github.com/shogo82148/goa-v1@v1.6.2/middleware.go (about)

     1  package goa
     2  
     3  import (
     4  	"context"
     5  	"fmt"
     6  	"net/http"
     7  )
     8  
     9  type (
    10  	// Middleware represents the canonical goa middleware signature.
    11  	Middleware func(Handler) Handler
    12  )
    13  
    14  // NewMiddleware creates a middleware from the given argument. The allowed types for the
    15  // argument are:
    16  //
    17  // - a goa middleware: goa.Middleware or func(goa.Handler) goa.Handler
    18  //
    19  // - a goa handler: goa.Handler or func(context.Context, http.ResponseWriter, *http.Request) error
    20  //
    21  // - an http middleware: func(http.Handler) http.Handler
    22  //
    23  // - or an http handler: http.Handler or func(http.ResponseWriter, *http.Request)
    24  //
    25  // An error is returned if the given argument is not one of the types above.
    26  func NewMiddleware(m interface{}) (mw Middleware, err error) {
    27  	switch m := m.(type) {
    28  	case Middleware:
    29  		mw = m
    30  	case func(Handler) Handler:
    31  		mw = m
    32  	case Handler:
    33  		mw = handlerToMiddleware(m)
    34  	case func(context.Context, http.ResponseWriter, *http.Request) error:
    35  		mw = handlerToMiddleware(m)
    36  	case func(http.Handler) http.Handler:
    37  		mw = func(h Handler) Handler {
    38  			return func(ctx context.Context, rw http.ResponseWriter, req *http.Request) (err error) {
    39  				m(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    40  					err = h(ctx, w, r)
    41  				})).ServeHTTP(rw, req)
    42  				return
    43  			}
    44  		}
    45  	case http.Handler:
    46  		mw = httpHandlerToMiddleware(m.ServeHTTP)
    47  	case func(http.ResponseWriter, *http.Request):
    48  		mw = httpHandlerToMiddleware(m)
    49  	default:
    50  		err = fmt.Errorf("invalid middleware %#v", m)
    51  	}
    52  	return
    53  }
    54  
    55  // handlerToMiddleware creates a middleware from a raw handler.
    56  // The middleware calls the handler and either breaks the middleware chain if the handler returns
    57  // an error by also returning the error or calls the next handler in the chain otherwise.
    58  func handlerToMiddleware(m Handler) Middleware {
    59  	return func(h Handler) Handler {
    60  		return func(ctx context.Context, rw http.ResponseWriter, req *http.Request) error {
    61  			if err := m(ctx, rw, req); err != nil {
    62  				return err
    63  			}
    64  			return h(ctx, rw, req)
    65  		}
    66  	}
    67  }
    68  
    69  // httpHandlerToMiddleware creates a middleware from a http.HandlerFunc.
    70  // The middleware calls the ServerHTTP method exposed by the http handler and then calls the next
    71  // middleware in the chain.
    72  func httpHandlerToMiddleware(m http.HandlerFunc) Middleware {
    73  	return func(h Handler) Handler {
    74  		return func(ctx context.Context, rw http.ResponseWriter, req *http.Request) error {
    75  			m.ServeHTTP(rw, req)
    76  			return h(ctx, rw, req)
    77  		}
    78  	}
    79  }