Store local credentials as structured JSON

config.go

@@ -16,6 +16,7 @@ package main
 import (
 	"crypto/rand"
 	"encoding/hex"
+	"encoding/json"
 	"fmt"
 	"log"
 	"os"
@@ -316,14 +317,22 @@ partner = ""
 // load a different save. With its own id, the hub keeps seeing the same
 // partner even if they switch characters, reconnect, or restart the
 // program.
+// clientIDFile is client-id.txt's on-disk shape.
+type clientIDFile struct {
+	ID string `json:"id"`
+}
+
 func clientID() string {
 	path := "client-id.txt"
 	if exe, err := os.Executable(); err == nil {
 		path = filepath.Join(filepath.Dir(exe), "client-id.txt")
 	}
 	if data, err := os.ReadFile(path); err == nil {
-		if id := strings.TrimSpace(string(data)); id != "" {
-			return id
+		var f clientIDFile
+		if jerr := json.Unmarshal(data, &f); jerr == nil {
+			if id := strings.TrimSpace(f.ID); id != "" {
+				return id
+			}
 		}
 	}
 	var b [8]byte
@@ -333,7 +342,12 @@ func clientID() string {
 		return fmt.Sprintf("pid-%d", os.Getpid())
 	}
 	id := hex.EncodeToString(b[:])
-	if err := os.WriteFile(path, []byte(id), 0644); err != nil {
+	blob, merr := json.MarshalIndent(clientIDFile{ID: id}, "", "  ")
+	if merr != nil {
+		log.Printf("couldn't encode client-id.txt (%v): using a fresh id every startup", merr)
+		return id
+	}
+	if err := os.WriteFile(path, blob, 0644); err != nil {
 		log.Printf("couldn't save client-id.txt (%v): using a fresh id every startup", err)
 	}
 	return id
@@ -345,7 +359,7 @@ func writeSampleConfig() {
 	if _, err := os.Stat(path); err == nil {
 		return
 	}
-	if err := os.WriteFile(path, []byte(sampleConfig), 0644); err != nil {
+	if err := os.WriteFile(path, []byte(sampleConfig), 0600); err != nil {
 		log.Printf("couldn't write the sample config.toml: %v", err)
 		return
 	}