Dockerfile

FROM golang:alpine AS builder
WORKDIR /app
ENV GOPROXY=https://proxy.golang.org CGO_ENABLED=0
COPY . .
RUN go build -ldflags='-s -w' -o server

FROM scratch
EXPOSE 8080
VOLUME /web
COPY --from=builder /app/server .
CMD ["./server", "-addr", ":8080", "-dir", "/web", "-ping"]

go.mod

module github.com/artyom/web-server

go 1.13

main.go

// TODO describe program
package main

import (
	"errors"
	"flag"
	"net/http"
	"os"
	"strings"
	"time"
)

func main() {
	p, dir, addr := "/", "/web", "localhost:8080"
	var withPing bool
	flag.StringVar(&p, "prefix", p, "path prefix to expose directory at")
	flag.StringVar(&dir, "dir", dir, "path to directory to serve")
	flag.StringVar(&addr, "addr", addr, "address to listen")
	flag.BoolVar(&withPing, "ping", false, "internally handle /ping endpoint (useful for health checks)")
	flag.Parse()
	if err := run(p, dir, addr, withPing); err != nil {
		os.Stderr.WriteString(err.Error() + "\n")
		os.Exit(1)
	}
}

func run(p, dir, addr string, withPing bool) error {
	if !strings.HasPrefix(p, "/") {
		return errors.New("prefix should be a /-separated path starting with /")
	}
	mux := http.NewServeMux()
	if withPing && p != "/ping" {
		mux.HandleFunc("/ping", func(w http.ResponseWriter, _ *http.Request) { w.Write([]byte("pong\n")) })
	}
	if !strings.HasSuffix(p, "/") {
		p += "/"
	}
	mux.Handle(p, http.StripPrefix(p, http.FileServer(http.Dir(dir))))
	server := &http.Server{
		Handler:      mux,
		Addr:         addr,
		ReadTimeout:  time.Second,
		WriteTimeout: time.Minute,
	}
	return server.ListenAndServe()
}