advanced-go-programming-book/vendor/github.com/grpc-ecosystem/grpc-gateway/examples/gateway/handlers.go

package gateway

import (
	"fmt"
	"net/http"
	"path"
	"strings"

	"github.com/golang/glog"
	"google.golang.org/grpc"
	"google.golang.org/grpc/connectivity"
)

func swaggerServer(dir string) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if !strings.HasSuffix(r.URL.Path, ".swagger.json") {
			glog.Errorf("Not Found: %s", r.URL.Path)
			http.NotFound(w, r)
			return
		}

		glog.Infof("Serving %s", r.URL.Path)
		p := strings.TrimPrefix(r.URL.Path, "/swagger/")
		p = path.Join(dir, p)
		http.ServeFile(w, r, p)
	}
}

// allowCORS allows Cross Origin Resoruce Sharing from any origin.
// Don't do this without consideration in production systems.
func allowCORS(h http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if origin := r.Header.Get("Origin"); origin != "" {
			w.Header().Set("Access-Control-Allow-Origin", origin)
			if r.Method == "OPTIONS" && r.Header.Get("Access-Control-Request-Method") != "" {
				preflightHandler(w, r)
				return
			}
		}
		h.ServeHTTP(w, r)
	})
}

func preflightHandler(w http.ResponseWriter, r *http.Request) {
	headers := []string{"Content-Type", "Accept"}
	w.Header().Set("Access-Control-Allow-Headers", strings.Join(headers, ","))
	methods := []string{"GET", "HEAD", "POST", "PUT", "DELETE"}
	w.Header().Set("Access-Control-Allow-Methods", strings.Join(methods, ","))
	glog.Infof("preflight request for %s", r.URL.Path)
}

func healthzServer(conn *grpc.ClientConn) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "text/plain")
		if s := conn.GetState(); s != connectivity.Ready {
			http.Error(w, fmt.Sprintf("grpc server is %s", s), http.StatusBadGateway)
			return
		}
		fmt.Fprintln(w, "ok")
	}
}