Add support for RZX file format

Author: voytas

…Extensions/ByteStreamReaderExtensions.cs …Extensions/ByteStreamReaderExtensions.cssrc/Spectron.Files/Szx/Extensions/ByteStreamReaderExtensions.cs renamed to src/Spectron.Files/Extensions/ByteStreamReaderExtensions.cs src/Spectron.Files/Szx/Extensions/ByteStreamReaderExtensions.cs renamed to src/Spectron.Files/Extensions/ByteStreamReaderExtensions.cs

@@ -1,7 +1,7 @@
 using System.Text;
 using OldBit.Spectron.Files.IO;
 
-namespace OldBit.Spectron.Files.Szx.Extensions;
+namespace OldBit.Spectron.Files.Extensions;
 
 internal static class ByteStreamReaderExtensions
 {

src/Spectron.Files/Extensions/BytesExtensions.cs

@@ -7,10 +7,17 @@ internal static class BytesExtensions
     internal static string ToAsciiString(this IEnumerable<byte> bytes)
     {
         var s = new StringBuilder();
+
         foreach (var b in bytes)
         {
+            if (b == 0)
+            {
+                continue;
+            }
+
             s.Append((char)b);
         }
+
         return s.ToString();
     }
 }

src/Spectron.Files/Extensions/StreamExtensions.cs

@@ -0,0 +1,41 @@
+using System.Text;
+
+namespace OldBit.Spectron.Files.Extensions;
+
+internal static class StreamExtensions
+{
+    extension(Stream stream)
+    {
+        internal void WriteWord(int value)
+        {
+            stream.WriteByte((byte)value);
+            stream.WriteByte((byte)(value >> 8));
+        }
+
+        internal void WriteDWord(DWord value)
+        {
+            stream.WriteByte((byte)value);
+            stream.WriteByte((byte)(value >> 8));
+            stream.WriteByte((byte)(value >> 16));
+            stream.WriteByte((byte)(value >> 24));
+        }
+
+        internal void WriteBytes(byte[] value) => stream.Write(value, 0, value.Length);
+
+        internal void WriteChars(string value, int length)
+        {
+            if (length == 0)
+            {
+                return;
+            }
+
+            var bytes = Encoding.ASCII.GetBytes(value);
+            stream.Write(bytes, 0, Math.Min(bytes.Length, length));
+
+            if (bytes.Length < length)
+            {
+                stream.Write(new byte[length - bytes.Length], 0, length - bytes.Length);
+            }
+        }
+    }
+}

src/Spectron.Files/IO/ByteStreamReader.cs

@@ -11,54 +11,27 @@ internal sealed class ByteStreamReader
     /// Create a new instance of the byte reader.
     /// </summary>
     /// <param name="stream">The stream that provides data for the reader.</param>
-    public ByteStreamReader(Stream stream)
-    {
-        _stream = stream;
-    }
+    public ByteStreamReader(Stream stream) => _stream = stream;
 
     /// <summary>
     /// Reads a byte from the stream and advances the position within the stream by one byte.
     /// </summary>
     /// <returns>The byte retrieved from the stream.</returns>
     /// <exception cref="EndOfStreamException">Thrown when not enough data is in the stream.</exception>
-    public byte ReadByte()
-    {
-        if (!TryReadByte( out var data))
-        {
-            throw new EndOfStreamException();
-        }
-
-        return data;
-    }
+    public byte ReadByte() => !TryReadByte( out var data) ? throw new EndOfStreamException() : data;
 
     /// <summary>
     /// Reads a word from the stream and advances the position within the stream by two bytes.
     /// </summary>
     /// <returns>The word retrieved from the stream.</returns>
     /// <exception cref="EndOfStreamException">Thrown when not enough data is in the stream.</exception>
-    public Word ReadWord()
-    {
-        if (!TryReadWord(out var data))
-        {
-            throw new EndOfStreamException();
-        }
-
-        return data;
-    }
+    public Word ReadWord() => !TryReadWord(out var data) ? throw new EndOfStreamException() : data;
 
     /// <summary>
     /// Reads a dword from the stream and advances the position within the stream by four bytes.
     /// </summary>
     /// <returns>The dword retrieved from the stream.</returns>
-    public DWord ReadDWord()
-    {
-        if (!TryReadDWord(out var data))
-        {
-            throw new EndOfStreamException();
-        }
-
-        return data;
-    }
+    public DWord ReadDWord() => !TryReadDWord(out var data) ? throw new EndOfStreamException() : data;
 
     /// <summary>
     /// Reads a sequence of bytes from the stream and advances the position within the stream by 'count' bytes.

src/Spectron.Files/IO/DataWriter.cs

@@ -1,5 +1,5 @@
+using OldBit.Spectron.Files.Extensions;
 using OldBit.Spectron.Files.Serialization;
-using OldBit.Spectron.Files.Szx.Extensions;
 using OldBit.Spectron.Files.Tap;
 using OldBit.Spectron.Files.Tzx.Blocks;
 

src/Spectron.Files/Rzx/BlockIds.cs

@@ -0,0 +1,10 @@
+namespace OldBit.Spectron.Files.Rzx;
+
+internal static class BlockIds
+{
+    internal const byte Creator = 0x10;
+    internal const byte Security = 0x20;
+    internal const byte Signature = 0x21;
+    internal const byte Snapshot = 0x30;
+    internal const byte Recording = 0x80;
+}

src/Spectron.Files/Rzx/Blocks/BlockHeader.cs

@@ -0,0 +1,19 @@
+using OldBit.Spectron.Files.IO;
+
+namespace OldBit.Spectron.Files.Rzx.Blocks;
+
+internal sealed class BlockHeader(byte blockId, DWord size)
+{
+    internal byte BlockId { get; } = blockId;
+    internal DWord Size { get; } = size;
+
+    internal static BlockHeader? Read(ByteStreamReader reader)
+    {
+        if (reader.TryReadByte(out var blockId) && reader.TryReadDWord(out var size))
+        {
+            return new BlockHeader(blockId, size);
+        }
+
+        return null;
+    }
+}

src/Spectron.Files/Rzx/Blocks/CreatorBlock.cs

@@ -0,0 +1,43 @@
+using OldBit.Spectron.Files.Extensions;
+using OldBit.Spectron.Files.IO;
+
+namespace OldBit.Spectron.Files.Rzx.Blocks;
+
+/// <summary>
+/// Information about the program which created the RZX.
+/// </summary>
+public class CreatorBlock
+{
+    /// <summary>
+    /// Creator's identification string.
+    /// </summary>≠≠
+    public string CreatorName { get; private set; } = string.Empty;
+
+    /// <summary>
+    /// Creator's major version number.
+    /// </summary>
+    public Word MajorVersion { get; private set; }
+
+    /// <summary>
+    /// Creator's minor version number.
+    /// </summary>
+    public Word MinorVersion { get; private set; }
+
+    /// <summary>
+    /// Creator's custom data (may be absent).
+    /// </summary>
+    public byte[]? Data { get; private set; }
+
+    internal static CreatorBlock Read(ByteStreamReader reader, DWord blockLength)
+    {
+        var block = new CreatorBlock();
+
+        var bytes = reader.ReadBytes(20);
+        block.CreatorName = bytes.ToAsciiString().Trim();
+        block.MajorVersion = reader.ReadWord();
+        block.MinorVersion = reader.ReadWord();
+        block.Data = reader.ReadBytes((int)(blockLength - 29));
+
+        return block;
+    }
+}

src/Spectron.Files/Rzx/Blocks/RecordingBlock.cs

@@ -0,0 +1,80 @@
+using OldBit.Spectron.Files.IO;
+using OldBit.Spectron.Files.Szx;
+
+namespace OldBit.Spectron.Files.Rzx.Blocks;
+
+/// <summary>
+/// Actual input recording data.
+/// </summary>
+public class RecordingBlock
+{
+    /// <summary>
+    /// Number of frames in the block.
+    /// </summary>
+    public DWord FrameCount { get; private init; }
+
+    /// <summary>
+    /// Reserved.
+    /// </summary>
+    public byte Reserved { get; private set; }
+
+    /// <summary>
+    /// T-STATES counter at the beginning.
+    /// </summary>
+    public DWord TStatesCounter { get; private set; }
+
+    /// <summary>
+    /// Flags (b0: Protected (frames are encrypted with x-key), b1: Compressed data.)
+    /// </summary>
+    public DWord Flags { get; private set; }
+
+    public List<RecordingFrame> Frames { get; } = [];
+
+    internal static RecordingBlock Read(ByteStreamReader reader, DWord blockLength)
+    {
+        var block = new RecordingBlock
+        {
+            FrameCount = reader.ReadDWord(),
+            Reserved = reader.ReadByte(),
+            TStatesCounter = reader.ReadDWord(),
+            Flags = reader.ReadDWord()
+        };
+
+        var isProtected = (block.Flags & 0x01) == 0x01;
+        if (isProtected)
+        {
+            throw new NotSupportedException("Protected recording blocks are not supported.");
+        }
+
+        var data = reader.ReadBytes((int)(blockLength - 18));
+
+        var isCompressed = (block.Flags & 0x02) == 0x02;
+        if (isCompressed)
+        {
+            data = ZLibHelper.Decompress(data);
+        }
+
+        ReadFrames(block, data);
+
+        return block;
+    }
+
+    private static void ReadFrames(RecordingBlock block, byte[] data)
+    {
+        var memoryStream = new MemoryStream(data);
+        var reader = new ByteStreamReader(memoryStream);
+
+        for (var i = 0; i < block.FrameCount; i++)
+        {
+            var frame = RecordingFrame.Read(reader);
+
+            if (frame.InCounter == 65535)
+            {
+                // Repeated frame, copy the values from the previous frame
+                frame.Values = block.Frames.LastOrDefault()?.Values ?? [];
+            }
+
+            block.Frames.Add(frame);
+        }
+    }
+}

src/Spectron.Files/Rzx/Blocks/RecordingFrame.cs

@@ -0,0 +1,41 @@
+using OldBit.Spectron.Files.IO;
+
+namespace OldBit.Spectron.Files.Rzx.Blocks;
+
+/// <summary>
+/// Layout of the input log for the frame.
+/// </summary>
+public class RecordingFrame
+{
+    /// <summary>
+    /// Fetch counter till next interrupt (i.e. number of R increments, INTA excluded)
+    /// </summary>
+    public Word FetchCounter { get; private set; }
+
+    /// <summary>
+    /// IN counter. Number of I/O port reads performed by the CPU in this frame (their return values follow).
+    /// If equal to 65,535, this was a repeated frame, i.e. the port reads were exactly the same of the last frame.
+    /// </summary>
+    public Word InCounter { get; private set; }
+
+    /// <summary>
+    /// Return values for the CPU I/O port reads.
+    /// </summary>
+    public byte[] Values { get; internal set; } = [];
+
+    internal static RecordingFrame Read(ByteStreamReader reader)
+    {
+        var block = new RecordingFrame
+        {
+            FetchCounter = reader.ReadWord(),
+            InCounter = reader.ReadWord()
+        };
+
+        if (block.InCounter != 65535)
+        {
+            block.Values = reader.ReadBytes(block.InCounter);
+        }
+
+        return block;
+    }
+}