Root config: Add env config (#6400)

https://github.com/XTLS/Xray-core/pull/6400#issuecomment-4880198100
https://github.com/XTLS/Xray-core/pull/6400#issuecomment-4916892425
https://github.com/XTLS/Xray-core/pull/6400#issuecomment-4929136670

common/buf/io.go

@@ -122,7 +122,7 @@ func NewReader(reader io.Reader) Reader {
 	}
 
 	_, isFile := reader.(*os.File)
-	if !isFile && useReadv {
+	if !isFile && useReadV() {
 		if sc, ok := reader.(syscall.Conn); ok {
 			rawConn, err := sc.SyscallConn()
 			if err != nil {

common/buf/readv_reader.go

@@ -5,6 +5,7 @@ package buf
 
 import (
 	"io"
+	"sync/atomic"
 	"syscall"
 
 	"github.com/xtls/xray-core/common/platform"
@@ -143,13 +144,24 @@ func (r *ReadVReader) ReadMultiBuffer() (MultiBuffer, error) {
 	return mb, nil
 }
 
-var useReadv bool
+var useReadv atomic.Bool
 
-func init() {
+func useReadV() bool {
+	return useReadv.Load()
+}
+
+func reloadEnvSettings() error {
 	const defaultFlagValue = "NOT_DEFINED_AT_ALL"
 	value := platform.NewEnvFlag(platform.UseReadV).GetValue(func() string { return defaultFlagValue })
+	enabled := false
 	switch value {
 	case defaultFlagValue, "auto", "enable":
-		useReadv = true
+		enabled = true
 	}
+	useReadv.Store(enabled)
+	return nil
+}
+
+func init() {
+	platform.RegisterEnvReload(reloadEnvSettings)
 }

common/buf/readv_reader_stub.go

@@ -10,7 +10,9 @@ import (
 	"github.com/xtls/xray-core/features/stats"
 )
 
-const useReadv = false
+func useReadV() bool {
+	return false
+}
 
 func NewReadVReader(reader io.Reader, rawConn syscall.RawConn, counter stats.Counter) Reader {
 	panic("not implemented")

common/platform/env_reload.go

@@ -0,0 +1,40 @@
+package platform
+
+import (
+	"errors"
+	"sync"
+)
+
+var envReloadRegistry = struct {
+	sync.RWMutex
+	handlers []func() error
+}{}
+
+// RegisterEnvReload registers an environment reload handler and runs it once
+// immediately so package defaults keep the same behavior as init-time reads.
+func RegisterEnvReload(handler func() error) {
+	if handler == nil {
+		return
+	}
+	envReloadRegistry.Lock()
+	envReloadRegistry.handlers = append(envReloadRegistry.handlers, handler)
+	envReloadRegistry.Unlock()
+	if err := handler(); err != nil {
+		panic(err)
+	}
+}
+
+// ReloadEnvSettings refreshes all registered environment-backed package state.
+func ReloadEnvSettings() error {
+	envReloadRegistry.RLock()
+	handlers := append([]func() error{}, envReloadRegistry.handlers...)
+	envReloadRegistry.RUnlock()
+
+	var errs []error
+	for _, handler := range handlers {
+		if err := handler(); err != nil {
+			errs = append(errs, err)
+		}
+	}
+	return errors.Join(errs...)
+}

common/xudp/xudp.go

@@ -8,7 +8,7 @@ import (
 	"io"
 	"strconv"
 	"strings"
-	"time"
+	"sync/atomic"
 
 	"github.com/xtls/xray-core/common/buf"
 	"github.com/xtls/xray-core/common/errors"
@@ -27,25 +27,39 @@ var AddrParser = protocol.NewAddressParser(
 )
 
 var (
-	Show    bool
-	BaseKey []byte
+	Show    atomic.Bool
+	baseKey atomic.Value
 )
 
-func init() {
-	if strings.ToLower(platform.NewEnvFlag(platform.XUDPLog).GetValue(func() string { return "" })) == "true" {
-		Show = true
+func reloadEnvSettings() error {
+	Show.Store(strings.ToLower(platform.NewEnvFlag(platform.XUDPLog).GetValue(func() string { return "" })) == "true")
+	raw := platform.NewEnvFlag(platform.XUDPBaseKey).GetValue(func() string { return "" })
+	if raw == "" {
+		ensureBaseKey()
+		return nil
 	}
-	BaseKey = make([]byte, 32)
-	rand.Read(BaseKey)
-	go func() {
-		time.Sleep(100 * time.Millisecond) // this is not nice, but need to give some time for Android to setup ENV
-		if raw := platform.NewEnvFlag(platform.XUDPBaseKey).GetValue(func() string { return "" }); raw != "" {
-			if BaseKey, _ = base64.RawURLEncoding.DecodeString(raw); len(BaseKey) == 32 {
-				return
-			}
-			panic(platform.XUDPBaseKey + ": invalid value (BaseKey must be 32 bytes): " + raw + " len " + strconv.Itoa(len(BaseKey)))
-		}
-	}()
+	key, _ := base64.RawURLEncoding.DecodeString(raw)
+	if len(key) != 32 {
+		return errors.New(platform.XUDPBaseKey + ": invalid value (BaseKey must be 32 bytes): " + raw + " len " + strconv.Itoa(len(key)))
+	}
+	baseKey.Store(append([]byte(nil), key...))
+	return nil
+}
+
+func ensureBaseKey() []byte {
+	if key := baseKey.Load(); key != nil {
+		return key.([]byte)
+	}
+	key := make([]byte, 32)
+	if _, err := rand.Read(key); err != nil {
+		panic(err)
+	}
+	baseKey.Store(key)
+	return key
+}
+
+func init() {
+	platform.RegisterEnvReload(reloadEnvSettings)
 }
 
 func GetGlobalID(ctx context.Context) (globalID [8]byte) {
@@ -54,10 +68,10 @@ func GetGlobalID(ctx context.Context) (globalID [8]byte) {
 	}
 	if inbound := session.InboundFromContext(ctx); inbound != nil && inbound.Source.Network == net.Network_UDP &&
 		(inbound.Name == "dokodemo-door" || inbound.Name == "socks" || inbound.Name == "shadowsocks" || inbound.Name == "tun") {
-		h := blake3.New(8, BaseKey)
+		h := blake3.New(8, ensureBaseKey())
 		h.Write([]byte(inbound.Source.String()))
 		copy(globalID[:], h.Sum(nil))
-		if Show {
+		if Show.Load() {
 			errors.LogInfo(ctx, fmt.Sprintf("XUDP inbound.Source.String(): %v\tglobalID: %v\n", inbound.Source.String(), globalID))
 		}
 	}