核心思想：核心逻辑与通用逻辑分离，适用于日志记录、性能统计、安全控制、事务处理、异常处理等。
- Handler是业务的核心逻辑，请求在进入核心业务逻辑之前会进过很多的中间层。比如一个请求在进入核心的Handler的时候会经过日志和Metric的中间层，产生相关的日志和打点。Response返回的时候会先经过Metrics，然后再经过日志。
- 中间件内部的执行顺序：
- 预处理：pre-handler。
- Next()：进入下一层函数。
- post-handler：后处理。
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import "context"
// Endpoint represent one method for calling from remote.
type Endpoint func(ctx context.Context, req, resp interface{}) (err error)
// Middleware deal with input Endpoint and output Endpoint.
type Middleware func(Endpoint) Endpoint
// MiddlewareBuilder builds a middleware with information from a context.
type MiddlewareBuilder func(ctx context.Context) Middleware
// Chain connect middlewares into one middleware.
func Chain(mws ...Middleware) Middleware {
return func(next Endpoint) Endpoint {
for i := len(mws) - 1; i >= 0; i-- {
next = mws[i](next)
}
return next
}
}
// Build builds the given middlewares into one middleware.
func Build(mws []Middleware) Middleware {
if len(mws) == 0 {
return DummyMiddleware
}
return func(next Endpoint) Endpoint {
return mws[0](Build(mws[1:])(next))
}
}
// DummyMiddleware is a dummy middleware.
func DummyMiddleware(next Endpoint) Endpoint {
return next
}
// DummyEndpoint is a dummy endpoint.
func DummyEndpoint(ctx context.Context, req, resp interface{}) (err error) {
return nil
}
