Server for HTTPS protocol. Redirects to canonical hosts, reverse proxies requests to internal backing servers.

main.go

// Server for HTTPS protocol. Redirects to canonical hosts, reverse proxies requests to internal backing servers.
package main

import (
	"crypto/tls"
	"flag"
	"log"
	"net/http"
	"net/http/httputil"
	"time"
)

var (
	httpsFlag = flag.String("https", ":https", "Listen for HTTPS connections on this address.")
)

func main() {
	flag.Parse()

	httpsCanonicalHostRedirector := &canonicalHostRedirector{"https", newRouter()}

	tlsConfig, err := loadCertificates()
	if err != nil {
		log.Fatalln(err)
	}
	server := &http.Server{Addr: *httpsFlag, TLSConfig: tlsConfig, Handler: httpsCanonicalHostRedirector}
	err = server.ListenAndServeTLS("", "")
	if err != nil {
		log.Fatalln(err)
	}
}

// canonicalHostRedirector redirects to a canonical host, when visiting a non-canonical one.
// Otherwise it defers to handler.
type canonicalHostRedirector struct {
	scheme  string       // Scheme to redirect to. E.g., "https".
	handler http.Handler // Handler to defer to when canonical host is used.
}

func (r *canonicalHostRedirector) ServeHTTP(w http.ResponseWriter, req *http.Request) {
	var canonicalHost string
	switch req.Host {
	default: // Primary domain.
		canonicalHost = "example.com"
	case "anotherdomain.org", "www.anotherdomain.org":
		canonicalHost = "anotherdomain.org"
	case "foobar.thirdexample.org", "www.thirdexample.org", "thirdexample.org":
		canonicalHost = "foobar.thirdexample.org"
	}

	// Redirect to canonical host, if needed.
	// TODO: Is it worth it to try to do a case insensitive comparison here, to avoid it needlessly triggerring redirection?
	//       It can only happen with weird clients; latest Chrome will always send requests with lowercase domains.
	if req.Host != canonicalHost {
		u := *req.URL
		u.Scheme = r.scheme
		u.Host = canonicalHost
		http.Redirect(w, req, u.String(), http.StatusTemporaryRedirect)
		return
	}

	r.handler.ServeHTTP(w, req)
}

// newRouter returns a reverse proxy that routes to internal backing servers for each domain.
func newRouter() http.Handler {
	director := func(req *http.Request) {
		switch req.Host {
		default: // Primary domain.
			req.URL.Scheme = "http"
			req.URL.Host = "127.0.0.1:10000"
		case "anotherdomain.org":
			req.URL.Scheme = "http"
			req.URL.Host = "127.0.0.1:10001"
		case "foobar.thirdexample.org":
			req.URL.Scheme = "http"
			req.URL.Host = "127.0.0.1:10002"
		}
		req.Host = "" // TODO: Figure out if this is needed; document it if so.
	}
	return &httputil.ReverseProxy{
		Director:      director,
		FlushInterval: 1 * time.Second,
	}
}

// HTTPS certificate details.

var domains = []struct {
	certFile, keyFile string
}{
	{
		certFile: "/home/user/.lego/certificates/example.com.crt",
		keyFile:  "/home/user/.lego/certificates/example.com.key",
	}, {
		certFile: "/home/user/.lego/certificates/anotherdomain.org.crt",
		keyFile:  "/home/user/.lego/certificates/anotherdomain.org.key",
	}, {
		certFile: "/home/user/.lego/certificates/foobar.thirdexample.org.crt",
		keyFile:  "/home/user/.lego/certificates/foobar.thirdexample.org.key",
	},
}

func loadCertificates() (*tls.Config, error) {
	c := &tls.Config{}
	for _, d := range domains {
		cert, err := tls.LoadX509KeyPair(d.certFile, d.keyFile)
		if err != nil {
			return nil, err
		}
		c.Certificates = append(c.Certificates, cert)
	}
	c.BuildNameToCertificate()
	return c, nil
}