Reduce memory consumption of MatFileWriter

MatFileHandler.Tests/ChecksumCalculatingStreamTests.cs

@@ -0,0 +1,106 @@
+// Copyright 2017-2018 Alexander Luzgarev
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text;
+using Xunit;
+
+namespace MatFileHandler.Tests
+{
+    /// <summary>
+    /// Tests for the <see cref="ChecksumCalculatingStream"/> class.
+    /// </summary>
+    public class ChecksumCalculatingStreamTests
+    {
+        /// <summary>
+        /// Test writing various things.
+        /// </summary>
+        /// <param name="action"></param>
+        [Theory]
+        [MemberData(nameof(TestData))]
+        public void Test(Action<Stream> action)
+        {
+            using var stream = new MemoryStream();
+            var sut = new ChecksumCalculatingStream(stream);
+            action(sut);
+            var actual = sut.GetCrc();
+            var expected = ReferenceCalculation(action);
+        }
+
+        /// <summary>
+        /// Test data for <see cref="Test"/>.
+        /// </summary>
+        /// <returns>Test data.</returns>
+        public static IEnumerable<object[]> TestData()
+        {
+            foreach (var data in TestData_Typed())
+            {
+                yield return new object[] { data };
+            }
+        }
+
+        private static IEnumerable<Action<Stream>> TestData_Typed()
+        {
+            yield return BinaryWriterAction(w => w.Write(true));
+            yield return BinaryWriterAction(w => w.Write(false));
+            yield return BinaryWriterAction(w => w.Write(byte.MinValue));
+            yield return BinaryWriterAction(w => w.Write(byte.MaxValue));
+            yield return BinaryWriterAction(w => w.Write(short.MinValue));
+            yield return BinaryWriterAction(w => w.Write(short.MaxValue));
+            yield return BinaryWriterAction(w => w.Write(int.MinValue));
+            yield return BinaryWriterAction(w => w.Write(int.MaxValue));
+            yield return BinaryWriterAction(w => w.Write(long.MinValue));
+            yield return BinaryWriterAction(w => w.Write(long.MaxValue));
+            yield return BinaryWriterAction(w => w.Write(decimal.MinValue));
+            yield return BinaryWriterAction(w => w.Write(decimal.MaxValue));
+            yield return BinaryWriterAction(w => w.Write(double.MinValue));
+            yield return BinaryWriterAction(w => w.Write(double.MaxValue));
+            yield return BinaryWriterAction(w => w.Write(double.PositiveInfinity));
+            yield return BinaryWriterAction(w => w.Write(double.NaN));
+            yield return BinaryWriterAction(w => w.Write(new byte[] { 1, 2, 3, 4, 5, 6, 7 }));
+            yield return BinaryWriterAction(w => w.Write(Enumerable.Range(0, 255).SelectMany(x => Enumerable.Range(0, 255)).Select(x => (byte)x).ToArray()));
+        }
+
+        private static Action<Stream> BinaryWriterAction(Action<BinaryWriter> action)
+        {
+            return stream =>
+            {
+                using var writer = new BinaryWriter(stream, Encoding.UTF8, leaveOpen: true);
+                action(writer);
+            };
+        }
+
+        private uint ReferenceCalculation(Action<Stream> action)
+        {
+            using var stream = new MemoryStream();
+            action(stream);
+            stream.Position = 0;
+            return CalculateAdler32Checksum(stream);
+        }
+
+        private static uint CalculateAdler32Checksum(Stream stream)
+        {
+            uint s1 = 1;
+            uint s2 = 0;
+            const uint bigPrime = 0xFFF1;
+            const int bufferSize = 2048;
+            var buffer = new byte[bufferSize];
+            while (true)
+            {
+                var bytesRead = stream.Read(buffer, 0, bufferSize);
+                for (var i = 0; i < bytesRead; i++)
+                {
+                    s1 = (s1 + buffer[i]) % bigPrime;
+                    s2 = (s2 + s1) % bigPrime;
+                }
+                if (bytesRead < bufferSize)
+                {
+                    break;
+                }
+            }
+            return (s2 << 16) | s1;
+        }
+    }
+}

MatFileHandler.Tests/MatFileHandler.Tests.csproj

@@ -2,6 +2,7 @@
   <PropertyGroup>
     <TargetFrameworks>net8.0;net472</TargetFrameworks>
     <IsPackable>false</IsPackable>
+	<LangVersion>10.0</LangVersion>
   </PropertyGroup>
   <PropertyGroup>
     <CodeAnalysisRuleSet>..\MatFileHandler.ruleset</CodeAnalysisRuleSet>

MatFileHandler.Tests/MatFileWriterTests.cs

@@ -17,8 +17,8 @@ namespace MatFileHandler.Tests
         /// <summary>
         /// Test writing a simple Double array.
         /// </summary>
-        [Fact]
-        public void TestWrite()
+        [Theory, MemberData(nameof(MatFileWritingMethods))]
+        public void TestWrite(MatFileWritingMethod method)
         {
             var builder = new DataBuilder();
             var array = builder.NewArray<double>(1, 2);
@@ -26,7 +26,7 @@ namespace MatFileHandler.Tests
             array[1] = 17.0;
             var variable = builder.NewVariable("test", array);
             var actual = builder.NewFile(new[] { variable });
-            MatCompareWithTestData("good", "double-array", actual);
+            MatCompareWithTestData("good", "double-array", actual, method);
         }
 
         /// <summary>
@@ -51,8 +51,8 @@ namespace MatFileHandler.Tests
         /// <summary>
         /// Test writing lower and upper limits of integer data types.
         /// </summary>
-        [Fact]
-        public void TestLimits()
+        [Theory, MemberData(nameof(MatFileWritingMethods))]
+        public void TestLimits(MatFileWritingMethod method)
         {
             var builder = new DataBuilder();
             var int8 = builder.NewVariable("int8_", builder.NewArray(CommonData.Int8Limits, 1, 2));
@@ -64,14 +64,14 @@ namespace MatFileHandler.Tests
             var int64 = builder.NewVariable("int64_", builder.NewArray(CommonData.Int64Limits, 1, 2));
             var uint64 = builder.NewVariable("uint64_", builder.NewArray(CommonData.UInt64Limits, 1, 2));
             var actual = builder.NewFile(new[] { int16, int32, int64, int8, uint16, uint32, uint64, uint8 });
-            MatCompareWithTestData("good", "limits", actual);
+            MatCompareWithTestData("good", "limits", actual, method);
         }
 
         /// <summary>
         /// Test writing lower and upper limits of integer-based complex data types.
         /// </summary>
-        [Fact]
-        public void TestLimitsComplex()
+        [Theory, MemberData(nameof(MatFileWritingMethods))]
+        public void TestLimitsComplex(MatFileWritingMethod method)
         {
             var builder = new DataBuilder();
             var int8Complex = builder.NewVariable(
@@ -103,26 +103,26 @@ namespace MatFileHandler.Tests
                 int16Complex, int32Complex, int64Complex, int8Complex,
                 uint16Complex, uint32Complex, uint64Complex, uint8Complex,
             });
-            MatCompareWithTestData("good", "limits_complex", actual);
+            MatCompareWithTestData("good", "limits_complex", actual, method);
         }
 
         /// <summary>
         /// Test writing a wide-Unicode symbol.
         /// </summary>
-        [Fact]
-        public void TestUnicodeWide()
+        [Theory, MemberData(nameof(MatFileWritingMethods))]
+        public void TestUnicodeWide(MatFileWritingMethod method)
         {
             var builder = new DataBuilder();
             var s = builder.NewVariable("s", builder.NewCharArray("🍆"));
             var actual = builder.NewFile(new[] { s });
-            MatCompareWithTestData("good", "unicode-wide", actual);
+            MatCompareWithTestData("good", "unicode-wide", actual, method);
         }
 
         /// <summary>
         /// Test writing a sparse array.
         /// </summary>
-        [Fact]
-        public void TestSparseArray()
+        [Theory, MemberData(nameof(MatFileWritingMethods))]
+        public void TestSparseArray(MatFileWritingMethod method)
         {
             var builder = new DataBuilder();
             var sparseArray = builder.NewSparseArray<double>(4, 5);
@@ -132,14 +132,14 @@ namespace MatFileHandler.Tests
             sparseArray[2, 3] = 4;
             var sparse = builder.NewVariable("sparse_", sparseArray);
             var actual = builder.NewFile(new[] { sparse });
-            MatCompareWithTestData("good", "sparse", actual);
+            MatCompareWithTestData("good", "sparse", actual, method);
         }
 
         /// <summary>
         /// Test writing a structure array.
         /// </summary>
-        [Fact]
-        public void TestStructure()
+        [Theory, MemberData(nameof(MatFileWritingMethods))]
+        public void TestStructure(MatFileWritingMethod method)
         {
             var builder = new DataBuilder();
             var structure = builder.NewStructureArray(new[] { "x", "y" }, 2, 3);
@@ -160,27 +160,27 @@ namespace MatFileHandler.Tests
             structure["y", 1, 2] = builder.NewEmpty();
             var struct_ = builder.NewVariable("struct_", structure);
             var actual = builder.NewFile(new[] { struct_ });
-            MatCompareWithTestData("good", "struct", actual);
+            MatCompareWithTestData("good", "struct", actual, method);
         }
 
         /// <summary>
         /// Test writing a logical array.
         /// </summary>
-        [Fact]
-        public void TestLogical()
+        [Theory, MemberData(nameof(MatFileWritingMethods))]
+        public void TestLogical(MatFileWritingMethod method)
         {
             var builder = new DataBuilder();
             var logical = builder.NewArray(new[] { true, false, true, true, false, true }, 2, 3);
             var logicalVariable = builder.NewVariable("logical_", logical);
             var actual = builder.NewFile(new[] { logicalVariable });
-            MatCompareWithTestData("good", "logical", actual);
+            MatCompareWithTestData("good", "logical", actual, method);
         }
 
         /// <summary>
         /// Test writing a sparse logical array.
         /// </summary>
-        [Fact]
-        public void TestSparseLogical()
+        [Theory, MemberData(nameof(MatFileWritingMethods))]
+        public void TestSparseLogical(MatFileWritingMethod method)
         {
             var builder = new DataBuilder();
             var array = builder.NewSparseArray<bool>(2, 3);
@@ -190,14 +190,14 @@ namespace MatFileHandler.Tests
             array[1, 2] = true;
             var sparseLogical = builder.NewVariable("sparse_logical", array);
             var actual = builder.NewFile(new[] { sparseLogical });
-            MatCompareWithTestData("good", "sparse_logical", actual);
+            MatCompareWithTestData("good", "sparse_logical", actual, method);
         }
 
         /// <summary>
         /// Test writing a sparse complex array.
         /// </summary>
-        [Fact]
-        public void TestSparseComplex()
+        [Theory, MemberData(nameof(MatFileWritingMethods))]
+        public void TestSparseComplex(MatFileWritingMethod method)
         {
             var builder = new DataBuilder();
             var array = builder.NewSparseArray<Complex>(2, 2);
@@ -206,20 +206,42 @@ namespace MatFileHandler.Tests
             array[1, 1] = 0.5 + Complex.ImaginaryOne;
             var sparseComplex = builder.NewVariable("sparse_complex", array);
             var actual = builder.NewFile(new[] { sparseComplex });
-            MatCompareWithTestData("good", "sparse_complex", actual);
+            MatCompareWithTestData("good", "sparse_complex", actual, method);
         }
 
         /// <summary>
         /// Test writing a global variable.
         /// </summary>
-        [Fact]
-        public void TestGlobal()
+        [Theory, MemberData(nameof(MatFileWritingMethods))]
+        public void TestGlobal(MatFileWritingMethod method)
         {
             var builder = new DataBuilder();
             var array = builder.NewArray(new double[] { 1, 3, 5 }, 1, 3);
             var global = builder.NewVariable("global_", array, true);
             var actual = builder.NewFile(new[] { global });
-            MatCompareWithTestData("good", "global", actual);
+            MatCompareWithTestData("good", "global", actual, method);
+        }
+
+        /// <summary>
+        /// Various writing methods for testing writing of .mat files.
+        /// </summary>
+        public static TheoryData<MatFileWritingMethod> MatFileWritingMethods
+        {
+            get
+            {
+                return new TheoryData<MatFileWritingMethod>
+                {
+                    new MatFileWritingToMemoryStream(null),
+                    new MatFileWritingToMemoryStream(new MatFileWriterOptions { UseCompression = CompressionUsage.Always }),
+                    new MatFileWritingToMemoryStream(new MatFileWriterOptions { UseCompression = CompressionUsage.Never }),
+                    new MatFileWritingToUnseekableStream(null),
+                    new MatFileWritingToUnseekableStream(new MatFileWriterOptions { UseCompression = CompressionUsage.Always }),
+                    new MatFileWritingToUnseekableStream(new MatFileWriterOptions { UseCompression = CompressionUsage.Never }),
+                    new MatFileWritingToUnalignedMemoryStream(null),
+                    new MatFileWritingToUnalignedMemoryStream(new MatFileWriterOptions { UseCompression = CompressionUsage.Always }),
+                    new MatFileWritingToUnalignedMemoryStream(new MatFileWriterOptions { UseCompression = CompressionUsage.Never }),
+                };
+            }
         }
 
         private static AbstractTestDataFactory<IMatFile> GetMatTestData(string factoryName) =>
@@ -375,40 +397,18 @@ namespace MatFileHandler.Tests
             }
         }
 
-        private void CompareTestDataWithWritingOptions(
-            IMatFile expected,
+        private void MatCompareWithTestData(
+            string factoryName,
+            string testName,
             IMatFile actual,
-            MatFileWriterOptions? maybeOptions)
-        {
-            byte[] buffer;
-            using (var stream = new MemoryStream())
-            {
-                var writer = maybeOptions is MatFileWriterOptions options
-                    ? new MatFileWriter(stream, options)
-                    : new MatFileWriter(stream);
-                writer.Write(actual);
-                buffer = stream.ToArray();
-            }
-            using (var stream = new MemoryStream(buffer))
-            {
-                var reader = new MatFileReader(stream);
-                var actualRead = reader.Read();
-                CompareMatFiles(expected, actualRead);
-            }
-        }
-
-        private void MatCompareWithTestData(string factoryName, string testName, IMatFile actual)
+            MatFileWritingMethod method)
         {
             var expected = GetMatTestData(factoryName)[testName];
-            CompareTestDataWithWritingOptions(expected, actual, null);
-            CompareTestDataWithWritingOptions(
-                expected,
-                actual,
-                new MatFileWriterOptions { UseCompression = CompressionUsage.Always });
-            CompareTestDataWithWritingOptions(
-                expected,
-                actual,
-                new MatFileWriterOptions { UseCompression = CompressionUsage.Never });
+            var buffer = method.WriteMatFile(actual);
+            using var stream = new MemoryStream(buffer);
+            var reader = new MatFileReader(stream);
+            var actualRead = reader.Read();
+            CompareMatFiles(expected, actualRead);
         }
 
         private ComplexOf<T>[] CreateComplexLimits<T>(T[] limits)

MatFileHandler.Tests/MatFileWritingMethod.cs

@@ -0,0 +1,17 @@
+// Copyright 2017-2018 Alexander Luzgarev
+
+namespace MatFileHandler.Tests
+{
+    /// <summary>
+    /// A method of writing IMatFile into a byte buffer.
+    /// </summary>
+    public abstract class MatFileWritingMethod
+    {
+        /// <summary>
+        /// Write an IMatFile into a byte buffer.
+        /// </summary>
+        /// <param name="matFile"></param>
+        /// <returns></returns>
+        public abstract byte[] WriteMatFile(IMatFile matFile);
+    }
+}

MatFileHandler.Tests/MatFileWritingToMemoryStream.cs

@@ -0,0 +1,37 @@
+// Copyright 2017-2018 Alexander Luzgarev
+
+using System.IO;
+
+namespace MatFileHandler.Tests
+{
+    /// <summary>
+    /// A method of writing an IMatFile into a MemoryStream.
+    /// </summary>
+    public class MatFileWritingToMemoryStream : MatFileWritingMethod
+    {
+        private readonly MatFileWriterOptions? _maybeOptions;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="MatFileWritingToMemoryStream"/> class.
+        /// </summary>
+        /// <param name="maybeOptions">Options for the <see cref="MatFileWriter"/>.</param>
+        public MatFileWritingToMemoryStream(MatFileWriterOptions? maybeOptions)
+        {
+            _maybeOptions = maybeOptions;
+        }
+
+        /// <inheritdoc />
+        public override byte[] WriteMatFile(IMatFile matFile)
+        {
+            using var memoryStream = new MemoryStream();
+            var matFileWriter = _maybeOptions switch
+            {
+                { } options => new MatFileWriter(memoryStream, options),
+                _ => new MatFileWriter(memoryStream),
+            };
+
+            matFileWriter.Write(matFile);
+            return memoryStream.ToArray();
+        }
+    }
+}

MatFileHandler.Tests/MatFileWritingToUnalignedMemoryStream.cs

@@ -0,0 +1,43 @@
+// Copyright 2017-2018 Alexander Luzgarev
+
+using System;
+using System.IO;
+
+namespace MatFileHandler.Tests
+{
+    /// <summary>
+    /// A method of writing an IMatFile into a stream that is "unaligned".
+    /// </summary>
+    public class MatFileWritingToUnalignedMemoryStream : MatFileWritingMethod
+    {
+        private readonly MatFileWriterOptions? _maybeOptions;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="MatFileWritingToUnalignedMemoryStream"/> class.
+        /// </summary>
+        /// <param name="maybeOptions">Options for the <see cref="MatFileWriter"/>.</param>
+        public MatFileWritingToUnalignedMemoryStream(MatFileWriterOptions? maybeOptions)
+        {
+            _maybeOptions = maybeOptions;
+        }
+
+        /// <inheritdoc />
+        public override byte[] WriteMatFile(IMatFile matFile)
+        {
+            using var memoryStream = new MemoryStream();
+            memoryStream.Seek(3, SeekOrigin.Begin);
+            var matFileWriter = _maybeOptions switch
+            {
+                { } options => new MatFileWriter(memoryStream, options),
+                _ => new MatFileWriter(memoryStream),
+            };
+
+            matFileWriter.Write(matFile);
+            var fullArray = memoryStream.ToArray();
+            var length = fullArray.Length - 3;
+            var result = new byte[length];
+            Buffer.BlockCopy(fullArray, 3, result, 0, length);
+            return result;
+        }
+    }
+}

MatFileHandler.Tests/MatFileWritingToUnseekableStream.cs

@@ -0,0 +1,38 @@
+// Copyright 2017-2018 Alexander Luzgarev
+
+using System.IO;
+
+namespace MatFileHandler.Tests
+{
+    /// <summary>
+    /// A method of writing an IMatFile into a stream that is not seekable.
+    /// </summary>
+    public class MatFileWritingToUnseekableStream : MatFileWritingMethod
+    {
+        private readonly MatFileWriterOptions? _maybeOptions;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="MatFileWritingToUnseekableStream"/> class.
+        /// </summary>
+        /// <param name="maybeOptions">Options for the <see cref="MatFileWriter"/>.</param>
+        public MatFileWritingToUnseekableStream(MatFileWriterOptions? maybeOptions)
+        {
+            _maybeOptions = maybeOptions;
+        }
+
+        /// <inheritdoc />
+        public override byte[] WriteMatFile(IMatFile matFile)
+        {
+            using var memoryStream = new MemoryStream();
+            using var unseekableStream = new UnseekableWriteStream(memoryStream);
+            var matFileWriter = _maybeOptions switch
+            {
+                { } options => new MatFileWriter(unseekableStream, options),
+                _ => new MatFileWriter(unseekableStream),
+            };
+
+            matFileWriter.Write(matFile);
+            return memoryStream.ToArray();
+        }
+    }
+}

MatFileHandler.Tests/PartialUnseekableReadStream.cs

@@ -6,7 +6,8 @@ using System.IO;
 namespace MatFileHandler.Tests
 {
     /// <summary>
-    /// A stream which wraps another stream and only reads one byte at a time.
+    /// A stream which wraps another stream and only reads one byte at a time,
+    /// while forbidding seeking in it.
     /// </summary>
     internal class PartialUnseekableReadStream : Stream
     {

MatFileHandler.Tests/UnseekableWriteStream.cs

@@ -0,0 +1,70 @@
+// Copyright 2017-2018 Alexander Luzgarev
+
+using System;
+using System.IO;
+
+namespace MatFileHandler.Tests
+{
+    /// <summary>
+    /// A stream which wraps another stream and forbids seeking in it.
+    /// </summary>
+    internal class UnseekableWriteStream : Stream
+    {
+        public UnseekableWriteStream(Stream baseStream)
+        {
+            _baseStream = baseStream;
+        }
+
+        private readonly Stream _baseStream;
+
+        public override bool CanRead => false;
+
+        public override bool CanSeek => false;
+
+        public override bool CanWrite => _baseStream.CanWrite;
+
+        public override long Length => _baseStream.Length;
+
+        public override long Position
+        {
+            get => throw new NotSupportedException();
+            set => throw new NotSupportedException();
+        }
+
+        public override void Flush()
+        {
+            _baseStream.Flush();
+        }
+
+        public override int Read(byte[] buffer, int offset, int count)
+        {
+            throw new NotImplementedException();
+        }
+
+        public override long Seek(long offset, SeekOrigin origin)
+        {
+            throw new NotSupportedException();
+        }
+
+        public override void SetLength(long value)
+        {
+            throw new NotSupportedException();
+        }
+
+        public override void Write(byte[] buffer, int offset, int count)
+        {
+            _baseStream.Write(buffer, offset, count);
+        }
+
+        /// <inheritdoc/>
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                _baseStream.Dispose();
+            }
+
+            base.Dispose(disposing);
+        }
+    }
+}

MatFileHandler/ChecksumCalculatingStream.cs

@@ -0,0 +1,92 @@
+// Copyright 2017-2018 Alexander Luzgarev
+
+using System;
+using System.IO;
+
+namespace MatFileHandler
+{
+    /// <summary>
+    /// A stream that calculates Adler32 checksum of everything
+    /// written to it before passing to another stream.
+    /// </summary>
+    internal class ChecksumCalculatingStream : Stream
+    {
+        private const uint BigPrime = 0xFFF1;
+        private readonly Stream _stream;
+        private uint s1 = 1;
+        private uint s2 = 0;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ChecksumCalculatingStream"/> class.
+        /// </summary>
+        /// <param name="stream">Wrapped stream.</param>
+        public ChecksumCalculatingStream(Stream stream)
+        {
+            _stream = stream;
+        }
+
+        /// <inheritdoc />
+        public override bool CanRead => false;
+
+        /// <inheritdoc />
+        public override bool CanSeek => false;
+
+        /// <inheritdoc />
+        public override bool CanWrite => true;
+
+        /// <inheritdoc />
+        public override long Length => throw new NotImplementedException();
+
+        /// <inheritdoc />
+        public override long Position
+        {
+            get => throw new NotImplementedException();
+            set => throw new NotImplementedException();
+        }
+
+        /// <inheritdoc />
+        public override void Flush()
+        {
+            _stream.Flush();
+        }
+
+        /// <inheritdoc />
+        public override int Read(byte[] buffer, int offset, int count)
+        {
+            throw new NotImplementedException();
+        }
+
+        /// <inheritdoc />
+        public override long Seek(long offset, SeekOrigin origin)
+        {
+            throw new NotImplementedException();
+        }
+
+        /// <inheritdoc />
+        public override void SetLength(long value)
+        {
+            throw new NotImplementedException();
+        }
+
+        /// <inheritdoc />
+        public override void Write(byte[] buffer, int offset, int count)
+        {
+            for (var i = offset; i < offset + count; i++)
+            {
+                s1 = (s1 + buffer[i]) % BigPrime;
+                s2 = (s2 + s1) % BigPrime;
+            }
+
+            _stream.Write(buffer, offset, count);
+        }
+
+        /// <summary>
+        /// Calculate the checksum of everything written to the stream so far.
+        /// </summary>
+        /// <returns>Checksum of everything written to the stream so far.</returns>
+        public uint GetCrc()
+        {
+            return (s2 << 16) | s1;
+        }
+    }
+}

MatFileHandler/FakeWriter.cs

@@ -0,0 +1,398 @@
+// Copyright 2017-2018 Alexander Luzgarev
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Numerics;
+using System.Text;
+
+namespace MatFileHandler
+{
+    /// <summary>
+    /// A simulated writer of .mat files that just calculate the length of data that would be written.
+    /// </summary>
+    internal class FakeWriter
+    {
+        /// <summary>
+        /// Gets current position of the writer.
+        /// </summary>
+        public int Position { get; private set; }
+
+        /// <summary>
+        /// Write contents of a numerical array.
+        /// </summary>
+        /// <param name="array">A numerical array.</param>
+        /// <param name="name">Name of the array.</param>
+        public void WriteNumericalArrayContents(IArray array, string name)
+        {
+            WriteArrayFlags();
+            WriteDimensions(array.Dimensions);
+            WriteName(name);
+            WriteNumericalArrayValues(array);
+        }
+
+        /// <summary>
+        /// Write contents of a char array.
+        /// </summary>
+        /// <param name="charArray">A char array.</param>
+        /// <param name="name">Name of the array.</param>
+        public void WriteCharArrayContents(ICharArray charArray, string name)
+        {
+            WriteArrayFlags();
+            WriteDimensions(charArray.Dimensions);
+            WriteName(name);
+            WriteDataElement(GetLengthOfByteArray<ushort>(charArray.String.Length));
+        }
+
+        /// <summary>
+        /// Write contents of a sparse array.
+        /// </summary>
+        /// <typeparam name="T">Array element type.</typeparam>
+        /// <param name="array">A sparse array.</param>
+        /// <param name="name">Name of the array.</param>
+        public void WriteSparseArrayContents<T>(
+            ISparseArrayOf<T> array,
+            string name)
+            where T : unmanaged, IEquatable<T>
+        {
+            (var rowsLength, var columnsLength, var dataLength, var nonZero) = PrepareSparseArrayData(array);
+            WriteSparseArrayFlags();
+            WriteDimensions(array.Dimensions);
+            WriteName(name);
+            WriteSparseArrayValues<T>(rowsLength, columnsLength, dataLength);
+        }
+
+        /// <summary>
+        /// Write contents of a structure array.
+        /// </summary>
+        /// <param name="array">A structure array.</param>
+        /// <param name="name">Name of the array.</param>
+        public void WriteStructureArrayContents(IStructureArray array, string name)
+        {
+            WriteArrayFlags();
+            WriteDimensions(array.Dimensions);
+            WriteName(name);
+            WriteFieldNames(array.FieldNames);
+            WriteStructureArrayValues(array);
+        }
+
+        /// <summary>
+        /// Write contents of a cell array.
+        /// </summary>
+        /// <param name="array">A cell array.</param>
+        /// <param name="name">Name of the array.</param>
+        public void WriteCellArrayContents(ICellArray array, string name)
+        {
+            WriteArrayFlags();
+            WriteDimensions(array.Dimensions);
+            WriteName(name);
+            WriteCellArrayValues(array);
+        }
+
+        private void WriteTag()
+        {
+            Position += 8;
+        }
+
+        private void WriteShortTag()
+        {
+            Position += 4;
+        }
+
+        private void WriteWrappingContents<T>(T array, Action<FakeWriter> writeContents)
+            where T : IArray
+        {
+            if (array.IsEmpty)
+            {
+                WriteTag();
+                return;
+            }
+
+            WriteTag();
+            writeContents(this);
+        }
+
+        private void WriteNumericalArrayValues(IArray value)
+        {
+            switch (value)
+            {
+                case IArrayOf<sbyte> sbyteArray:
+                    WriteDataElement(GetLengthOfByteArray<sbyte>(sbyteArray.Data.Length));
+                    break;
+                case IArrayOf<byte> byteArray:
+                    WriteDataElement(GetLengthOfByteArray<byte>(byteArray.Data.Length));
+                    break;
+                case IArrayOf<short> shortArray:
+                    WriteDataElement(GetLengthOfByteArray<short>(shortArray.Data.Length));
+                    break;
+                case IArrayOf<ushort> ushortArray:
+                    WriteDataElement(GetLengthOfByteArray<ushort>(ushortArray.Data.Length));
+                    break;
+                case IArrayOf<int> intArray:
+                    WriteDataElement(GetLengthOfByteArray<int>(intArray.Data.Length));
+                    break;
+                case IArrayOf<uint> uintArray:
+                    WriteDataElement(GetLengthOfByteArray<uint>(uintArray.Data.Length));
+                    break;
+                case IArrayOf<long> longArray:
+                    WriteDataElement(GetLengthOfByteArray<long>(longArray.Data.Length));
+                    break;
+                case IArrayOf<ulong> ulongArray:
+                    WriteDataElement(GetLengthOfByteArray<ulong>(ulongArray.Data.Length));
+                    break;
+                case IArrayOf<float> floatArray:
+                    WriteDataElement(GetLengthOfByteArray<float>(floatArray.Data.Length));
+                    break;
+                case IArrayOf<double> doubleArray:
+                    WriteDataElement(GetLengthOfByteArray<double>(doubleArray.Data.Length));
+                    break;
+                case IArrayOf<bool> boolArray:
+                    WriteDataElement(boolArray.Data.Length);
+                    break;
+                case IArrayOf<ComplexOf<sbyte>> complexSbyteArray:
+                    WriteComplexValues(GetLengthOfPairOfByteArrays(complexSbyteArray.Data));
+                    break;
+                case IArrayOf<ComplexOf<byte>> complexByteArray:
+                    WriteComplexValues(GetLengthOfPairOfByteArrays(complexByteArray.Data));
+                    break;
+                case IArrayOf<ComplexOf<short>> complexShortArray:
+                    WriteComplexValues(GetLengthOfPairOfByteArrays(complexShortArray.Data));
+                    break;
+                case IArrayOf<ComplexOf<ushort>> complexUshortArray:
+                    WriteComplexValues(GetLengthOfPairOfByteArrays(complexUshortArray.Data));
+                    break;
+                case IArrayOf<ComplexOf<int>> complexIntArray:
+                    WriteComplexValues(GetLengthOfPairOfByteArrays(complexIntArray.Data));
+                    break;
+                case IArrayOf<ComplexOf<uint>> complexUintArray:
+                    WriteComplexValues(GetLengthOfPairOfByteArrays(complexUintArray.Data));
+                    break;
+                case IArrayOf<ComplexOf<long>> complexLongArray:
+                    WriteComplexValues(GetLengthOfPairOfByteArrays(complexLongArray.Data));
+                    break;
+                case IArrayOf<ComplexOf<ulong>> complexUlongArray:
+                    WriteComplexValues(GetLengthOfPairOfByteArrays(complexUlongArray.Data));
+                    break;
+                case IArrayOf<ComplexOf<float>> complexFloatArray:
+                    WriteComplexValues(GetLengthOfPairOfByteArrays(complexFloatArray.Data));
+                    break;
+                case IArrayOf<Complex> complexDoubleArray:
+                    WriteComplexValues(GetLengthOfPairOfByteArrays(complexDoubleArray.Data));
+                    break;
+                default:
+                    throw new NotSupportedException();
+            }
+        }
+
+        private void WriteName(string name)
+        {
+            var nameBytes = Encoding.ASCII.GetBytes(name);
+            WriteDataElement(nameBytes.Length);
+        }
+
+        private void WriteArrayFlags()
+        {
+            WriteTag();
+            Position += 8;
+        }
+
+        private void WriteDimensions(int[] dimensions)
+        {
+            var buffer = GetLengthOfByteArray<int>(dimensions.Length);
+            WriteDataElement(buffer);
+        }
+
+        private unsafe int GetLengthOfByteArray<T>(int dataLength)
+            where T : unmanaged
+        {
+            return dataLength * sizeof(T);
+        }
+
+        private unsafe int GetLengthOfPairOfByteArrays<T>(ComplexOf<T>[] data)
+            where T : unmanaged
+        {
+            return data.Length * sizeof(T);
+        }
+
+        private unsafe int GetLengthOfPairOfByteArrays(Complex[] data)
+        {
+            return data.Length * sizeof(double);
+        }
+
+        private int CalculatePadding(int length)
+        {
+            var rem = length % 8;
+            if (rem == 0)
+            {
+                return 0;
+            }
+
+            return 8 - rem;
+        }
+
+        private void WriteDataElement(int dataLength)
+        {
+            var maybePadding = 0;
+            if (dataLength > 4)
+            {
+                WriteTag();
+                Position += dataLength;
+                maybePadding = CalculatePadding(dataLength + 8);
+            }
+            else
+            {
+                WriteShortTag();
+                Position += 4;
+            }
+
+            Position += maybePadding;
+        }
+
+        private void WriteComplexValues(
+            int dataLength)
+        {
+            WriteDataElement(dataLength);
+            WriteDataElement(dataLength);
+        }
+
+        private void WriteSparseArrayValues<T>(int rowsLength, int columnsLength, int dataLength)
+          where T : unmanaged
+        {
+            WriteDataElement(GetLengthOfByteArray<int>(rowsLength));
+            WriteDataElement(GetLengthOfByteArray<int>(columnsLength));
+            if (typeof(T) == typeof(double))
+            {
+                WriteDataElement(GetLengthOfByteArray<double>(dataLength));
+            }
+            else if (typeof(T) == typeof(Complex))
+            {
+                WriteDataElement(GetLengthOfByteArray<double>(dataLength));
+                WriteDataElement(GetLengthOfByteArray<double>(dataLength));
+            }
+            else if (typeof(T) == typeof(bool))
+            {
+                WriteDataElement(dataLength);
+            }
+        }
+
+        private (int rowIndexLength, int columnIndexLength, int dataLength, uint nonZero) PrepareSparseArrayData<T>(
+            ISparseArrayOf<T> array)
+            where T : struct, IEquatable<T>
+        {
+            var numberOfColumns = array.Dimensions[1];
+            var numberOfElements = array.Data.Values.Count(value => !value.Equals(default));
+            return (numberOfElements, numberOfColumns + 1, numberOfElements, (uint)numberOfElements);
+        }
+
+        private void WriteSparseArrayFlags()
+        {
+            WriteTag();
+            Position += 8;
+        }
+
+        private void WriteFieldNames(IEnumerable<string> fieldNames)
+        {
+            var fieldNamesArray = fieldNames.Select(name => Encoding.ASCII.GetBytes(name)).ToArray();
+            var maxFieldName = fieldNamesArray.Select(name => name.Length).Max() + 1;
+            WriteDataElement(GetLengthOfByteArray<int>(1));
+            var buffer = new byte[fieldNamesArray.Length * maxFieldName];
+            var startPosition = 0;
+            foreach (var name in fieldNamesArray)
+            {
+                for (var i = 0; i < name.Length; i++)
+                {
+                    buffer[startPosition + i] = name[i];
+                }
+                startPosition += maxFieldName;
+            }
+            WriteDataElement(buffer.Length);
+        }
+
+        private void WriteStructureArrayValues(IStructureArray array)
+        {
+            for (var i = 0; i < array.Count; i++)
+            {
+                foreach (var name in array.FieldNames)
+                {
+                    WriteArray(array[name, i]);
+                }
+            }
+        }
+
+        private void WriteArray(IArray array, string variableName = "", bool isGlobal = false)
+        {
+            switch (array)
+            {
+                case ICharArray charArray:
+                    WriteCharArray(charArray, variableName);
+                    break;
+                case ISparseArrayOf<double> doubleSparseArray:
+                    WriteSparseArray(doubleSparseArray, variableName);
+                    break;
+                case ISparseArrayOf<Complex> complexSparseArray:
+                    WriteSparseArray(complexSparseArray, variableName);
+                    break;
+                case ISparseArrayOf<bool> boolSparseArray:
+                    WriteSparseArray(boolSparseArray, variableName);
+                    break;
+                case ICellArray cellArray:
+                    WriteCellArray(cellArray, variableName);
+                    break;
+                case IStructureArray structureArray:
+                    WriteStructureArray(structureArray, variableName);
+                    break;
+                default:
+                    WriteNumericalArray(array, variableName);
+                    break;
+            }
+        }
+
+        private void WriteCharArray(ICharArray charArray, string name)
+        {
+            WriteWrappingContents(
+                charArray,
+                fakeWriter => fakeWriter.WriteCharArrayContents(charArray, name));
+        }
+
+        private void WriteSparseArray<T>(ISparseArrayOf<T> sparseArray, string name)
+            where T : unmanaged, IEquatable<T>
+        {
+            WriteWrappingContents(
+                sparseArray,
+                fakeWriter => fakeWriter.WriteSparseArrayContents(sparseArray, name));
+        }
+
+        private void WriteCellArray(ICellArray cellArray, string name)
+        {
+            WriteWrappingContents(
+                cellArray,
+                fakeWriter => fakeWriter.WriteCellArrayContents(cellArray, name));
+        }
+
+        private void WriteCellArrayValues(ICellArray array)
+        {
+            for (var i = 0; i < array.Count; i++)
+            {
+                WriteArray(array[i]);
+            }
+        }
+
+        private void WriteStructureArray(
+            IStructureArray structureArray,
+            string name)
+        {
+            WriteWrappingContents(
+                structureArray,
+                fakeWriter => fakeWriter.WriteStructureArrayContents(structureArray, name));
+        }
+
+        private void WriteNumericalArray(
+            IArray numericalArray,
+            string name = "")
+        {
+            WriteWrappingContents(
+                numericalArray,
+                fakeWriter => fakeWriter.WriteNumericalArrayContents(numericalArray, name));
+        }
+    }
+}

MatFileHandler/MatFileHandler.csproj

@@ -22,6 +22,7 @@
     <IncludeSymbols>true</IncludeSymbols>
     <EmbedUntrackedSources>true</EmbedUntrackedSources>
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
 
   <ItemGroup>
@@ -46,4 +47,7 @@
   <ItemGroup>
     <None Include="..\README.md" Pack="true" PackagePath="\"/>
   </ItemGroup>
+  <ItemGroup>
+    <InternalsVisibleTo Include="MatFileHandler.Tests" />
+  </ItemGroup>
 </Project>

MatFileHandler/MatFileWriter.cs

@@ -55,7 +55,15 @@ namespace MatFileHandler
                     switch (_options.UseCompression)
                     {
                         case CompressionUsage.Always:
-                            WriteCompressedVariable(writer, variable);
+                            if (Stream.CanSeek)
+                            {
+                                WriteCompressedVariableToSeekableStream(writer, variable);
+                            }
+                            else
+                            {
+                                WriteCompressedVariableToUnseekableStream(writer, variable);
+                            }
+
                             break;
                         case CompressionUsage.Never:
                             WriteVariable(writer, variable);
@@ -125,6 +133,12 @@ namespace MatFileHandler
             {
                 WriteTag(writer, new Tag(type, data.Length));
                 writer.Write(data);
+                var rem = data.Length % 8;
+                if (rem > 0)
+                {
+                    var padding = new byte[8 - rem];
+                    writer.Write(padding);
+                }
             }
             else
             {
@@ -136,7 +150,6 @@ namespace MatFileHandler
                     writer.Write(padding);
                 }
             }
-            WritePadding(writer);
         }
 
         private void WriteDimensions(BinaryWriter writer, int[] dimensions)
@@ -393,7 +406,11 @@ namespace MatFileHandler
             return new ArrayFlags(ArrayType.MxChar, isGlobal ? Variable.IsGlobal : 0);
         }
 
-        private void WriteWrappingContents<T>(BinaryWriter writer, T array, Action<BinaryWriter> writeContents)
+        private void WriteWrappingContents<T>(
+            BinaryWriter writer,
+            T array,
+            Action<FakeWriter> lengthCalculator,
+            Action<BinaryWriter> writeContents)
             where T : IArray
         {
             if (array.IsEmpty)
@@ -401,16 +418,12 @@ namespace MatFileHandler
                 WriteTag(writer, new Tag(DataType.MiMatrix, 0));
                 return;
             }
-            using (var contents = new MemoryStream())
-            {
-                using (var contentsWriter = new BinaryWriter(contents))
-                {
-                    writeContents(contentsWriter);
-                    WriteTag(writer, new Tag(DataType.MiMatrix, (int)contents.Length));
-                    contents.Position = 0;
-                    contents.CopyTo(writer.BaseStream);
-                }
-            }
+
+            var fakeWriter = new FakeWriter();
+            lengthCalculator(fakeWriter);
+            var calculatedLength = fakeWriter.Position;
+            WriteTag(writer, new Tag(DataType.MiMatrix, calculatedLength));
+            writeContents(writer);
         }
 
         private void WriteNumericalArrayContents(BinaryWriter writer, IArray array, string name, bool isGlobal)
@@ -430,6 +443,7 @@ namespace MatFileHandler
             WriteWrappingContents(
                 writer,
                 numericalArray,
+                fakeWriter => fakeWriter.WriteNumericalArrayContents(numericalArray, name),
                 contentsWriter => { WriteNumericalArrayContents(contentsWriter, numericalArray, name, isGlobal); });
         }
 
@@ -447,6 +461,7 @@ namespace MatFileHandler
             WriteWrappingContents(
                 writer,
                 charArray,
+                fakeWriter => fakeWriter.WriteCharArrayContents(charArray, name),
                 contentsWriter => { WriteCharArrayContents(contentsWriter, charArray, name, isGlobal); });
         }
 
@@ -520,11 +535,12 @@ namespace MatFileHandler
         }
 
         private void WriteSparseArray<T>(BinaryWriter writer, ISparseArrayOf<T> sparseArray, string name, bool isGlobal)
-            where T : struct, IEquatable<T>
+            where T : unmanaged, IEquatable<T>
         {
             WriteWrappingContents(
                 writer,
                 sparseArray,
+                fakeWriter => fakeWriter.WriteSparseArrayContents(sparseArray, name),
                 contentsWriter => { WriteSparseArrayContents(contentsWriter, sparseArray, name, isGlobal); });
         }
 
@@ -575,6 +591,7 @@ namespace MatFileHandler
             WriteWrappingContents(
                 writer,
                 structureArray,
+                fakeWriter => fakeWriter.WriteStructureArrayContents(structureArray, name),
                 contentsWriter => { WriteStructureArrayContents(contentsWriter, structureArray, name, isGlobal); });
         }
 
@@ -599,6 +616,7 @@ namespace MatFileHandler
             WriteWrappingContents(
                 writer,
                 cellArray,
+                fakeWriter => fakeWriter.WriteCellArrayContents(cellArray, name),
                 contentsWriter => { WriteCellArrayContents(contentsWriter, cellArray, name, isGlobal); });
         }
 
@@ -635,7 +653,33 @@ namespace MatFileHandler
             WriteArray(writer, variable.Value, variable.Name, variable.IsGlobal);
         }
 
-        private void WriteCompressedVariable(BinaryWriter writer, IVariable variable)
+        private void WriteCompressedVariableToSeekableStream(BinaryWriter writer, IVariable variable)
+        {
+            var position = writer.BaseStream.Position;
+            WriteTag(writer, new Tag(DataType.MiCompressed, 0));
+            writer.Write((byte)0x78);
+            writer.Write((byte)0x9c);
+            int compressedLength;
+            uint crc;
+            var before = writer.BaseStream.Position;
+            using (var compressionStream = new DeflateStream(writer.BaseStream, CompressionMode.Compress, leaveOpen: true))
+            {
+                using var checksumStream = new ChecksumCalculatingStream(compressionStream);
+                using var internalWriter = new BinaryWriter(checksumStream, Encoding.UTF8, leaveOpen: true);
+                WriteVariable(internalWriter, variable);
+                crc = checksumStream.GetCrc();
+            }
+
+            var after = writer.BaseStream.Position;
+            compressedLength = (int)(after - before) + 6;
+
+            writer.Write(BitConverter.GetBytes(crc).Reverse().ToArray());
+            writer.BaseStream.Position = position;
+            WriteTag(writer, new Tag(DataType.MiCompressed, compressedLength));
+            writer.BaseStream.Seek(0, SeekOrigin.End);
+        }
+
+        private void WriteCompressedVariableToUnseekableStream(BinaryWriter writer, IVariable variable)
         {
             using (var compressedStream = new MemoryStream())
             {