Little fileserver that will allow CORS by default, inspired by wanting to use the swagger ui from any directory containing a swagger.json

servedir.go

package main

import (
	"flag"
	"fmt"
	"log"
	"net/http"
	"os"
	"strings"
)

type middleware func(http.Handler) http.Handler

func main() {
	wd, err := os.Getwd()

	if err != nil {
		log.Fatal(err)
	}

	var port int
	var disableCors bool
	var resHeaders string
	var workingDir string

	flag.IntVar(&port, "port", 3000, "Port on which to serve this directory")
	flag.BoolVar(&disableCors, "disable.cors", false, "Disable the wildcard Access-Control-Allow-Origin header")
	flag.StringVar(&resHeaders, "res.headers", "", "CSV of header names and values to add to server responses")
	flag.StringVar(&workingDir, "working.dir", wd, "What directory to serve files from. Defaults to the current working directory.")
	flag.Parse()

	var h http.Handler
	{
		// Set up the file server
		h = http.FileServer(http.Dir(workingDir))
		if !disableCors {
			// Add CORS to the response headers
			h = corsMW(h)
		}
		// Add any custom response headers the user chooses.
		h = responseHeadersMW(headersMap(resHeaders))(h)
	}

	log.Printf("Serving %s on %d\n", workingDir, port)

	http.Handle("/", h)
	log.Fatal(http.ListenAndServe(fmt.Sprintf(":%d", port), nil))
}

func corsMW(next http.Handler) http.Handler {
	return responseHeadersMW(map[string]string{
		"Access-Control-Allow-Origin": "*",
	})(next)
}

func responseHeadersMW(headers map[string]string) middleware {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
			for h, v := range headers {
				rw.Header().Add(h, v)
			}
			next.ServeHTTP(rw, req)
		})
	}
}

func headersMap(headersCsv string) map[string]string {
	tkns := strings.Split(headersCsv, ",")

	headers := map[string]string{}
	if len(tkns)%2 == 0 {
		for i := 0; i < len(tkns); i += 2 {
			key := tkns[i]
			value := tkns[i+1]
			headers[key] = value
		}
	}

	return headers
}