Merge pull request #624 from adamhathcock/issue-617

Add test and probable fix for Issue 617

src/SharpCompress/Algorithms/Alder32.cs

@@ -51,11 +51,6 @@ namespace SharpCompress.Algorithms
         /// <returns>The <see cref="uint"/>.</returns>
         public static uint Calculate(uint adler, ReadOnlySpan<byte> buffer)
         {
-            if (buffer.IsEmpty)
-            {
-                return SeedValue;
-            }
-
 #if !NETSTANDARD2_0 && !NETSTANDARD2_1 && !NETFRAMEWORK
             if (Sse3.IsSupported && buffer.Length >= MinBufferSize)
             {

src/SharpCompress/SharpCompress.csproj

@@ -2,9 +2,9 @@
   <PropertyGroup>
     <AssemblyTitle>SharpCompress - Pure C# Decompression/Compression</AssemblyTitle>
     <NeutralLanguage>en-US</NeutralLanguage>
-    <VersionPrefix>0.30.0</VersionPrefix>
-    <AssemblyVersion>0.30.0</AssemblyVersion>
-    <FileVersion>0.30.0</FileVersion>
+    <VersionPrefix>0.30.1</VersionPrefix>
+    <AssemblyVersion>0.30.1</AssemblyVersion>
+    <FileVersion>0.30.1</FileVersion>
     <Authors>Adam Hathcock</Authors>
     <TargetFrameworks>net461;netstandard2.0;netstandard2.1;netcoreapp3.1;net5.0</TargetFrameworks>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>

tests/SharpCompress.Test/SharpCompress.Test.csproj

@@ -12,8 +12,9 @@
     <ProjectReference Include="..\..\src\SharpCompress\SharpCompress.csproj" />
   </ItemGroup>
   <ItemGroup>
+    <PackageReference Include="FluentAssertions" Version="6.2.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.11.0" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3"/>
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3" />
     <PackageReference Include="xunit" Version="2.4.1" />
     <PackageReference Include="Xunit.SkippableFact" Version="1.4.13" />
   </ItemGroup>

tests/SharpCompress.Test/Streams/ZlibBaseStreamTests.cs

@@ -1,6 +1,9 @@
 using System.IO;
+using System.Text;
+using FluentAssertions;
 using SharpCompress.Compressors;
 using SharpCompress.Compressors.Deflate;
+using SharpCompress.IO;
 using Xunit;
 
 namespace SharpCompress.Test.Streams
@@ -31,5 +34,55 @@ namespace SharpCompress.Test.Streams
 
             Assert.Equal(total, realCompressedSize);
         }
+        
+        [Fact]
+        public void Zlib_should_read_the_previously_written_message()
+        {
+            var message = new string('a', 131073);  // 131073 causes the failure, but 131072 (-1) doesn't
+            var bytes = Encoding.ASCII.GetBytes(message);
+
+            using (var inputStream = new MemoryStream(bytes))
+            {
+                using (var compressedStream = new MemoryStream())
+                using (var byteBufferStream = new BufferedStream(inputStream)) // System.IO
+                {
+                    Compress(byteBufferStream, compressedStream, compressionLevel: 1);
+                    compressedStream.Position = 0;
+
+                    using (var decompressedStream = new MemoryStream())
+                    {
+                        Decompress(compressedStream, decompressedStream);
+
+                        byteBufferStream.Position = 0;
+                        var result = Encoding.ASCII.GetString(GetBytes(byteBufferStream));
+                        result.Should().Be(message);
+                    }
+                }
+            }
+        }
+
+        public void Compress(Stream input, Stream output, int compressionLevel)
+        {
+            using (var zlibStream = new ZlibStream(new NonDisposingStream(output), CompressionMode.Compress, (CompressionLevel)compressionLevel))
+            {
+                zlibStream.FlushMode = FlushType.Sync;
+                input.CopyTo(zlibStream);
+            }
+        }
+
+        public void Decompress(Stream input, Stream output)
+        {
+            using (var zlibStream = new ZlibStream(new NonDisposingStream(input), CompressionMode.Decompress))
+            {
+                zlibStream.CopyTo(output);
+            }
+        }
+
+        byte[] GetBytes(BufferedStream stream)
+        {
+            byte[] bytes = new byte[stream.Length];
+            stream.Read(bytes, 0, (int)stream.Length);
+            return bytes;
+        }
     }
 }