read old report for later use

init.go

@@ -19,7 +19,7 @@ func Init() {
 	}
 
 	conf := DsnetConfig{
-		PrivateKey:    GenerateJSONPrivateKey()
+		PrivateKey:    GenerateJSONPrivateKey(),
 		ListenPort:    DEFAULT_LISTEN_PORT,
 		Network:       getRandomNetwork(),
 		Peers:         []PeerConfig{},

report.go

@@ -17,6 +17,7 @@ func Report() {
 		ExitFail("Could not retrieve device '%s' (%v)", conf.InterfaceName, err)
 	}
 
-	report := GenerateReport(dev, conf)
+	oldReport := MustLoadDsnetReport()
+	report := GenerateReport(dev, conf, oldReport)
 	report.MustSave(conf.ReportFile)
 }

reporttypes.go

@@ -4,8 +4,10 @@ import (
 	"encoding/json"
 	"io/ioutil"
 	"net"
+	"os"
 	"time"
 
+	"github.com/go-playground/validator/v10"
 	"golang.zx2c4.com/wireguard/wgctrl/wgtypes"
 )
 
@@ -60,7 +62,7 @@ type DsnetReport struct {
 	Peers   []PeerReport
 }
 
-func GenerateReport(dev *wgtypes.Device, conf *DsnetConfig) DsnetReport {
+func GenerateReport(dev *wgtypes.Device, conf *DsnetConfig, oldReport *DsnetReport) DsnetReport {
 	wgPeerIndex := make(map[wgtypes.Key]wgtypes.Peer)
 	peerReports := make([]PeerReport, len(conf.Peers))
 
@@ -114,6 +116,27 @@ func (report *DsnetReport) MustSave(filename string) {
 	check(err)
 }
 
+func MustLoadDsnetReport() *DsnetReport {
+	raw, err := ioutil.ReadFile(CONFIG_FILE)
+
+	if os.IsNotExist(err) {
+		return nil
+	} else if os.IsPermission(err) {
+		ExitFail("%s cannot be accessed. Check read permissions.", CONFIG_FILE)
+	} else {
+		check(err)
+	}
+
+	report := DsnetReport{}
+	err = json.Unmarshal(raw, &report)
+	check(err)
+
+	err = validator.New().Struct(report)
+	check(err)
+
+	return &report
+}
+
 type PeerReport struct {
 	// Used to update DNS
 	Hostname string