Implement KuCoin orderbook WebSocket listener (#828)

src/ExchangeSharp/API/Exchanges/Kraken/ExchangeKrakenAPI.cs

@@ -1484,7 +1484,7 @@ private async Task<List<string>> GetMarketSymbolList(string[] marketSymbols)
 		/// <returns></returns>
 		protected override async Task<IWebSocket> OnGetDeltaOrderBookWebSocketAsync(
 				Action<ExchangeOrderBook> callback,
-				int maxCount = 20,
+				int maxCount = 100,
 				params string[] marketSymbols
 		)
 		{
@@ -1639,7 +1639,7 @@ params string[] marketSymbols
 						{
 							Event = ActionType.Subscribe,
 							Pairs = marketSymbols.ToList(),
-							SubscriptionSettings = new Subscription { Name = "book", Depth = 100 }
+							SubscriptionSettings = new Subscription { Name = "book", Depth = maxCount }
 						};
 						await _socket.SendMessageAsync(channelAction);
 					}

src/ExchangeSharp/API/Exchanges/KuCoin/ExchangeKuCoinAPI.cs

@@ -20,6 +20,8 @@ The above copyright notice and this permission notice shall be included in all c
 using System.Security.Cryptography;
 using System.Text;
 using System.Threading.Tasks;
+using ExchangeSharp.API.Exchanges.Kraken.Models.Request;
+using ExchangeSharp.API.Exchanges.Kraken.Models.Types;
 using Newtonsoft.Json;
 using Newtonsoft.Json.Linq;
 
@@ -39,6 +41,7 @@ private ExchangeKuCoinAPI()
 			NonceEndPointStyle = NonceStyle.UnixMilliseconds;
 			MarketSymbolSeparator = "-";
 			RateLimit = new RateGate(20, TimeSpan.FromSeconds(60.0));
+			WebSocketOrderBookType = WebSocketOrderBookType.FullBookFirstThenDeltas;
 		}
 
 		public override string PeriodSecondsToString(int seconds)
@@ -233,7 +236,9 @@ protected override async Task<ExchangeOrderBook> OnGetOrderBookAsync(
 			JToken token = await MakeJsonRequestAsync<JToken>(
 					"/market/orderbook/level2_" + maxCount + "?symbol=" + marketSymbol
 			);
-			return token.ParseOrderBookFromJTokenArrays(asks: "asks", bids: "bids");
+			var book = token.ParseOrderBookFromJTokenArrays(asks: "asks", bids: "bids", sequence: "sequence");
+			book.MarketSymbol = marketSymbol;
+			return book;
 		}
 
 		protected override async Task<ExchangeTicker> OnGetTickerAsync(string marketSymbol)
@@ -804,6 +809,127 @@ await _socket.SendMessageAsync(
 			);
 		}
 
+		protected override async Task<IWebSocket> OnGetDeltaOrderBookWebSocketAsync(
+				Action<ExchangeOrderBook> callback,
+				int maxCount = 20,
+				params string[] marketSymbols
+		)
+		{
+			if (marketSymbols == null || marketSymbols.Length == 0)
+			{
+				marketSymbols = (await GetMarketSymbolsAsync(true)).ToArray();
+			}
+
+			var initialSequenceIds = new Dictionary<string, long>();
+
+			var websocketUrlToken = GetWebsocketBulletToken();
+
+			return await ConnectPublicWebSocketAsync(
+					$"?token={websocketUrlToken}&acceptUserMessage=true",
+					messageCallback: (_socket, msg) =>
+					{
+						var message = msg.ToStringFromUTF8();
+						var deserializedMessage = JsonConvert.DeserializeObject(message) as JObject;
+
+						var data = deserializedMessage["data"];
+						if (data is null)
+						{
+							return Task.CompletedTask;
+						}
+
+						var changes = data["changes"];
+						var time = data["time"];
+						var symbol = data["symbol"];
+						if (changes is null || time is null || symbol is null)
+						{
+							return Task.CompletedTask;
+						}
+
+						var parsedTime = time.ConvertInvariant<long>();
+						var lastUpdatedDateTime = DateTimeOffset
+							.FromUnixTimeMilliseconds(parsedTime)
+							.DateTime;
+
+						var deltaBook = new ExchangeOrderBook
+						{
+							IsFromSnapshot = false,
+							ExchangeName = ExchangeName.Kucoin,
+							SequenceId = parsedTime,
+							MarketSymbol = symbol.ToString(),
+							LastUpdatedUtc = lastUpdatedDateTime,
+						};
+
+						var rawAsks = changes["asks"] as JArray;
+						foreach (var rawAsk in rawAsks)
+						{
+							var sequence = rawAsk[2].ConvertInvariant<long>();
+							if (sequence <= initialSequenceIds[deltaBook.MarketSymbol])
+							{
+								// A deprecated update should be ignored
+								continue;
+							}
+
+							var price = rawAsk[0].ConvertInvariant<decimal>();
+							var quantity = rawAsk[1].ConvertInvariant<decimal>();
+
+							deltaBook.Asks[price] = new ExchangeOrderPrice
+							{
+								Price = price,
+								Amount = quantity,
+							};
+						}
+
+						var rawBids = changes["bids"] as JArray;
+						foreach (var rawBid in rawBids)
+						{
+							var sequence = rawBid[2].ConvertInvariant<long>();
+							if (sequence <= initialSequenceIds[deltaBook.MarketSymbol])
+							{
+								// A deprecated update should be ignored
+								continue;
+							}
+
+							var price = rawBid[0].ConvertInvariant<decimal>();
+							var quantity = rawBid[1].ConvertInvariant<decimal>();
+
+							deltaBook.Bids[price] = new ExchangeOrderPrice
+							{
+								Price = price,
+								Amount = quantity,
+							};
+						}
+
+						callback(deltaBook);
+
+						return Task.CompletedTask;
+					},
+					connectCallback: async (_socket) =>
+					{
+						// Get full order book snapshot when connecting
+						foreach (var marketSymbol in marketSymbols)
+						{
+							var initialBook = await OnGetOrderBookAsync(marketSymbol, maxCount);
+							initialBook.IsFromSnapshot = true;
+
+							callback(initialBook);
+
+							initialSequenceIds[marketSymbol] = initialBook.SequenceId;
+						}
+
+						var id = CryptoUtility.UtcNow.Ticks;
+						var topic = $"/market/level2:{string.Join(",", marketSymbols)}";
+						await _socket.SendMessageAsync(
+								new
+								{
+									id = id++,
+									type = "subscribe",
+									topic = topic,
+								}
+						);
+					}
+			);
+		}
+
 		#endregion Websockets
 
 		#region Private Functions

src/ExchangeSharp/API/Exchanges/_Base/ExchangeAPIExtensions.cs

@@ -45,7 +45,7 @@ public static class ExchangeAPIExtensions
 		public static async Task<IWebSocket> GetFullOrderBookWebSocketAsync(
 				this IOrderBookProvider api,
 				Action<ExchangeOrderBook> callback,
-				int maxCount = 20,
+				int maxCount = 100,
 				params string[] symbols
 		)
 		{