From 7d70bc6dc0eb87675736832705d29303bb7cc184 Mon Sep 17 00:00:00 2001
From: mr-sven <sven.fabricius@livediesel.de>
Date: Mon, 14 Feb 2022 10:20:18 +0100
Subject: [PATCH 1/2] Add can seek for filestream read

---
 LiteDB/Client/Storage/LiteFileStream.Read.cs | 16 ++++++++++
 LiteDB/Client/Storage/LiteFileStream.cs      | 31 +++++++++++++++-----
 2 files changed, 40 insertions(+), 7 deletions(-)

diff --git a/LiteDB/Client/Storage/LiteFileStream.Read.cs b/LiteDB/Client/Storage/LiteFileStream.Read.cs
index e60aeb0f9..ed4d4e158 100644
--- a/LiteDB/Client/Storage/LiteFileStream.Read.cs
+++ b/LiteDB/Client/Storage/LiteFileStream.Read.cs
@@ -44,5 +44,21 @@ private byte[] GetChunkData(int index)
             // if chunk is null there is no more chunks
             return chunk?["data"].AsBinary;
         }
+
+        private void SetReadStreamPosition(long newPosition)
+        {
+            if (newPosition < 0 && newPosition > Length)
+            {
+                throw new ArgumentOutOfRangeException();
+            }
+            _streamPosition = newPosition;
+
+            // calculate new chunk position
+            _currentChunkIndex = (int)_streamPosition / MAX_CHUNK_SIZE;
+            _positionInChunk = (int)_streamPosition % MAX_CHUNK_SIZE;
+
+            // get current chunk
+            _currentChunkData = this.GetChunkData(_currentChunkIndex);
+        }
     }
 }
\ No newline at end of file
diff --git a/LiteDB/Client/Storage/LiteFileStream.cs b/LiteDB/Client/Storage/LiteFileStream.cs
index dea5edd91..abde415fa 100644
--- a/LiteDB/Client/Storage/LiteFileStream.cs
+++ b/LiteDB/Client/Storage/LiteFileStream.cs
@@ -66,12 +66,34 @@ internal LiteFileStream(ILiteCollection<LiteFileInfo<TFileId>> files, ILiteColle
 
         public override bool CanWrite { get { return _mode == FileAccess.Write; } }
 
-        public override bool CanSeek { get { return false; } }
+        public override bool CanSeek { get { return _mode == FileAccess.Read; } }
 
         public override long Position
         {
             get { return _streamPosition; }
-            set { throw new NotSupportedException(); }
+            set { if (_mode == FileAccess.Read) { this.SetReadStreamPosition(value); } else { throw new NotSupportedException(); } }
+        }
+
+        public override long Seek(long offset, SeekOrigin origin)
+        {
+            if (_mode == FileAccess.Write)
+            {
+                throw new NotSupportedException();
+            }
+
+            switch (origin)
+            {
+                case SeekOrigin.Begin:
+                    this.SetReadStreamPosition(offset);
+                    break;
+                case SeekOrigin.Current:
+                    this.SetReadStreamPosition(_streamPosition + offset);
+                    break;
+                case SeekOrigin.End:
+                    this.SetReadStreamPosition(Length - offset);
+                    break;
+            }
+            return _streamPosition;
         }
 
         #region Dispose
@@ -97,11 +119,6 @@ protected override void Dispose(bool disposing)
 
         #region Not supported operations
 
-        public override long Seek(long offset, SeekOrigin origin)
-        {
-            throw new NotSupportedException();
-        }
-
         public override void SetLength(long value)
         {
             throw new NotSupportedException();

From a04a931f6a6def44f704c8806d417322756449e6 Mon Sep 17 00:00:00 2001
From: mr-sven <sven.fabricius@livediesel.de>
Date: Mon, 14 Feb 2022 13:18:35 +0100
Subject: [PATCH 2/2] Seek from end gets negative value

---
 LiteDB/Client/Storage/LiteFileStream.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/LiteDB/Client/Storage/LiteFileStream.cs b/LiteDB/Client/Storage/LiteFileStream.cs
index abde415fa..1b476f645 100644
--- a/LiteDB/Client/Storage/LiteFileStream.cs
+++ b/LiteDB/Client/Storage/LiteFileStream.cs
@@ -90,7 +90,7 @@ public override long Seek(long offset, SeekOrigin origin)
                     this.SetReadStreamPosition(_streamPosition + offset);
                     break;
                 case SeekOrigin.End:
-                    this.SetReadStreamPosition(Length - offset);
+                    this.SetReadStreamPosition(Length + offset);
                     break;
             }
             return _streamPosition;