JsonObjectStore.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using Newtonsoft.Json;
using Newtonsoft.Json.Bson;

namespace Ramp.Data
{
    /// <summary>
    ///     An interface to a key value store that provides support for JSON object serialization.
    /// </summary>
    public class JsonObjectStore
    {
        public const string IndexBucketName = "_JS_IDX";
        public const string VersionKey = "JS_Version";
        public const string BinaryKey = "JS_Binary";
        public const ushort Version = 1;

        private readonly IKeyValueStore _store;
        private readonly bool _binary;
        private readonly JsonSerializer _serializer;
        private readonly Encoding _encoding = new UTF8Encoding(false, true); // do not write utf8 byte mark

        /// <summary>
        ///     Initialize the store.
        /// </summary>
        /// <param name="store"> The underlying key value store. </param>
        /// <param name="settings"> The JSON serializer settings. If null, uses default settings. </param>
        /// <param name="binary"> True to serialize using the binary BSON format. </param>
        public JsonObjectStore(IKeyValueStore store, JsonSerializerSettings settings = null, bool binary = false)
        {
            if (store == null)
                throw new ArgumentNullException("store");
            _store = store;
            _binary = binary;
            _serializer = settings == null ? JsonSerializer.CreateDefault() : JsonSerializer.Create(settings);
            Initialize();
        }

        /// <summary>
        ///     Gets whether BSON is being used to store objects.
        /// </summary>
        public bool Binary
        {
            get { return _binary; }
        }

        /// <summary>
        ///     Gets the underlying key value store.
        /// </summary>
        public IKeyValueStore Store
        {
            get { return _store; }
        }

        /// <summary>
        ///     Get an object from the store.
        /// </summary>
        /// <typeparam name="T"> The object type. </typeparam>
        /// <param name="bucket"> The bucket. </param>
        /// <param name="key"> The key. </param>
        /// <param name="serializer"> The serializer to use for deserializing the object. If null, uses the default. </param>
        /// <returns> The deserialized object. </returns>
        public T GetObject<T>(string bucket, string key, JsonSerializer serializer = null)
        {
            serializer = serializer ?? _serializer;
            byte[] data = _store.GetBytesOrDefault(bucket, key);
            if (data == null)
                return default(T);
            using (JsonReader jreader = GetReader(data))
            {
                return serializer.Deserialize<T>(jreader);
            }
        }

        /// <summary>
        ///     Set an object in the store.
        /// </summary>
        /// <typeparam name="T"> The object type. </typeparam>
        /// <param name="bucket"> The bucket. </param>
        /// <param name="key"> The key. </param>
        /// <param name="value"> The object. </param>
        /// <param name="serializer"> The serializer to use for serializing the object. If null, uses the default. </param>
        public void SetObject<T>(string bucket, string key, T value, JsonSerializer serializer = null)
        {
            serializer = serializer ?? _serializer;
            MemoryStream mstream;
            using (JsonWriter jwriter = GetWriter(out mstream))
            {
                serializer.Serialize(jwriter, value, typeof(T));
                jwriter.Flush();
                _store.Set(bucket, key, mstream.ToArray());
            }
        }

        /// <summary>
        ///     Gets all objects in a bucket.
        /// </summary>
        /// <typeparam name="T"> The object type. </typeparam>
        /// <param name="bucket"> The bucket. </param>
        /// <param name="serializer"> The serializer to use for serializing the object. If null, uses the default. </param>
        /// <returns> An enumerable object providing all keys and objects in the specified bucket. </returns>
        public IEnumerable<KeyValuePair<string, T>> GetObjects<T>(string bucket, JsonSerializer serializer)
        {
            serializer = serializer ?? _serializer;
            foreach (KeyValuePair<string, byte[]> item in _store.GetItemBytes(bucket))
            {
                using (JsonReader jreader = GetReader(item.Value))
                {
                    yield return new KeyValuePair<string, T>(item.Key, serializer.Deserialize<T>(jreader));
                }
            }
        }

        private void Initialize()
        {
            // Verison check
            var version = _store.GetValueOrDefault<int>(_store.MetadataBucketName, VersionKey);
            if (version > Version)
                throw new InvalidDataException("Store version is higher than current verison.");
            version = 1;
            _store.Set(_store.MetadataBucketName, VersionKey, version);

            // Format check
            bool currentlyBinary = _store.GetValueOrDefault<bool?>(_store.MetadataBucketName, BinaryKey) ?? _binary;
            if (currentlyBinary != _binary)
                throw new InvalidOperationException("Existing store has different format.");
            _store.Set(_store.MetadataBucketName, BinaryKey, _binary);
        }

        private JsonReader GetReader(byte[] data)
        {
            if (_binary)
                return new BsonReader(new BinaryReader(new MemoryStream(data, false), _encoding), false,
                                      DateTimeKind.Utc);
            return new JsonTextReader(new StreamReader(new MemoryStream(data, false), _encoding));
        }

        private JsonWriter GetWriter(out MemoryStream stream)
        {
            stream = new MemoryStream();
            if (_binary)
                return new BsonWriter(new BinaryWriter(stream, _encoding)) { DateTimeKindHandling = DateTimeKind.Utc };
            return new JsonTextWriter(new StreamWriter(stream, _encoding));
        }
    }
}