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vm.go
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vm.go
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// (c) 2019-2020, Ava Labs, Inc. All rights reserved.
// See the file LICENSE for licensing terms.
package timestampvm
import (
"errors"
"fmt"
"time"
"github.com/ava-labs/avalanchego/codec"
"github.com/ava-labs/avalanchego/codec/linearcodec"
"github.com/ava-labs/avalanchego/database/manager"
"github.com/ava-labs/avalanchego/ids"
"github.com/ava-labs/avalanchego/snow"
"github.com/ava-labs/avalanchego/snow/consensus/snowman"
"github.com/ava-labs/avalanchego/snow/engine/common"
"github.com/ava-labs/avalanchego/snow/engine/snowman/block"
"github.com/ava-labs/avalanchego/vms/components/core"
)
const (
dataLen = 32
codecVersion = 0
)
var (
errNoPendingBlocks = errors.New("there is no block to propose")
errBadGenesisBytes = errors.New("genesis data should be bytes (max length 32)")
_ block.ChainVM = &VM{}
_ common.StaticVM = &VM{}
)
// VM implements the snowman.VM interface
// Each block in this chain contains a Unix timestamp
// and a piece of data (a string)
type VM struct {
core.SnowmanVM
codec codec.Manager
// Proposed pieces of data that haven't been put into a block and proposed yet
mempool [][dataLen]byte
}
// Initialize this vm
// [ctx] is this vm's context
// [dbManager] is the manager of this vm's database
// [toEngine] is used to notify the consensus engine that new blocks are
// ready to be added to consensus
// The data in the genesis block is [genesisData]
func (vm *VM) Initialize(
ctx *snow.Context,
dbManager manager.Manager,
genesisData []byte,
upgradeData []byte,
configData []byte,
toEngine chan<- common.Message,
_ []*common.Fx,
) error {
if err := vm.SnowmanVM.Initialize(ctx, dbManager.Current().Database, vm.ParseBlock, toEngine); err != nil {
ctx.Log.Error("error initializing SnowmanVM: %v", err)
return err
}
c := linearcodec.NewDefault()
manager := codec.NewDefaultManager()
if err := manager.RegisterCodec(codecVersion, c); err != nil {
return err
}
vm.codec = manager
// If database is empty, create it using the provided genesis data
if !vm.DBInitialized() {
if len(genesisData) > dataLen {
return errBadGenesisBytes
}
// genesisData is a byte slice but each block contains an byte array
// Take the first [dataLen] bytes from genesisData and put them in an array
var genesisDataArr [dataLen]byte
copy(genesisDataArr[:], genesisData)
// Create the genesis block
// Timestamp of genesis block is 0. It has no parent.
genesisBlock, err := vm.NewBlock(ids.Empty, 0, genesisDataArr, time.Unix(0, 0))
if err != nil {
vm.Ctx.Log.Error("error while creating genesis block: %v", err)
return err
}
if err := vm.SaveBlock(vm.DB, genesisBlock); err != nil {
vm.Ctx.Log.Error("error while saving genesis block: %v", err)
return err
}
// Accept the genesis block
// Sets [vm.lastAccepted] and [vm.preferred]
if err := genesisBlock.Accept(); err != nil {
return fmt.Errorf("error accepting genesis block: %w", err)
}
if err := vm.SetDBInitialized(); err != nil {
return fmt.Errorf("error while setting db to initialized: %w", err)
}
// Flush VM's database to underlying db
if err := vm.DB.Commit(); err != nil {
vm.Ctx.Log.Error("error while committing db: %v", err)
return err
}
}
return nil
}
// CreateHandlers returns a map where:
// Keys: The path extension for this VM's API (empty in this case)
// Values: The handler for the API
func (vm *VM) CreateHandlers() (map[string]*common.HTTPHandler, error) {
handler, err := vm.NewHandler("timestamp", &Service{vm})
return map[string]*common.HTTPHandler{
"": handler,
}, err
}
// CreateStaticHandlers returns a map where:
// Keys: The path extension for this VM's static API
// Values: The handler for that static API
// We return nil because this VM has no static API
func (vm *VM) CreateStaticHandlers() (map[string]*common.HTTPHandler, error) { return nil, nil }
// Health implements the common.VM interface
func (vm *VM) HealthCheck() (interface{}, error) { return nil, nil }
// BuildBlock returns a block that this vm wants to add to consensus
func (vm *VM) BuildBlock() (snowman.Block, error) {
if len(vm.mempool) == 0 { // There is no block to be built
return nil, errNoPendingBlocks
}
// Get the value to put in the new block
value := vm.mempool[0]
vm.mempool = vm.mempool[1:]
// Notify consensus engine that there are more pending data for blocks
// (if that is the case) when done building this block
if len(vm.mempool) > 0 {
defer vm.NotifyBlockReady()
}
preferredIntf, err := vm.GetBlock(vm.Preferred())
if err != nil {
return nil, fmt.Errorf("couldn't get preferred block")
}
preferredHeight := preferredIntf.(*Block).Height()
// Build the block
block, err := vm.NewBlock(vm.Preferred(), preferredHeight+1, value, time.Now())
if err != nil {
return nil, err
}
return block, nil
}
// proposeBlock appends [data] to [p.mempool].
// Then it notifies the consensus engine
// that a new block is ready to be added to consensus
// (namely, a block with data [data])
func (vm *VM) proposeBlock(data [dataLen]byte) {
vm.mempool = append(vm.mempool, data)
vm.NotifyBlockReady()
}
// ParseBlock parses [bytes] to a snowman.Block
// This function is used by the vm's state to unmarshal blocks saved in state
func (vm *VM) ParseBlock(bytes []byte) (snowman.Block, error) {
block := &Block{}
_, err := vm.codec.Unmarshal(bytes, block)
block.Initialize(bytes, &vm.SnowmanVM)
return block, err
}
// NewBlock returns a new Block where:
// - the block's parent is [parentID]
// - the block's data is [data]
// - the block's timestamp is [timestamp]
// The block is persisted in storage
func (vm *VM) NewBlock(parentID ids.ID, height uint64, data [dataLen]byte, timestamp time.Time) (*Block, error) {
block := &Block{
Block: core.NewBlock(parentID, height),
Data: data,
Timestamp: timestamp.Unix(),
}
blockBytes, err := vm.codec.Marshal(codecVersion, block)
if err != nil {
return nil, err
}
block.Initialize(blockBytes, &vm.SnowmanVM)
return block, nil
}
func (vm *VM) Connected(id ids.ShortID) error {
return nil // noop
}
func (vm *VM) Disconnected(id ids.ShortID) error {
return nil // noop
}