Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Web/Util/CultureUtil.cs

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+//------------------------------------------------------------------------------
+// <copyright file="CultureUtil.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>                                                                
+//------------------------------------------------------------------------------
+
+namespace System.Web.Util {
+    using System;
+    using System.Globalization;
+
+    // This class contains helper methods for obtaining a CultureInfo instance from a list of candidates.
+
+    internal static class CultureUtil {
+
+        // Given a single culture name, attempts to turn it into a CultureInfo.
+        // If 'requireSpecific' is set, this method attempts to return an object where IsNeutral = false.
+        public static CultureInfo CreateReadOnlyCulture(string cultureName, bool requireSpecific) {
+            if (requireSpecific) {
+                return HttpServerUtility.CreateReadOnlySpecificCultureInfo(cultureName);
+            }
+            else {
+                return HttpServerUtility.CreateReadOnlyCultureInfo(cultureName);
+            }
+        }
+
+        // Given a list of culture names, loop through them until we find one we understand.
+        // We expect 'cultureNames' to be the raw Accept-Languages header value, as we'll strip q-values.
+        // Otherwise equivalent to the single-element overload.
+        public static CultureInfo CreateReadOnlyCulture(string[] cultureNames, bool requireSpecific) {
+            return ExtractCultureImpl(cultureNames, requireSpecific, AppSettings.MaxAcceptLanguageFallbackCount);
+        }
+
+        // for unit testing, uses 'maxCount' instead of the <appSettings> switch
+        internal static CultureInfo ExtractCultureImpl(string[] cultureNames, bool requireSpecific, int maxCount) {
+            int lastIndex = Math.Min(cultureNames.Length, maxCount) - 1;
+
+            for (int i = 0; i < cultureNames.Length; i++) {
+                string candidate = StripQValue(cultureNames[i]);
+
+                try {
+                    return CreateReadOnlyCulture(candidate, requireSpecific);
+                }
+                catch (CultureNotFoundException) {
+                    // If this is the last iteration before giving up, let the exception propagate upward.
+                    // Otherwise just ---- and move on to the next candidate.
+                    if (i == lastIndex) {
+                        throw;
+                    }
+                }
+            }
+
+            return null;
+        }
+
+        // Given an input "foo;q=xx", returns "foo".
+        private static string StripQValue(string input) {
+            if (input != null) {
+                int indexOfSemicolon = input.IndexOf(';');
+                if (indexOfSemicolon >= 0) {
+                    return input.Substring(0, indexOfSemicolon);
+                }
+            }
+            return input;
+        }
+
+    }
+}