LeaveOpen ctor for CryptoStream

src/System.Security.Cryptography.Primitives/ref/System.Security.Cryptography.Primitives.cs

@@ -35,6 +35,7 @@ public CryptographicException(string format, string insert) { }
     public partial class CryptoStream : System.IO.Stream, System.IDisposable
     {
         public CryptoStream(System.IO.Stream stream, System.Security.Cryptography.ICryptoTransform transform, System.Security.Cryptography.CryptoStreamMode mode) { }
+        public CryptoStream(System.IO.Stream stream, System.Security.Cryptography.ICryptoTransform transform, System.Security.Cryptography.CryptoStreamMode mode, bool leaveOpen) { }
         public override bool CanRead { get { return default(bool); } }
         public override bool CanSeek { get { return default(bool); } }
         public override bool CanWrite { get { return default(bool); } }

src/System.Security.Cryptography.Primitives/src/System/Security/Cryptography/CryptoStream.cs

@@ -25,15 +25,22 @@ public class CryptoStream : Stream, IDisposable
         private bool _canWrite;
         private bool _finalBlockTransformed;
         private SemaphoreSlim _lazyAsyncActiveSemaphore;
-
+        private readonly bool _leaveOpen;
+
         // Constructors
 
         public CryptoStream(Stream stream, ICryptoTransform transform, CryptoStreamMode mode)
+            : this(stream, transform, mode, false)
+        {
+        }
+
+        public CryptoStream(Stream stream, ICryptoTransform transform, CryptoStreamMode mode, bool leaveOpen)
         {
 
             _stream = stream;
             _transformMode = mode;
             _transform = transform;
+            _leaveOpen = leaveOpen;
             switch (_transformMode)
             {
                 case CryptoStreamMode.Read:
@@ -523,7 +530,10 @@ protected override void Dispose(bool disposing)
                     {
                         FlushFinalBlock();
                     }
-                    _stream.Dispose();
+                    if (!_leaveOpen)
+                    {
+                        _stream.Dispose();
+                    }
                 }
             }
             finally

src/System.Security.Cryptography.Primitives/tests/CryptoStream.cs

@@ -162,10 +162,35 @@ public static void NestedCryptoStreams()
         public static void MultipleDispose()
         {
             ICryptoTransform encryptor = new IdentityTransform(1, 1, true);
+
+            using (MemoryStream output = new MemoryStream())
+            {
+                using (CryptoStream encryptStream = new CryptoStream(output, encryptor, CryptoStreamMode.Write))
+                {
+                    encryptStream.Dispose();
+                }
+
+                Assert.Equal(false, output.CanRead);
+            }
+
+            using (MemoryStream output = new MemoryStream())
+            {
+                using (CryptoStream encryptStream = new CryptoStream(output, encryptor, CryptoStreamMode.Write, leaveOpen: false))
+                {
+                    encryptStream.Dispose();
+                }
+
+                Assert.Equal(false, output.CanRead);
+            }
+
             using (MemoryStream output = new MemoryStream())
-            using (CryptoStream encryptStream = new CryptoStream(output, encryptor, CryptoStreamMode.Write))
             {
-                encryptStream.Dispose();
+                using (CryptoStream encryptStream = new CryptoStream(output, encryptor, CryptoStreamMode.Write, leaveOpen: true))
+                {
+                    encryptStream.Dispose();
+                }
+
+                Assert.Equal(true, output.CanRead);
             }
         }