Day 10 ASP.NET Core Middleware

Day 10 ASP.NET Core Middleware

Don't be evil——Google (Google座右铭)

The ASP.NET Core request pipeline consists of a sequence of request delegates, called one after the other.
ASP.NET Core框架的“请求流水线”机制是由一系列被顺序执行的请求代理组成的。

Each delegate can perform operations before and after the next delegate.
每一个代理可以在将请求传递给下一个代理之前、或者之后进行操作。

A delegate can also decide to not pass a request to the next delegate, which is called short-circuiting the request pipeline. Short-circuiting is often desirable because it avoids unnecessary work.
当前代理也可以决定不把请求传递给下一个代理，这种情况称为“将请求流水线短路”。“短路”常常是有价值的，因为这么做可以避免一些不必要的工作。

For example, the static file middleware can return a request for a static file and short-circuit the rest of the pipeline.
比如，静态文件的中间件可以直接将文件返回给相关的请求，并将余下的流水线短路掉。

Exception-handling delegates need to be called early in the pipeline, so they can catch exceptions that occur in later stages of the pipeline.
负责异常处理的代理需要在流水线的早期阶段就被调用，这样这类代理就可以捕捉之后发生在流水线各环节的异常了。

The simplest possible ASP.NET Core app sets up a single request delegate that handles all requests.
最简单的ASP.NET Core应用可能就只设置一个请求代理，来处理所有的请求。

This case doesn't include an actual request pipeline. Instead, a single anonymous function is called in response to every HTTP request.
（由于只有一个代理）这种情况就没有包含一个真正的“请求流水线”了。同一个匿名函数会负责响应所有的HTTP请求。

You can chain multiple request delegates together with app.Use. The next parameter represents the next delegate in the pipeline.
你可以调用app.Use方法，把多个请求代理串联起来。”next”这个参数，代表了流水线中的下一个代理。

Remember that you can short-circuit the pipeline by not calling the next parameter. You can typically perform actions both before and after the next delegate.
记住，如果你想将流水线短路掉,你就不要调用next这个参数.。通常，你可以在下一个代理之前以及之后进行操作。

本文选自：
https://docs.microsoft.com/en-us/aspnet/core/fundamentals/middleware/?view=aspnetcore-2.1&tabs=aspnetcore2x