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block.go
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block.go
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// Copyright (C) 2019-2023, Ava Labs, Inc. All rights reserved.
// See the file LICENSE for licensing terms.
package chain
import (
"context"
"errors"
"time"
"github.com/ava-labs/avalanchego/database"
"github.com/ava-labs/avalanchego/database/versiondb"
"github.com/ava-labs/avalanchego/ids"
"github.com/ava-labs/avalanchego/snow"
"github.com/ava-labs/avalanchego/snow/choices"
"github.com/ava-labs/avalanchego/snow/consensus/snowman"
"github.com/ava-labs/avalanchego/utils/set"
"github.com/ava-labs/avalanchego/vms/example/xsvm/execute"
"github.com/ava-labs/avalanchego/vms/example/xsvm/state"
smblock "github.com/ava-labs/avalanchego/snow/engine/snowman/block"
xsblock "github.com/ava-labs/avalanchego/vms/example/xsvm/block"
)
const maxClockSkew = 10 * time.Second
var (
_ Block = (*block)(nil)
errMissingParent = errors.New("missing parent block")
errMissingChild = errors.New("missing child block")
errParentNotVerified = errors.New("parent block has not been verified")
errMissingState = errors.New("missing state")
errFutureTimestamp = errors.New("future timestamp")
errTimestampBeforeParent = errors.New("timestamp before parent")
errWrongHeight = errors.New("wrong height")
)
type Block interface {
snowman.Block
smblock.WithVerifyContext
// State intends to return the new chain state following this block's
// acceptance. The new chain state is built (but not persisted) following a
// block's verification to allow block's descendants verification before
// being accepted.
State() (database.Database, error)
}
type block struct {
*xsblock.Stateless
chain *chain
id ids.ID
status choices.Status
bytes []byte
state *versiondb.Database
verifiedChildrenIDs set.Set[ids.ID]
}
func (b *block) ID() ids.ID {
return b.id
}
func (b *block) Status() choices.Status {
if !b.status.Decided() {
b.status = b.calculateStatus()
}
return b.status
}
func (b *block) Parent() ids.ID {
return b.ParentID
}
func (b *block) Bytes() []byte {
return b.bytes
}
func (b *block) Height() uint64 {
return b.Stateless.Height
}
func (b *block) Timestamp() time.Time {
return b.Time()
}
func (b *block) Verify(ctx context.Context) error {
return b.VerifyWithContext(ctx, nil)
}
func (b *block) Accept(context.Context) error {
if err := b.state.Commit(); err != nil {
return err
}
// Following this block's acceptance, make sure that it's direct children
// point to the base state, which now also contains this block's changes.
for childID := range b.verifiedChildrenIDs {
child, exists := b.chain.verifiedBlocks[childID]
if !exists {
return errMissingChild
}
if err := child.state.SetDatabase(b.chain.acceptedState); err != nil {
return err
}
}
b.status = choices.Accepted
b.chain.lastAccepted = b.id
delete(b.chain.verifiedBlocks, b.ParentID)
return nil
}
func (b *block) Reject(context.Context) error {
b.status = choices.Rejected
delete(b.chain.verifiedBlocks, b.id)
// TODO: push transactions back into the mempool
return nil
}
func (b *block) ShouldVerifyWithContext(context.Context) (bool, error) {
return execute.ExpectsContext(b.Stateless)
}
func (b *block) VerifyWithContext(ctx context.Context, blockContext *smblock.Context) error {
timestamp := b.Time()
if time.Until(timestamp) > maxClockSkew {
return errFutureTimestamp
}
// parent block must be verified or accepted
parent, exists := b.chain.verifiedBlocks[b.ParentID]
if !exists {
return errMissingParent
}
if b.Stateless.Height != parent.Stateless.Height+1 {
return errWrongHeight
}
parentTimestamp := parent.Time()
if timestamp.Before(parentTimestamp) {
return errTimestampBeforeParent
}
parentState, err := parent.State()
if err != nil {
return err
}
// This block's state is a versionDB built on top of it's parent state. This
// block's changes are pushed atomically to the parent state when accepted.
blkState := versiondb.New(parentState)
err = execute.Block(
ctx,
b.chain.chainContext,
blkState,
b.chain.chainState == snow.Bootstrapping,
blockContext,
b.Stateless,
)
if err != nil {
return err
}
// Make sure to only state the state the first time we verify this block.
if b.state == nil {
b.state = blkState
parent.verifiedChildrenIDs.Add(b.id)
b.chain.verifiedBlocks[b.id] = b
}
return nil
}
func (b *block) State() (database.Database, error) {
if b.id == b.chain.lastAccepted {
return b.chain.acceptedState, nil
}
// States of accepted blocks other than the lastAccepted are undefined.
if b.Status() == choices.Accepted {
return nil, errMissingState
}
// We should not be calling State on an unverified block.
if b.state == nil {
return nil, errParentNotVerified
}
return b.state, nil
}
func (b *block) calculateStatus() choices.Status {
if b.chain.lastAccepted == b.id {
return choices.Accepted
}
if _, ok := b.chain.verifiedBlocks[b.id]; ok {
return choices.Processing
}
_, err := state.GetBlock(b.chain.acceptedState, b.id)
switch {
case err == nil:
return choices.Accepted
case errors.Is(err, database.ErrNotFound):
// This block hasn't been verified yet.
return choices.Processing
default:
// TODO: correctly report this error to the consensus engine.
return choices.Processing
}
}