Improve exception messages in IPAddress class for (ReadOnlyIPAddress, AddressFamily IPv4/IPv6)

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

@@ -117,4 +117,10 @@
   <data name="PlatformNotSupported_NetPrimitives" xml:space="preserve">
     <value>System.Net.Primitives is not supported on this platform.</value>
   </data>
+  <data name="net_SocketException_OperationNotSupported" xml:space="preserve">
+    <value>The requested property is not supported for the '{0}' AddressFamily.</value>
+  </data>
+  <data name="net_SocketException_OperationNotSupported_ReadOnlyIPAddress" xml:space="preserve">
+    <value>This operation is not supported on a read-only IPAddress instance.</value>
+  </data>
 </root>

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

@@ -438,7 +438,7 @@ public long ScopeId
 
                 if (this is ReadOnlyIPAddress)
                 {
-                    ThrowSocketOperationNotSupported();
+                    ThrowSocketOperationNotSupportedReadOnly();
                 }
 
                 // Consider: Since scope is only valid for link-local and site-local
@@ -668,7 +668,7 @@ public long Address
                 {
                     if (this is ReadOnlyIPAddress)
                     {
-                        ThrowSocketOperationNotSupported();
+                        ThrowSocketOperationNotSupportedReadOnly();
                     }
 
                     PrivateAddress = unchecked((uint)value);
@@ -769,7 +769,10 @@ public IPAddress MapToIPv4()
         private static byte[] ThrowAddressNullException() => throw new ArgumentNullException("address");
 
         [DoesNotReturn]
-        private static void ThrowSocketOperationNotSupported() => throw new SocketException(SocketError.OperationNotSupported);
+        private void ThrowSocketOperationNotSupported() => throw new SocketException(SocketError.OperationNotSupported, SR.Format(SR.net_SocketException_OperationNotSupported, AddressFamily));
+
+        [DoesNotReturn]
+        private static void ThrowSocketOperationNotSupportedReadOnly() => throw new SocketException(SocketError.OperationNotSupported, SR.net_SocketException_OperationNotSupported_ReadOnlyIPAddress);
 
         private sealed class ReadOnlyIPAddress : IPAddress
         {

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

@@ -306,7 +306,7 @@ public static IEnumerable<object[]> GetValidIPAddresses()
         {
             return IPAddressParsingFormatting.ValidIpv4Addresses
                 .Concat(IPAddressParsingFormatting.ValidIpv6Addresses)
-                .Select(array => new object[] {IPAddress.Parse((string)array[0])});
+                .Select(array => new object[] { IPAddress.Parse((string)array[0]) });
         }
 
         public static readonly object[][] GeneratedIPAddresses =
@@ -351,6 +351,34 @@ public static void Address_ReadOnlyStatics_Set_Failure()
             Assert.Throws<SocketException>(() => IPAddress.IPv6Loopback.ScopeId = 1);
             Assert.Throws<SocketException>(() => IPAddress.IPv6None.ScopeId = 1);
         }
+
+        [Fact]
+        public static void ScopeId_Throws_SocketException_IPv4Message()
+        {
+            IPAddress ip = IPV4Address1();
+            SocketException ex = Assert.Throws<SocketException>(() => _ = ip.ScopeId);
+            Assert.Equal(SocketError.OperationNotSupported, ex.SocketErrorCode);
+            Assert.Contains($"'{ip.AddressFamily}' {nameof(AddressFamily)}.", ex.Message, StringComparison.OrdinalIgnoreCase);
+        }
+
+        [Fact]
+        public static void Address_Throws_SocketException_IPv6Message()
+        {
+            IPAddress ip = IPV6Address1();
+            SocketException ex = Assert.Throws<SocketException>(() => _ = ip.Address);
+            Assert.Equal(SocketError.OperationNotSupported, ex.SocketErrorCode);
+            Assert.Contains($"'{ip.AddressFamily}' {nameof(AddressFamily)}.", ex.Message, StringComparison.OrdinalIgnoreCase);
+        }
+
+        [Fact]
+        public static void Address_Throws_SocketException_ReadOnlyMessage()
+        {
+            IPAddress ip1 = IPAddress.Loopback; // This is readonly
+            IPAddress ip2 = IPV4Address1();
+            SocketException ex = Assert.Throws<SocketException>(() => ip1.Address = ip2.Address);
+            Assert.Equal(SocketError.OperationNotSupported, ex.SocketErrorCode);
+            Assert.Contains("read-only", ex.Message, StringComparison.OrdinalIgnoreCase);
+        }
 #pragma warning restore 618
     }
 }