b/src/ajax.js
@@ -459,12 +459,14 @@ jQuery.extend( {
 						if ( !responseHeaders ) {
 							responseHeaders = {};
 							while ( ( match = rheaders.exec( responseHeadersString ) ) ) {
-								responseHeaders[ match[ 1 ].toLowerCase() ] = match[ 2 ];
+								responseHeaders[ match[ 1 ].toLowerCase() + " " ] =
+									( responseHeaders[ match[ 1 ].toLowerCase() + " " ] || [] )
+										.concat( match[ 2 ] );
 							}
 						}
-						match = responseHeaders[ key.toLowerCase() ];
+						match = responseHeaders[ key.toLowerCase() + " " ];
 					}
-					return match == null ? null : match;
+					return match == null ? null : match.join( ", " );
 				},
 
 				// Raw string
diff --git a/test/data/mock.php b/test/data/mock.php
index 692c417e8c..937e331bff 100644
--- a/test/data/mock.php
+++ b/test/data/mock.php
@@ -114,6 +114,9 @@ ok( true, "mock executed");';
 		header( 'Sample-Header: Hello World' );
 		header( 'Empty-Header: ' );
 		header( 'Sample-Header2: Hello World 2' );
+		header( 'List-Header: Item 1' );
+		header( 'list-header: Item 2' );
+		header( 'constructor: prototype collision (constructor)' );
 
 		foreach ( explode( '|' , $req->query[ 'keys' ] ) as $key ) {
 			// Only echo if key exists in the header
diff --git a/test/middleware-mockserver.js b/test/middleware-mockserver.js
index 35623761de..09371bbe90 100644
--- a/test/middleware-mockserver.js
+++ b/test/middleware-mockserver.js
@@ -132,7 +132,10 @@ var mocks = {
 		resp.writeHead( 200, {
 			"Sample-Header": "Hello World",
 			"Empty-Header": "",
-			"Sample-Header2": "Hello World 2"
+			"Sample-Header2": "Hello World 2",
+			"List-Header": "Item 1",
+			"list-header": "Item 2",
+			"constructor": "prototype collision (constructor)"
 		} );
 		req.query.keys.split( "|" ).forEach( function( key ) {
 			if ( req.headers[ key.toLowerCase() ] ) {
diff --git a/test/unit/ajax.js b/test/unit/ajax.js
index b8b46e245c..f9cd3668d9 100644
--- a/test/unit/ajax.js
+++ b/test/unit/ajax.js
@@ -252,7 +252,7 @@ QUnit.module( "ajax", {
 		} );
 	} );
 
-	ajaxTest( "jQuery.ajax() - headers", 5, function( assert ) {
+	ajaxTest( "jQuery.ajax() - headers", 8, function( assert ) {
 		return {
 			setup: function() {
 				jQuery( document ).ajaxSend( function( evt, xhr ) {
@@ -293,6 +293,9 @@ QUnit.module( "ajax", {
 					assert.strictEqual( emptyHeader, "", "Empty header received" );
 				}
 				assert.strictEqual( xhr.getResponseHeader( "Sample-Header2" ), "Hello World 2", "Second sample header received" );
+				assert.strictEqual( xhr.getResponseHeader( "List-Header" ), "Item 1, Item 2", "List header received" );
+				assert.strictEqual( xhr.getResponseHeader( "constructor" ), "prototype collision (constructor)", "constructor header received" );
+				assert.strictEqual( xhr.getResponseHeader( "__proto__" ), null, "Undefined __proto__ header not received" );
 			}
 		};
 	} );