From 58a989198ca46388bddb40cf83d13a35bb3d8244 Mon Sep 17 00:00:00 2001
From: midhun <midhun@bakedev>
Date: Tue, 1 Apr 2025 12:35:31 +0000
Subject: [PATCH 1/2] Fix crash when Data Source starts with a comma

---
 .../src/Microsoft/Data/Common/AdapterUtil.cs      | 15 +++++++++++++--
 .../tests/FunctionalTests/SqlConnectionTest.cs    | 12 ++++++++++++
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/src/Microsoft.Data.SqlClient/src/Microsoft/Data/Common/AdapterUtil.cs b/src/Microsoft.Data.SqlClient/src/Microsoft/Data/Common/AdapterUtil.cs
index da8b65f837..f51723ace2 100644
--- a/src/Microsoft.Data.SqlClient/src/Microsoft/Data/Common/AdapterUtil.cs
+++ b/src/Microsoft.Data.SqlClient/src/Microsoft/Data/Common/AdapterUtil.cs
@@ -792,8 +792,19 @@ private static bool IsEndpoint(string dataSource, string prefix)
                 length = foundIndex;
             }
 
-            // check for the instance name
-            foundIndex = dataSource.LastIndexOf('\\', length - 1, length - 1);
+            // Safeguard LastIndexOf call to avoid ArgumentOutOfRangeException when length is 0
+            if (length > 0)
+            {
+                // check for the instance name
+                foundIndex = dataSource.LastIndexOf('\\', length - 1, length - 1);
+            }
+            else
+            {
+                foundIndex = -1;
+            }
+
+
+  
             if (foundIndex > 0)
             {
                 length = foundIndex;
diff --git a/src/Microsoft.Data.SqlClient/tests/FunctionalTests/SqlConnectionTest.cs b/src/Microsoft.Data.SqlClient/tests/FunctionalTests/SqlConnectionTest.cs
index 75fb85b384..75b19260d7 100644
--- a/src/Microsoft.Data.SqlClient/tests/FunctionalTests/SqlConnectionTest.cs
+++ b/src/Microsoft.Data.SqlClient/tests/FunctionalTests/SqlConnectionTest.cs
@@ -1082,6 +1082,18 @@ public void ConnectionRetryForNonAzureEndpoints()
             Assert.Equal(1, (int)field.GetValue(cn));
         }
 
+
+
+        [Fact]
+        public void ConnectionString_WithOnlyComma_ShouldNotThrow()
+        {
+            SqlConnection cn = new SqlConnection("Data Source=,;Initial Catalog=master;Integrated Security=True");
+            Exception ex = Record.Exception(() => cn.Open());
+
+            Assert.NotNull(ex);
+            Assert.False(ex is ArgumentOutOfRangeException);
+        }
+
         [Theory]
         [InlineData("myserver.database.windows.net")]
         [InlineData("myserver.database.cloudapi.de")]

From ccbf5109823c14d457859291fa5ca4e1db8d0f32 Mon Sep 17 00:00:00 2001
From: midhun <midhun@bakedev>
Date: Tue, 1 Apr 2025 19:30:02 +0000
Subject: [PATCH 2/2] Refine test to expect SqlException

---
 .../tests/FunctionalTests/SqlConnectionTest.cs         | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/Microsoft.Data.SqlClient/tests/FunctionalTests/SqlConnectionTest.cs b/src/Microsoft.Data.SqlClient/tests/FunctionalTests/SqlConnectionTest.cs
index 75b19260d7..d3b906c6b5 100644
--- a/src/Microsoft.Data.SqlClient/tests/FunctionalTests/SqlConnectionTest.cs
+++ b/src/Microsoft.Data.SqlClient/tests/FunctionalTests/SqlConnectionTest.cs
@@ -1085,13 +1085,15 @@ public void ConnectionRetryForNonAzureEndpoints()
 
 
         [Fact]
-        public void ConnectionString_WithOnlyComma_ShouldNotThrow()
+        public void ConnectionString_WithOnlyComma()
         {
+            // Test Case for https://github.com/dotnet/SqlClient/issues/3110
+            // Validates that a single-comma Data Source (e.g., "Data Source=,") no longer causes ArgumentOutOfRangeException
+            // Instead, it should throw a SqlException indicating a connection failure
+
             SqlConnection cn = new SqlConnection("Data Source=,;Initial Catalog=master;Integrated Security=True");
-            Exception ex = Record.Exception(() => cn.Open());
+            Assert.Throws<SqlException>(() => { cn.Open(); });
 
-            Assert.NotNull(ex);
-            Assert.False(ex is ArgumentOutOfRangeException);
         }
 
         [Theory]