.Net Task<T>的一种比较神奇的卡死情况(Wait/Result卡死, await能得到结果)

1     public classCorsMessageHandler : DelegatingHandler
2 {
3         private static readonly CorsAttribute DEFAULT_CORS = new CorsAttribute("*");//默认支持所有
4 
5         protected override async Task<HttpResponseMessage>SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
6 {
7 cancellationToken.ThrowIfCancellationRequested();
8             try
9 {
10                 //得到描述目标Action的HttpActionDescriptor
11                 HttpMethod originalMethod =request.Method;
12                 bool isPreflightRequest =request.IsPreflightRequest();
13                 if(isPreflightRequest)
14 {
15                     string method = request.Headers.GetValues("Access-Control-Request-Method").First();
16                     request.Method = newHttpMethod(method);
17 }
18                 HttpConfiguration configuration =request.GetConfiguration();
19                 HttpControllerDescriptor controllerDescriptor =configuration.Services.GetHttpControllerSelector().SelectController(request);
20                 HttpControllerContext controllerContext = newHttpControllerContext(request.GetConfiguration(), request.GetRouteData(), request)
21 {
22                     ControllerDescriptor =controllerDescriptor
23 };
24                 //避免权限错误
25                 //HttpActionDescriptor actionDescriptor = configuration.Services.GetActionSelector().SelectAction(controllerContext);
26 
27                 //根据HttpActionDescriptor得到应用的CorsAttribute特性
28                 CorsAttribute corsAttribute = null;
29                 //corsAttribute = actionDescriptor.GetCustomAttributes<CorsAttribute>().FirstOrDefault();
30                 corsAttribute = corsAttribute?? controllerDescriptor.GetCustomAttributes<CorsAttribute>().FirstOrDefault();
31                 if (null ==corsAttribute)
32 {
33                     corsAttribute =DEFAULT_CORS;
34                     //return base.SendAsync(request, cancellationToken);
35 }
36 
37                 //利用CorsAttribute实施授权并生成响应报头
38                 IDictionary<string, string>headers;
39                 request.Method =originalMethod;
40                 bool authorized = corsAttribute.TryEvaluate(request, outheaders);
41 HttpResponseMessage response;
42                 if(isPreflightRequest)
43 {
44                     if(authorized)
45 {
46                         response = newHttpResponseMessage(HttpStatusCode.OK);
47 }
48                     else
49 {
50                         response =request.CreateErrorResponse(HttpStatusCode.BadRequest, corsAttribute.ErrorMessage);
51 }
52 }
53                 else
54 {
55                     var tmp = base.SendAsync(request, cancellationToken);
56 tmp.Wait();
57                     response =tmp.Result;
58 }
59 
60                 if (headers != null)
61 {
62                     foreach (var item inheaders)
63 {
64 response.Headers.Add(item.Key, item.Value);
65 }
66 }
67                 returnresponse;
68 }
69             catch
70 {
71 }
72             //catch -> fallback
73             return await base.SendAsync(request, cancellationToken);
74 }
75 }
76     [AttributeUsage(AttributeTargets.Class |AttributeTargets.Method)]
77     public classCorsAttribute : Attribute
78 {
79         public Uri[] AllowOrigins { get; private set; }
80         public string ErrorMessage { get; private set; }
81 
82         public CorsAttribute(params string[] allowOrigins)
83 {
84             var tmp = (allowOrigins ?? new string[0]);
85             if (tmp.Length == 1 && "*" == tmp[0])
86 {
87                 this.AllowOrigins = null;
88 }
89             else
90 {
91                 this.AllowOrigins = tmp.Select(origin => newUri(origin)).ToArray();
92 }
93 }
94 
95         public bool TryEvaluate(HttpRequestMessage request, out IDictionary<string, string>headers)
96 {
97             headers = null;
98 
99             //bugfix: GetValues在找不到时会报错
100             IEnumerable<string>origins;
101             if (request.Headers.TryGetValues("Origin", outorigins))
102 {
103                 string origin =origins.FirstOrDefault();
104                 if (!String.IsNullOrEmpty(origin))
105 {
106                     Uri originUri = newUri(origin);
107                     if (this.AllowOrigins == null || this.AllowOrigins.Contains(originUri))//支持"*"
108 {
109                         headers = this.GenerateResponseHeaders(request);
110                         return true;
111 }
112 }
113 }
114             this.ErrorMessage = "Cross-origin request denied";
115             return false;
116 }
117 
118         private IDictionary<string, string>GenerateResponseHeaders(HttpRequestMessage request)
119 {
120             //设置响应报头"Access-Control-Allow-Methods"
121             string origin = request.Headers.GetValues("Origin").First();
122             Dictionary<string, string> headers = new Dictionary<string, string>();
123             headers.Add("Access-Control-Allow-Origin", origin);
124             if(request.IsPreflightRequest())
125 {
126                 //设置响应报头"Access-Control-Request-Headers"
127                 //和"Access-Control-Allow-Headers"
128                 string requestHeaders = request.Headers.GetValues("Access-Control-Request-Headers").FirstOrDefault();
129                 if (!string.IsNullOrEmpty(requestHeaders))
130 {
131                     headers.Add("Access-Control-Allow-Headers", requestHeaders);
132 }
133                 //string requestMethods = request.Headers.GetValues("Access-Control-Request-Method").FirstOrDefault();
134                 //if (!string.IsNullOrEmpty(requestHeaders))
135                 //{
136                 //headers.Add("Access-Control-Allow-Methods", requestMethods + ", OPTIONS");
137                 //}
138                 //else
139                 //{
140                     headers.Add("Access-Control-Allow-Methods", "*");
141                 //}
142 }
143             headers.Add("Access-Control-Allow-Credentials", "true");//true, 允许跨域传cookie, 要在POST的返回值中也存在
144             returnheaders;
145 }
146     }

1     public class JsonExceptionFilter : FilterAttribute, IExceptionFilter//, IActionFilter
2 {
3 
4         publicTask ExecuteExceptionFilterAsync(HttpActionExecutedContext actionExecutedContext, CancellationToken cancellationToken)
5 {
6             return Task.Factory.StartNew((obj) =>
7 {
8                 CancellationToken ct =(CancellationToken)obj;
9                 if (actionExecutedContext.Exception != null)
10 {
11                     var res = new ResultModel<String>(false, actionExecutedContext.Exception.GetType().ToString());
12                     var resText =JsonConvert.SerializeObject(res);
13                     if (actionExecutedContext.Response == null)
14 {
15                         actionExecutedContext.Response = newHttpResponseMessage();
16 }
17                     actionExecutedContext.Response.Content = new StringContent("{"State":-255}", Encoding.UTF8, "application/json");
18 }
19 }, cancellationToken, cancellationToken);
20 }
21     }