前端：

1、优化消息排序逻辑
2、新增加载历史消息
3、修复已知问题
后端：
1、优化消息排序逻辑
2、增加用户信息缓存机制
3、修改日期类型为DateTimeOffset改善时区信息丢失问题
3、修复了已知问题
数据库：
1、新增SequenceId字段用于消息排序
2、新增ClientMsgId字段用于客户端消息回执

backend/IM_API/Services/SequenceIdService.cs

@@ -0,0 +1,46 @@
+using IM_API.Interface.Services;
+using IM_API.Models;
+using IM_API.Tools;
+using Microsoft.EntityFrameworkCore;
+using RedLockNet;
+using StackExchange.Redis;
+
+namespace IM_API.Services
+{
+    public class SequenceIdService : ISequenceIdService
+    {
+        private IDatabase _database;
+        private IDistributedLockFactory _lockFactory;
+        private ImContext _context;
+        public SequenceIdService(IConnectionMultiplexer connectionMultiplexer, 
+            IDistributedLockFactory distributedLockFactory, ImContext imContext)
+        {
+            _database = connectionMultiplexer.GetDatabase();
+            _lockFactory = distributedLockFactory;
+            _context = imContext;
+        }
+        public async Task<long> GetNextSquenceIdAsync(string streamKey)
+        {
+            string key = RedisKeys.GetSequenceIdKey(streamKey);
+            string lockKey = RedisKeys.GetSequenceIdLockKey(streamKey);
+            var exists = await _database.KeyExistsAsync(key);
+            if (!exists)
+            {
+                using (var _lock = await _lockFactory.CreateLockAsync(lockKey, TimeSpan.FromSeconds(5)))
+                {
+                    if (_lock.IsAcquired)
+                    {
+                        if(!await _database.KeyExistsAsync(key))
+                        {
+                            var max = await _context.Messages
+                            .Where(x => x.StreamKey == streamKey)
+                            .MaxAsync(m => (long?)m.SequenceId) ?? 0;
+                            await _database.StringSetAsync(key, max, TimeSpan.FromDays(7));
+                        }
+                    }
+                }
+            }
+            return await _database.StringIncrementAsync(key);
+        }
+    }
+}