Compose middlewares in go-chi?

Question

I am writing an API using go-chi and my endpoint can be authenticated either via Basic Auth or an API Key. How can I compose two independently functioning middlewares?

Here is what the router looks like:

router := chi.NewRouter()
router.Use(BasicAuthMiddleware)
router.Use(APIKeyMiddleware)

What I really want is to say "If there is a header called X-API-KEY then authenticate the endpoint using APIKeyMiddleware, otherwise use BasicAuthMiddleware."

func CustomMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // What goes here?
    })
}

poundifdef · Accepted Answer · 2024-03-10 00:20:16Z

2

Middlewares can be composed by calling ServeHTTP(). For example:

func CustomMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // Look at the values of r to determine which middleware to use
        BasicAuthMiddleware(next).ServeHTTP(w, r)
    })
}

answered Mar 10, 2024 at 0:20

poundifdef

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gallyamb · Accepted Answer · 2024-12-10 11:53:01Z

I'm not familiar with go-chi, but for any kind of middlewares in any language the pattern is almost the same

In your case you should write something like this:

func CustomMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // your custom logic before request processing started
        next.Handle(w, r)
        // your custom logic after request processed
    })
}

To make the example more expressive, let's write a middleware for writing metrics

type MetricsHandler interface {
    Increment(key string, tags ...string)
}

type responseWrapper struct {
    http.ResponseWriter
    statusCode int
}

func (r *responseWrapper) WriteHeader(statusCode int) {
    r.statusCode = statusCode
    r.ResponseWriter.WriteHeader(statusCode)
}

func MetricsMiddleware(m MetricsHandler) func(http.Handler) http.Handler {
    return func(next http.Handler) http.Handler {
        return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
            tags := []string{"path", request.URL.Path}
            m.Increment("requests.incoming.count", tags...)
            response := &responseWrapper{w}
            defer func() {
                if response.statusCode < http.StatusBadRequest {
                    m.Increment("requests.incoming.processed", tags...)
                } else {
                    m.Increment("requests.incoming.failed", tags...)
                }
            }()
            next.Handle(response, r)
        })
    }
}

And now you can use this middleware in your application and metrics will be sent with tags for each endpoint

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