Create class for reading Json files in chunks

src/NuGet.Core/NuGet.ProjectModel/Utf8JsonReaderExtensions.cs

@@ -0,0 +1,40 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Text.Json;
+
+namespace NuGet.ProjectModel
+{
+    internal static class Utf8JsonReaderExtensions
+    {
+        internal static string ReadTokenAsString(this ref Utf8JsonReader reader)
+        {
+            switch (reader.TokenType)
+            {
+                case JsonTokenType.True:
+                    return bool.TrueString;
+                case JsonTokenType.False:
+                    return bool.FalseString;
+                case JsonTokenType.Number:
+                    return reader.ReadNumberAsString();
+                case JsonTokenType.String:
+                    return reader.GetString();
+                case JsonTokenType.None:
+                case JsonTokenType.Null:
+                    return null;
+                default:
+                    throw new InvalidCastException();
+            }
+        }
+
+        private static string ReadNumberAsString(this ref Utf8JsonReader reader)
+        {
+            if (reader.TryGetInt64(out long value))
+            {
+                return value.ToString();
+            }
+            return reader.GetDouble().ToString();
+        }
+    }
+}

src/NuGet.Core/NuGet.ProjectModel/Utf8JsonStreamReader.cs

@@ -0,0 +1,273 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Buffers;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text.Json;
+
+namespace NuGet.ProjectModel
+{
+    /// <summary>
+    /// This struct is used to read over a memeory stream in parts, in order to avoid reading the entire stream into memory.
+    /// It functions as a wrapper around <see cref="Utf8JsonStreamReader"/>, while maintaining a stream and a buffer to read from.
+    /// </summary>
+    internal ref struct Utf8JsonStreamReader
+    {
+        private static readonly char[] DelimitedStringDelimiters = [' ', ','];
+        private static readonly byte[] Utf8Bom = [0xEF, 0xBB, 0xBF];
+
+        private const int BufferSizeDefault = 16 * 1024;
+        private const int MinBufferSize = 1024;
+        private Utf8JsonReader _reader;
+#pragma warning disable CA2213 // Disposable fields should be disposed
+        private Stream _stream;
+#pragma warning restore CA2213 // Disposable fields should be disposed
+        // The buffer is used to read from the stream in chunks.
+        private byte[] _buffer;
+        private bool _disposed;
+        private ArrayPool<byte> _bufferPool;
+        private int _bufferUsed = 0;
+
+        internal Utf8JsonStreamReader(Stream stream, int bufferSize = BufferSizeDefault, ArrayPool<byte> arrayPool = null)
+        {
+            if (stream is null)
+            {
+                throw new ArgumentNullException(nameof(stream));
+            }
+
+            if (bufferSize < MinBufferSize)
+            {
+                throw new ArgumentException($"Buffer size must be at least {MinBufferSize} bytes", nameof(bufferSize));
+            }
+
+            _bufferPool = arrayPool ?? ArrayPool<byte>.Shared;
+            _buffer = _bufferPool.Rent(bufferSize);
+            _disposed = false;
+            _stream = stream;
+            _stream.Read(_buffer, 0, 3);
+            if (!Utf8Bom.AsSpan().SequenceEqual(_buffer.AsSpan(0, 3)))
+            {
+                _bufferUsed = 3;
+            }
+
+            var iniialJsonReaderState = new JsonReaderState(new JsonReaderOptions
+            {
+                AllowTrailingCommas = true,
+                CommentHandling = JsonCommentHandling.Skip,
+            });
+
+            ReadStreamIntoBuffer(iniialJsonReaderState);
+            _reader.Read();
+        }
+
+        internal bool IsFinalBlock => _reader.IsFinalBlock;
+
+        internal JsonTokenType TokenType => _reader.TokenType;
+
+        internal bool ValueTextEquals(ReadOnlySpan<byte> utf8Text) => _reader.ValueTextEquals(utf8Text);
+
+        internal bool TryGetInt32(out int value) => _reader.TryGetInt32(out value);
+
+        internal string GetString() => _reader.GetString();
+
+        internal bool GetBoolean() => _reader.GetBoolean();
+
+        internal int GetInt32() => _reader.GetInt32();
+
+        internal bool Read()
+        {
+            ThrowExceptionIfDisposed();
+
+            bool wasRead;
+            while (!(wasRead = _reader.Read()) && !_reader.IsFinalBlock)
+            {
+                GetMoreBytesFromStream();
+            }
+            return wasRead;
+        }
+
+        internal void Skip()
+        {
+            ThrowExceptionIfDisposed();
+
+            bool wasSkipped;
+            while (!(wasSkipped = _reader.TrySkip()) && !_reader.IsFinalBlock)
+            {
+                GetMoreBytesFromStream();
+            }
+            if (!wasSkipped)
+            {
+                _reader.Skip();
+            }
+        }
+
+        internal string ReadNextTokenAsString()
+        {
+            ThrowExceptionIfDisposed();
+
+            if (Read())
+            {
+                return _reader.ReadTokenAsString();
+            }
+
+            return null;
+        }
+
+        internal IList<string> ReadStringArrayAsIList(IList<string> strings = null)
+        {
+            if (TokenType == JsonTokenType.StartArray)
+            {
+                while (Read() && TokenType != JsonTokenType.EndArray)
+                {
+                    string value = _reader.ReadTokenAsString();
+
+                    strings = strings ?? new List<string>();
+
+                    strings.Add(value);
+                }
+            }
+            return strings;
+        }
+
+        internal IReadOnlyList<string> ReadDelimitedString()
+        {
+            ThrowExceptionIfDisposed();
+
+            if (Read())
+            {
+                switch (TokenType)
+                {
+                    case JsonTokenType.String:
+                        var value = GetString();
+
+                        return value.Split(DelimitedStringDelimiters, StringSplitOptions.RemoveEmptyEntries);
+
+                    default:
+                        var invalidCastException = new InvalidCastException();
+                        throw new JsonException(invalidCastException.Message, invalidCastException);
+                }
+            }
+
+            return null;
+        }
+
+        internal bool ReadNextTokenAsBoolOrFalse()
+        {
+            ThrowExceptionIfDisposed();
+
+            if (Read() && (TokenType == JsonTokenType.False || TokenType == JsonTokenType.True))
+            {
+                return GetBoolean();
+            }
+            return false;
+        }
+
+        internal IReadOnlyList<string> ReadNextStringOrArrayOfStringsAsReadOnlyList()
+        {
+            ThrowExceptionIfDisposed();
+
+            if (Read())
+            {
+                switch (_reader.TokenType)
+                {
+                    case JsonTokenType.String:
+                        return new[] { (string)_reader.GetString() };
+
+                    case JsonTokenType.StartArray:
+                        return ReadStringArrayAsReadOnlyListFromArrayStart();
+
+                    case JsonTokenType.StartObject:
+                        return null;
+                }
+            }
+
+            return null;
+        }
+
+        internal IReadOnlyList<string> ReadStringArrayAsReadOnlyListFromArrayStart()
+        {
+            ThrowExceptionIfDisposed();
+
+            List<string> strings = null;
+
+            while (Read() && _reader.TokenType != JsonTokenType.EndArray)
+            {
+                string value = _reader.ReadTokenAsString();
+
+                strings = strings ?? new List<string>();
+
+                strings.Add(value);
+            }
+
+            return (IReadOnlyList<string>)strings ?? Array.Empty<string>();
+        }
+
+        // This function is called when Read() returns false and we're not already in the final block
+        private void GetMoreBytesFromStream()
+        {
+            if (_reader.BytesConsumed < _bufferUsed)
+            {
+                // If the number of bytes consumed by the reader is less than the amount set in the buffer then we have leftover bytes
+                var oldBuffer = _buffer;
+                ReadOnlySpan<byte> leftover = oldBuffer.AsSpan((int)_reader.BytesConsumed);
+                _bufferUsed = leftover.Length;
+
+                // If the leftover bytes are the same as the buffer size then we are at capacity and need to double the buffer size
+                if (leftover.Length == _buffer.Length)
+                {
+                    _buffer = _bufferPool.Rent(_buffer.Length * 2);
+                    leftover.CopyTo(_buffer);
+                    _bufferPool.Return(oldBuffer, true);
+                }
+                else
+                {
+                    leftover.CopyTo(_buffer);
+                }
+            }
+            else
+            {
+                _bufferUsed = 0;
+            }
+
+            ReadStreamIntoBuffer(_reader.CurrentState);
+        }
+
+        /// <summary>
+        /// Loops through the stream and reads it into the buffer until the buffer is full or the stream is empty, creates the Utf8JsonReader. 
+        /// </summary>
+        private void ReadStreamIntoBuffer(JsonReaderState jsonReaderState)
+        {
+            int bytesRead;
+            do
+            {
+                var spaceLeftInBuffer = _buffer.Length - _bufferUsed;
+                bytesRead = _stream.Read(_buffer, _bufferUsed, spaceLeftInBuffer);
+                _bufferUsed += bytesRead;
+            }
+            while (bytesRead != 0 && _bufferUsed != _buffer.Length);
+            _reader = new Utf8JsonReader(_buffer.AsSpan(0, _bufferUsed), isFinalBlock: bytesRead == 0, jsonReaderState);
+        }
+
+        public void Dispose()
+        {
+            if (!_disposed)
+            {
+                _disposed = true;
+                byte[] toReturn = _buffer;
+                _buffer = null!;
+                _bufferPool.Return(toReturn, true);
+            }
+        }
+
+        private void ThrowExceptionIfDisposed()
+        {
+            if (_disposed)
+            {
+                throw new ObjectDisposedException(nameof(Utf8JsonStreamReader));
+            }
+        }
+    }
+}

src/NuGet.Core/NuGet.ProjectModel/Utf8JsonStreamReaderConverter.cs

@@ -0,0 +1,13 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+namespace NuGet.ProjectModel
+{
+    /// <summary>
+    /// An abstract class that defines a function for reading a <see cref="Utf8JsonStreamReader"/> into a <typeparamref name="T"/>
+    /// </summary>
+    /// <typeparam name="T"></typeparam>
+    internal abstract class Utf8JsonStreamReaderConverter<T>
+    {
+        public abstract T Read(ref Utf8JsonStreamReader reader);
+    }
+}

test/NuGet.Core.Tests/NuGet.ProjectModel.Test/LockFileFormatTests.cs

@@ -213,7 +213,6 @@ public void LockFileFormat_ReadsLockFileWithNoTools()
 
             var target = lockFile.Targets.Single();
             Assert.Equal(NuGetFramework.Parse("dotnet"), target.TargetFramework);
-
             var runtimeTargetLibrary = target.Libraries.Single();
             Assert.Equal("System.Runtime", runtimeTargetLibrary.Name);
             Assert.Equal(NuGetVersion.Parse("4.0.20-beta-22927"), runtimeTargetLibrary.Version);

test/NuGet.Core.Tests/NuGet.ProjectModel.Test/Utf8JsonReaderExtensionsTests.cs

@@ -0,0 +1,35 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Text;
+using System.Text.Json;
+using Xunit;
+
+namespace NuGet.ProjectModel.Test
+{
+    [UseCulture("")] // Fix tests failing on systems with non-English locales
+    public class Utf8JsonReaderExtensionsTests
+    {
+        [Theory]
+        [InlineData("null", null)]
+        [InlineData("true", "True")]
+        [InlineData("false", "False")]
+        [InlineData("-2", "-2")]
+        [InlineData("9223372036854775807", "9223372036854775807")]
+        [InlineData("3.14", "3.14")]
+        [InlineData("\"b\"", "b")]
+        public void ReadTokenAsString_WhenValueIsConvertibleToString_ReturnsValueAsString(
+            string value,
+            string expectedResult)
+        {
+            var json = $"{{\"a\":{value}}}";
+            var encodedBytes = Encoding.UTF8.GetBytes(json);
+            var reader = new Utf8JsonReader(encodedBytes);
+            reader.Read();
+            reader.Read();
+            reader.Read();
+            string actualResult = reader.ReadTokenAsString();
+            Assert.Equal(expectedResult, actualResult);
+        }
+    }
+}