structtype.go

// Copyright 2019 Huan Du. All rights reserved.
// Licensed under the MIT license that can be found in the LICENSE file.

package clone

import (
	"crypto/elliptic"
	"fmt"
	"reflect"
	"sync"
	"sync/atomic"
	"time"
	"unsafe"
)

type structType struct {
	ZeroFields    []structFieldSize
	PointerFields []structFieldType
	fn            Func
}

type structFieldSize struct {
	Offset uintptr // The offset from the beginning of the struct.
	Size   uintptr // The size of the field.
}

type structFieldType struct {
	Offset uintptr // The offset from the beginning of the struct.
	Index  int     // The index of the field.
}

var zeroStructType = structType{}

func init() {
	// Some well-known scalar-like structs.
	MarkAsScalar(reflect.TypeOf(time.Time{}))
	MarkAsScalar(reflect.TypeOf(reflect.Value{}))

	// Special case for elliptic.Curve which is used by TLS ECC certificate.
	// Package crypto/tls uses elliptic.Curve as enum values
	// so that they should be treated as opaque pointers.
	//
	// As elliptic.Curve is an interface, it can be *elliptic.CurveParam or elliptic.p256Curve.
	MarkAsOpaquePointer(reflect.TypeOf(&elliptic.CurveParams{}))
	curves := []elliptic.Curve{
		elliptic.P224(),
		elliptic.P256(),
		elliptic.P384(),
		elliptic.P521(),
	}

	for _, curve := range curves {
		MarkAsOpaquePointer(reflect.ValueOf(curve).Type())
	}

	// Special case for reflect.Type (actually *reflect.rtype):
	// The *reflect.rtype should not be copied as it is immutable and
	// may point to a variable that actual type is not reflect.rtype,
	// e.g. *reflect.arrayType or *reflect.chanType.
	MarkAsOpaquePointer(reflect.TypeOf(reflect.TypeOf(0)))

	// Some well-known no-copy structs.
	//
	// Almost all structs defined in package "sync" and "sync/atomic" are set
	// except `sync.Once` which can be safely cloned with a correct done value.
	SetCustomFunc(reflect.TypeOf(sync.Mutex{}), emptyCloneFunc)
	SetCustomFunc(reflect.TypeOf(sync.RWMutex{}), emptyCloneFunc)
	SetCustomFunc(reflect.TypeOf(sync.WaitGroup{}), emptyCloneFunc)
	SetCustomFunc(reflect.TypeOf(sync.Cond{}), func(allocator *Allocator, old, new reflect.Value) {
		// Copy the New func from old value.
		oldL := old.FieldByName("L")
		newL := allocator.Clone(oldL)
		new.FieldByName("L").Set(newL)
	})
	SetCustomFunc(reflect.TypeOf(sync.Pool{}), func(allocator *Allocator, old, new reflect.Value) {
		// Copy the New func from old value.
		oldFn := old.FieldByName("New")
		newFn := allocator.Clone(oldFn)
		new.FieldByName("New").Set(newFn)
	})
	SetCustomFunc(reflect.TypeOf(sync.Map{}), func(allocator *Allocator, old, new reflect.Value) {
		if !old.CanAddr() {
			return
		}

		// Clone all values inside sync.Map.
		oldMap := old.Addr().Interface().(*sync.Map)
		newMap := new.Addr().Interface().(*sync.Map)
		oldMap.Range(func(key, value interface{}) bool {
			k := clone(allocator, key)
			v := clone(allocator, value)
			newMap.Store(k, v)
			return true
		})
	})
	SetCustomFunc(reflect.TypeOf(atomic.Value{}), func(allocator *Allocator, old, new reflect.Value) {
		if !old.CanAddr() {
			return
		}

		// Clone value inside atomic.Value.
		oldValue := old.Addr().Interface().(*atomic.Value)
		newValue := new.Addr().Interface().(*atomic.Value)
		v := oldValue.Load()
		cloned := clone(allocator, v)
		newValue.Store(cloned)
	})
}

// MarkAsScalar marks t as a scalar type in heap allocator,
// so that all clone methods will copy t by value.
// If t is not struct or pointer to struct, MarkAsScalar ignores t.
//
// In the most cases, it's not necessary to call it explicitly.
// If a struct type contains scalar type fields only, the struct will be marked as scalar automatically.
//
// Here is a list of types marked as scalar by default:
//   - time.Time
//   - reflect.Value
func MarkAsScalar(t reflect.Type) {
	defaultAllocator.MarkAsScalar(t)
}

// MarkAsOpaquePointer marks t as an opaque pointer in heap allocator,
// so that all clone methods will copy t by value.
// If t is not a pointer, MarkAsOpaquePointer ignores t.
//
// Here is a list of types marked as opaque pointers by default:
//   - `elliptic.Curve`, which is `*elliptic.CurveParam` or `elliptic.p256Curve`;
//   - `reflect.Type`, which is `*reflect.rtype` defined in `runtime`.
func MarkAsOpaquePointer(t reflect.Type) {
	defaultAllocator.MarkAsOpaquePointer(t)
}

// Func is a custom func to clone value from old to new.
// The new is a zero value
// which `new.CanSet()` and `new.CanAddr()` is guaranteed to be true.
//
// Func must update the new to return result.
type Func func(allocator *Allocator, old, new reflect.Value)

// emptyCloneFunc is used to disable shadow copy.
// It's useful when cloning sync.Mutex as cloned value must be a zero value.
func emptyCloneFunc(allocator *Allocator, old, new reflect.Value) {}

// SetCustomFunc sets a custom clone function for type t in heap allocator.
// If t is not struct or pointer to struct, SetCustomFunc ignores t.
//
// If fn is nil, remove the custom clone function for type t.
func SetCustomFunc(t reflect.Type, fn Func) {
	defaultAllocator.SetCustomFunc(t, fn)
}

// Init creates a new value of src.Type() and shadow copies all content from src.
// If noCustomFunc is set to true, custom clone function will be ignored.
//
// Init returns true if the value is cloned by a custom func.
// Caller should skip cloning struct fields in depth.
func (st *structType) Init(allocator *Allocator, src, nv reflect.Value, noCustomFunc bool) (done bool) {
	dst := nv.Elem()

	if !noCustomFunc && st.fn != nil {
		if !src.CanInterface() {
			src = forceClearROFlag(src)
		}

		st.fn(allocator, src, dst)
		done = true
		return
	}

	ptr := unsafe.Pointer(nv.Pointer())
	shadowCopy(src, ptr)
	done = len(st.PointerFields) == 0
	return
}

func (st *structType) CanShadowCopy() bool {
	return len(st.PointerFields) == 0 && st.fn == nil
}

// IsScalar returns true if k should be considered as a scalar type.
//
// For the sake of performance, string is considered as a scalar type unless arena is enabled.
// If we need to deep copy string value in some cases, we can create a new allocator with custom isScalar function
// in which we can return false when k is reflect.String.
//
//	// Create a new allocator which treats string as non-scalar type.
//	allocator := NewAllocator(nil, &AllocatorMethods{
//		IsScalar: func(k reflect.Kind) bool {
//			return k != reflect.String && IsScalar(k)
//		},
//	})
func IsScalar(k reflect.Kind) bool {
	switch k {
	case reflect.Bool,
		reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
		reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr,
		reflect.Float32, reflect.Float64,
		reflect.Complex64, reflect.Complex128,
		reflect.Func,
		reflect.UnsafePointer,
		reflect.Invalid:
		return true

	case reflect.String:
		// If arena is not enabled, string can be copied as scalar safely
		// as it's immutable by design.
		return !arenaIsEnabled
	}

	return false
}

func copyScalarValue(src reflect.Value) reflect.Value {
	if src.CanInterface() {
		return src
	}

	dst := newScalarValue(src)
	return dst.Convert(src.Type())
}

func newScalarValue(src reflect.Value) reflect.Value {
	// src is an unexported field value. Copy its value.
	switch src.Kind() {
	case reflect.Bool:
		return reflect.ValueOf(src.Bool())

	case reflect.Int:
		return reflect.ValueOf(int(src.Int()))
	case reflect.Int8:
		return reflect.ValueOf(int8(src.Int()))
	case reflect.Int16:
		return reflect.ValueOf(int16(src.Int()))
	case reflect.Int32:
		return reflect.ValueOf(int32(src.Int()))
	case reflect.Int64:
		return reflect.ValueOf(src.Int())

	case reflect.Uint:
		return reflect.ValueOf(uint(src.Uint()))
	case reflect.Uint8:
		return reflect.ValueOf(uint8(src.Uint()))
	case reflect.Uint16:
		return reflect.ValueOf(uint16(src.Uint()))
	case reflect.Uint32:
		return reflect.ValueOf(uint32(src.Uint()))
	case reflect.Uint64:
		return reflect.ValueOf(src.Uint())
	case reflect.Uintptr:
		return reflect.ValueOf(uintptr(src.Uint()))

	case reflect.Float32:
		return reflect.ValueOf(float32(src.Float()))
	case reflect.Float64:
		return reflect.ValueOf(src.Float())

	case reflect.Complex64:
		return reflect.ValueOf(complex64(src.Complex()))
	case reflect.Complex128:
		return reflect.ValueOf(src.Complex())

	case reflect.String:
		return reflect.ValueOf(src.String())
	case reflect.Func:
		t := src.Type()

		if src.IsNil() {
			return reflect.Zero(t)
		}

		// Don't use this trick unless we have no choice.
		return forceClearROFlag(src)
	case reflect.UnsafePointer:
		return reflect.ValueOf(unsafe.Pointer(src.Pointer()))
	}

	panic(fmt.Errorf("go-clone: <bug> impossible type `%v` when cloning private field", src.Type()))
}

var typeOfInterface = reflect.TypeOf((*interface{})(nil)).Elem()

// forceClearROFlag clears all RO flags in v to make v accessible.
// It's a hack based on the fact that InterfaceData is always available on RO data.
// This hack can be broken in any Go version.
// Don't use it unless we have no choice, e.g. copying func in some edge cases.
func forceClearROFlag(v reflect.Value) reflect.Value {
	var i interface{}
	indirect := 0

	// Save flagAddr.
	for v.CanAddr() {
		v = v.Addr()
		indirect++
	}

	v = v.Convert(typeOfInterface)
	nv := reflect.ValueOf(&i)
	*(*interfaceData)(unsafe.Pointer(nv.Pointer())) = parseReflectValue(v)
	cleared := nv.Elem().Elem()

	for indirect > 0 {
		cleared = cleared.Elem()
		indirect--
	}

	return cleared
}