mitchellh/copystructure/copystructure.go

package copystructure

import (
	"errors"
	"reflect"
	"sync"

	"github.com/mitchellh/reflectwalk"
)

// Copy returns a deep copy of v.
func Copy(v interface{}) (interface{}, error) {
	return Config{}.Copy(v)
}

// CopierFunc is a function that knows how to deep copy a specific type.
// Register these globally with the Copiers variable.
type CopierFunc func(interface{}) (interface{}, error)

// Copiers is a map of types that behave specially when they are copied.
// If a type is found in this map while deep copying, this function
// will be called to copy it instead of attempting to copy all fields.
//
// The key should be the type, obtained using: reflect.TypeOf(value with type).
//
// It is unsafe to write to this map after Copies have started. If you
// are writing to this map while also copying, wrap all modifications to
// this map as well as to Copy in a mutex.
var Copiers map[reflect.Type]CopierFunc = make(map[reflect.Type]CopierFunc)

// Must is a helper that wraps a call to a function returning
// (interface{}, error) and panics if the error is non-nil. It is intended
// for use in variable initializations and should only be used when a copy
// error should be a crashing case.
func Must(v interface{}, err error) interface{} {
	if err != nil {
		panic("copy error: " + err.Error())
	}

	return v
}

var errPointerRequired = errors.New("Copy argument must be a pointer when Lock is true")

type Config struct {
	// Lock any types that are a sync.Locker and are not a mutex while copying.
	// If there is an RLocker method, use that to get the sync.Locker.
	Lock bool

	// Copiers is a map of types associated with a CopierFunc. Use the global
	// Copiers map if this is nil.
	Copiers map[reflect.Type]CopierFunc
}

func (c Config) Copy(v interface{}) (interface{}, error) {
	if c.Lock && reflect.ValueOf(v).Kind() != reflect.Ptr {
		return nil, errPointerRequired
	}

	w := new(walker)
	if c.Lock {
		w.useLocks = true
	}

	if c.Copiers == nil {
		c.Copiers = Copiers
	}

	err := reflectwalk.Walk(v, w)
	if err != nil {
		return nil, err
	}

	// Get the result. If the result is nil, then we want to turn it
	// into a typed nil if we can.
	result := w.Result
	if result == nil {
		val := reflect.ValueOf(v)
		result = reflect.Indirect(reflect.New(val.Type())).Interface()
	}

	return result, nil
}

// Return the key used to index interfaces types we've seen. Store the number
// of pointers in the upper 32bits, and the depth in the lower 32bits. This is
// easy to calculate, easy to match a key with our current depth, and we don't
// need to deal with initializing and cleaning up nested maps or slices.
func ifaceKey(pointers, depth int) uint64 {
	return uint64(pointers)<<32 | uint64(depth)
}

type walker struct {
	Result interface{}

	depth       int
	ignoreDepth int
	vals        []reflect.Value
	cs          []reflect.Value

	// This stores the number of pointers we've walked over, indexed by depth.
	ps []int

	// If an interface is indirected by a pointer, we need to know the type of
	// interface to create when creating the new value.  Store the interface
	// types here, indexed by both the walk depth and the number of pointers
	// already seen at that depth. Use ifaceKey to calculate the proper uint64
	// value.
	ifaceTypes map[uint64]reflect.Type

	// any locks we've taken, indexed by depth
	locks []sync.Locker
	// take locks while walking the structure
	useLocks bool
}

func (w *walker) Enter(l reflectwalk.Location) error {
	w.depth++

	// ensure we have enough elements to index via w.depth
	for w.depth >= len(w.locks) {
		w.locks = append(w.locks, nil)
	}

	for len(w.ps) < w.depth+1 {
		w.ps = append(w.ps, 0)
	}

	return nil
}

func (w *walker) Exit(l reflectwalk.Location) error {
	locker := w.locks[w.depth]
	w.locks[w.depth] = nil
	if locker != nil {
		defer locker.Unlock()
	}

	// clear out pointers and interfaces as we exit the stack
	w.ps[w.depth] = 0

	for k := range w.ifaceTypes {
		mask := uint64(^uint32(0))
		if k&mask == uint64(w.depth) {
			delete(w.ifaceTypes, k)
		}
	}

	w.depth--
	if w.ignoreDepth > w.depth {
		w.ignoreDepth = 0
	}

	if w.ignoring() {
		return nil
	}

	switch l {
	case reflectwalk.Array:
		fallthrough
	case reflectwalk.Map:
		fallthrough
	case reflectwalk.Slice:
		w.replacePointerMaybe()

		// Pop map off our container
		w.cs = w.cs[:len(w.cs)-1]
	case reflectwalk.MapValue:
		// Pop off the key and value
		mv := w.valPop()
		mk := w.valPop()
		m := w.cs[len(w.cs)-1]

		// If mv is the zero value, SetMapIndex deletes the key form the map,
		// or in this case never adds it. We need to create a properly typed
		// zero value so that this key can be set.
		if !mv.IsValid() {
			mv = reflect.Zero(m.Elem().Type().Elem())
		}
		m.Elem().SetMapIndex(mk, mv)
	case reflectwalk.ArrayElem:
		// Pop off the value and the index and set it on the array
		v := w.valPop()
		i := w.valPop().Interface().(int)
		if v.IsValid() {
			a := w.cs[len(w.cs)-1]
			ae := a.Elem().Index(i) // storing array as pointer on stack - so need Elem() call
			if ae.CanSet() {
				ae.Set(v)
			}
		}
	case reflectwalk.SliceElem:
		// Pop off the value and the index and set it on the slice
		v := w.valPop()
		i := w.valPop().Interface().(int)
		if v.IsValid() {
			s := w.cs[len(w.cs)-1]
			se := s.Elem().Index(i)
			if se.CanSet() {
				se.Set(v)
			}
		}
	case reflectwalk.Struct:
		w.replacePointerMaybe()

		// Remove the struct from the container stack
		w.cs = w.cs[:len(w.cs)-1]
	case reflectwalk.StructField:
		// Pop off the value and the field
		v := w.valPop()
		f := w.valPop().Interface().(reflect.StructField)
		if v.IsValid() {
			s := w.cs[len(w.cs)-1]
			sf := reflect.Indirect(s).FieldByName(f.Name)

			if sf.CanSet() {
				sf.Set(v)
			}
		}
	case reflectwalk.WalkLoc:
		// Clear out the slices for GC
		w.cs = nil
		w.vals = nil
	}

	return nil
}

func (w *walker) Map(m reflect.Value) error {
	if w.ignoring() {
		return nil
	}
	w.lock(m)

	// Create the map. If the map itself is nil, then just make a nil map
	var newMap reflect.Value
	if m.IsNil() {
		newMap = reflect.New(m.Type())
	} else {
		newMap = wrapPtr(reflect.MakeMap(m.Type()))
	}

	w.cs = append(w.cs, newMap)
	w.valPush(newMap)
	return nil
}

func (w *walker) MapElem(m, k, v reflect.Value) error {
	return nil
}

func (w *walker) PointerEnter(v bool) error {
	if v {
		w.ps[w.depth]++
	}
	return nil
}

func (w *walker) PointerExit(v bool) error {
	if v {
		w.ps[w.depth]--
	}
	return nil
}

func (w *walker) Interface(v reflect.Value) error {
	if !v.IsValid() {
		return nil
	}
	if w.ifaceTypes == nil {
		w.ifaceTypes = make(map[uint64]reflect.Type)
	}

	w.ifaceTypes[ifaceKey(w.ps[w.depth], w.depth)] = v.Type()
	return nil
}

func (w *walker) Primitive(v reflect.Value) error {
	if w.ignoring() {
		return nil
	}
	w.lock(v)

	// IsValid verifies the v is non-zero and CanInterface verifies
	// that we're allowed to read this value (unexported fields).
	var newV reflect.Value
	if v.IsValid() && v.CanInterface() {
		newV = reflect.New(v.Type())
		newV.Elem().Set(v)
	}

	w.valPush(newV)
	w.replacePointerMaybe()
	return nil
}

func (w *walker) Slice(s reflect.Value) error {
	if w.ignoring() {
		return nil
	}
	w.lock(s)

	var newS reflect.Value
	if s.IsNil() {
		newS = reflect.New(s.Type())
	} else {
		newS = wrapPtr(reflect.MakeSlice(s.Type(), s.Len(), s.Cap()))
	}

	w.cs = append(w.cs, newS)
	w.valPush(newS)
	return nil
}

func (w *walker) SliceElem(i int, elem reflect.Value) error {
	if w.ignoring() {
		return nil
	}

	// We don't write the slice here because elem might still be
	// arbitrarily complex. Just record the index and continue on.
	w.valPush(reflect.ValueOf(i))

	return nil
}

func (w *walker) Array(a reflect.Value) error {
	if w.ignoring() {
		return nil
	}
	w.lock(a)

	newA := reflect.New(a.Type())

	w.cs = append(w.cs, newA)
	w.valPush(newA)
	return nil
}

func (w *walker) ArrayElem(i int, elem reflect.Value) error {
	if w.ignoring() {
		return nil
	}

	// We don't write the array here because elem might still be
	// arbitrarily complex. Just record the index and continue on.
	w.valPush(reflect.ValueOf(i))

	return nil
}

func (w *walker) Struct(s reflect.Value) error {
	if w.ignoring() {
		return nil
	}
	w.lock(s)

	var v reflect.Value
	if c, ok := Copiers[s.Type()]; ok {
		// We have a Copier for this struct, so we use that copier to
		// get the copy, and we ignore anything deeper than this.
		w.ignoreDepth = w.depth

		dup, err := c(s.Interface())
		if err != nil {
			return err
		}

		// We need to put a pointer to the value on the value stack,
		// so allocate a new pointer and set it.
		v = reflect.New(s.Type())
		reflect.Indirect(v).Set(reflect.ValueOf(dup))
	} else {
		// No copier, we copy ourselves and allow reflectwalk to guide
		// us deeper into the structure for copying.
		v = reflect.New(s.Type())
	}

	// Push the value onto the value stack for setting the struct field,
	// and add the struct itself to the containers stack in case we walk
	// deeper so that its own fields can be modified.
	w.valPush(v)
	w.cs = append(w.cs, v)

	return nil
}

func (w *walker) StructField(f reflect.StructField, v reflect.Value) error {
	if w.ignoring() {
		return nil
	}

	// If PkgPath is non-empty, this is a private (unexported) field.
	// We do not set this unexported since the Go runtime doesn't allow us.
	if f.PkgPath != "" {
		return reflectwalk.SkipEntry
	}

	// Push the field onto the stack, we'll handle it when we exit
	// the struct field in Exit...
	w.valPush(reflect.ValueOf(f))
	return nil
}

// ignore causes the walker to ignore any more values until we exit this on
func (w *walker) ignore() {
	w.ignoreDepth = w.depth
}

func (w *walker) ignoring() bool {
	return w.ignoreDepth > 0 && w.depth >= w.ignoreDepth
}

func (w *walker) pointerPeek() bool {
	return w.ps[w.depth] > 0
}

func (w *walker) valPop() reflect.Value {
	result := w.vals[len(w.vals)-1]
	w.vals = w.vals[:len(w.vals)-1]

	// If we're out of values, that means we popped everything off. In
	// this case, we reset the result so the next pushed value becomes
	// the result.
	if len(w.vals) == 0 {
		w.Result = nil
	}

	return result
}

func (w *walker) valPush(v reflect.Value) {
	w.vals = append(w.vals, v)

	// If we haven't set the result yet, then this is the result since
	// it is the first (outermost) value we're seeing.
	if w.Result == nil && v.IsValid() {
		w.Result = v.Interface()
	}
}

func (w *walker) replacePointerMaybe() {
	// Determine the last pointer value. If it is NOT a pointer, then
	// we need to push that onto the stack.
	if !w.pointerPeek() {
		w.valPush(reflect.Indirect(w.valPop()))
		return
	}

	v := w.valPop()

	// If the expected type is a pointer to an interface of any depth,
	// such as *interface{}, **interface{}, etc., then we need to convert
	// the value "v" from *CONCRETE to *interface{} so types match for
	// Set.
	//
	// Example if v is type *Foo where Foo is a struct, v would become
	// *interface{} instead. This only happens if we have an interface expectation
	// at this depth.
	//
	// For more info, see GH-16
	if iType, ok := w.ifaceTypes[ifaceKey(w.ps[w.depth], w.depth)]; ok && iType.Kind() == reflect.Interface {
		y := reflect.New(iType)           // Create *interface{}
		y.Elem().Set(reflect.Indirect(v)) // Assign "Foo" to interface{} (dereferenced)
		v = y                             // v is now typed *interface{} (where *v = Foo)
	}

	for i := 1; i < w.ps[w.depth]; i++ {
		if iType, ok := w.ifaceTypes[ifaceKey(w.ps[w.depth]-i, w.depth)]; ok {
			iface := reflect.New(iType).Elem()
			iface.Set(v)
			v = iface
		}

		p := reflect.New(v.Type())
		p.Elem().Set(v)
		v = p
	}

	w.valPush(v)
}

// if this value is a Locker, lock it and add it to the locks slice
func (w *walker) lock(v reflect.Value) {
	if !w.useLocks {
		return
	}

	if !v.IsValid() || !v.CanInterface() {
		return
	}

	type rlocker interface {
		RLocker() sync.Locker
	}

	var locker sync.Locker

	// We can't call Interface() on a value directly, since that requires
	// a copy. This is OK, since the pointer to a value which is a sync.Locker
	// is also a sync.Locker.
	if v.Kind() == reflect.Ptr {
		switch l := v.Interface().(type) {
		case rlocker:
			// don't lock a mutex directly
			if _, ok := l.(*sync.RWMutex); !ok {
				locker = l.RLocker()
			}
		case sync.Locker:
			locker = l
		}
	} else if v.CanAddr() {
		switch l := v.Addr().Interface().(type) {
		case rlocker:
			// don't lock a mutex directly
			if _, ok := l.(*sync.RWMutex); !ok {
				locker = l.RLocker()
			}
		case sync.Locker:
			locker = l
		}
	}

	// still no callable locker
	if locker == nil {
		return
	}

	// don't lock a mutex directly
	switch locker.(type) {
	case *sync.Mutex, *sync.RWMutex:
		return
	}

	locker.Lock()
	w.locks[w.depth] = locker
}

// wrapPtr is a helper that takes v and always make it *v. copystructure
// stores things internally as pointers until the last moment before unwrapping
func wrapPtr(v reflect.Value) reflect.Value {
	if !v.IsValid() {
		return v
	}
	vPtr := reflect.New(v.Type())
	vPtr.Elem().Set(v)
	return vPtr
}