From 8d39156d37d675bc35223ef1583d51b563b3849d Mon Sep 17 00:00:00 2001
From: Robert Hague <rh@johnstreetcapital.com>
Date: Wed, 1 Jan 2025 13:32:47 +0100
Subject: [PATCH] Fix partial reads on compressed data

---
 MatFileHandler.Tests/MatFileReaderTests.cs    |  2 +-
 .../PartialReadMatTestDataFactory.cs          | 35 ++++++++
 MatFileHandler.Tests/PartialReadStream.cs     | 84 +++++++++++++++++++
 MatFileHandler/DataElementReader.cs           |  3 +-
 4 files changed, 121 insertions(+), 3 deletions(-)
 create mode 100644 MatFileHandler.Tests/PartialReadMatTestDataFactory.cs
 create mode 100644 MatFileHandler.Tests/PartialReadStream.cs

diff --git a/MatFileHandler.Tests/MatFileReaderTests.cs b/MatFileHandler.Tests/MatFileReaderTests.cs
index 41e408d..8645b82 100755
--- a/MatFileHandler.Tests/MatFileReaderTests.cs
+++ b/MatFileHandler.Tests/MatFileReaderTests.cs
@@ -529,7 +529,7 @@ namespace MatFileHandler.Tests
         }
 
         private static AbstractTestDataFactory<IMatFile> GetTests(string factoryName) =>
-            new MatTestDataFactory(Path.Combine(TestDirectory, factoryName));
+            new PartialReadMatTestDataFactory(Path.Combine(TestDirectory, factoryName));
 
         private static void CheckLimits<T>(IArrayOf<T> array, T[] limits)
             where T : struct
diff --git a/MatFileHandler.Tests/PartialReadMatTestDataFactory.cs b/MatFileHandler.Tests/PartialReadMatTestDataFactory.cs
new file mode 100644
index 0000000..f77f7f1
--- /dev/null
+++ b/MatFileHandler.Tests/PartialReadMatTestDataFactory.cs
@@ -0,0 +1,35 @@
+// Copyright 2017-2018 Alexander Luzgarev
+
+using System.IO;
+
+namespace MatFileHandler.Tests
+{
+    /// <summary>
+    /// Factory providing the parsed contents of .mat files,
+    /// wrapped in a <see cref="PartialReadStream"/>.
+    /// </summary>
+    public class PartialReadMatTestDataFactory : MatTestDataFactory
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="PartialReadMatTestDataFactory"/> class.
+        /// </summary>
+        /// <param name="testDirectory">Directory containing test files.</param>
+        public PartialReadMatTestDataFactory(string testDirectory)
+            : base(testDirectory)
+        {
+        }
+
+        /// <summary>
+        /// Read and parse data from a .mat file.
+        /// </summary>
+        /// <param name="stream">Input stream.</param>
+        /// <returns>Parsed contents of the file.</returns>
+        protected override IMatFile ReadDataFromStream(Stream stream)
+        {
+            using (var wrapper = new PartialReadStream(stream))
+            {
+                return base.ReadDataFromStream(wrapper);
+            }
+        }
+    }
+}
diff --git a/MatFileHandler.Tests/PartialReadStream.cs b/MatFileHandler.Tests/PartialReadStream.cs
new file mode 100644
index 0000000..b056457
--- /dev/null
+++ b/MatFileHandler.Tests/PartialReadStream.cs
@@ -0,0 +1,84 @@
+// Copyright 2017-2018 Alexander Luzgarev
+
+using System;
+using System.IO;
+
+namespace MatFileHandler.Tests
+{
+    /// <summary>
+    /// A stream which wraps another stream and only reads one byte at a time.
+    /// </summary>
+    internal class PartialReadStream : Stream
+    {
+        private readonly Stream _baseStream;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="PartialReadStream"/> class.
+        /// </summary>
+        /// <param name="baseStream">The stream to wrap.</param>
+        public PartialReadStream(Stream baseStream)
+        {
+            _baseStream = baseStream;
+        }
+
+        /// <inheritdoc/>
+        public override bool CanRead => _baseStream.CanRead;
+
+        /// <inheritdoc/>
+        public override bool CanSeek => _baseStream.CanSeek;
+
+        /// <inheritdoc/>
+        public override bool CanWrite => false;
+
+        /// <inheritdoc/>
+        public override long Length => _baseStream.Length;
+
+        /// <inheritdoc/>
+        public override long Position
+        {
+            get => _baseStream.Position;
+            set => _baseStream.Position = value;
+        }
+
+        /// <inheritdoc/>
+        public override void Flush()
+        {
+            _baseStream.Flush();
+        }
+
+        /// <inheritdoc/>
+        public override int Read(byte[] buffer, int offset, int count)
+        {
+            return _baseStream.Read(buffer, offset, Math.Min(1, count));
+        }
+
+        /// <inheritdoc/>
+        public override long Seek(long offset, SeekOrigin origin)
+        {
+            return _baseStream.Seek(offset, origin);
+        }
+
+        /// <inheritdoc/>
+        public override void SetLength(long value)
+        {
+            _baseStream.SetLength(value);
+        }
+
+        /// <inheritdoc/>
+        public override void Write(byte[] buffer, int offset, int count)
+        {
+            throw new NotImplementedException();
+        }
+
+        /// <inheritdoc/>
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                _baseStream.Dispose();
+            }
+
+            base.Dispose(disposing);
+        }
+    }
+}
diff --git a/MatFileHandler/DataElementReader.cs b/MatFileHandler/DataElementReader.cs
index b678566..a116c80 100755
--- a/MatFileHandler/DataElementReader.cs
+++ b/MatFileHandler/DataElementReader.cs
@@ -354,8 +354,7 @@ namespace MatFileHandler
         private DataElement ReadCompressed(Tag tag, BinaryReader reader)
         {
             reader.ReadBytes(2);
-            var compressedData = new byte[tag.Length - 6];
-            reader.BaseStream.Read(compressedData, 0, tag.Length - 6);
+            var compressedData = reader.ReadBytes(tag.Length - 6);
             reader.ReadBytes(4);
             var resultStream = new MemoryStream();
             using (var compressedStream = new MemoryStream(compressedData))