Added support for caching GET requests

CryptoExchange.Net/Caching/MemoryCache.cs

@@ -0,0 +1,54 @@
+using System;
+using System.Collections.Concurrent;
+
+namespace CryptoExchange.Net.Caching
+{
+    internal class MemoryCache
+    {
+        private readonly ConcurrentDictionary<string, CacheItem> _cache = new ConcurrentDictionary<string, CacheItem>();
+
+        /// <summary>
+        /// Add a new cache entry. Will override an existing entry if it already exists
+        /// </summary>
+        /// <param name="key">The key identifier</param>
+        /// <param name="value">Cache value</param>
+        public void Add(string key, object value)
+        {
+            var cacheItem = new CacheItem(DateTime.UtcNow, value);
+            _cache.AddOrUpdate(key, cacheItem, (key, val1) => cacheItem);
+        }
+
+        /// <summary>
+        /// Get a cached value
+        /// </summary>
+        /// <param name="key">The key identifier</param>
+        /// <param name="maxAge">The max age of the cached entry</param>
+        /// <returns>Cached value if it was in cache</returns>
+        public object? Get(string key, TimeSpan maxAge)
+        {
+            _cache.TryGetValue(key, out CacheItem value);
+            if (value == null)
+                return null;
+
+            if (DateTime.UtcNow - value.CacheTime > maxAge)
+            {
+                _cache.TryRemove(key, out _);
+                return null;
+            }
+
+            return value.Value;
+        }
+
+        private class CacheItem
+        {
+            public DateTime CacheTime { get; }
+            public object Value { get; }
+
+            public CacheItem(DateTime cacheTime, object value)
+            {
+                CacheTime = cacheTime;
+                Value = value;
+            }
+        }
+    }
+}

CryptoExchange.Net/Clients/RestApiClient.cs

@@ -8,6 +8,7 @@ using System.Net;
 using System.Net.Http;
 using System.Threading;
 using System.Threading.Tasks;
+using CryptoExchange.Net.Caching;
 using CryptoExchange.Net.Converters.JsonNet;
 using CryptoExchange.Net.Interfaces;
 using CryptoExchange.Net.Logging.Extensions;
@@ -17,6 +18,7 @@ using CryptoExchange.Net.RateLimiting;
 using CryptoExchange.Net.RateLimiting.Interfaces;
 using CryptoExchange.Net.Requests;
 using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
 
 namespace CryptoExchange.Net.Clients
 {
@@ -85,6 +87,10 @@ namespace CryptoExchange.Net.Clients
         /// <inheritdoc />
         public new RestApiOptions ApiOptions => (RestApiOptions)base.ApiOptions;
 
+        /// <summary>
+        /// Memory cache
+        /// </summary>
+        private static MemoryCache _cache = new MemoryCache();
 
         /// <summary>
         /// ctor
@@ -190,6 +196,21 @@ namespace CryptoExchange.Net.Clients
             Dictionary<string, string>? additionalHeaders = null,
             int? weight = null) where T : class
         {
+            var key = baseAddress + definition + uriParameters?.ToFormData();
+            if (ShouldCache(definition))
+            {
+                _logger.CheckingCache(key);
+                var cachedValue = _cache.Get(key, ClientOptions.CachingMaxAge);
+                if (cachedValue != null)
+                {
+                    _logger.CacheHit(key);
+                    var original = (WebCallResult<T>)cachedValue;
+                    return original.Cached();
+                }
+
+                _logger.CacheNotHit(key);
+            }
+
             int currentTry = 0;
             while (true)
             {
@@ -215,6 +236,12 @@ namespace CryptoExchange.Net.Clients
                 if (await ShouldRetryRequestAsync(definition.RateLimitGate, result, currentTry).ConfigureAwait(false))
                     continue;
 
+                if (result.Success &&
+                    ShouldCache(definition))
+                {
+                    _cache.Add(key, result);
+                }
+
                 return result;
             }
         }
@@ -445,6 +472,7 @@ namespace CryptoExchange.Net.Clients
         /// <param name="requestWeight">Credits used for the request</param>
         /// <param name="additionalHeaders">Additional headers to send with the request</param>
         /// <param name="gate">The ratelimit gate to use</param>
+        /// <param name="preventCaching">Whether caching should be prevented for this request</param>
         /// <returns></returns>
         [return: NotNull]
         protected virtual async Task<WebCallResult<T>> SendRequestAsync<T>(
@@ -458,9 +486,25 @@ namespace CryptoExchange.Net.Clients
             ArrayParametersSerialization? arraySerialization = null,
             int requestWeight = 1,
             Dictionary<string, string>? additionalHeaders = null,
-            IRateLimitGate? gate = null
+            IRateLimitGate? gate = null,
+            bool preventCaching = false
             ) where T : class
         {
+            var key = uri.ToString() + method + signed + parameters?.ToFormData();
+            if (ShouldCache(method) && !preventCaching)
+            {
+                _logger.CheckingCache(key);
+                var cachedValue = _cache.Get(key, ClientOptions.CachingMaxAge);
+                if (cachedValue != null)
+                {
+                    _logger.CacheHit(key);
+                    var original = (WebCallResult<T>)cachedValue;
+                    return original.Cached();
+                }
+
+                _logger.CacheNotHit(key);
+            }
+
             int currentTry = 0;
             while (true)
             {
@@ -478,6 +522,13 @@ namespace CryptoExchange.Net.Clients
                 if (await ShouldRetryRequestAsync(gate, result, currentTry).ConfigureAwait(false))
                     continue;
 
+                if (result.Success &&
+                    ShouldCache(method) && 
+                    !preventCaching)
+                {
+                    _cache.Add(key, result);
+                }
+
                 return result;
             }
         }
@@ -949,5 +1000,14 @@ namespace CryptoExchange.Net.Clients
 
             return new WebCallResult<bool>(null, null, null, null, null, null, null, null, null, null, true, null);
         }
+
+        private bool ShouldCache(RequestDefinition definition)
+            => ClientOptions.CachingEnabled
+            && definition.Method == HttpMethod.Get
+            && !definition.PreventCaching;
+
+        private bool ShouldCache(HttpMethod method)
+            => ClientOptions.CachingEnabled
+            && method == HttpMethod.Get;
     }
 }

CryptoExchange.Net/Logging/Extensions/RestApiClientLoggingExtensions.cs

@@ -17,6 +17,9 @@ namespace CryptoExchange.Net.Logging.Extensions
         private static readonly Action<ILogger, int, DateTime, Exception?> _restApiRateLimitRetry;
         private static readonly Action<ILogger, int, DateTime, Exception?> _restApiRateLimitPauseUntil;
         private static readonly Action<ILogger, int, RequestDefinition, string?, string, string, Exception?> _restApiSendRequest;
+        private static readonly Action<ILogger, string, Exception?> _restApiCheckingCache;
+        private static readonly Action<ILogger, string, Exception?> _restApiCacheHit;
+        private static readonly Action<ILogger, string, Exception?> _restApiCacheNotHit;
 
 
         static RestApiClientLoggingExtensions()
@@ -65,6 +68,21 @@ namespace CryptoExchange.Net.Logging.Extensions
                 LogLevel.Debug,
                 new EventId(4008, "RestApiSendRequest"),
                 "[Req {RequestId}] Sending {Definition} request with body {Body}, query parameters {Query} and headers {Headers}");
+
+            _restApiCheckingCache = LoggerMessage.Define<string>(
+                LogLevel.Trace,
+                new EventId(4009, "RestApiCheckingCache"),
+                "Checking cache for key {Key}");
+
+            _restApiCacheHit = LoggerMessage.Define<string>(
+                LogLevel.Trace,
+                new EventId(4010, "RestApiCacheHit"),
+                "Cache hit for key {Key}");
+
+            _restApiCacheNotHit = LoggerMessage.Define<string>(
+                LogLevel.Trace,
+                new EventId(4011, "RestApiCacheNotHit"),
+                "Cache not hit for key {Key}");
         }
 
         public static void RestApiErrorReceived(this ILogger logger, int? requestId, HttpStatusCode? responseStatusCode, long responseTime, string? error)
@@ -111,5 +129,20 @@ namespace CryptoExchange.Net.Logging.Extensions
         {
             _restApiSendRequest(logger, requestId, definition, body, query, headers, null);
         }
+
+        public static void CheckingCache(this ILogger logger, string key)
+        {
+            _restApiCheckingCache(logger, key, null);
+        }
+
+        public static void CacheHit(this ILogger logger, string key)
+        {
+            _restApiCacheHit(logger, key, null);
+        }
+
+        public static void CacheNotHit(this ILogger logger, string key)
+        {
+            _restApiCacheNotHit(logger, key, null);
+        }
     }
 }

CryptoExchange.Net/Objects/CallResult.cs

@@ -331,6 +331,11 @@ namespace CryptoExchange.Net.Objects
         /// </summary>
         public TimeSpan? ResponseTime { get; set; }
 
+        /// <summary>
+        /// The data source of this result
+        /// </summary>
+        public ResultDataSource DataSource { get; set; } = ResultDataSource.Server;
+
         /// <summary>
         /// Create a new result
         /// </summary>
@@ -417,6 +422,17 @@ namespace CryptoExchange.Net.Objects
             return new WebCallResult<K>(ResponseStatusCode, ResponseHeaders, ResponseTime, ResponseLength, OriginalData, RequestId, RequestUrl, RequestBody, RequestMethod, RequestHeaders, default, error);
         }
 
+        /// <summary>
+        /// Return a copy of this result with data source set to cache
+        /// </summary>
+        /// <returns></returns>
+        internal WebCallResult<T> Cached()
+        {
+            var result = new WebCallResult<T>(ResponseStatusCode, ResponseHeaders, ResponseTime, ResponseLength, OriginalData, RequestId, RequestUrl, RequestBody, RequestMethod, RequestHeaders, default, Error);
+            result.DataSource = ResultDataSource.Cache;
+            return result;
+        }
+
         /// <inheritdoc />
         public override string ToString()
         {

CryptoExchange.Net/Objects/Enums.cs

@@ -188,4 +188,19 @@
         /// </summary>
         ExponentialBackoff
     }
+
+    /// <summary>
+    /// The data source of the result
+    /// </summary>
+    public enum ResultDataSource
+    {
+        /// <summary>
+        /// From server
+        /// </summary>
+        Server,
+        /// <summary>
+        /// From cache
+        /// </summary>
+        Cache
+    }
 }

CryptoExchange.Net/Objects/Options/RestExchangeOptions.cs

@@ -18,6 +18,16 @@ namespace CryptoExchange.Net.Objects.Options
         /// </summary>
         public TimeSpan TimestampRecalculationInterval { get; set; } = TimeSpan.FromHours(1);
 
+        /// <summary>
+        /// Whether caching is enabled. Caching will only be applied to GET http requests. The lifetime of cached results can be determined by the `CachingMaxAge` option
+        /// </summary>
+        public bool CachingEnabled { get; set; } = false;
+
+        /// <summary>
+        /// The max age of a cached entry, only used when the `CachingEnabled` options is set to true. When a cached entry is older than the max age it will be discarded and a new server request will be done
+        /// </summary>
+        public TimeSpan CachingMaxAge { get; set; } = TimeSpan.FromSeconds(5);
+
         /// <summary>
         /// Create a copy of this options
         /// </summary>
@@ -34,7 +44,9 @@ namespace CryptoExchange.Net.Objects.Options
                 Proxy = Proxy,
                 RequestTimeout = RequestTimeout,
                 RateLimiterEnabled = RateLimiterEnabled,
-                RateLimitingBehaviour = RateLimitingBehaviour
+                RateLimitingBehaviour = RateLimitingBehaviour,
+                CachingEnabled = CachingEnabled,
+                CachingMaxAge = CachingMaxAge,
             };
         }
     }

CryptoExchange.Net/Objects/RequestDefinition.cs

@@ -61,6 +61,12 @@ namespace CryptoExchange.Net.Objects
         /// </summary>
         public TimeSpan? EndpointLimitPeriod { get; set; }
 
+
+        /// <summary>
+        /// Whether this request should never be cached
+        /// </summary>
+        public bool PreventCaching { get; set; }
+
         /// <summary>
         /// ctor
         /// </summary>

CryptoExchange.Net/Objects/RequestDefinitionCache.cs

@@ -48,6 +48,7 @@ namespace CryptoExchange.Net.Objects
         /// <param name="requestBodyFormat">Request body format</param>
         /// <param name="parameterPosition">Parameter position</param>
         /// <param name="arraySerialization">Array serialization type</param>
+        /// <param name="preventCaching">Prevent request caching</param>
         /// <returns></returns>
         public RequestDefinition GetOrCreate(
             HttpMethod method,
@@ -59,7 +60,8 @@ namespace CryptoExchange.Net.Objects
             TimeSpan? endpointLimitPeriod = null,
             RequestBodyFormat? requestBodyFormat = null,
             HttpMethodParameterPosition? parameterPosition = null,
-            ArrayParametersSerialization? arraySerialization = null)
+            ArrayParametersSerialization? arraySerialization = null,
+            bool? preventCaching = null)
         {
 
             if (!_definitions.TryGetValue(method + path, out var def))
@@ -74,6 +76,7 @@ namespace CryptoExchange.Net.Objects
                     ArraySerialization = arraySerialization,
                     RequestBodyFormat = requestBodyFormat,
                     ParameterPosition = parameterPosition,
+                    PreventCaching = preventCaching ?? false
                 };
                 _definitions.TryAdd(method + path, def);
             }