Use interned strings for websockets

Author: benaadams

src/Middleware/WebSockets/src/Constants.cs

@@ -6,10 +6,9 @@ namespace Microsoft.AspNetCore.WebSockets
     internal static class Constants
     {
         public static class Headers
-        {                  
-            public const string UpgradeWebSocket = "websocket"; 
-            public const string ConnectionUpgrade = "Upgrade";
-            public const string SupportedVersion = "13";
+        {
+            public readonly static string UpgradeWebSocket = "websocket";
+            public readonly static string SupportedVersion = "13";
         }
     }
 }

src/Middleware/WebSockets/src/HandshakeHelpers.cs

@@ -34,7 +34,7 @@ internal static class HandshakeHelpers
         };
 
         // Verify Method, Upgrade, Connection, version,  key, etc..
-        public static bool CheckSupportedWebSocketRequest(string method, List<KeyValuePair<string, string>> headers)
+        public static bool CheckSupportedWebSocketRequest(string method, List<KeyValuePair<string, string>> interestingHeaders, IHeaderDictionary requestHeaders)
         {
             bool validUpgrade = false, validConnection = false, validKey = false, validVersion = false;
 
@@ -43,11 +43,11 @@ public static bool CheckSupportedWebSocketRequest(string method, List<KeyValuePa
                 return false;
             }
 
-            foreach (var pair in headers)
+            foreach (var pair in interestingHeaders)
             {
                 if (string.Equals(HeaderNames.Connection, pair.Key, StringComparison.OrdinalIgnoreCase))
                 {
-                    if (string.Equals(Constants.Headers.ConnectionUpgrade, pair.Value, StringComparison.OrdinalIgnoreCase))
+                    if (string.Equals(HeaderNames.Upgrade, pair.Value, StringComparison.OrdinalIgnoreCase))
                     {
                         validConnection = true;
                     }
@@ -72,12 +72,26 @@ public static bool CheckSupportedWebSocketRequest(string method, List<KeyValuePa
                 }
             }
 
+            // WebSockets are long lived; so if the header values are valid we switch them out for the interned versions.
+            if (validConnection && requestHeaders[HeaderNames.Connection].Count == 1)
+            {
+                requestHeaders[HeaderNames.Connection] = HeaderNames.Upgrade;
+            }
+            if (validUpgrade && requestHeaders[HeaderNames.Upgrade].Count == 1)
+            {
+                requestHeaders[HeaderNames.Upgrade] = Constants.Headers.UpgradeWebSocket;
+            }
+            if (validVersion && requestHeaders[HeaderNames.SecWebSocketVersion].Count == 1)
+            {
+                requestHeaders[HeaderNames.SecWebSocketVersion] = Constants.Headers.SupportedVersion;
+            }
+
             return validConnection && validUpgrade && validVersion && validKey;
         }
 
         public static void GenerateResponseHeaders(string key, string? subProtocol, IHeaderDictionary headers)
         {
-            headers[HeaderNames.Connection] = Constants.Headers.ConnectionUpgrade;
+            headers[HeaderNames.Connection] = HeaderNames.Upgrade;
             headers[HeaderNames.Upgrade] = Constants.Headers.UpgradeWebSocket;
             headers[HeaderNames.SecWebSocketAccept] = CreateResponseKey(key);
             if (!string.IsNullOrWhiteSpace(subProtocol))

src/Middleware/WebSockets/src/WebSocketMiddleware.cs

@@ -118,15 +118,16 @@ public bool IsWebSocketRequest
                         }
                         else
                         {
-                            var headers = new List<KeyValuePair<string, string>>();
-                            foreach (string headerName in HandshakeHelpers.NeededHeaders)
+                            var requestHeaders = _context.Request.Headers;
+                            var interestingHeaders = new List<KeyValuePair<string, string>>();
+                            foreach (var headerName in HandshakeHelpers.NeededHeaders)
                             {
-                                foreach (var value in _context.Request.Headers.GetCommaSeparatedValues(headerName))
+                                foreach (var value in requestHeaders.GetCommaSeparatedValues(headerName))
                                 {
-                                    headers.Add(new KeyValuePair<string, string>(headerName, value));
+                                    interestingHeaders.Add(new KeyValuePair<string, string>(headerName, value));
                                 }
                             }
-                            _isWebSocketRequest = HandshakeHelpers.CheckSupportedWebSocketRequest(_context.Request.Method, headers);
+                            _isWebSocketRequest = HandshakeHelpers.CheckSupportedWebSocketRequest(_context.Request.Method, interestingHeaders, requestHeaders);
                         }
                     }
                     return _isWebSocketRequest.Value;