Web API Request Content多次读取

使用自宿主OWIN

项目中要做日志过滤器

新建类ApiLogAttribute

继承ActionFilterAttribute

ApiLogAttribute :  ActionFilterAttribute

public override Task OnActionExecutingAsync(HttpActionContext actionContext, CancellationToken cancellationToken)
        {
            string result = null;
            Stream stream = actionContext?.Request?.Content?.ReadAsStreamAsync().Result;
            if(stream=null)                return base.OnActionExecutingAsync(actionContext,cancellationToken);

            stream.Position = 0L;             Encoding encoding = Encoding.UTF8;            /* 这个StreamReader不能关闭，也不能dispose 因为你关掉后，后面的管道 或拦截器就没办法读取了 */             var reader = new StreamReader(stream, encoding);             result = reader.ReadToEnd();             /* 这里也要注意： stream.Position = 0;               当你读取完之后必须把stream的位置设为开始                因为request和response读取完以后Position到最后一个位置，交给下一个方法处理的时候就会读不到内容了。             */             stream.Position = 0L;             Console.WriteLine(result);             return base.OnActionExecutingAsync(actionContext, cancellationToken); }

结果发现stream Position 无法设置，CanSeek为false

用 流复制也不管用

MemoryStream stream = new MemoryStream();
Stream.CopyToAsync(stream);
始终读取不到内容

最后读取文档得知 OWIN 中 Request 的content 只能读取一次，已经被解析，无法再次读取

搜索了一番

https://stackoverflow.com/questions/31389781/read-request-body-twice/31395692#31395692

解决办法如下

在Startup中添加添加中间件

这里的流还没有被读取过，直接复制一份CanSeek为false的stream 流 ，进行替换

//Request stream重用
            app.Use(async (context, next) =>
            {
                // Keep the original stream in a separate
                // variable to restore it later if necessary.
                var stream = context.Request.Body;

                // Optimization: don't buffer the request if
                // there was no stream or if it is rewindable.
                if (stream == Stream.Null || stream.CanSeek)
                {

                    await next.Invoke();

                    return;
                }

                try
                {
                    using (var buffer = new MemoryStream())
                    {
                        // Copy the request stream to the memory stream.
                        await stream.CopyToAsync(buffer);

                        // Rewind the memory stream.
                        buffer.Position = 0L;

                        // Replace the request stream by the memory stream.
                        context.Request.Body = buffer;

                        // Invoke the rest of the pipeline.
                        await next.Invoke();
                    }
                }

                finally
                {
                    // Restore the original stream.
                    context.Request.Body = stream;
                }
            });

或者 在过滤器中 通过如下放法 直接 取出已经被解析的参数

/// <summary>
        /// 读取request 的提交内容
        /// </summary>
        /// <param name="actionContext"></param>
        /// <returns></returns>
        public string GetRequestValues(HttpActionContext actionContext)
        {
            string result = null;
            foreach (var arg in actionContext.ActionArguments)
            {
                result += $"key={arg.Key};";
                result += $"value={JsonConvert.SerializeObject(arg.Value)};{Environment.NewLine}";
            }

            return result;
        }