From 4c6097c969c57c46eae93d58678542c53e6e77e0 Mon Sep 17 00:00:00 2001
From: Richard Webb <webby@beardmouse.co.uk>
Date: Mon, 1 Mar 2021 15:40:35 +0000
Subject: [PATCH] Add an implementation of ReadAsync to PartialInputStream

---
 src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs | 31 ++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs b/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs
index 704911b3f..c0bf53060 100644
--- a/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs
+++ b/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs
@@ -9,6 +9,8 @@
 using System.IO;
 using System.Security.Cryptography;
 using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
 
 namespace ICSharpCode.SharpZipLib.Zip
 {
@@ -4223,6 +4225,35 @@ public override int Read(byte[] buffer, int offset, int count)
 				}
 			}
 
+			///<inheritdoc/>
+			public override async Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+			{
+				// lock (baseStream_)
+				{
+					if (count > end_ - readPos_)
+					{
+						count = (int)(end_ - readPos_);
+						if (count == 0)
+						{
+							return 0;
+						}
+					}
+					// Protect against Stream implementations that throw away their buffer on every Seek
+					// (for example, Mono FileStream)
+					if (baseStream_.Position != readPos_)
+					{
+						baseStream_.Seek(readPos_, SeekOrigin.Begin);
+					}
+
+					int readCount = await baseStream_.ReadAsync(buffer, offset, count, cancellationToken);
+					if (readCount > 0)
+					{
+						readPos_ += readCount;
+					}
+					return readCount;
+				}
+			}
+
 			/// <summary>
 			/// Writes a sequence of bytes to the current stream and advances the current position within this stream by the number of bytes written.
 			/// </summary>