ODataMessageWriter can't dispose the stream if there's no write metho…

…d called (#1714)

* ODataMessageWriter can't dispose the stream if there's no write method
called. This is an edge case because customer creates the message writer
to write something. However, if there's some control to prevent the
message writer writing anything, the outside stream still needs to
dispose. This PR is to resolve this edge problem.

* Address the comments

src/Microsoft.OData.Core/ODataMessageWriter.cs

@@ -1212,6 +1212,14 @@ private void Dispose(bool disposing)
                     {
                         this.outputContext.Dispose();
                     }
+                    else if (this.settings.EnableMessageStreamDisposal)
+                    {
+                        Stream stream = this.message.GetStream();
+                        if (stream != null)
+                        {
+                            stream.Dispose();
+                        }
+                    }
                 }
                 finally
                 {

test/FunctionalTests/Microsoft.OData.Core.Tests/ODataMessageWriterTests.cs

@@ -184,5 +184,51 @@ public void WriteUndeclaredUIntValueShouldFail()
             Action write = () => writer.WriteValue((UInt16)123);
             write.Throws<ODataException>("The value of type 'System.UInt16' could not be converted to a raw string.");
         }
+
+        [Theory]
+        [InlineData(true)]
+        [InlineData(false)]
+        public void CanDisposeStreamWithOrWithoutAnyWriteCalled(bool withWriteCalled)
+        {
+            var settings = new ODataMessageWriterSettings();
+            var model = new EdmModel();
+
+            DisposeMemoryStream stream = new DisposeMemoryStream();
+            Assert.False(stream.DisposeCalled); // Guard;
+
+            IODataRequestMessage request = new InMemoryMessage()
+            {
+                Stream = stream
+            };
+
+            using (var writer = new ODataMessageWriter(request, settings, model))
+            {
+                if (withWriteCalled)
+                {
+                    writer.WriteProperty(new ODataProperty()
+                    {
+                        Name = "Name",
+                        Value = "abc"
+                    });
+                }
+                else
+                {
+                    // nothing here
+                }
+            }
+
+            Assert.True(stream.DisposeCalled);
+        }
+    }
+
+    public class DisposeMemoryStream : MemoryStream
+    {
+        public bool DisposeCalled { get; set; }
+
+        protected override void Dispose(bool disposing)
+        {
+            DisposeCalled = true;
+            base.Dispose(disposing);
+        }
     }
 }