Add NetworkError.TimedOut, rename Unknown to Other (#40841)

Adds NetworkError.TimedOut,
Renames Unknown to Other assuming my proposal gets accepted, will revert if not,
Improves exception message

src/libraries/Common/src/System/Net/NetworkErrorHelper.cs

@@ -18,7 +18,8 @@ internal static NetworkException MapSocketException(SocketException socketExcept
                 SocketError.OperationAborted => NetworkError.OperationAborted,
                 SocketError.ConnectionAborted => NetworkError.ConnectionAborted,
                 SocketError.ConnectionReset => NetworkError.ConnectionReset,
-                _ => NetworkError.Unknown
+                SocketError.TimedOut => NetworkError.TimedOut,
+                _ => NetworkError.Other
             };
 
             return new NetworkException(error, socketException);

src/libraries/System.Net.Connections/tests/System.Net.Connections.Tests/Sockets/SocketsConnectionFactoryTests.cs

@@ -134,8 +134,8 @@ public async Task ConnectAsync_TimedOut_ThrowsNetworkException()
 
             IPEndPoint doesNotExist = new IPEndPoint(IPAddress.Parse("1.2.3.4"), 23);
 
-            // SocketError.TimedOut currently maps to SocketError.Unknown, so no asserion
-            await Assert.ThrowsAsync<NetworkException>(() => factory.ConnectAsync(doesNotExist).AsTask());
+            NetworkException ex = await Assert.ThrowsAsync<NetworkException>(() => factory.ConnectAsync(doesNotExist).AsTask());
+            Assert.Equal(NetworkError.TimedOut, ex.NetworkError);
         }
 
         // On Windows, connection timeout takes 21 seconds. Abusing this behavior to test the cancellation logic

src/libraries/System.Net.Primitives/ref/System.Net.Primitives.cs

@@ -324,9 +324,10 @@ protected TransportContext() { }
     }
     public enum NetworkError : int
     {
-        Unknown = 0,
+        Other = 0,
         EndPointInUse,
         HostNotFound,
+        TimedOut,
         ConnectionRefused,
         OperationAborted,
         ConnectionAborted,

src/libraries/System.Net.Primitives/src/Resources/Strings.resx

@@ -114,8 +114,8 @@
   <data name="bad_endpoint_string" xml:space="preserve">
     <value>An invalid IPEndPoint was specified.</value>
   </data>
-  <data name="networkerror_unknown" xml:space="preserve">
-    <value>An unknown network error occurred.</value>
+  <data name="networkerror_other" xml:space="preserve">
+    <value>A network error has occured, see InnerException for more details.</value>
   </data>
   <data name="networkerror_addressinuse" xml:space="preserve">
     <value>The requested EndPoint is already in use.</value>
@@ -135,4 +135,7 @@
   <data name="networkerror_connectionreset" xml:space="preserve">
     <value>The connection was forcibly closed by the remote host.</value>
   </data>
+  <data name="networkerror_timedout" xml:space="preserve">
+    <value>The connection attempt has timed out.</value>
+  </data>
 </root>

src/libraries/System.Net.Primitives/src/System/Net/NetworkError.cs

@@ -6,15 +6,22 @@ namespace System.Net
     /// <summary>Defines a set of error codes for use with <see cref='System.Net.NetworkException'/>.</summary>
     public enum NetworkError : int
     {
-        /// <summary>An unknown network error occurred.</summary>
-        Unknown = 0,
+        /// <summary>A network error has occurred.</summary>
+        /// <remarks>
+        /// This value indicates a non-generic, implementation-specific error.
+        /// Details could be obtained from <see cref="NetworkException"/>'s inner exception.
+        /// </remarks>
+        Other = 0,
 
         /// <summary>The requested EndPoint is already in use.</summary>
         EndPointInUse,
 
         /// <summary>No such host is known.</summary>
         HostNotFound,
 
+        /// <summary>The connection attempt has timed out.</summary>
+        TimedOut,
+
         /// <summary>No connection could be made because the remote host actively refused it.</summary>
         ConnectionRefused,
 

src/libraries/System.Net.Primitives/src/System/Net/NetworkException.cs

@@ -41,12 +41,13 @@ public override void GetObjectData(SerializationInfo serializationInfo, Streamin
         private static string GetExceptionMessage(NetworkError error) => error switch
         {
             NetworkError.EndPointInUse => SR.networkerror_addressinuse,
+            NetworkError.TimedOut => SR.networkerror_timedout,
             NetworkError.HostNotFound => SR.networkerror_hostnotfound,
             NetworkError.ConnectionRefused => SR.networkerror_connectionrefused,
             NetworkError.ConnectionAborted => SR.networkerror_connectionaborted,
             NetworkError.ConnectionReset => SR.networkerror_connectionreset,
             NetworkError.OperationAborted => SR.networkerror_operationaborted,
-            _ => SR.networkerror_unknown
+            _ => SR.networkerror_other
         };
     }
 }

src/libraries/System.Net.Primitives/tests/FunctionalTests/NetworkExceptionTest.cs

@@ -25,7 +25,7 @@ public static void Create_InnerExceptionAndMessage_Success()
             const string Message = "Hello";
             Exception inner = new Exception();
 
-            NetworkException e = new NetworkException(Message, NetworkError.Unknown, inner);
+            NetworkException e = new NetworkException(Message, NetworkError.Other, inner);
 
             Assert.Equal(inner, e.InnerException);
             Assert.Equal(Message, e.Message);

src/libraries/System.Net.Sockets/src/System/Net/Sockets/NetworkStream.cs

@@ -795,7 +795,7 @@ private void ThrowIfDisposed()
 
         private static NetworkException GetCustomNetworkException(string message, Exception? innerException = null)
         {
-            return new NetworkException(message, NetworkError.Unknown, innerException);
+            return new NetworkException(message, NetworkError.Other, innerException);
         }
     }
 }