feat(dns): add Lua scripting for DNS queries

common/lua/program.go

@@ -0,0 +1,56 @@
+// Package lua provides shared GopherLua programs and state management for Xray scripts.
+package lua
+
+import (
+	"bufio"
+	"context"
+	"os"
+
+	glua "github.com/yuin/gopher-lua"
+	"github.com/yuin/gopher-lua/parse"
+)
+
+// Program holds immutable bytecode that can be run by independent LStates.
+type Program struct {
+	proto *glua.FunctionProto
+}
+
+// CompileFile reads and compiles a Lua file once.
+func CompileFile(path string) (*Program, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	chunk, err := parse.Parse(bufio.NewReader(f), path)
+	if err != nil {
+		return nil, err
+	}
+	proto, err := glua.Compile(chunk, path)
+	if err != nil {
+		return nil, err
+	}
+	return &Program{proto: proto}, nil
+}
+
+// NewState creates a VM, makes modules available, and executes the file top level.
+// Module loaders run only when Lua calls require. Each state gets its own globals.
+// The caller owns the returned state.
+func (p *Program) NewState(ctx context.Context, register func(*glua.LState)) (*glua.LState, error) {
+	L := glua.NewState()
+	if register != nil {
+		register(L)
+	}
+	L.SetContext(ctx)
+	L.Push(L.NewFunctionFromProto(p.proto))
+	err := L.PCall(0, 0, nil)
+	L.RemoveContext()
+	if err == nil {
+		err = ctx.Err()
+	}
+	if err != nil {
+		L.Close()
+		return nil, err
+	}
+	return L, nil
+}