CSHARP-1488: Properly implement Flush and FlushAsync for GridFS streams.

Author: rstam

src/MongoDB.Driver.GridFS.Tests/GridFSDownloadStreamBaseTests.cs

@@ -18,6 +18,7 @@
 using System.IO;
 using System.Linq;
 using System.Text;
+using System.Threading;
 using System.Threading.Tasks;
 using FluentAssertions;
 using MongoDB.Bson;
@@ -71,6 +72,28 @@ public void CopyTo_should_copy_stream(
             }
         }
 
+        [Test]
+        public void Flush_should_throw(
+            [Values(false, true)] bool async)
+        {
+            var bucket = CreateBucket(128);
+            var content = CreateContent();
+            var id = CreateGridFSFile(bucket, content);
+            var subject = bucket.OpenDownloadStream(id);
+
+            Action action;
+            if (async)
+            {
+                action = () => subject.FlushAsync(CancellationToken.None).GetAwaiter().GetResult(); ;
+            }
+            else
+            {
+                action = () => subject.Flush();
+            }
+
+            action.ShouldThrow<NotSupportedException>();
+        }
+
         // private methods
         private IGridFSBucket CreateBucket(int chunkSize)
         {
@@ -81,7 +104,7 @@ private IGridFSBucket CreateBucket(int chunkSize)
             return new GridFSBucket(database, bucketOptions);
         }
 
-        private byte[] CreateContent(int contentSize)
+        private byte[] CreateContent(int contentSize = 0)
         {
             return Enumerable.Range(0, contentSize).Select(i => (byte)i).ToArray();
         }

src/MongoDB.Driver.GridFS.Tests/GridFSUploadStreamTests.cs

@@ -15,6 +15,7 @@
 
 using System;
 using System.IO;
+using System.Threading;
 using FluentAssertions;
 using MongoDB.Driver.Tests;
 using NUnit.Framework;
@@ -48,6 +49,26 @@ public void CopyTo_should_throw(
             }
         }
 
+        [Test]
+        public void Flush_should_not_throw(
+            [Values(false, true)] bool async)
+        {
+            var bucket = CreateBucket();
+            var subject = bucket.OpenUploadStream("Filename");
+
+            Action action;
+            if (async)
+            {
+                action = () => subject.FlushAsync(CancellationToken.None).GetAwaiter().GetResult(); ;
+            }
+            else
+            {
+                action = () => subject.Flush();
+            }
+
+            action.ShouldNotThrow();
+        }
+
         // private methods
         private IGridFSBucket CreateBucket()
         {

src/MongoDB.Driver.GridFS/GridFSForwardOnlyUploadStream.cs

@@ -27,6 +27,11 @@ namespace MongoDB.Driver.GridFS
 {
     internal class GridFSForwardOnlyUploadStream : GridFSUploadStream
     {
+        #region static
+        // private static fields
+        private static readonly Task __completedTask = Task.FromResult(true);
+        #endregion
+
         // fields
         private bool _aborted;
         private readonly List<string> _aliases;
@@ -179,12 +184,13 @@ public override void Close(CancellationToken cancellationToken)
 
         public override void Flush()
         {
-            throw new NotSupportedException();
+            // do nothing
         }
 
         public override Task FlushAsync(CancellationToken cancellationToken)
         {
-            throw new NotSupportedException();
+            // do nothing
+            return __completedTask;
         }
 
         public override int Read(byte[] buffer, int offset, int count)