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common_blocks.go
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/
common_blocks.go
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// Copyright (C) 2019-2021, Ava Labs, Inc. All rights reserved.
// See the file LICENSE for licensing terms.
package platformvm
import (
"errors"
"fmt"
"time"
"github.com/ava-labs/avalanchego/ids"
"github.com/ava-labs/avalanchego/snow/choices"
"github.com/ava-labs/avalanchego/snow/consensus/snowman"
"github.com/ava-labs/avalanchego/utils/hashing"
)
// When one stakes, one must specify the time one will start to validate and
// the time one will stop validating. The latter must be after the former, and both
// times must be in the future.
//
// When one wants to start staking:
// * They issue a transaction to that effect to an existing staker.
// * The staker checks whether the specified "start staking time" is in the past relative to
// their wall clock.
// ** If so, the staker ignores the transaction
// ** If not, the staker issues a proposal block (see below) on behalf of the would-be staker.
//
// When one is done staking:
// * The staking set decides whether the staker should receive either:
// ** Only the tokens that the staker put up as a bond
// ** The tokens the staker put up as a bond, and also a reward for staking
//
// This chain has three types of blocks:
// 1. A proposal block
// - Contains a proposal to do one of the following:
// * Change the chain time from t to t'. (This doubles as
// proposing to update the staking set.)
// ** It must be that: t' > t
// ** It must be that: t' <= [time at which the next staker stops staking]
// * Reward a staker upon their leaving the staking pool
// ** It must be that chain time == [time for this staker to stop staking]
// ** It must be that this staker is the next staker to stop staking
// * Add a staker to the staking pool
// ** It must be that: staker.startTime < chain time
// - A proposal block is always followed by either a commit block or a rejection block
// 2. A commit block
// - Does one of the following:
// * Approve a proposal to change the chain time from t to t'
// ** This should be the initial preference if t' <= Wall clock time
// * Approve a proposal to reward for a staker upon their leaving the staking pool
// ** It must be that: chain time == [time for this staker to stop staking]
// ** It must be that: this staker is the next staker to stop staking
// * Approve a proposal to add a staker to the staking pool
// ** This should be the initial preference if staker.startTime > Wall clock
// time
// - A commit block must always be preceded on the chain by the proposal block whose
// proposal is being committed
// 3. A rejection block
// - Does one of the following:
// * Reject a proposal to change the chain time from t to t' (therefore keeping it at t)
// ** This should be the initial preference if t' > [this node's wall clock time + Delta],
// where Delta is our synchrony assumption
// * Reject a proposal to reward for a staker upon their leaving the staking pool.
// ** The staker only has their bond (locked tokens) returned
// ** This should be the initial preference if the staker has had < Chi uptime
// ** It must be that: t == [time for this staker to stop staking]
// ** It must be that: this staker is the next staker to stop staking
// * Reject a proposal to add a staker to the staking set.
// ** Increase the timestamp to the would-be staker's start time
// ** This should be the initial preference if staker.startTime <= Wall clock
// time
// - A rejection block must always be preceded on the chain by the proposal block whose
// proposal is being rejected
var (
errBlockNil = errors.New("block is nil")
errInvalidBlockType = errors.New("invalid block type")
)
// Block is the common interface that all staking blocks must have
type Block interface {
snowman.Block
// initialize this block's non-serialized fields.
//
// This method should be called when a block is unmarshaled from bytes.
//
// [vm] is the vm the block exists in
// [bytes] is the byte representation of this block
// [status] is the current status of this block
// [self] is the lowest implementing struct of this block
initialize(vm *VM, bytes []byte, status choices.Status, self Block) error
// returns true if this block or any processing ancestors consume any of the
// named atomic imports.
conflicts(ids.Set) (bool, error)
// parent returns the parent block, similarly to Parent. However, it
// provides the more specific Block interface.
parentBlock() (Block, error)
// addChild notifies this block that it has a child block building on it.
// When this block commits its changes, it should set the child's base state
// to the internal state. This ensures that the state versions do not
// recurse the length of the chain.
addChild(Block)
// free all the references of this block from the vm's memory
free()
// Set the block's underlying state to the chain's internal state
setBaseState()
}
// A decision block (either Commit, Abort, or DecisionBlock.) represents a
// decision to either commit (accept) or abort (reject) the changes specified in
// its parent, if its parent is a proposal. Otherwise, the changes are committed
// immediately.
type decision interface {
// This function should only be called after Verify is called.
// onAccept returns:
// 1) The current state of the chain, if this block is decided or hasn't
// been verified.
// 2) The state of the chain after this block is accepted, if this block was
// verified successfully.
onAccept() MutableState
}
// CommonBlock contains fields and methods common to all blocks in this VM.
type CommonBlock struct {
PrntID ids.ID `serialize:"true" json:"parentID"` // parent's ID
Hght uint64 `serialize:"true" json:"height"` // This block's height. The genesis block is at height 0.
self Block // self is a reference to this block's implementing struct
id ids.ID
bytes []byte
timestamp time.Time // Time this block was proposed at
status choices.Status
vm *VM
// This block's children
children []Block
}
func (b *CommonBlock) initialize(vm *VM, bytes []byte, status choices.Status, self Block) error {
b.self = self
b.id = hashing.ComputeHash256Array(bytes)
b.bytes = bytes
b.status = status
b.vm = vm
return nil
}
// ID returns the ID of this block
func (b *CommonBlock) ID() ids.ID { return b.id }
// Bytes returns the binary representation of this block
func (b *CommonBlock) Bytes() []byte { return b.bytes }
// Status returns the status of this block
func (b *CommonBlock) Status() choices.Status { return b.status }
// Parent returns this block's parent's ID
func (b *CommonBlock) Parent() ids.ID { return b.PrntID }
// Height returns this block's height. The genesis block has height 0.
func (b *CommonBlock) Height() uint64 { return b.Hght }
// Timestamp returns this block's time.
func (b *CommonBlock) Timestamp() time.Time {
// If this is the last accepted block and the block was loaded from disk
// since it was accepted, then the timestamp wouldn't be set correctly. So,
// we explicitly return the chain time.
if b.id == b.vm.lastAcceptedID {
return b.vm.internalState.GetTimestamp()
}
return b.timestamp
}
// Parent returns [b]'s parent
func (b *CommonBlock) parentBlock() (Block, error) {
return b.vm.getBlock(b.Parent())
}
func (b *CommonBlock) addChild(child Block) {
b.children = append(b.children, child)
}
func (b *CommonBlock) free() {
delete(b.vm.currentBlocks, b.ID())
b.children = nil
}
func (b *CommonBlock) conflicts(s ids.Set) (bool, error) {
if b.Status() == choices.Accepted {
return false, nil
}
parent, err := b.parentBlock()
if err != nil {
return false, err
}
return parent.conflicts(s)
}
func (b *CommonBlock) Verify() error {
if b == nil {
return errBlockNil
}
parent, err := b.parentBlock()
if err != nil {
return err
}
if expectedHeight := parent.Height() + 1; expectedHeight != b.Hght {
return fmt.Errorf(
"expected block to have height %d, but found %d",
expectedHeight,
b.Hght,
)
}
return nil
}
func (b *CommonBlock) Reject() error {
defer b.free()
b.status = choices.Rejected
// TODO: don't write rejected blocks to disk
b.vm.internalState.AddBlock(b.self)
return b.vm.internalState.Commit()
}
func (b *CommonBlock) Accept() error {
blkID := b.ID()
b.status = choices.Accepted
b.vm.internalState.AddBlock(b.self)
b.vm.internalState.SetLastAccepted(blkID)
b.vm.internalState.SetHeight(b.Hght)
b.vm.lastAcceptedID = blkID
b.vm.recentlyAccepted.Add(blkID)
return b.vm.metrics.AcceptBlock(b.self)
}
// CommonDecisionBlock contains the fields and methods common to all decision blocks
type CommonDecisionBlock struct {
CommonBlock `serialize:"true"`
// state of the chain if this block is accepted
onAcceptState VersionedState
// to be executed if this block is accepted
onAcceptFunc func() error
}
func (cdb *CommonDecisionBlock) free() {
cdb.CommonBlock.free()
cdb.onAcceptState = nil
}
func (cdb *CommonDecisionBlock) setBaseState() {
cdb.onAcceptState.SetBase(cdb.vm.internalState)
}
func (cdb *CommonDecisionBlock) onAccept() MutableState {
if cdb.Status().Decided() || cdb.onAcceptState == nil {
return cdb.vm.internalState
}
return cdb.onAcceptState
}
func (cdb *CommonDecisionBlock) Reject() error {
defer cdb.free()
cdb.status = choices.Rejected
// TODO: don't write rejected blocks to disk
cdb.vm.internalState.AddBlock(cdb.self)
return cdb.vm.internalState.Commit()
}
// DoubleDecisionBlock contains the accept for a pair of blocks
type DoubleDecisionBlock struct {
CommonDecisionBlock `serialize:"true"`
}
func (ddb *DoubleDecisionBlock) Accept() error {
ddb.vm.ctx.Log.Verbo("Accepting block with ID %s", ddb.ID())
parentIntf, err := ddb.parentBlock()
if err != nil {
return err
}
parent, ok := parentIntf.(*ProposalBlock)
if !ok {
ddb.vm.ctx.Log.Error("double decision block should only follow a proposal block")
return errInvalidBlockType
}
if err := parent.CommonBlock.Accept(); err != nil {
return fmt.Errorf("failed to accept parent's CommonBlock: %w", err)
}
if err := ddb.CommonBlock.Accept(); err != nil {
return fmt.Errorf("failed to accept CommonBlock: %w", err)
}
// Update the state of the chain in the database
ddb.onAcceptState.Apply(ddb.vm.internalState)
if err := ddb.vm.internalState.Commit(); err != nil {
return fmt.Errorf("failed to commit vm's state: %w", err)
}
for _, child := range ddb.children {
child.setBaseState()
}
if ddb.onAcceptFunc != nil {
if err := ddb.onAcceptFunc(); err != nil {
return fmt.Errorf("failed to execute OnAcceptFunc: %w", err)
}
}
// remove this block and its parent from memory
parent.free()
ddb.free()
return nil
}