implement ICMP ping

routine.go

@@ -4,7 +4,10 @@ import (
 	"bytes"
 	"context"
 	"crypto/subtle"
+	"encoding/json"
 	"errors"
+	"golang.org/x/net/icmp"
+	"golang.org/x/net/ipv4"
 	"golang.zx2c4.com/wireguard/device"
 	"io"
 	"log"
@@ -15,6 +18,7 @@ import (
 	"path"
 	"strconv"
 	"strings"
+	"time"
 
 	"github.com/sourcegraph/conc"
 	"github.com/things-go/go-socks5"
@@ -39,6 +43,9 @@ type VirtualTun struct {
 	Tnet      *netstack.Net
 	Dev       *device.Device
 	SystemDNS bool
+	Conf      *DeviceConfig
+	// PingRecord stores the last time an IP was pinged
+	PingRecord map[string]uint64
 }
 
 // RoutineSpawner spawns a routine (e.g. socks5, tcp static routes) after the configuration is parsed
@@ -341,7 +348,26 @@ func (d VirtualTun) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	log.Printf("Health metric request: %s\n", r.URL.Path)
 	switch path.Clean(r.URL.Path) {
 	case "/readyz":
-		w.WriteHeader(http.StatusOK)
+		body, err := json.Marshal(d.PingRecord)
+		if err != nil {
+			errorLogger.Printf("Failed to get device metrics: %s\n", err.Error())
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		}
+
+		status := http.StatusOK
+		for _, record := range d.PingRecord {
+			lastPong := time.Unix(int64(record), 0)
+			// +2 seconds to account for the time it takes to ping the IP
+			if time.Since(lastPong) > time.Duration(d.Conf.CheckAliveInterval+2)*time.Second {
+				status = http.StatusServiceUnavailable
+				break
+			}
+		}
+
+		w.WriteHeader(status)
+		_, _ = w.Write(body)
+		_, _ = w.Write([]byte("\n"))
 	case "/metrics":
 		get, err := d.Dev.IpcGet()
 		if err != nil {
@@ -371,3 +397,71 @@ func (d VirtualTun) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusNotFound)
 	}
 }
+
+func (d VirtualTun) pingIPs() {
+	for _, addr := range d.Conf.CheckAlive {
+		socket, err := d.Tnet.Dial("ping", addr.String())
+		if err != nil {
+			errorLogger.Printf("Failed to ping %s: %s\n", addr, err.Error())
+			continue
+		}
+
+		data := make([]byte, 16)
+		rand.Read(data)
+
+		requestPing := icmp.Echo{
+			Seq:  rand.Intn(1 << 16),
+			Data: data,
+		}
+
+		icmpBytes, _ := (&icmp.Message{Type: ipv4.ICMPTypeEcho, Code: 0, Body: &requestPing}).Marshal(nil)
+		_ = socket.SetReadDeadline(time.Now().Add(time.Duration(d.Conf.CheckAliveInterval) * time.Second))
+		_, err = socket.Write(icmpBytes)
+		if err != nil {
+			errorLogger.Printf("Failed to ping %s: %s\n", addr, err.Error())
+			continue
+		}
+
+		addr := addr
+		go func() {
+			n, err := socket.Read(icmpBytes[:])
+			if err != nil {
+				errorLogger.Printf("Failed to read ping response from %s: %s\n", addr, err.Error())
+				return
+			}
+
+			replyPacket, err := icmp.ParseMessage(1, icmpBytes[:n])
+			if err != nil {
+				errorLogger.Printf("Failed to parse ping response from %s: %s\n", addr, err.Error())
+				return
+			}
+
+			replyPing, ok := replyPacket.Body.(*icmp.Echo)
+			if !ok {
+				errorLogger.Printf("Failed to parse ping response from %s: invalid reply type: %v\n", addr, replyPacket)
+				return
+			}
+			if !bytes.Equal(replyPing.Data, requestPing.Data) || replyPing.Seq != requestPing.Seq {
+				errorLogger.Printf("Failed to parse ping response from %s: invalid ping reply: %v\n", addr, replyPing)
+				return
+			}
+
+			d.PingRecord[addr.String()] = uint64(time.Now().Unix())
+
+			defer socket.Close()
+		}()
+	}
+}
+
+func (d VirtualTun) StartPingIPs() {
+	for _, addr := range d.Conf.CheckAlive {
+		d.PingRecord[addr.String()] = 0
+	}
+
+	go func() {
+		for {
+			d.pingIPs()
+			time.Sleep(time.Duration(d.Conf.CheckAliveInterval) * time.Second)
+		}
+	}()
+}