main.go

/*Example Usage:
 *
 * $ PORT=3000 HOST=0.0.0.0 STATIC=./static PROXY_TARGET=http://localhost:5000 PROXY_PATH=/api go run main.go
 */

package main

import (
	"fmt"
	"log"
	"net/http"
	"net/http/httputil"
	"net/url"
	"os"
)

var (
	port      string
	host      string
	static    string
	proxyURL  *url.URL
	proxyPath string
)

func init() {
	// Set basic logging defaults.
	log.SetFlags(0)
	log.SetOutput(os.Stdout)

	// Get or set PORT
	port = os.Getenv("PORT")
	if port == "" {
		port = "3000"
	}

	// Get or set HOST
	host = os.Getenv("HOST")
	if host == "" {
		host = "localhost"
	}

	// Get or set STATIC
	// - source location for static file server
	static = os.Getenv("STATIC")
	if static == "" {
		static = "./static"
	}

	// Get (if present) PROXY_TARGET
	// - target URL to proxy requests to
	proxyTarget := os.Getenv("PROXY_TARGET")
	if proxyTarget != "" {
		var err error
		proxyURL, err = url.Parse(proxyTarget)
		if err != nil {
			log.Fatalf("ns=init at=proxyURL error=%q", err)
		}
	}

	// Get (if present) PROXY_PATH
	// - path matcher for proxied requests
	proxyPath = os.Getenv("PROXY_PATH")
}

func logRequest(r *http.Request, isProxy bool) {
	log.Printf("method=%s proto=%s path=%s referer=%s user_agent=%q content_length=%d proxy=%v",
		r.Method,
		r.Proto,
		r.URL.String(),
		r.Referer(),
		r.UserAgent(),
		r.ContentLength,
		isProxy,
	)
}

func main() {
	// Handle reverse proxy on 'proxyPath' to 'proxyURL' when both are set.
	if proxyPath != "" && proxyURL != nil {
		// Reverse proxy handler.
		proxy := httputil.NewSingleHostReverseProxy(proxyURL)

		http.HandleFunc(proxyPath, func(w http.ResponseWriter, r *http.Request) {
			// Set any custom headers here.
			//w.Header().Set("X-Go-Proxy", "Go-Proxy")

			// Serve proxy request
			proxy.ServeHTTP(w, r)

			// Log request
			logRequest(r, true)
		})
	}

	// Static file handler.
	server := http.FileServer(http.Dir(static))

	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		// Set any custom headers here.
		//w.Header().Set("X-Go-Proxy", "Go-Proxy")

		// Serve static request
		server.ServeHTTP(w, r)

		// Log request
		logRequest(r, false)
	})

	// Log start up.
	log.Printf("ns=main at=http.ListenAndServe on=start host=%s port=%s", host, port)

	// Format listener string.
	listener := fmt.Sprintf("%s:%s", host, port)

	// Start http server.
	err := http.ListenAndServe(listener, nil)

	// Log http server fatal error and exit.
	log.Fatalf("ns=main at=http.ListenAndServe error=%q", err)
}