Serializer: Fixes unsafe stream cast in FromStream<T>

Microsoft.Azure.Cosmos.Encryption.Custom/src/Common/CosmosJsonDotNetSerializer.cs

@@ -42,9 +42,9 @@ public T FromStream<T>(Stream stream)
         {
             ArgumentValidation.ThrowIfNull(stream);
 
-            if (typeof(Stream).IsAssignableFrom(typeof(T)))
+            if (typeof(Stream).IsAssignableFrom(typeof(T)) && stream is T typedStream)
             {
-                return (T)(object)stream;
+                return typedStream;
             }
 
             using (StreamReader sr = new (stream))

Microsoft.Azure.Cosmos.Encryption/src/CosmosJsonDotNetSerializer.cs

@@ -45,9 +45,9 @@ public T FromStream<T>(Stream stream)
                 throw new ArgumentNullException(nameof(stream));
             }
 
-            if (typeof(Stream).IsAssignableFrom(typeof(T)))
+            if (typeof(Stream).IsAssignableFrom(typeof(T)) && stream is T typedStream)
             {
-                return (T)(object)stream;
+                return typedStream;
             }
 
             using (StreamReader sr = new StreamReader(stream))

Microsoft.Azure.Cosmos.Samples/Usage/ItemManagement/Program.cs

@@ -640,9 +640,9 @@ private static T FromStream<T>(Stream stream)
         {
             using (stream)
             {
-                if (typeof(Stream).IsAssignableFrom(typeof(T)))
+                if (typeof(Stream).IsAssignableFrom(typeof(T)) && stream is T typedStream)
                 {
-                    return (T)(object)stream;
+                    return typedStream;
                 }
 
                 using (StreamReader sr = new StreamReader(stream))

Microsoft.Azure.Cosmos.Samples/Usage/ReEncryption/ReEncryptionSupport/ReEncryptionJsonSerializer.cs

@@ -38,9 +38,9 @@ public T FromStream<T>(Stream stream)
                 throw new ArgumentNullException(nameof(stream));
             }
 
-            if (typeof(Stream).IsAssignableFrom(typeof(T)))
+            if (typeof(Stream).IsAssignableFrom(typeof(T)) && stream is T typedStream)
             {
-                return (T)(object)stream;
+                return typedStream;
             }
 
             using (StreamReader sr = new StreamReader(stream))

Microsoft.Azure.Cosmos.Samples/Usage/SystemTextJson/CosmosSystemTextJsonSerializer.cs

@@ -35,9 +35,9 @@ public override T FromStream<T>(Stream stream)
                     return default;
                 }
 
-                if (typeof(Stream).IsAssignableFrom(typeof(T)))
+                if (typeof(Stream).IsAssignableFrom(typeof(T)) && stream is T typedStream)
                 {
-                    return (T)(object)stream;
+                    return typedStream;
                 }
 
                 return (T)this.systemTextJsonSerializer.Deserialize(stream, typeof(T), default);

Microsoft.Azure.Cosmos/src/Serializer/CosmosJsonDotNetSerializer.cs

@@ -91,9 +91,9 @@ public override T FromStream<T>(Stream stream)
         {
             using (stream)
             {
-                if (typeof(Stream).IsAssignableFrom(typeof(T)))
+                if (typeof(Stream).IsAssignableFrom(typeof(T)) && stream is T typedStream)
                 {
-                    return (T)(object)stream;
+                    return typedStream;
                 }
 
                 JsonSerializer jsonSerializer = this.GetSerializer();

Microsoft.Azure.Cosmos/src/Serializer/CosmosSystemTextJsonSerializer.cs

@@ -40,9 +40,9 @@ public override T FromStream<T>(Stream stream)
             if (stream == null)
                 throw new ArgumentNullException(nameof(stream));
 
-            if (typeof(Stream).IsAssignableFrom(typeof(T)))
+            if (typeof(Stream).IsAssignableFrom(typeof(T)) && stream is T typedStream)
             {
-                return (T)(object)stream;
+                return typedStream;
             }
 
             if (stream.CanSeek && stream.Length == 0)

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.Tests/CosmosJsonSerializerUnitTests.cs

@@ -32,6 +32,18 @@ public class CosmosJsonSerializerUnitTests
 
         private readonly string toDoActivityJson = @"{""id"":""c1d433c1-369d-430e-91e5-14e3ce588f71"",""taskNum"":42,""cost"":1.7976931348623157E+308,""description"":""cosmos json serializer"",""status"":""TBD""}";
 
+        [TestMethod]
+        public void ValidateFromStreamWithBaseStreamType()
+        {
+            CosmosJsonDotNetSerializer cosmosDefaultJsonSerializer = new CosmosJsonDotNetSerializer();
+            using MemoryStream memoryStream = new MemoryStream(new byte[] { 1, 2, 3 });
+
+            // FromStream<Stream> with a MemoryStream should succeed
+            Stream result = cosmosDefaultJsonSerializer.FromStream<Stream>(memoryStream);
+            Assert.IsNotNull(result);
+            Assert.AreSame(memoryStream, result);
+        }
+
         [TestMethod]
         public void ValidateSerializer()
         {

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.Tests/Json/CosmosSystemTextJsonSerializerTest.cs

@@ -226,5 +226,19 @@ public void TestPolymorphicSerialization_SerializeDeserialize_PreservesType()
             Assert.AreEqual(original.Color, deserializedCircle.Color);
             Assert.AreEqual(((Circle)original).Radius, deserializedCircle.Radius);
         }
+        [TestMethod]
+        public void TestFromStreamWithBaseStreamType()
+        {
+            // Arrange.
+            MemoryStream memoryStream = new MemoryStream(new byte[] { 1, 2, 3 });
+
+            // Act - FromStream<Stream> with a MemoryStream should succeed.
+            Stream result = this.stjSerializer.FromStream<Stream>(memoryStream);
+
+            // Assert.
+            Assert.IsNotNull(result);
+            Assert.AreSame(memoryStream, result);
+        }
+
     }
-}
+}