Imported Upstream version 4.0.0~alpha1

Former-commit-id: 806294f5ded97629b74c85c09952f2a74fe182d9

external/referencesource/System.Web.Extensions/Util/HeaderUtility.cs

@@ -0,0 +1,37 @@
+//------------------------------------------------------------------------------
+// <copyright file="HeaderUtility.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+//------------------------------------------------------------------------------
+ 
+namespace System.Web.Util {
+    using System;
+
+    internal static class HeaderUtility {
+        public static bool IsEncodingInAcceptList(string acceptEncodingHeader, string expectedEncoding) {
+            if (String.IsNullOrEmpty(acceptEncodingHeader)) {
+                return false;
+            }
+
+            foreach (string encoding in acceptEncodingHeader.Split(',')) {
+                string e = encoding.Trim();
+
+                // This code will typically handle all existing browsers, which
+                // use "encoding1, encoding2" for this header.
+                // IE, Firefox and Safari are sending "gzip, deflate"
+                // Opera is sending "deflate, gzip, x-gzip, identity, *;q=0"
+                // There is a currently hypothetical case where a browser would use the quantified syntax
+                // on specific encodings ("encoding1;q=0.8, encoding2 ;q=0.2") which we don't handle here.
+                // For those situations, the browser would get the uncompressed version.
+                // See RFC 2068 for details.
+                if (String.Equals(e, expectedEncoding, StringComparison.Ordinal)) {
+                    return true;
+                }
+            }
+
+            // no match found
+            return false;
+        }
+
+    }
+}