Add regression test

Author: JKamsker

LiteDB.Tests/Issues/Issue2523_ReadFull_Tests.cs

@@ -0,0 +1,158 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using FluentAssertions;
+using LiteDB.Engine;
+using Xunit;
+
+namespace LiteDB.Tests.Issues;
+
+public class Issue2523_ReadFull_Tests
+{
+    [Fact]
+    public void ReadFull_Must_See_Log_Page_Written_In_Same_Tick()
+    {
+        using var logStream = new DelayedPublishLogStream(); // <-- changed
+        using var dataStream = new MemoryStream();
+
+        var settings = new EngineSettings
+        {
+            DataStream = dataStream,
+            LogStream = logStream
+        };
+
+        var state = new EngineState(null, settings);
+        var disk = new DiskService(settings, state, new[] { 10 });
+
+        try
+        {
+            // Arrange: create a single, full page
+            var page = disk.NewPage();
+            page.Fill(0xAC);
+
+            // Act: write the page to the WAL/log
+            disk.WriteLogDisk(new[] { page });
+
+            // Assert: immediately read the log back fully.
+            // Pre-fix: throws (ReadFull must read PAGE_SIZE bytes)
+            // Post-fix: returns 1 page, filled with 0xAC
+            var logPages = disk.ReadFull(FileOrigin.Log).ToList();
+
+            logPages.Should().HaveCount(1);
+            logPages[0].All(0xAC).Should().BeTrue();
+        }
+        finally
+        {
+            disk.Dispose();
+        }
+    }
+
+    /// <summary>
+    /// Stream that "accepts" writes (increases Length as the writer would see it),
+    /// but hides the bytes from readers until Flush/FlushAsync publishes them.
+    /// This mirrors the visibility gap the fix (stream.Flush()) closes.
+    /// </summary>
+    private sealed class DelayedPublishLogStream : Stream
+    {
+        private readonly MemoryStream _committed = new(); // bytes visible to readers
+        private readonly List<(long Position, byte[] Data)> _pending = new();
+
+        private long _writerLength;    // total bytes "written" by Write(...)
+        private long _visibleLength;   // committed length visible to Read(...)
+        private long _position;        // logical cursor for both read/write
+
+        public override bool CanRead  => true;
+        public override bool CanSeek  => true;
+        public override bool CanWrite => true;
+
+        // IMPORTANT: advertise writer's view of length (includes pending).
+        public override long Length => _writerLength;
+
+        public override long Position
+        {
+            get => _position;
+            set => _position = value;
+        }
+
+        public override void Flush()
+        {
+            // Publish pending bytes
+            foreach (var (pos, data) in _pending)
+            {
+                _committed.Position = pos;
+                _committed.Write(data, 0, data.Length);
+            }
+            _pending.Clear();
+            _committed.Flush();
+
+            // Make everything visible
+            _visibleLength = _writerLength;
+        }
+
+        public override System.Threading.Tasks.Task FlushAsync(System.Threading.CancellationToken cancellationToken)
+        {
+            Flush();
+            return System.Threading.Tasks.Task.CompletedTask;
+        }
+
+        public override int Read(byte[] buffer, int offset, int count)
+        {
+            // Serve only what has been published (visibleLength)
+            if (_position >= _visibleLength) return 0;
+
+            var available = (int)Math.Min(count, _visibleLength - _position);
+            _committed.Position = _position;
+            var read = _committed.Read(buffer, offset, available);
+            _position += read;
+            return read;
+        }
+
+        public override long Seek(long offset, SeekOrigin origin)
+        {
+            _position = origin switch
+            {
+                SeekOrigin.Begin => offset,
+                SeekOrigin.Current => _position + offset,
+                // IMPORTANT: base End on the *advertised* writer length, not committed length
+                SeekOrigin.End => _writerLength + offset,
+                _ => throw new ArgumentOutOfRangeException(nameof(origin))
+            };
+
+            if (_position < 0) throw new IOException("Negative position.");
+            return _position;
+        }
+
+        public override void SetLength(long value)
+        {
+            if (value < 0) throw new IOException("Negative length.");
+            // Adjust both writer length and (if shrinking) visible length.
+            _writerLength = value;
+            if (_visibleLength > value) _visibleLength = value;
+            if (_committed.Length < value) _committed.SetLength(value);
+            if (_position > value) _position = value;
+        }
+
+        public override void Write(byte[] buffer, int offset, int count)
+        {
+            if (buffer is null) throw new ArgumentNullException(nameof(buffer));
+            if ((uint)offset > buffer.Length) throw new ArgumentOutOfRangeException(nameof(offset));
+            if ((uint)count > buffer.Length - offset) throw new ArgumentOutOfRangeException(nameof(count));
+
+            // Capture write into pending (not visible yet)
+            var copy = new byte[count];
+            Buffer.BlockCopy(buffer, offset, copy, 0, count);
+            _pending.Add((_position, copy));
+
+            _position += count;
+            if (_position > _writerLength) _writerLength = _position;
+            // NOTE: _visibleLength is NOT updated here; only Flush() publishes writes.
+        }
+
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing) _committed.Dispose();
+            base.Dispose(disposing);
+        }
+    }
+}