DiskDataCacheProvider.cs

/*
 * QUANTCONNECT.COM - Democratizing Finance, Empowering Individuals.
 * Lean Algorithmic Trading Engine v2.0. Copyright 2014 QuantConnect Corporation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
*/
 
using System.IO;
using Ionic.Zip;
using System.Linq;
using QuantConnect.Util;
using QuantConnect.Logging;
using QuantConnect.Interfaces;
using System.Collections.Generic;
 
namespace QuantConnect.Data
{
    /// <summary>
    /// Simple data cache provider, writes and reads directly from disk
    /// Used as default for <see cref="LeanDataWriter"/>
    /// </summary>
    public class DiskDataCacheProvider : IDataCacheProvider
    {
        private readonly KeyStringSynchronizer _synchronizer;
 
        /// <summary>
        /// Property indicating the data is temporary in nature and should not be cached.
        /// </summary>
        public bool IsDataEphemeral => false;
 
        /// <summary>
        /// Creates a new instance
        /// </summary>
        public DiskDataCacheProvider() : this(new KeyStringSynchronizer())
        {
        }
 
        /// <summary>
        /// Creates a new instance using the given synchronizer
        /// </summary>
        /// <param name="locker">The synchronizer instance to use</param>
        public DiskDataCacheProvider(KeyStringSynchronizer locker)
        {
            _synchronizer = locker;
        }
 
        /// <summary>
        /// Fetch data from the cache
        /// </summary>
        /// <param name="key">A string representing the key of the cached data</param>
        /// <returns>An <see cref="Stream"/> of the cached data</returns>
        public Stream Fetch(string key)
        {
            LeanData.ParseKey(key, out var filePath, out var entryName);
 
            return _synchronizer.Execute(filePath, () =>
            {
                if (!File.Exists(filePath))
                {
                    return null;
                }
 
                try
                {
                    using (var zip = ZipFile.Read(filePath))
                    {
                        ZipEntry entry;
                        if (entryName.IsNullOrEmpty())
                        {
                            // Return the first entry
                            entry = zip[0];
                        }
                        else
                        {
                            // Attempt to find our specific entry
                            if (!zip.ContainsEntry(entryName))
                            {
                                return null;
                            }
 
                            entry = zip[entryName];
                        }
 
                        // Extract our entry and return it
                        var stream = new MemoryStream();
                        entry.Extract(stream);
                        stream.Position = 0;
                        return stream;
                    }
                }
                catch (ZipException exception)
                {
                    Log.Error("DiskDataCacheProvider.Fetch(): Corrupt file: " + key + " Error: " + exception);
                    return null;
                }
            });
        }
 
        /// <summary>
        /// Store the data in the cache. Not implemented in this instance of the IDataCacheProvider
        /// </summary>
        /// <param name="key">The source of the data, used as a key to retrieve data in the cache</param>
        /// <param name="data">The data as a byte array</param>
        public void Store(string key, byte[] data)
        {
            LeanData.ParseKey(key, out var filePath, out var entryName);
 
            _synchronizer.Execute(filePath, singleExecution: false, () =>
            {
                Compression.ZipCreateAppendData(filePath, entryName, data, true);
            });
        }
 
        /// <summary>
        /// Returns a list of zip entries in a provided zip file
        /// </summary>
        public List<string> GetZipEntries(string zipFile)
        {
            return _synchronizer.Execute(zipFile, () =>
            {
                using var stream = new FileStream(FileExtension.ToNormalizedPath(zipFile), FileMode.Open, FileAccess.Read);
                return Compression.GetZipEntryFileNames(stream).ToList();
            });
        }
 
        /// <summary>
        /// Dispose for this class
        /// </summary>
        public void Dispose()
        {
            //NOP
        }
    }
}