Xray-core: Add Lua script for dns and routing (#6823)

https://github.com/XTLS/Xray-core/pull/6823#issuecomment-5843754759
https://github.com/XTLS/Xray-core/pull/6823#issuecomment-5861456450
https://github.com/XTLS/Xray-core/pull/6823#issuecomment-6093596069

common/log/lua.go

@@ -0,0 +1,61 @@
+package log
+
+import (
+	"path/filepath"
+	"strings"
+
+	lua "github.com/yuin/gopher-lua"
+)
+
+// RegisterLua makes xray.log available to require in an LState.
+func RegisterLua(L *lua.LState) {
+	L.PreloadModule("xray.log", func(L *lua.LState) int {
+		module := L.CreateTable(0, 4)
+		var source, prefix string // cache
+		for name, severity := range map[string]Severity{
+			"Debug":   Severity_Debug,
+			"Info":    Severity_Info,
+			"Warning": Severity_Warning,
+			"Error":   Severity_Error,
+		} {
+			module.RawSetString(name, L.NewFunction(func(L *lua.LState) int {
+				if GetSeverity() < severity {
+					return 0
+				}
+				var content strings.Builder
+				// Prefix with the calling script's filename.
+				if caller, ok := L.GetStack(1); ok {
+					if _, err := L.GetInfo("S", caller, lua.LNil); err == nil && caller.Source != "" {
+						if caller.Source != source {
+							source = caller.Source
+							prefix = filepath.Base(strings.TrimPrefix(source, "@")) + ": "
+						}
+						content.WriteString(prefix)
+					}
+				}
+				for i := 1; i <= L.GetTop(); i++ {
+					content.WriteString(luaLogString(L, L.Get(i)))
+				}
+				Record(&GeneralMessage{
+					Severity: severity,
+					Content:  content.String(),
+				})
+				return 0
+			}))
+		}
+		L.Push(module)
+		return 1
+	})
+}
+
+func luaLogString(L *lua.LState, value lua.LValue) string {
+	if ud, ok := value.(*lua.LUserData); ok {
+		if err, ok := ud.Value.(error); ok {
+			return err.Error()
+		}
+	}
+	if _, ok := L.GetMetaField(value, "__tostring").(*lua.LFunction); ok {
+		return L.ToStringMeta(value).String()
+	}
+	return value.String()
+}