用SignalR实现实时查看WebAPI请求日志

实现的原理比较直接，定义一个MessageHandler记录WebAPI的请求记录，然后将这些请求日志推送到客户端，客户端就是一个查看日志的页面，实时将请求日志展示在页面中。

这个例子的目的是演示如何在PersistentConnection类外部给Clients推送消息

实现过程

一、服务端

服务端同时具备SignalR和WebAPI的功能，通过定义一个记录日志的MessageHandler实现对WebAPI请求的拦截，并生成请求记录，然后推送到客户端

step 1

创建一个具备WebAPI功能的站点，为了简化起见，设置Authentication为No Authentication

step 2

创建一个DelegatingHandler，用于记录WebAPI日志，代码如下

下面代码没有涉及到SignalR的功能，日志展示是通过ILoggingDisplay接口传入

public class LoggingHandler : DelegatingHandler 
    { 
        private static readonly string _loggingInfoKey = "loggingInfo";

        private ILoggingDisplay _loggingDisplay;

        public LoggingHandler(ILoggingDisplay loggingDisplay) 
        { 
            _loggingDisplay = loggingDisplay; 
        }

        public LoggingHandler(HttpMessageHandler innerHandler, ILoggingDisplay loggingDisplay) 
            : base(innerHandler) 
        { 
            _loggingDisplay = loggingDisplay; 
        }

        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) 
        { 
            LogRequestLoggingInfo(request); 
            return base.SendAsync(request, cancellationToken).ContinueWith(task => 
            { 
                var response = task.Result; 
                LogResponseLoggingInfo(response); 
                return response; 
            }); 
        }

        private void LogRequestLoggingInfo(HttpRequestMessage request) 
        { 
            var info = new ApiLoggingInfo(); 
            info.HttpMethod = request.Method.Method; 
            info.UriAccessed = request.RequestUri.AbsoluteUri; 
            info.IpAddress = HttpContext.Current != null ? HttpContext.Current.Request.UserHostAddress : "0.0.0.0"; 
            info.StartTime = DateTime.Now; 
            ExtractMessageHeadersIntoLoggingInfo(info, request.Headers.ToList()); 
            request.Properties.Add(_loggingInfoKey, info); 
        }

        private void LogResponseLoggingInfo(HttpResponseMessage response) 
        { 
            object loggingInfoObject = null; 
            if (!response.RequestMessage.Properties.TryGetValue(_loggingInfoKey, out loggingInfoObject)) 
            { 
                return; 
            } 
            var info = loggingInfoObject as ApiLoggingInfo; 
            if (info == null) 
            { 
                return; 
            } 
            info.HttpMethod = response.RequestMessage.Method.ToString(); 
            info.ResponseStatusCode = response.StatusCode; 
            info.ResponseStatusMessage = response.ReasonPhrase; 
            info.UriAccessed = response.RequestMessage.RequestUri.AbsoluteUri; 
            info.IpAddress = HttpContext.Current != null ? HttpContext.Current.Request.UserHostAddress : "0.0.0.0"; 
            info.EndTime = DateTime.Now; 
            info.TotalTime = (info.EndTime - info.StartTime).TotalMilliseconds; 
            _loggingDisplay.Display(info); 
        }

        private void ExtractMessageHeadersIntoLoggingInfo(ApiLoggingInfo info, List<KeyValuePair<string, IEnumerable<string>>> headers) 
        { 
            headers.ForEach(h => 
            { 
                var headerValues = new StringBuilder();

                if (h.Value != null) 
                { 
                    foreach (var hv in h.Value) 
                    { 
                        if (headerValues.Length > 0) 
                        { 
                            headerValues.Append(", "); 
                        } 
                        headerValues.Append(hv); 
                    } 
                } 
                info.Headers.Add(string.Format("{0}: {1}", h.Key, headerValues.ToString())); 
            }); 
        } 
    }

LoggingHandler