httprouter configuring NotFound

问题:

I'm using httprouter for an API and I'm trying to work out how to handle 404s. It does say in the docs that 404's can be handled manually but I don't really have an idea how to write my own custom handler.

I've tried the following after my other routes...

router.NotFound(pageNotFound)

But I get the error not enough arguments in call to router.NotFound.

If anyone could point me in the right direction it would be great.

回答1:

The type httprouter.Router is a struct which has a field:

NotFound http.Handler

So type of NotFound is http.Handler, an interface type which has a single method:

ServeHTTP(ResponseWriter, *Request)

If you want your own custom "Not Found" handler, you have to set a value that implements this interface.

The easiest way is to define a function with signature:

func(http.ResponseWriter, *http.Request)

And use the http.HandlerFunc() helper function to "convert" it to a value that implements the http.Handler interface, whose ServeHTTP() method simply calls the function with the above signature.

For example:

func MyNotFound(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "text/plain; charset=utf-8")
    w.WriteHeader(http.StatusNotFound) // StatusNotFound = 404
    w.Write([]byte("My own Not Found handler."))
    w.Write([]byte(" The page you requested could not be found."))
}

var router *httprouter.Router = ... // Your router value
router.NotFound = http.HandlerFunc(MyNotFound)

This NotFound handler will be invoked by the httprouter package. If you would want to call it manually from one of your other handlers, you would have to pass a ResponseWriter and a *Request to it, something like this:

func ResourceHandler(w http.ResponseWriter, r *http.Request) {
    exists := ... // Find out if requested resource is valid and available
    if !exists {
        MyNotFound(w, r) // Pass ResponseWriter and Request
        // Or via the Router:
        // router.NotFound(w, r)
        return
    }

    // Resource exists, serve it
    // ...
}

回答2:

NotFound is a function pointer of type http.HandlerFunc. You will have to put a function with the signature Func(w ResponseWriter, r *Request) somewhere and assign it to NotFound (router.NotFound = Func).