clientinfo: skip unavailable Ubios Mongo discovery

internal/clientinfo/ubios.go

@@ -3,8 +3,10 @@ package clientinfo
 import (
 	"bytes"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
+	"os"
 	"os/exec"
 	"strings"
 	"sync"
@@ -13,9 +15,12 @@ import (
 	"github.com/Control-D-Inc/ctrld/internal/router/ubios"
 )
 
+const defaultUbiosMongoPath = "/usr/bin/mongo"
+
 // ubiosDiscover provides client discovery functionality on Ubios routers.
 type ubiosDiscover struct {
-	hostname sync.Map // mac => hostname
+	hostname  sync.Map // mac => hostname
+	mongoPath string
 }
 
 // refresh reloads unifi devices from database.
@@ -42,7 +47,19 @@ func (u *ubiosDiscover) LookupHostnameByMac(mac string) string {
 
 // refreshDevices updates unifi devices name from local mongodb.
 func (u *ubiosDiscover) refreshDevices() error {
-	cmd := exec.Command("/usr/bin/mongo", "localhost:27117/ace", "--quiet", "--eval", `
+	mongoPath := u.mongoExecutable()
+	fi, err := os.Stat(mongoPath)
+	if errors.Is(err, os.ErrNotExist) {
+		return nil
+	}
+	if err != nil {
+		return fmt.Errorf("stat mongo executable: %w", err)
+	}
+	if !fi.Mode().IsRegular() || fi.Mode().Perm()&0111 == 0 {
+		return nil
+	}
+
+	cmd := exec.Command(mongoPath, "localhost:27117/ace", "--quiet", "--eval", `
 		DBQuery.shellBatchSize = 256;
 		db.user.find({name: {$exists: true, $ne: ""}}, {_id:0, mac:1, name:1});`)
 	b, err := cmd.CombinedOutput()
@@ -52,6 +69,13 @@ func (u *ubiosDiscover) refreshDevices() error {
 	return u.storeDevices(bytes.NewReader(b))
 }
 
+func (u *ubiosDiscover) mongoExecutable() string {
+	if u.mongoPath != "" {
+		return u.mongoPath
+	}
+	return defaultUbiosMongoPath
+}
+
 // storeDevices saves unifi devices name for caching.
 func (u *ubiosDiscover) storeDevices(r io.Reader) error {
 	decoder := json.NewDecoder(r)