Fix bug 48516

2 files changed, 29 insertions, 6 deletions

diff --git a/mcs/class/System.IO.Compression/Test/System.IO.Compression/ZipTest.cs b/mcs/class/System.IO.Compression/Test/System.IO.Compression/ZipTest.cs
index f1b83746b47..343746863e3 100644
--- a/mcs/class/System.IO.Compression/Test/System.IO.Compression/ZipTest.cs
+++ b/mcs/class/System.IO.Compression/Test/System.IO.Compression/ZipTest.cs
@@ -507,6 +507,11 @@ namespace MonoTests.System.IO.Compression
 			/// Simulate "CanSeek" is false, which is the case when you are retreiving data from web.
 			/// </summary>
 			public override bool CanSeek => false;
+
+			public override long Position {
+				get {throw new NotSupportedException();}
+				set {throw new NotSupportedException();}
+			}
 		}
 
 		[Test]
@@ -517,5 +522,16 @@ namespace MonoTests.System.IO.Compression
 			{
 			}
 		}
+
+		[Test]
+		public void ZipWriteNonSeekableStream() {
+			var stream = new MyFakeStream( "test.nupkg", FileMode.Open );
+			using ( var archive = new ZipArchive( stream, ZipArchiveMode.Create ) ) {
+				var entry = archive.CreateEntry( "foo" );
+				using ( var es = entry.Open() ) {
+					es.Write( new byte[] { 4, 2 }, 0, 2 );
+				}
+			}
+		}
 	}
 }
diff --git a/mcs/class/System.IO.Compression/ZipArchive.cs b/mcs/class/System.IO.Compression/ZipArchive.cs
index 5df9434321c..4aa7318e4c8 100644
--- a/mcs/class/System.IO.Compression/ZipArchive.cs
+++ b/mcs/class/System.IO.Compression/ZipArchive.cs
@@ -227,13 +227,20 @@ namespace System.IO.Compression
 
 		private void Save()
 		{
-			using (var newZip = new MemoryStream()) {
-				zipFile.SaveTo(newZip, CompressionType.Deflate, entryNameEncoding ?? Encoding.UTF8);
+			if (mode == ZipArchiveMode.Create)
+			{
+				zipFile.SaveTo(stream, CompressionType.Deflate, entryNameEncoding ?? Encoding.UTF8);
+			}
+			else {
+				using (var newZip = new MemoryStream())
+				{
+					zipFile.SaveTo(newZip, CompressionType.Deflate, entryNameEncoding ?? Encoding.UTF8);
 
-				stream.SetLength(0);
-				stream.Position = 0;
-				newZip.Position = 0;
-				newZip.CopyTo(stream);
+					stream.SetLength(0);
+					stream.Position = 0;
+					newZip.Position = 0;
+					newZip.CopyTo(stream);
+				}
 			}
 		}