proxy.go

package portpxy

import (
	"fmt"
	"net/http"
	"net/http/httputil"
	"net/url"
	"strconv"
	"strings"
	"time"

	"github.com/prometheus/client_golang/prometheus"
	"go.uber.org/zap"
)

// Pmx struct for storing metrics
type Pmx struct {
	Requests prometheus.Counter
	Latency  prometheus.Summary
}

type Proxy struct {
	BackendHost     string
	BackendProto    string
	AllowRangeBegin int
	AllowRangeEnd   int
	Logger          *zap.Logger
	Pmx             *Pmx
}

// Handle proxy requests
func (p *Proxy) Handle(w http.ResponseWriter, r *http.Request) {
	var admit = true

	p.Pmx.Requests.Inc()

	start := time.Now()
	reqPath := strings.TrimLeft(r.URL.Path, "/")
	reqMethod := r.Method

	backend := fmt.Sprintf("%s://%s", p.BackendProto, p.BackendHost)
	port := ""

	pathParts := strings.Split(reqPath, "/")
	port = pathParts[0]
	portInt, err := strconv.Atoi(port)
	if err != nil {
		admit = false
		w.Header().Set("Content-Type", "application/json")
		w.WriteHeader(http.StatusBadRequest)
		_, _ = w.Write([]byte("{\"status\": \"port must be a number\"}"))
	}

	if admit && (portInt < p.AllowRangeBegin || portInt > p.AllowRangeEnd) {
		admit = false
		w.Header().Set("Content-Type", "application/json")
		w.WriteHeader(http.StatusBadRequest)
		_, _ = w.Write([]byte("{\"status\": \"port must be in range\"}"))
	}

	if admit {
		backend = fmt.Sprintf("%s:%s", backend, port)

		// Backend Configuration
		targetUrl, err := url.Parse(backend)
		if err != nil {
			admit = false
			w.Header().Set("Content-Type", "application/json")
			w.WriteHeader(http.StatusBadRequest)
			_, _ = w.Write([]byte("{\"status\": \"unable to parse URL\"}"))
		}

		if admit {

			r.RequestURI = strings.Replace(r.RequestURI, "/"+port, "", 1)

			r.URL, _ = url.Parse(r.RequestURI)
			r.Host = fmt.Sprintf("%s:%s", p.BackendHost, port)

			// PROXY REQUEST
			pxy := httputil.NewSingleHostReverseProxy(targetUrl)
			pxy.ServeHTTP(w, r)
		}
	}

	end := time.Now()
	p.Pmx.Latency.Observe(float64(end.Sub(start)))

	p.Logger.Info("Proxy Result",
		zap.String("r.URL", r.URL.String()),
		zap.String("r.Host", r.Host),
		zap.String("backend", backend),
		zap.String("method", reqMethod),
		zap.String("path", reqPath),
		zap.String("time", end.Format(time.RFC3339)),
		zap.Any("header", r.Header),
		zap.Any("URL", r.URL),
		zap.Any("RequestURI", r.RequestURI),
	)
}