Enable User Agent Extension

src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SqlInternalConnectionTds.cs

@@ -210,9 +210,6 @@ internal bool IsDNSCachingBeforeRedirectSupported
         // Json Support Flag
         internal bool IsJsonSupportEnabled = false;
 
-        // User Agent Flag
-        internal bool IsUserAgentEnabled = true;
-
         // Vector Support Flag
         internal bool IsVectorSupportEnabled = false;
 
@@ -1414,10 +1411,7 @@ private void Login(ServerInfo server, TimeoutTimer timeout, string newPassword,
             requestedFeatures |= TdsEnums.FeatureExtension.SQLDNSCaching;
             requestedFeatures |= TdsEnums.FeatureExtension.JsonSupport;
             requestedFeatures |= TdsEnums.FeatureExtension.VectorSupport;
-
-        #if DEBUG
             requestedFeatures |= TdsEnums.FeatureExtension.UserAgent;
-        #endif
 
             _parser.TdsLogin(login, requestedFeatures, _recoverySessionData, _fedAuthFeatureExtensionData, encrypt);
         }
@@ -3023,6 +3017,12 @@ internal void OnFeatureExtAck(int featureId, byte[] data)
                         IsVectorSupportEnabled = true;
                         break;
                     }
+                case TdsEnums.FEATUREEXT_USERAGENT:
+                    {
+                        // Unexpected ack from server but we ignore it entirely
+                        SqlClientEventSource.Log.TryAdvancedTraceEvent("<sc.SqlInternalConnectionTds.OnFeatureExtAck|ADV> {0}, Received feature extension acknowledgement for USERAGENTSUPPORT (ignored)", ObjectID);
+                        break;
+                    }
 
                 default:
                     {

src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/SqlClient/SqlInternalConnectionTds.cs

@@ -214,9 +214,6 @@ internal bool IsDNSCachingBeforeRedirectSupported
         // Vector Support Flag
         internal bool IsVectorSupportEnabled = false;
 
-        // User Agent Flag
-        internal bool IsUserAgentEnabled = true;
-
         // TCE flags
         internal byte _tceVersionSupported;
 
@@ -3068,7 +3065,18 @@ internal void OnFeatureExtAck(int featureId, byte[] data)
                         IsVectorSupportEnabled = true;
                         break;
                     }
+                case TdsEnums.FEATUREEXT_USERAGENT:
+                    {
+                        // TODO: Verify that the server sends an acknowledgment (Ack)
+                        // using this log message in the future.
 
+                        // This Ack from the server is unexpected and is ignored completely.
+                        // According to the TDS specification, an Ack is not defined/expected
+                        // for this scenario. We handle it only for completeness
+                        // and to support testing.
+                        SqlClientEventSource.Log.TryAdvancedTraceEvent("<sc.SqlInternalConnectionTds.OnFeatureExtAck|ADV> {0}, Received feature extension acknowledgement for USERAGENTSUPPORT (ignored)", ObjectID);
+                        break;
+                    }
                 default:
                     {
                         // Unknown feature ack

src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsEnums.cs

@@ -241,8 +241,7 @@ public enum EnvChangeType : byte
         public const byte FEATUREEXT_SQLDNSCACHING = 0x0B;
         public const byte FEATUREEXT_JSONSUPPORT = 0x0D;
         public const byte FEATUREEXT_VECTORSUPPORT = 0x0E;
-        // TODO: re-verify if this byte competes with another feature
-        public const byte FEATUREEXT_USERAGENT = 0x0F;
+        public const byte FEATUREEXT_USERAGENT = 0x10;
 
         [Flags]
         public enum FeatureExtension : uint

src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsParser.SSPI.cs

@@ -2,6 +2,7 @@
 using System.Buffers;
 using System.Diagnostics;
 using System.Text;
+using Microsoft.Data.SqlClient.UserAgent;
 using Microsoft.Data.SqlClient.Utilities;
 
 #nullable enable
@@ -192,7 +193,19 @@ internal void TdsLogin(
 
                 int feOffset = length;
                 // calculate and reserve the required bytes for the featureEx
-                length = ApplyFeatureExData(requestedFeatures, recoverySessionData, fedAuthFeatureExtensionData, useFeatureExt, length);
+
+                // NOTE: This approach of pre-calculating the packet length is inefficient.
+                // We're making 2 passes over the data to be written.
+                // Instead, we should be writing everything to the buffer once,
+                // leaving a hole where the header length goes. 
+                length = ApplyFeatureExData(
+                    requestedFeatures, 
+                    recoverySessionData, 
+                    fedAuthFeatureExtensionData,
+                    UserAgentInfo.UserAgentCachedJsonPayload.ToArray(),
+                    useFeatureExt, 
+                    length
+                    );
 
                 WriteLoginData(rec,
                                requestedFeatures,

src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsParser.cs

@@ -29,6 +29,8 @@
 using Microsoft.Data.SqlClient.DataClassification;
 using Microsoft.Data.SqlClient.LocalDb;
 using Microsoft.Data.SqlClient.Server;
+using Microsoft.Data.SqlClient.UserAgent;
+
 #if NETFRAMEWORK
 using Microsoft.Data.SqlTypes;
 #endif
@@ -9235,7 +9237,15 @@ private void WriteLoginData(SqlLogin rec,
                     }
                 }
 
-                ApplyFeatureExData(requestedFeatures, recoverySessionData, fedAuthFeatureExtensionData, useFeatureExt, length, true);
+                ApplyFeatureExData(
+                    requestedFeatures, 
+                    recoverySessionData, 
+                    fedAuthFeatureExtensionData,
+                    UserAgentInfo.UserAgentCachedJsonPayload.ToArray(),
+                    useFeatureExt, 
+                    length, 
+                    true
+                    );
             }
             catch (Exception e)
             {
@@ -9254,6 +9264,7 @@ private void WriteLoginData(SqlLogin rec,
         private int ApplyFeatureExData(TdsEnums.FeatureExtension requestedFeatures,
                                        SessionData recoverySessionData,
                                        FederatedAuthenticationFeatureExtensionData fedAuthFeatureExtensionData,
+                                       byte[] userAgentJsonPayload,
                                        bool useFeatureExt,
                                        int length,
                                        bool write = false)
@@ -9262,6 +9273,11 @@ private int ApplyFeatureExData(TdsEnums.FeatureExtension requestedFeatures,
             {
                 checked
                 {
+                    // NOTE: As part of TDS spec UserAgent feature extension should be the first feature extension in the list.
+                    if ((requestedFeatures & TdsEnums.FeatureExtension.UserAgent) != 0)
+                    {
+                        length += WriteUserAgentFeatureRequest(userAgentJsonPayload, write);
+                    }
                     if ((requestedFeatures & TdsEnums.FeatureExtension.SessionRecovery) != 0)
                     {
                         length += WriteSessionRecoveryFeatureRequest(recoverySessionData, write);

src/Microsoft.Data.SqlClient/tests/UnitTests/SimulatedServerTests/ConnectionTests.cs

@@ -828,5 +828,81 @@ public void TestConnWithVectorFeatExtVersionNegotiation(bool expectedConnectionR
                 Assert.Throws<InvalidOperationException>(() => connection.Open());
             }
         }
+
+        // Test to verify that the client sends a UserAgent version
+        // and driver behaves correctly even if server sent an Ack
+        [Theory]
+        [InlineData(false)] // We do not force test server to send an Ack
+        [InlineData(true)] // Server is forced to send an Ack
+        public void TestConnWithUserAgentFeatureExtension(bool forceAck)
+        {
+            using var server = new TdsServer();
+            server.Start();
+
+            // Configure the server to support UserAgent version 0x01
+            server.ServerSupportedUserAgentFeatureExtVersion = 0x01;
+
+            // Opt in to forced ACK for UserAgentSupport (no negotiation)
+            server.EnableUserAgentFeatureExt = forceAck;
+
+            bool loginFound = false;
+
+            // Captured from LOGIN7 as parsed by the test server
+            byte observedVersion = 0;
+            byte[] observedJsonBytes = Array.Empty<byte>();
+
+            // Inspect what the client sends in the LOGIN7 packet
+            server.OnLogin7Validated = loginToken =>
+            {
+                var tdsFeatureExt = loginToken.FeatureExt
+                                      .OfType<TDSLogin7GenericOptionToken>().ToArray();
+                var token = tdsFeatureExt?.FirstOrDefault(t => t.FeatureID == TDSFeatureID.UserAgentSupport);
+
+                Assert.Equal(TDSFeatureID.UserAgentSupport, tdsFeatureExt?[0].FeatureID);
+                Assert.NotNull(token);
+                var data = token.Data;
+                Assert.True(data.Length >= 2);
+
+                observedVersion = data[0];
+                observedJsonBytes = data.AsSpan(1).ToArray();
+                loginFound = true;
+            };
+
+            // Connect to the test TDS server.
+            var connStr = new SqlConnectionStringBuilder
+            {
+                DataSource = $"localhost,{server.EndPoint.Port}",
+                Encrypt = SqlConnectionEncryptOption.Optional,
+            }.ConnectionString;
+
+            // TODO: Confirm the server sent an Ack by reading log message from SqlInternalConnectionTds
+            using var connection = new SqlConnection(connStr);
+            connection.Open();
+
+            // Verify the connection itself succeeded
+            Assert.Equal(ConnectionState.Open, connection.State);
+
+            // Verify client did offer UserAgent
+            Assert.True(loginFound, "Expected UserAgent extension in LOGIN7");
+            Assert.Equal(0x1, observedVersion);
+
+            // Note: Accessing UserAgentInfo via Reflection.
+            // We cannot use InternalsVisibleTo here because making internals visible to FunctionalTests
+            // causes the *.TestHarness.cs stubs to clash with the real internal types in SqlClient.
+            var asm = typeof(SqlConnection).Assembly;
+            var userAgentInfoType =
+                asm.GetTypes().FirstOrDefault(t => string.Equals(t.Name, "UserAgentInfo", StringComparison.Ordinal)) ??
+                asm.GetTypes().FirstOrDefault(t => t.FullName?.EndsWith(".UserAgentInfo", StringComparison.Ordinal) == true);
+
+            Assert.NotNull(userAgentInfoType);
+
+            // Try to get the property
+            var prop = userAgentInfoType.GetProperty("UserAgentCachedJsonPayload",
+                BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic);
+            Assert.NotNull(prop);
+
+            ReadOnlyMemory<byte> cachedPayload = (ReadOnlyMemory<byte>)prop.GetValue(null)!;
+            Assert.Equal(cachedPayload.ToArray(), observedJsonBytes.ToArray());
+        }
     }
 }

src/Microsoft.Data.SqlClient/tests/tools/TDS/TDS.EndPoint/ITDSServerSession.cs

@@ -93,5 +93,10 @@ public interface ITDSServerSession
         /// Indicates whether the client supports Vector column type
         /// </summary>
         bool IsVectorSupportEnabled { get; set; }
+
+        /// <summary>
+        /// Indicates whether the client supports UserAgent
+        /// </summary>
+        bool IsUserAgentSupportEnabled { get; set; }
     }
 }