Fix infinite loop in BrotliEncoder

Author: hadashiA

src/MemoryPack.Core/Compression/BrotliCompressor.cs

@@ -262,7 +262,7 @@ static int CompressCore<TBufferWriter>(ref BrotliEncoder encoder, ReadOnlySpan<b
         var lastResult = OperationStatus.DestinationTooSmall;
         while (lastResult == OperationStatus.DestinationTooSmall)
         {
-            ref var spanRef = ref destBufferWriter.GetSpanReference(initialLength ?? source.Length);
+            ref var spanRef = ref destBufferWriter.GetSpanReference(Math.Max(initialLength ?? source.Length, 1));
             var dest = MemoryMarshal.CreateSpan(ref spanRef, destBufferWriter.BufferLength);
 
             lastResult = encoder.Compress(source, dest, out int bytesConsumed, out int bytesWritten, isFinalBlock: isFinalBlock);

tests/MemoryPack.Tests/BrotliTest.cs

@@ -1,5 +1,7 @@
 using MemoryPack.Compression;
 using System;
+using System.Buffers;
+using System.IO.Compression;
 
 namespace MemoryPack.Tests;
 
@@ -14,6 +16,44 @@ public void LargeByteArray()
         data.MemDecmpDeserialize(bin);
     }
 
+    [Fact]
+    public void EncodeEmptyCntent()
+    {
+        var buffer = new ArrayBufferWriter<byte>();
+        using var state = MemoryPackWriterOptionalStatePool.Rent(null);
+        var writer = new MemoryPackWriter<ArrayBufferWriter<byte>>(ref buffer, state);
+
+        using var compressor = new BrotliCompressor(CompressionLevel.Fastest);
+        compressor.CopyTo(ref writer);
+
+        using var decompressor = new BrotliDecompressor();
+        decompressor.Decompress(compressor.ToArray()).ToArray().Should().BeEmpty();
+    }
+
+    [Fact]
+    public void EncodeEmptyFinalBlock()
+    {
+        using var state = MemoryPackWriterOptionalStatePool.Rent(null);
+
+        var compressor = new BrotliCompressor(CompressionLevel.Fastest);
+        var coWriter = new MemoryPackWriter<BrotliCompressor>(ref compressor, state);
+
+        var bytes = new byte[248];
+        Random.Shared.NextBytes(bytes);
+        coWriter.WriteUnmanagedArray(bytes);
+        coWriter.Flush();
+
+        var buffer = new ArrayBufferWriter<byte>();
+        compressor.CopyTo(buffer);
+
+        using var readerState = MemoryPackReaderOptionalStatePool.Rent(null);
+        using var decompressor = new BrotliDecompressor();
+        var decompressed = decompressor.Decompress(compressor.ToArray());
+        var reader = new MemoryPackReader(in decompressed, readerState);
+
+        reader.ReadArray<byte>().Should().BeEquivalentTo(bytes);
+        compressor.Dispose();
+    }
 }
 
 [MemoryPackable]