add test for #731

test/ICSharpCode.SharpZipLib.Tests/TestSupport/Streams.cs

@@ -177,13 +177,15 @@ public class MemoryStreamWithoutSeek : TrackedMemoryStream
 		/// </summary>
 		/// <value></value>
 		/// <returns>true if the stream is open.</returns>
-		public override bool CanSeek
+		public override bool CanSeek => false;
+
+		/// <inheritdoc />
+		public override long Position
 		{
-			get
-			{
-				return false;
-			}
+			get => throw new NotSupportedException("Getting position is not supported");
+			set => throw new NotSupportedException("Setting position is not supported");
 		}
+
 	}
 
 	/// <summary>

test/ICSharpCode.SharpZipLib.Tests/Zip/StreamHandling.cs

@@ -111,11 +111,10 @@ public void ReadAndWriteZip64NonSeekable()
 				outStream.Close();
 			}
 
-			Assert.That(msw.ToArray(), Does.PassTestArchive());
-
-			msw.Position = 0;
+			var msBytes = msw.ToArray();
+			Assert.That(msBytes, Does.PassTestArchive());
 
-			using (var zis = new ZipInputStream(msw))
+			using (var zis = new ZipInputStream(new MemoryStream(msBytes)))
 			{
 				while (zis.GetNextEntry() != null)
 				{

test/ICSharpCode.SharpZipLib.Tests/Zip/ZipStreamAsyncTests.cs

@@ -97,5 +97,26 @@ public async Task WriteZipStreamWithZipCryptoAsync()
 			ZipTesting.AssertValidZip(ms, password, false);
 		}
 
+		[Test]
+		[Category("Zip")]
+		[Category("Async")]
+		public async Task WriteReadOnlyZipStreamAsync ()
+		{
+			using var ms = new MemoryStreamWithoutSeek();
+
+			using(var outStream = new ZipOutputStream(ms) { IsStreamOwner = false })
+			{
+				await outStream.PutNextEntryAsync(new ZipEntry("FirstFile"));
+				await Utils.WriteDummyDataAsync(outStream, 12);
+
+				await outStream.PutNextEntryAsync(new ZipEntry("SecondFile"));
+				await Utils.WriteDummyDataAsync(outStream, 12);
+
+				await outStream.FinishAsync(CancellationToken.None);
+			}
+
+			ZipTesting.AssertValidZip(new MemoryStream(ms.ToArray()));
+		}
+
 	}
 }