tun2: expvar counters for each backend

internal/tun2/connection.go

@@ -4,6 +4,7 @@ import (
 	"bufio"
 	"bytes"
 	"context"
+	"expvar"
 	"io/ioutil"
 	"net"
 	"net/http"
@@ -30,6 +31,8 @@ type Connection struct {
 	detector      *failure.Detector
 	Auth          *Auth
 	usable        bool
+
+	counter *expvar.Int
 }
 
 func (c *Connection) cancel() {
@@ -150,5 +153,7 @@ func (c *Connection) RoundTrip(req *http.Request) (*http.Response, error) {
 	resp.Body = ioutil.NopCloser(bytes.NewBuffer(body))
 	resp.ContentLength = int64(len(body))
 
+	c.counter.Add(1)
+
 	return resp, nil
 }

internal/tun2/server.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
+	"expvar"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -308,6 +309,7 @@ func (s *Server) HandleConn(c net.Conn, isKCP bool) {
 		detector: failure.New(15, 1),
 		Auth:     auth,
 	}
+	connection.counter = expvar.NewInt("http.backend." + connection.id + ".hits")
 
 	defer func() {
 		if r := recover(); r != nil {