mediocre-blog/src/http/csrf.go

package http

import (
	"errors"
	"net"
	"net/http"
	"net/url"

	"github.com/mediocregopher/blog.mediocregopher.com/srv/http/apiutil"
)

func checkCSRF(r *http.Request, publicURL *url.URL) error {

	if ipStr, _, err := net.SplitHostPort(r.Host); err == nil {
		if ip := net.ParseIP(ipStr); ip != nil && ip.IsLoopback() {
			return nil
		}
	}

	refererURL, err := url.Parse(r.Referer())
	if err != nil {
		return errors.New("invalid Referer")
	}

	if refererURL.Scheme != publicURL.Scheme ||
		refererURL.Host != publicURL.Host {
		return errors.New("invalid Referer")
	}

	return nil
}

func (a *api) checkCSRFMiddleware(h http.Handler) http.Handler {
	return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {

		if err := checkCSRF(r, a.params.PublicURL); err != nil {
			apiutil.BadRequest(rw, r, errors.New("invalid Referer"))
			return
		}

		h.ServeHTTP(rw, r)
	})
}