Add Android client support and unify cross-platform builds

internal/client/tunnel/identity.go

@@ -0,0 +1,90 @@
+package tunnel
+
+import (
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+
+	"github.com/google/uuid"
+)
+
+const clientIDFileName = "client.id"
+
+func resolveDataDir(explicit string) string {
+	if explicit != "" {
+		return explicit
+	}
+
+	if envDir := strings.TrimSpace(os.Getenv("GOTUNNEL_DATA_DIR")); envDir != "" {
+		return envDir
+	}
+
+	if configDir, err := os.UserConfigDir(); err == nil && configDir != "" {
+		return filepath.Join(configDir, "gotunnel")
+	}
+
+	if home, err := os.UserHomeDir(); err == nil && home != "" {
+		return filepath.Join(home, ".gotunnel")
+	}
+
+	if cwd, err := os.Getwd(); err == nil && cwd != "" {
+		return filepath.Join(cwd, ".gotunnel")
+	}
+
+	return ".gotunnel"
+}
+
+func resolveClientName(explicit string) string {
+	if explicit != "" {
+		return explicit
+	}
+
+	if hostname, err := os.Hostname(); err == nil && hostname != "" {
+		return hostname
+	}
+
+	if runtime.GOOS == "android" {
+		return "android-device"
+	}
+
+	return "gotunnel-client"
+}
+
+func resolveClientID(dataDir, explicit string) string {
+	if explicit != "" {
+		_ = persistClientID(dataDir, explicit)
+		return explicit
+	}
+
+	if id := loadClientID(dataDir); id != "" {
+		return id
+	}
+
+	if id := getMachineID(); id != "" {
+		_ = persistClientID(dataDir, id)
+		return id
+	}
+
+	id := strings.ReplaceAll(uuid.NewString(), "-", "")[:16]
+	_ = persistClientID(dataDir, id)
+	return id
+}
+
+func loadClientID(dataDir string) string {
+	data, err := os.ReadFile(filepath.Join(dataDir, clientIDFileName))
+	if err != nil {
+		return ""
+	}
+	return strings.TrimSpace(string(data))
+}
+
+func persistClientID(dataDir, id string) error {
+	if id == "" {
+		return nil
+	}
+	if err := os.MkdirAll(dataDir, 0755); err != nil {
+		return err
+	}
+	return os.WriteFile(filepath.Join(dataDir, clientIDFileName), []byte(id+"\n"), 0600)
+}