[System.IO.Compression] Fixes ZipArchive to support non-seekable streams.

This is the same behavior as documented on MSDN.

Fixes https://bugzilla.xamarin.com/show_bug.cgi?id=30686.

2 files changed, 36 insertions, 5 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 b9bb8101185..2d03d559d4e 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
@@ -480,5 +480,24 @@ namespace MonoTests.System.IO.Compression
 			}
 			File.Delete ("empty.zip");
 		}
+
+		class MyFakeStream : FileStream 
+		{
+			public MyFakeStream (string path, FileMode mode) : base(path, mode) {}
+
+			/// <summary>
+			/// Simulate "CanSeek" is false, which is the case when you are retreiving data from web.
+			/// </summary>
+			public override bool CanSeek => false;
+		}
+
+		[Test]
+		public void ZipReadNonSeekableStream()
+		{
+			var stream = new MyFakeStream("test.nupkg", FileMode.Open);
+			using (var archive = new ZipArchive (stream, ZipArchiveMode.Read))
+			{
+			}
+		}
 	}
 }
diff --git a/mcs/class/System.IO.Compression/ZipArchive.cs b/mcs/class/System.IO.Compression/ZipArchive.cs
index 9dbf04cd339..c1a3df57566 100644
--- a/mcs/class/System.IO.Compression/ZipArchive.cs
+++ b/mcs/class/System.IO.Compression/ZipArchive.cs
@@ -49,7 +49,7 @@ namespace System.IO.Compression
 
 			this.stream = stream;
 			mode = ZipArchiveMode.Read;
-			CreateZip(stream, mode);
+			CreateZip(mode);
 		}
 
 		public ZipArchive (Stream stream, ZipArchiveMode mode)
@@ -59,7 +59,7 @@ namespace System.IO.Compression
 
 			this.stream = stream;
 			this.mode = mode;
-			CreateZip(stream, mode);
+			CreateZip(mode);
 		}
 
 		public ZipArchive (Stream stream, ZipArchiveMode mode, bool leaveOpen)
@@ -70,7 +70,7 @@ namespace System.IO.Compression
 			this.stream = stream;
 			this.mode = mode;
 			leaveStreamOpen = leaveOpen;
-			CreateZip(stream, mode);
+			CreateZip(mode);
 		}
 
 		public ZipArchive (Stream stream, ZipArchiveMode mode, bool leaveOpen, Encoding entryNameEncoding)
@@ -82,10 +82,10 @@ namespace System.IO.Compression
 			this.mode = mode;
 			leaveStreamOpen = leaveOpen;
 			this.entryNameEncoding = entryNameEncoding;
-			CreateZip(stream, mode);
+			CreateZip(mode);
 		}
 
-		private void CreateZip(Stream stream, ZipArchiveMode mode)
+		private void CreateZip(ZipArchiveMode mode)
 		{
 			try {
 				if (mode != ZipArchiveMode.Read && mode != ZipArchiveMode.Create && mode != ZipArchiveMode.Update)
@@ -103,6 +103,18 @@ namespace System.IO.Compression
 				if (mode == ZipArchiveMode.Update && (!stream.CanRead || !stream.CanWrite || !stream.CanSeek))
 					throw new ArgumentException("Stream must support reading, writing and seeking for Update archive mode");
 
+				// If the stream is not seekable, then buffer it into memory (same behavior as .NET). 
+				if (mode == ZipArchiveMode.Read && !stream.CanSeek)
+				{
+					var memoryStream = new MemoryStream();
+					stream.CopyTo(memoryStream);
+
+					if (!leaveStreamOpen)
+						stream.Dispose();
+
+					this.stream = memoryStream;
+				}
+
 				try {
 					zipFile = mode != ZipArchiveMode.Create && stream.Length != 0
 						? SharpCompress.Archive.Zip.ZipArchive.Open(stream)