From f3a3dd2629489afbc0b7239b4976f95848a869a1 Mon Sep 17 00:00:00 2001
From: Boris <boris.dogadov@mongodb.com>
Date: Tue, 5 Jan 2021 12:47:44 -0800
Subject: [PATCH] CSHARP-1525: JsonReader auto reset buffer

---
 src/MongoDB.Bson/IO/JsonBuffer.cs         | 22 +++++++++++++---------
 src/MongoDB.Bson/IO/JsonReader.cs         | 19 +++++++++++++++++--
 src/MongoDB.Bson/IO/JsonReaderSettings.cs | 15 +++++++++++++++
 3 files changed, 45 insertions(+), 11 deletions(-)

diff --git a/src/MongoDB.Bson/IO/JsonBuffer.cs b/src/MongoDB.Bson/IO/JsonBuffer.cs
index 83b824a5e2e..4b44b1c9158 100644
--- a/src/MongoDB.Bson/IO/JsonBuffer.cs
+++ b/src/MongoDB.Bson/IO/JsonBuffer.cs
@@ -25,6 +25,8 @@ namespace MongoDB.Bson.IO
     internal class JsonBuffer
     {
         // private fields
+        private readonly int _readChunkSize;
+        private readonly int _minDiscardBufferSize;
         private readonly StringBuilder _buffer;
         private int _position;
         private readonly TextReader _reader;
@@ -43,11 +45,11 @@ public JsonBuffer(string json)
             _buffer = new StringBuilder(json);
         }
 
-        /// <summary>
-        /// Initializes a new instance of the <see cref="JsonBuffer" /> class.
-        /// </summary>
+        /// <summary>Initializes a new instance of the <see cref="JsonBuffer" /> class.</summary>
         /// <param name="reader">The reader.</param>
-        public JsonBuffer(TextReader reader)
+        /// <param name="readChunkSize"></param>
+        /// <param name="minResetBufferSize"></param>
+        public JsonBuffer(TextReader reader, int readChunkSize, int minResetBufferSize)
         {
             if (reader == null)
             {
@@ -55,6 +57,10 @@ public JsonBuffer(TextReader reader)
             }
             _buffer = new StringBuilder(256); // start out with a reasonable initial capacity
             _reader = reader;
+
+            // TODO BD validation
+            _readChunkSize = readChunkSize;
+            _minDiscardBufferSize = minResetBufferSize;
         }
 
         // public properties
@@ -146,8 +152,7 @@ public int Read()
         public void ResetBuffer()
         {
             // only trim the buffer if enough space will be reclaimed to make it worthwhile
-            var minimumTrimCount = 256; // TODO: make configurable?
-            if (_position >= minimumTrimCount)
+            if (_position >= _minDiscardBufferSize)
             {
                 _buffer.Remove(0, _position);
                 _position = 0;
@@ -189,9 +194,8 @@ private void ReadMoreIfAtEndOfBuffer()
             {
                 if (_reader != null)
                 {
-                    var blockSize = 1024; // TODO: make configurable?
-                    var block = new char[blockSize];
-                    var actualCount = _reader.ReadBlock(block, 0, blockSize);
+                    var block = new char[_readChunkSize];
+                    var actualCount = _reader.ReadBlock(block, 0, _readChunkSize);
 
                     if (actualCount > 0)
                     {
diff --git a/src/MongoDB.Bson/IO/JsonReader.cs b/src/MongoDB.Bson/IO/JsonReader.cs
index e640585a256..a0c67c95412 100644
--- a/src/MongoDB.Bson/IO/JsonReader.cs
+++ b/src/MongoDB.Bson/IO/JsonReader.cs
@@ -72,6 +72,8 @@ public class JsonReader : BsonReader
         private BsonValue _currentValue;
         private JsonToken _pushedToken;
 
+        private readonly List<JsonReaderBookmark> _bookmarks = new List<JsonReaderBookmark>();
+
         // constructors
         /// <summary>
         /// Initializes a new instance of the JsonReader class.
@@ -107,7 +109,7 @@ public JsonReader(TextReader textReader)
         /// <param name="textReader">The TextReader.</param>
         /// <param name="settings">The reader settings.</param>
         public JsonReader(TextReader textReader, JsonReaderSettings settings)
-            : this(new JsonBuffer(textReader), settings)
+            : this(new JsonBuffer(textReader, settings.ReadChunkSize, settings.MinResetBufferSize), settings)
         {
         }
 
@@ -135,7 +137,10 @@ public override void Close()
         /// <returns>A bookmark.</returns>
         public override BsonReaderBookmark GetBookmark()
         {
-            return new JsonReaderBookmark(State, CurrentBsonType, CurrentName, _context, _currentToken, _currentValue, _pushedToken, _buffer.Position);
+            var bookmark = new JsonReaderBookmark(State, CurrentBsonType, CurrentName, _context, _currentToken, _currentValue, _pushedToken, _buffer.Position);
+            _bookmarks.Add(bookmark);
+
+            return bookmark;
         }
 
         /// <summary>
@@ -399,6 +404,12 @@ public override BsonType ReadBsonType()
                     State = BsonReaderState.Value;
                     break;
             }
+
+            if (_jsonReaderSettings.AutoBufferReset && _bookmarks.Count == 0)
+            {
+                _buffer.ResetBuffer();
+            }
+
             return CurrentBsonType;
         }
 
@@ -749,6 +760,7 @@ public override void ReadUndefined()
         public override void ReturnToBookmark(BsonReaderBookmark bookmark)
         {
             if (Disposed) { ThrowObjectDisposedException(); }
+
             var jsonReaderBookmark = (JsonReaderBookmark)bookmark;
             State = jsonReaderBookmark.State;
             CurrentBsonType = jsonReaderBookmark.CurrentBsonType;
@@ -758,6 +770,9 @@ public override void ReturnToBookmark(BsonReaderBookmark bookmark)
             _currentValue = jsonReaderBookmark.CurrentValue;
             _pushedToken = jsonReaderBookmark.PushedToken;
             _buffer.Position = jsonReaderBookmark.Position;
+
+            // TODO BD throw if not found?
+            _bookmarks.Remove(jsonReaderBookmark);
         }
 
         /// <summary>
diff --git a/src/MongoDB.Bson/IO/JsonReaderSettings.cs b/src/MongoDB.Bson/IO/JsonReaderSettings.cs
index 2c00ea2b54a..4d98d2bfd61 100644
--- a/src/MongoDB.Bson/IO/JsonReaderSettings.cs
+++ b/src/MongoDB.Bson/IO/JsonReaderSettings.cs
@@ -28,6 +28,21 @@ public class JsonReaderSettings : BsonReaderSettings
         // private static fields
         private static JsonReaderSettings __defaults = null; // delay creation to pick up the latest default values
 
+        /// <summary>
+        /// TODO BD
+        /// </summary>
+        public bool AutoBufferReset { get; set; } = true;
+
+        /// <summary>
+        /// TODO BD
+        /// </summary>
+        public int ReadChunkSize { get; set; } = 2048;
+
+        /// <summary>
+        /// TODO BD
+        /// </summary>
+        public int MinResetBufferSize { get; set; } = 512;
+
         // constructors
         /// <summary>
         /// Initializes a new instance of the JsonReaderSettings class.