Add plumbing to get a connection's instance name.

edwardneal · edwardneal · commit 8ea6742bfc75 · 2026-01-24T22:11:49.000Z
diff --git a/src/Microsoft.Data.SqlClient/netcore/src/Microsoft.Data.SqlClient.csproj b/src/Microsoft.Data.SqlClient/netcore/src/Microsoft.Data.SqlClient.csproj
@@ -1031,6 +1031,9 @@
     <Compile Include="$(CommonSourceRoot)Resources\StringsHelper.cs">
       <Link>Resources\StringsHelper.cs</Link>
     </Compile>
+    <Compile Include="$(CommonSourceRoot)System\Text\EncodingExtensions.cs">
+      <Link>System\Text\EncodingExtensions.cs</Link>
+    </Compile>
     <Compile Include="$(CommonSourceRoot)TypeForwards.netcore.cs">
       <Link>TypeForwards.netcore.cs</Link>
     </Compile>
diff --git a/src/Microsoft.Data.SqlClient/netfx/src/Microsoft.Data.SqlClient.csproj b/src/Microsoft.Data.SqlClient/netfx/src/Microsoft.Data.SqlClient.csproj
@@ -1020,6 +1020,9 @@
     <Compile Include="$(CommonSourceRoot)System\IO\StreamExtensions.netfx.cs">
       <Link>System\IO\StreamExtensions.netfx.cs</Link>
     </Compile>
+    <Compile Include="$(CommonSourceRoot)System\Text\EncodingExtensions.cs">
+      <Link>System\Text\EncodingExtensions.cs</Link>
+    </Compile>
     <Compile Include="$(CommonSourceRoot)System\Runtime\CompilerServices\IsExternalInit.netfx.cs">
       <Link>System\Runtime\CompilerServices\IsExternalInit.netfx.cs</Link>
     </Compile>
diff --git a/src/Microsoft.Data.SqlClient/src/Interop/Windows/Sni/SniNativeWrapper.cs b/src/Microsoft.Data.SqlClient/src/Interop/Windows/Sni/SniNativeWrapper.cs
@@ -171,7 +171,7 @@ internal static unsafe uint SniOpenSyncEx(
             string connString,
             ref IntPtr pConn,
             ref string spn,
-            byte[] instanceName,
+            ref string instanceName,
             bool fOverrideCache,
             bool fSync,
             int timeout,
@@ -186,9 +186,13 @@ internal static unsafe uint SniOpenSyncEx(
             SQLDNSInfo cachedDnsInfo,
             string hostNameInCertificate)
         {
-            fixed (byte* pInstanceName = instanceName)
+            // Size of this buffer is as specified by netlibs.
+            ReadOnlySpan<byte> instanceNameBuffer = stackalloc byte[256];
+
+            fixed (byte* pInstanceName = instanceNameBuffer)
             {
                 SniClientConsumerInfo clientConsumerInfo = new SniClientConsumerInfo();
+                uint result;
 
                 // initialize client ConsumerInfo part first
                 MarshalConsumerInfo(consumerInfo, ref clientConsumerInfo.ConsumerInfo);
@@ -197,7 +201,7 @@ internal static unsafe uint SniOpenSyncEx(
                 clientConsumerInfo.HostNameInCertificate = hostNameInCertificate;
                 clientConsumerInfo.networkLibrary = Prefix.UNKNOWN_PREFIX;
                 clientConsumerInfo.szInstanceName = pInstanceName;
-                clientConsumerInfo.cchInstanceName = (uint)instanceName.Length;
+                clientConsumerInfo.cchInstanceName = (uint)instanceNameBuffer.Length;
                 clientConsumerInfo.fOverrideLastConnectCache = fOverrideCache;
                 clientConsumerInfo.fSynchronousConnection = fSync;
                 clientConsumerInfo.timeout = timeout;
@@ -236,22 +240,21 @@ internal static unsafe uint SniOpenSyncEx(
                     {
                         // An empty string implies we need to find the SPN so we supply a buffer for the max size
                         var array = ArrayPool<byte>.Shared.Rent(SniMaxComposedSpnLength);
-                        array.AsSpan().Clear();
+                        Span<byte> arraySpan = array.AsSpan();
 
+                        arraySpan.Clear();
                         try
                         {
-                            fixed (byte* pin_spnBuffer = array)
+                            fixed (byte* pin_spnBuffer = arraySpan)
                             {
                                 clientConsumerInfo.szSPN = pin_spnBuffer;
                                 clientConsumerInfo.cchSPN = (uint)SniMaxComposedSpnLength;
 
-                                var result = s_nativeMethods.SniOpenSyncExWrapper(ref clientConsumerInfo, out pConn);
-                                if (result == 0)
+                                result = s_nativeMethods.SniOpenSyncExWrapper(ref clientConsumerInfo, out pConn);
+                                if (result is TdsEnums.SNI_SUCCESS)
                                 {
-                                    spn = Encoding.Unicode.GetString(array).TrimEnd('\0');
+                                    spn = Encoding.Unicode.CreateStringFromNullTerminated(arraySpan);
                                 }
-
-                                return result;
                             }
                         }
                         finally
@@ -275,7 +278,7 @@ internal static unsafe uint SniOpenSyncEx(
                             {
                                 clientConsumerInfo.szSPN = pin_spnBuffer;
                                 clientConsumerInfo.cchSPN = (uint)writer.WrittenCount;
-                                return s_nativeMethods.SniOpenSyncExWrapper(ref clientConsumerInfo, out pConn);
+                                result = s_nativeMethods.SniOpenSyncExWrapper(ref clientConsumerInfo, out pConn);
                             }
                         }
                         finally
@@ -284,9 +287,18 @@ internal static unsafe uint SniOpenSyncEx(
                         }
                     }
                 }
+                else
+                {
+                    // Otherwise leave szSPN null (SQL Auth)
+                    result = s_nativeMethods.SniOpenSyncExWrapper(ref clientConsumerInfo, out pConn);
+                }
+
+                if (result is TdsEnums.SNI_SUCCESS)
+                {
+                    instanceName = Encoding.UTF8.CreateStringFromNullTerminated(instanceNameBuffer);
+                }
 
-                // Otherwise leave szSPN null (SQL Auth)
-                return s_nativeMethods.SniOpenSyncExWrapper(ref clientConsumerInfo, out pConn);
+                return result;
             }
         }
 
diff --git a/src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/Connection/SqlConnectionInternal.cs b/src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/Connection/SqlConnectionInternal.cs
@@ -601,6 +601,8 @@ internal bool IgnoreEnvChange
 
         internal string UserInstanceName { get; private set; } = string.Empty;
 
+        internal string InstanceName { get; set; }
+
         internal bool Is2008OrNewer
         {
             get => _parser.Is2008OrNewer;
diff --git a/src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/ManagedSni/SniProxy.netcore.cs b/src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/ManagedSni/SniProxy.netcore.cs
@@ -49,7 +49,7 @@ internal class SniProxy
         internal static SniHandle CreateConnectionHandle(
             string fullServerName,
             TimeoutTimer timeout,
-            out byte[] instanceName,
+            out string instanceName,
             out ResolvedServerSpn resolvedSpn,
             string serverSPN,
             bool flushCache,
@@ -63,7 +63,7 @@ internal static SniHandle CreateConnectionHandle(
             string hostNameInCertificate,
             string serverCertificateFilename)
         {
-            instanceName = new byte[1];
+            instanceName = null;
             resolvedSpn = default;
 
             bool errorWithLocalDBProcessing;
@@ -99,6 +99,8 @@ internal static SniHandle CreateConnectionHandle(
                     break;
             }
 
+            instanceName = details.InstanceName;
+
             if (isIntegratedSecurity)
             {
                 try
diff --git a/src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsParser.cs b/src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsParser.cs
@@ -449,7 +449,7 @@ bool withFailover
                 trustServerCert = false;
             }
 
-            byte[] instanceName = null;
+            string instanceName = null;
 
             Debug.Assert(_connHandler != null, "SqlConnectionInternalTds handler can not be null at this point.");
             _connHandler.TimeoutErrorInternal.EndPhase(SqlConnectionTimeoutErrorPhase.PreLoginBegin);
@@ -490,6 +490,7 @@ bool withFailover
             }
 
             _connHandler.pendingSQLDNSObject = null;
+            _connHandler.InstanceName = null;
 
             // AD Integrated behaves like Windows integrated when connecting to a non-fedAuth server
             _physicalStateObj.CreatePhysicalSNIHandle(
@@ -569,7 +570,7 @@ bool withFailover
 
             // UNDONE - send "" for instance now, need to fix later
             SqlClientEventSource.Log.TryTraceEvent("<sc.TdsParser.Connect|SEC> Sending prelogin handshake");
-            SendPreLoginHandshake(instanceName, encrypt, integratedSecurity, serverCertificateFilename);
+            SendPreLoginHandshake(encrypt, integratedSecurity, serverCertificateFilename);
 
             _connHandler.TimeoutErrorInternal.EndPhase(SqlConnectionTimeoutErrorPhase.SendPreLoginHandshake);
             _connHandler.TimeoutErrorInternal.SetAndBeginPhase(SqlConnectionTimeoutErrorPhase.ConsumePreLoginHandshake);
@@ -629,7 +630,7 @@ bool withFailover
                     _physicalStateObj.AssignPendingDNSInfo(serverInfo.UserProtocol, FQDNforDNSCache, ref _connHandler.pendingSQLDNSObject);
                 }
 
-                SendPreLoginHandshake(instanceName, encrypt, integratedSecurity, serverCertificateFilename);
+                SendPreLoginHandshake(encrypt, integratedSecurity, serverCertificateFilename);
                 status = ConsumePreLoginHandshake(
                     encrypt,
                     trustServerCert,
@@ -649,6 +650,7 @@ bool withFailover
             }
             SqlClientEventSource.Log.TryTraceEvent("<sc.TdsParser.Connect|SEC> Prelogin handshake successful");
 
+            _connHandler.InstanceName = instanceName;
             if (_authenticationProvider is { })
             {
                 _authenticationProvider.Initialize(serverInfo, _physicalStateObj, this, resolvedServerSpn.Primary, resolvedServerSpn.Secondary);
@@ -773,7 +775,6 @@ internal void PutSession(TdsParserStateObject session)
         }
 
         private void SendPreLoginHandshake(
-            byte[] instanceName,
             SqlConnectionEncryptOption encrypt,
             bool integratedSecurity,
             string serverCertificateFilename)
@@ -868,21 +869,12 @@ private void SendPreLoginHandshake(
                         break;
 
                     case (int)PreLoginOptions.INSTANCE:
-                        int i = 0;
+                        // Always send an empty null-terminated string
+                        payload[payloadLength] = 0;
 
-                        while (instanceName[i] != 0)
-                        {
-                            payload[payloadLength] = instanceName[i];
-                            payloadLength++;
-                            i++;
-                        }
-
-                        payload[payloadLength] = 0; // null terminate
                         payloadLength++;
-                        i++;
-
-                        offset += i;
-                        optionDataSize = i;
+                        offset += 1;
+                        optionDataSize = 1;
                         break;
 
                     case (int)PreLoginOptions.THREADID:
diff --git a/src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsParserSafeHandles.windows.cs b/src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsParserSafeHandles.windows.cs
@@ -146,7 +146,7 @@ internal SNIHandle(
             string serverName,
             ref string spn,
             int timeout,
-            out byte[] instanceName,
+            out string instanceName,
             bool flushCache,
             bool fSync,
             bool fParallel,
@@ -160,7 +160,7 @@ internal SNIHandle(
             : base(IntPtr.Zero, true)
         {
             _fSync = fSync;
-            instanceName = new byte[256]; // Size as specified by netlibs.
+            instanceName = null;
             // Option ignoreSniOpenTimeout is no longer available
             //if (ignoreSniOpenTimeout)
             //{
@@ -177,7 +177,7 @@ internal SNIHandle(
                 serverName,
                 ref base.handle,
                 ref spn,
-                instanceName,
+                ref instanceName,
                 flushCache,
                 fSync,
                 timeout,
@@ -193,7 +193,7 @@ internal SNIHandle(
                 serverName,
                 ref base.handle,
                 ref spn,
-                instanceName,
+                ref instanceName,
                 flushCache,
                 fSync,
                 timeout,
diff --git a/src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsParserStateObject.cs b/src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsParserStateObject.cs
@@ -556,7 +556,7 @@ internal long TimeoutTime
         internal abstract void CreatePhysicalSNIHandle(
             string serverName,
             TimeoutTimer timeout,
-            out byte[] instanceName,
+            out string instanceName,
             out ResolvedServerSpn resolvedSpn,
             bool flushCache,
             bool async,
diff --git a/src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsParserStateObjectManaged.netcore.cs b/src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsParserStateObjectManaged.netcore.cs
@@ -82,7 +82,7 @@ protected override uint SniPacketGetData(PacketHandle packet, byte[] inBuff, ref
         internal override void CreatePhysicalSNIHandle(
             string serverName,
             TimeoutTimer timeout,
-            out byte[] instanceName,
+            out string instanceName,
             out ResolvedServerSpn resolvedSpn,
             bool flushCache,
             bool async,
diff --git a/src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsParserStateObjectNative.windows.cs b/src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsParserStateObjectNative.windows.cs
@@ -139,7 +139,7 @@ private ConsumerInfo CreateConsumerInfo(bool async)
         internal override void CreatePhysicalSNIHandle(
             string serverName,
             TimeoutTimer timeout,
-            out byte[] instanceName,
+            out string instanceName,
             out ManagedSni.ResolvedServerSpn resolvedSpn,
             bool flushCache,
             bool async,
diff --git a/src/Microsoft.Data.SqlClient/src/System/Text/EncodingExtensions.cs b/src/Microsoft.Data.SqlClient/src/System/Text/EncodingExtensions.cs
@@ -0,0 +1,72 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Diagnostics;
+
+namespace System.Text;
+
+internal static class EncodingExtensions
+{
+    private const byte NullByte = 0x00;
+    private static ReadOnlySpan<byte> MultiByteNull => [NullByte, NullByte];
+
+    /// <summary>
+    /// Creates a new string from a null-terminated sequence of bytes, decoding them using the specified encoding.
+    /// </summary>
+    /// <param name="encoding">The encoding to use to decode the bytes.</param>
+    /// <param name="nullTerminatedBytes">The null-terminated sequence of bytes to decode.</param>
+    /// <returns>The decoded string.</returns>
+    public static unsafe string CreateStringFromNullTerminated(this Encoding encoding, ReadOnlySpan<byte> nullTerminatedBytes)
+    {
+        int preNullBytes = nullTerminatedBytes.IndexOf(MultiByteNull);
+
+        // If the sequence starts with a null terminator, avoid allocating a new zero-length string.
+        if (preNullBytes == 0 || nullTerminatedBytes.Length == 0)
+        {
+            return string.Empty;
+        }
+
+        // IndexOf has searched for a multi-byte null terminator. This will work in most circumstances, assuming that
+        // every value after the end of the string is zeroed out.
+        if (preNullBytes == -1)
+        {
+            // If the byte sequence is [NullByte], we're in the same position as before. Return an empty string.
+            if (nullTerminatedBytes.Length == 1
+                && nullTerminatedBytes[0] == NullByte)
+            {
+                return string.Empty;
+            }
+            // If the byte sequence is only long enough to contain an encoded string followed by a single null byte,
+            // adjust the null index to account for the false positive.
+            else if (nullTerminatedBytes.Length > 1
+                && nullTerminatedBytes[nullTerminatedBytes.Length - 1] == NullByte)
+            {
+                preNullBytes = nullTerminatedBytes.Length - 1;
+            }
+            // Otherwise, there is no null terminator. Use the entire byte array.
+            else
+            {                
+                preNullBytes = nullTerminatedBytes.Length;
+            }
+        }
+        // If we work with unicode encodings and strings containing nothing but ASCII characters, every other byte will
+        // be a null byte. In such a case, the last byte of the string will be null. This means that preNullBytes will be
+        // one byte too long. Adjust to account for that.
+        else if (encoding is UnicodeEncoding)
+        {
+            if (preNullBytes % 2 != 0)
+            {
+                // If we have a match, we already know that it'll be less than or equal to [array size - search string length].
+                Debug.Assert(preNullBytes + 1 <= nullTerminatedBytes.Length);
+
+                preNullBytes++;
+            }
+        }
+
+        fixed (byte* pBytes = nullTerminatedBytes)
+        {
+            return encoding.GetString(pBytes, preNullBytes);
+        }
+    }
+}

Original file line number	Diff line number	Diff line change
`@@ -171,7 +171,7 @@ internal static unsafe uint SniOpenSyncEx(`
`171`	`171`	`string connString,`
`172`	`172`	`ref IntPtr pConn,`
`173`	`173`	`ref string spn,`
`174`		`- byte[] instanceName,`
	`174`	`+ ref string instanceName,`
`175`	`175`	`bool fOverrideCache,`
`176`	`176`	`bool fSync,`
`177`	`177`	`int timeout,`
`@@ -186,9 +186,13 @@ internal static unsafe uint SniOpenSyncEx(`
`186`	`186`	`SQLDNSInfo cachedDnsInfo,`
`187`	`187`	`string hostNameInCertificate)`
`188`	`188`	`{`
`189`		`- fixed (byte* pInstanceName = instanceName)`
	`189`	`+ // Size of this buffer is as specified by netlibs.`
	`190`	`+ ReadOnlySpan<byte> instanceNameBuffer = stackalloc byte[256];`
	`191`	`+`
	`192`	`+ fixed (byte* pInstanceName = instanceNameBuffer)`
`190`	`193`	`{`
`191`	`194`	`SniClientConsumerInfo clientConsumerInfo = new SniClientConsumerInfo();`
	`195`	`+ uint result;`
`192`	`196`
`193`	`197`	`// initialize client ConsumerInfo part first`
`194`	`198`	`MarshalConsumerInfo(consumerInfo, ref clientConsumerInfo.ConsumerInfo);`
`@@ -197,7 +201,7 @@ internal static unsafe uint SniOpenSyncEx(`
`197`	`201`	`clientConsumerInfo.HostNameInCertificate = hostNameInCertificate;`
`198`	`202`	`clientConsumerInfo.networkLibrary = Prefix.UNKNOWN_PREFIX;`
`199`	`203`	`clientConsumerInfo.szInstanceName = pInstanceName;`
`200`		`- clientConsumerInfo.cchInstanceName = (uint)instanceName.Length;`
	`204`	`+ clientConsumerInfo.cchInstanceName = (uint)instanceNameBuffer.Length;`
`201`	`205`	`clientConsumerInfo.fOverrideLastConnectCache = fOverrideCache;`
`202`	`206`	`clientConsumerInfo.fSynchronousConnection = fSync;`
`203`	`207`	`clientConsumerInfo.timeout = timeout;`
`@@ -236,22 +240,21 @@ internal static unsafe uint SniOpenSyncEx(`
`236`	`240`	`{`
`237`	`241`	`// An empty string implies we need to find the SPN so we supply a buffer for the max size`
`238`	`242`	`var array = ArrayPool<byte>.Shared.Rent(SniMaxComposedSpnLength);`
`239`		`- array.AsSpan().Clear();`
	`243`	`+ Span<byte> arraySpan = array.AsSpan();`
`240`	`244`
	`245`	`+ arraySpan.Clear();`
`241`	`246`	`try`
`242`	`247`	`{`
`243`		`- fixed (byte* pin_spnBuffer = array)`
	`248`	`+ fixed (byte* pin_spnBuffer = arraySpan)`
`244`	`249`	`{`
`245`	`250`	`clientConsumerInfo.szSPN = pin_spnBuffer;`
`246`	`251`	`clientConsumerInfo.cchSPN = (uint)SniMaxComposedSpnLength;`
`247`	`252`
`248`		`- var result = s_nativeMethods.SniOpenSyncExWrapper(ref clientConsumerInfo, out pConn);`
`249`		`- if (result == 0)`
	`253`	`+ result = s_nativeMethods.SniOpenSyncExWrapper(ref clientConsumerInfo, out pConn);`
	`254`	`+ if (result is TdsEnums.SNI_SUCCESS)`
`250`	`255`	`{`
`251`		`- spn = Encoding.Unicode.GetString(array).TrimEnd('\0');`
	`256`	`+ spn = Encoding.Unicode.CreateStringFromNullTerminated(arraySpan);`
`252`	`257`	`}`
`253`		`-`
`254`		`- return result;`
`255`	`258`	`}`
`256`	`259`	`}`
`257`	`260`	`finally`
`@@ -275,7 +278,7 @@ internal static unsafe uint SniOpenSyncEx(`
`275`	`278`	`{`
`276`	`279`	`clientConsumerInfo.szSPN = pin_spnBuffer;`
`277`	`280`	`clientConsumerInfo.cchSPN = (uint)writer.WrittenCount;`
`278`		`- return s_nativeMethods.SniOpenSyncExWrapper(ref clientConsumerInfo, out pConn);`
	`281`	`+ result = s_nativeMethods.SniOpenSyncExWrapper(ref clientConsumerInfo, out pConn);`
`279`	`282`	`}`
`280`	`283`	`}`
`281`	`284`	`finally`
`@@ -284,9 +287,18 @@ internal static unsafe uint SniOpenSyncEx(`
`284`	`287`	`}`
`285`	`288`	`}`
`286`	`289`	`}`
	`290`	`+ else`
	`291`	`+ {`
	`292`	`+ // Otherwise leave szSPN null (SQL Auth)`
	`293`	`+ result = s_nativeMethods.SniOpenSyncExWrapper(ref clientConsumerInfo, out pConn);`
	`294`	`+ }`
	`295`	`+`
	`296`	`+ if (result is TdsEnums.SNI_SUCCESS)`
	`297`	`+ {`
	`298`	`+ instanceName = Encoding.UTF8.CreateStringFromNullTerminated(instanceNameBuffer);`
	`299`	`+ }`
`287`	`300`
`288`		`- // Otherwise leave szSPN null (SQL Auth)`
`289`		`- return s_nativeMethods.SniOpenSyncExWrapper(ref clientConsumerInfo, out pConn);`
	`301`	`+ return result;`
`290`	`302`	`}`
`291`	`303`	`}`
`292`	`304`
Original file line number	Diff line number	Diff line change
`@@ -601,6 +601,8 @@ internal bool IgnoreEnvChange`
`601`	`601`
`602`	`602`	`internal string UserInstanceName { get; private set; } = string.Empty;`
`603`	`603`
	`604`	`+ internal string InstanceName { get; set; }`
	`605`	`+`
`604`	`606`	`internal bool Is2008OrNewer`
`605`	`607`	`{`
`606`	`608`	`get => _parser.Is2008OrNewer;`