lotus/chain/events/state/diff_adt.go

package state

import (
	"github.com/filecoin-project/specs-actors/actors/util/adt"
	typegen "github.com/whyrusleeping/cbor-gen"
)

// AdtArrayDiff generalizes adt.Array diffing by accepting a Deferred type that can unmarshalled to its corresponding struct
// in an interface implantation.
// Add should be called when a new k,v is added to the array
// Modify should be called when a value is modified in the array
// Remove should be called when a value is removed from the array
type AdtArrayDiff interface {
	Add(key uint64, val *typegen.Deferred) error
	Modify(key uint64, from, to *typegen.Deferred) error
	Remove(key uint64, val *typegen.Deferred) error
}

// TODO Performance can be improved by diffing the underlying IPLD graph, e.g. https://github.com/ipfs/go-merkledag/blob/749fd8717d46b4f34c9ce08253070079c89bc56d/dagutils/diff.go#L104
// CBOR Marshaling will likely be the largest performance bottleneck here.

// DiffAdtArray accepts two *adt.Array's and an AdtArrayDiff implementation. It does the following:
// - All values that exist in preArr and not in curArr are passed to AdtArrayDiff.Remove()
// - All values that exist in curArr nnd not in prevArr are passed to adtArrayDiff.Add()
// - All values that exist in preArr and in curArr are passed to AdtArrayDiff.Modify()
//  - It is the responsibility of AdtArrayDiff.Modify() to determine if the values it was passed have been modified.
func DiffAdtArray(preArr, curArr *adt.Array, out AdtArrayDiff) error {
	prevVal := new(typegen.Deferred)
	if err := preArr.ForEach(prevVal, func(i int64) error {
		curVal := new(typegen.Deferred)
		found, err := curArr.Get(uint64(i), curVal)
		if err != nil {
			return err
		}
		if !found {
			if err := out.Remove(uint64(i), prevVal); err != nil {
				return err
			}
			return nil
		}

		if err := out.Modify(uint64(i), prevVal, curVal); err != nil {
			return err
		}

		return curArr.Delete(uint64(i))
	}); err != nil {
		return err
	}

	curVal := new(typegen.Deferred)
	return curArr.ForEach(curVal, func(i int64) error {
		return out.Add(uint64(i), curVal)
	})
}