如何解决如何在 ASP.Net Core 中实现自定义控制器动作选择？
我有一个 ASP.Net Core API 项目。我希望能够编写自定义路由逻辑，以便能够根据 HTTP 正文参数选择不同的控制器操作。为了说明我的问题，这是我的 Controller 类：
[ApiController]
[Route("api/[controller]")]
public class TestController
{
// should be called when HTTP Body contains json: '{ method: "SetValue1" }'
public void SetValue1()
{
// some logic
}
// should be called when HTTP Body contains json: '{ method: "SetValue2" }'
public void SetValue2()
{
// some logic
}
}
从我的评论中可以看出，我想根据 HTTP 正文选择不同的操作方法。
这是我的 Startup 课：
public class Startup
{
public void ConfigureServices(IServiceCollection services)
{
services.AddControllers();
}
public void Configure(IApplicationBuilder app,IWebHostEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
// I assume instead of this built in routing middleware,// I will have to implement custom middleware to choose the correct endpoints,from HTTP body,// any ideas how I can go about this?
app.UseRouting();
app.UseEndpoints(endpoints =>
{
endpoints.MapControllers();
});
}
}
我可以使用的一个选项是使用一个入口 Action 方法，该方法将根据 HTTP 正文内容调用不同的方法，但我想避免这种情况并将此逻辑封装在自定义路由中的某处。
在旧的 APS.Net Web API 中有一个方便的类 ApiControllerActionSelector，我可以扩展它，并定义我选择 Action 方法的自定义逻辑，但是在新的 ASP.Net Core 中不支持。我想我必须实现我自己的 app.UseRouting 中间件版本。关于如何做到这一点的任何想法？
解决方法
在旧的 asp.net core 中（在 3.0 之前），我们可以实现自定义的 IActionSelector，当 ActionSelector 仍然公开时特别方便。但是使用新的端点路由，它更改为所谓的 EndpointSelector。实现完全相同，重点是我们如何提取放在 ActionDescriptor 中的 Endpoint 作为元数据。下面的实现需要一个默认的 EndpointSelector（即 DefaultEndpointSelector），但不幸的是它是内部实现的。因此，我们需要使用一个技巧来获取该默认实现的实例，以便在我们的自定义实现中使用。
public class RequestBodyEndpointSelector : EndpointSelector
{
readonly IEnumerable<Endpoint> _controllerEndPoints;
readonly EndpointSelector _defaultSelector;
public RequestBodyEndpointSelector(EndpointSelector defaultSelector,EndpointDataSource endpointDataSource)
{
_defaultSelector = defaultSelector;
_controllerEndPoints = endpointDataSource.Endpoints
.Where(e => e.Metadata.GetMetadata<ControllerActionDescriptor>() != null).ToList();
}
public override async Task SelectAsync(HttpContext httpContext,CandidateSet candidates)
{
var request = httpContext.Request;
request.EnableBuffering();
//don't use "using" here,otherwise the request.Body will be disposed and cannot be used later in the pipeline (an exception will be thrown).
var sr = new StreamReader(request.Body);
try
{
var body = sr.ReadToEnd();
if (!string.IsNullOrEmpty(body))
{
try
{
var actionInfo = Newtonsoft.Json.JsonConvert.DeserializeObject<ActionInfo>(body);
var controllerActions = new HashSet<(MethodInfo method,Endpoint endpoint,RouteValueDictionary routeValues,int score)>();
var constrainedControllerTypes = new HashSet<Type>();
var routeValues = new List<RouteValueDictionary>();
var validIndices = new HashSet<int>();
for (var i = 0; i < candidates.Count; i++)
{
var candidate = candidates[i];
var endpoint = candidates[i].Endpoint;
var actionDescriptor = endpoint.Metadata.GetMetadata<ControllerActionDescriptor>();
if (actionDescriptor == null) continue;
routeValues.Add(candidate.Values);
constrainedControllerTypes.Add(actionDescriptor.MethodInfo.DeclaringType);
if (!string.Equals(actionInfo.MethodName,actionDescriptor.MethodInfo.Name,StringComparison.OrdinalIgnoreCase)) continue;
if (!controllerActions.Add((actionDescriptor.MethodInfo,endpoint,candidate.Values,candidate.Score))) continue;
validIndices.Add(i);
}
if (controllerActions.Count == 0)
{
var bestCandidates = _controllerEndPoints.Where(e => string.Equals(actionInfo.MethodName,e.Metadata.GetMetadata<ControllerActionDescriptor>().MethodInfo.Name,StringComparison.OrdinalIgnoreCase)).ToArray();
var routeValuesArray = request.RouteValues == null ? routeValues.ToArray() : new[] { request.RouteValues };
candidates = new CandidateSet(bestCandidates,routeValuesArray,new[] { 0 });
}
else
{
for(var i = 0; i < candidates.Count; i++)
{
candidates.SetValidity(i,validIndices.Contains(i));
}
}
//call the default selector after narrowing down the candidates
await _defaultSelector.SelectAsync(httpContext,candidates);
//if some endpoint found
var selectedEndpoint = httpContext.GetEndpoint();
if (selectedEndpoint != null)
{
//update the action in the RouteData to found endpoint
request.RouteValues["action"] = selectedEndpoint.Metadata.GetMetadata<ControllerActionDescriptor>().ActionName;
}
return;
}
catch { }
}
}
finally
{
request.Body.Position = 0;
}
await _defaultSelector.SelectAsync(httpContext,candidates);
}
}
注册码有点像这样：
//define an extension method for registering conveniently
public static class EndpointSelectorServiceCollectionExtensions
{
public static IServiceCollection AddRequestBodyEndpointSelector(this IServiceCollection services)
{
//build a dummy service container to get an instance of
//the DefaultEndpointSelector
var sc = new ServiceCollection();
sc.AddMvc();
var defaultEndpointSelector = sc.BuildServiceProvider().GetRequiredService<EndpointSelector>();
return services.Replace(new ServiceDescriptor(typeof(EndpointSelector),sp => new RequestBodyEndpointSelector(defaultEndpointSelector,sp.GetRequiredService<EndpointDataSource>()),ServiceLifetime.Singleton));
}
}
//inside the Startup.ConfigureServices
services.AddRequestBodyEndpointSelector();
针对asp.net core 2.2中使用的旧常规路由的旧解决方案
您的要求有点奇怪，您可能不得不为此接受一些权衡。首先，该要求可能要求您阅读 Request.Body 两次（当所选操作方法有一些模型绑定参数时）。即使框架在 EnableBuffering 上支持所谓的 HttpRequest，接受它仍然有点权衡。其次，在选择最佳动作的方法中（定义在 IActionSelector 上），我们不能使用 async，因此读取请求正文当然不能用 async 完成。
对于高性能网络应用程序，绝对应该避免这种情况。但是，如果您可以接受这种权衡，我们可以通过实现自定义 IActionSelector 来提供解决方案，最多让它继承默认 ActionSelector。我们可以覆盖的方法是 ActionSelector.SelectBestActions。但是，该方法不提供 RouteContext（我们需要访问它来更新 RouteData），因此我们将重新实现名为 IActionSelector 的 IActionSelector.SelectBestCandidate 的另一个方法提供一个 RouteContext。
具体代码如下：
//first we define a base model for parsing the request body
public class ActionInfo
{
[JsonProperty("method")]
public string MethodName { get; set; }
}
//here's our custom ActionSelector
public class RequestBodyActionSelector : ActionSelector,IActionSelector
{
readonly IEnumerable<ActionDescriptor> _actions;
public RequestBodyActionSelector(IActionDescriptorCollectionProvider actionDescriptorCollectionProvider,ActionConstraintCache actionConstraintCache,ILoggerFactory loggerFactory)
: base(actionDescriptorCollectionProvider,actionConstraintCache,loggerFactory)
{
_actions = actionDescriptorCollectionProvider.ActionDescriptors.Items;
}
ActionDescriptor IActionSelector.SelectBestCandidate(RouteContext context,IReadOnlyList<ActionDescriptor> candidates)
{
var request = context.HttpContext.Request;
//supports reading the request body multiple times
request.EnableBuffering();
var sr = new StreamReader(request.Body);
try
{
var body = sr.ReadToEnd();
if (!string.IsNullOrEmpty(body))
{
try
{
//here I use the old Newtonsoft.Json
var actionInfo = JsonConvert.DeserializeObject<ActionInfo>(body);
//the best actions should be on these controller types.
var controllerTypes = new HashSet<TypeInfo>(candidates.OfType<ControllerActionDescriptor>().Select(e => e.ControllerTypeInfo));
//filter for the best by matching the controller types and
//the method name from the request body
var bestActions = _actions.Where(e => e is ControllerActionDescriptor ca &&
controllerTypes.Contains(ca.ControllerTypeInfo) &&
string.Equals(actionInfo.MethodName,ca.MethodInfo.Name,StringComparison.OrdinalIgnoreCase)).ToList();
//only override the default if any method name matched
if (bestActions.Count > 0)
{
//before reaching here,//the RouteData has already been populated with
//what from the request's URL
//By overriding this way,that RouteData's action
//may be changed,so we need to update it here.
var newActionName = (bestActions[0] as ControllerActionDescriptor).ActionName;
context.RouteData.PushState(null,new RouteValueDictionary(new { action = newActionName }),null);
return SelectBestCandidate(context,bestActions);
}
}
catch { }
}
}
finally
{
request.Body.Position = 0;
}
return SelectBestCandidate(context,candidates);
}
}
要在 IActionSelector 中注册自定义 Startup.ConfigureServices：
services.AddSingleton<IActionSelector,RequestBodyActionSelector>();
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