Asp.net Core 使用Redis儲存Session

　http://www.cnblogs.com/hantianwei/p/5723959.html

　Asp.net Core 改變了之前的封閉，現在開源且開放，下面我們來用Redis儲存Session來做一個簡單的測試，或者叫做中介軟體（middleware）。

　　對於Session來說褒貶不一，很多人直接說不要用，也有很多人在用，這個也沒有絕對的這義，個人認為只要不影什麼且又可以方便實現的東西是可以用的，現在不對可不可用做表態，我們只關心實現。 類庫引用

　　這個相對於之前的.net是方便了不少，需要在project.json中的dependencies節點中添加如下內容：

    "StackExchange.Redis": "1.1.604-alpha",    "Microsoft.AspNetCore.Session": "1.1.0-alpha1-21694"

Redis實現

這裡並非我實現，而是借用https://github.com/aspnet/Caching/tree/dev/src/Microsoft.Extensions.Caching.Redis代碼來實現，不知道為什麼之前還有這個類庫，而現在NUGET止沒有了，為了不影響日後升級我的命名空間也用 Microsoft.Extensions.Caching.Redis

可以看到微軟這裡有四個類，其實我們只需要三個，第四個拿過來反而會出錯：

using System;using System.Threading.Tasks;using Microsoft.Extensions.Caching.Distributed;using Microsoft.Extensions.Options;using StackExchange.Redis;namespace Microsoft.Extensions.Caching.Redis{    public class RedisCache : IDistributedCache, IDisposable    {        // KEYS[1] = = key        // ARGV[1] = absolute-expiration - ticks as long (-1 for none)        // ARGV[2] = sliding-expiration - ticks as long (-1 for none)        // ARGV[3] = relative-expiration (long, in seconds, -1 for none) - Min(absolute-expiration - Now, sliding-expiration)        // ARGV[4] = data - byte[]        // this order should not change LUA script depends on it        private const string SetScript = (@"                redis.call('HMSET', KEYS[1], 'absexp', ARGV[1], 'sldexp', ARGV[2], 'data', ARGV[4])                if ARGV[3] ~= '-1' then                  redis.call('EXPIRE', KEYS[1], ARGV[3])                end                return 1");        private const string AbsoluteExpirationKey = "absexp";        private const string SlidingExpirationKey = "sldexp";        private const string DataKey = "data";        private const long NotPresent = -1;        private ConnectionMultiplexer _connection;        private IDatabase _cache;        private readonly RedisCacheOptions _options;        private readonly string _instance;        public RedisCache(IOptions<RedisCacheOptions> optionsAccessor)        {            if (optionsAccessor == null)            {                throw new ArgumentNullException(nameof(optionsAccessor));            }            _options = optionsAccessor.Value;            // This allows partitioning a single backend cache for use with multiple apps/services.            _instance = _options.InstanceName ?? string.Empty;        }        public byte[] Get(string key)        {            if (key == null)            {                throw new ArgumentNullException(nameof(key));            }            return GetAndRefresh(key, getData: true);        }        public async Task<byte[]> GetAsync(string key)        {            if (key == null)            {                throw new ArgumentNullException(nameof(key));            }            return await GetAndRefreshAsync(key, getData: true);        }        public void Set(string key, byte[] value, DistributedCacheEntryOptions options)        {            if (key == null)            {                throw new ArgumentNullException(nameof(key));            }            if (value == null)            {                throw new ArgumentNullException(nameof(value));            }            if (options == null)            {                throw new ArgumentNullException(nameof(options));            }            Connect();            var creationTime = DateTimeOffset.UtcNow;            var absoluteExpiration = GetAbsoluteExpiration(creationTime, options);            var result = _cache.ScriptEvaluate(SetScript, new RedisKey[] { _instance + key },                new RedisValue[]                {                        absoluteExpiration?.Ticks ?? NotPresent,                        options.SlidingExpiration?.Ticks ?? NotPresent,                        GetExpirationInSeconds(creationTime, absoluteExpiration, options) ?? NotPresent,                        value                });        }        public async Task SetAsync(string key, byte[] value, DistributedCacheEntryOptions options)        {            if (key == null)            {                throw new ArgumentNullException(nameof(key));            }            if (value == null)            {                throw new ArgumentNullException(nameof(value));            }            if (options == null)            {                throw new ArgumentNullException(nameof(options));            }            await ConnectAsync();            var creationTime = DateTimeOffset.UtcNow;            var absoluteExpiration = GetAbsoluteExpiration(creationTime, options);            await _cache.ScriptEvaluateAsync(SetScript, new RedisKey[] { _instance + key },                new RedisValue[]                {                        absoluteExpiration?.Ticks ?? NotPresent,                        options.SlidingExpiration?.Ticks ?? NotPresent,                        GetExpirationInSeconds(creationTime, absoluteExpiration, options) ?? NotPresent,                        value                });        }        public void Refresh(string key)        {            if (key == null)            {                throw new ArgumentNullException(nameof(key));            }            GetAndRefresh(key, getData: false);        }        public async Task RefreshAsync(string key)        {            if (key == null)            {                throw new ArgumentNullException(nameof(key));            }            await GetAndRefreshAsync(key, getData: false);        }        private void Connect()        {            if (_connection == null)            {                _connection = ConnectionMultiplexer.Connect(_options.Configuration);                _cache = _connection.GetDatabase();            }        }        private async Task ConnectAsync()        {            if (_connection == null)            {                _connection = await ConnectionMultiplexer.ConnectAsync(_options.Configuration);                _cache = _connection.GetDatabase();            }        }        private byte[] GetAndRefresh(string key, bool getData)        {            if (key == null)            {                throw new ArgumentNullException(nameof(key));            }            Connect();            // This also resets the LRU status as desired.            // TODO: Can this be done in one operation on the server side? Probably, the trick would just be the DateTimeOffset math.            RedisValue[] results;            if (getData)            {                results = _cache.HashMemberGet(_instance + key, AbsoluteExpirationKey, SlidingExpirationKey, DataKey);            }            else            {                results = _cache.HashMemberGet(_instance + key, AbsoluteExpirationKey, SlidingExpirationKey);            }            // TODO: Error handling            if (results.Length >= 2)            {                // Note we always get back two results, even if they are all null.                // These operations will no-op in the null scenario.                DateTimeOffset? absExpr;                TimeSpan? sldExpr;                MapMetadata(results, out absExpr, out sldExpr);                Refresh(key, absExpr, sldExpr);            }            if (results.Length >= 3 && results[