HIP-30: Balance migration (#4499)

* flags: set up preimage flags * hip30: set up preimage import, export, api * save pre-images by default * add pre images api * goimports * commit rpc preimages file * preimages: re-generate them using CLI * add metrics and numbers for pre-images * automate generation after import * move from rpc to core * goimports * add back core/preimages.go file * HIP-30: sharding configuration boilerplate * update comments * goimports * HIP-30: minimum validator commission of 7% Based on #4495, which must be merged before this PR. This PR should be rebased with dev after #4495 is merged to retain atomicity of changes by pull request. * goimports * HIP-30: Emission split implementation Note that the allocated split of the emission goes directly to the recipient (and not via the Reward). This is because rewards are indexed by validator and not by delegator, and the recipient may/may not have any delegations which we can reward. Even if one was guaranteed to exist, it would mess up the math of the validator. * set up mainnet recipient of emission split * HIP-30: Emission split addresses for non mainnet * HIP-30: deactivate shard 2 and 3 validators * goimports * update test * goimports * migrate balance uring epoch T - 1 highly untested code. also missing is the ability to generate a pre-migration report for future verification. * update test * export prometheus metric when no error importing preimage * add comment * test account migration in localnet * add preimages flags to rootflags * enable preimages on the whitelist * add the generate method * fix cropping log * fix cropping log * cropping startpoint when bigger than endpoint * add support for the rpcblocknumer type * enable import api * use earlies block * debug logs * debug logs * debug logs * debug logs * fix error catching * fix error catching * make end optional for the comand line * fix cropping logic * improve error when apply message fails * add balance on the error * fix importing * remove unused imports --------- Co-authored-by: Nita Neou (Soph) <soph@harmony.one> Co-authored-by: Soph <35721420+sophoah@users.noreply.github.com> Co-authored-by: Diego Nava <diego.nava77@hotmail.com> Co-authored-by: Diego Nava <8563843+diego1q2w@users.noreply.github.com>
1 year ago · 688b9335da
parent 115e434f73
commit 688b9335da
10 changed files with 453 additions and 131 deletions
--- a/cmd/harmony/main.go
+++ b/cmd/harmony/main.go
@ -1,9 +1,7 @@
 package main

 import (
-	"encoding/csv"
 	"fmt"
-	"io"
 	"io/ioutil"
 	"math/big"
 	"math/rand"
@ -32,7 +30,6 @@ import (

 	ethCommon "github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/common/hexutil"
-	"github.com/ethereum/go-ethereum/crypto"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/pkg/errors"
 	"github.com/spf13/cobra"
@ -48,7 +45,6 @@ import (
 	"github.com/harmony-one/harmony/common/ntp"
 	"github.com/harmony-one/harmony/consensus"
 	"github.com/harmony-one/harmony/core"
-	"github.com/harmony-one/harmony/core/rawdb"
 	"github.com/harmony-one/harmony/hmy/downloader"
 	"github.com/harmony-one/harmony/internal/cli"
 	"github.com/harmony-one/harmony/internal/common"
@ -64,7 +60,6 @@ import (
 	"github.com/harmony-one/harmony/p2p"
 	"github.com/harmony-one/harmony/shard"
 	"github.com/harmony-one/harmony/webhooks"
-	prom "github.com/prometheus/client_golang/prometheus"
 )

 // Host
@ -384,86 +379,13 @@ func setupNodeAndRun(hc harmonyconfig.HarmonyConfig) {
 	//// code to handle pre-image export, import and generation
 	if hc.Preimage != nil {
 		if hc.Preimage.ImportFrom != "" {
-			reader, err := os.Open(hc.Preimage.ImportFrom)
-			if err != nil {
-				fmt.Println("Could not open file for reading", err)
-				os.Exit(1)
-			}
-			csvReader := csv.NewReader(reader)
-			chain := currentNode.Blockchain()
-			dbReader := chain.ChainDb()
-			imported := uint64(0)
-			for {
-				record, err := csvReader.Read()
-				if err == io.EOF {
-					fmt.Println("MyBlockNumber field missing, cannot proceed")
-					os.Exit(1)
-				}
-				if err != nil {
-					fmt.Println("Could not read from reader", err)
-					os.Exit(1)
-				}
-				// this means the address is a number
-				if blockNumber, err := strconv.ParseUint(record[1], 10, 64); err == nil {
-					if record[0] == "MyBlockNumber" {
-						// set this value in database, and prometheus, if needed
-						prev, err := rawdb.ReadPreimageImportBlock(dbReader)
-						if err != nil {
-							fmt.Println("No prior value found, overwriting")
-						}
-						if blockNumber > prev {
-							if rawdb.WritePreimageImportBlock(dbReader, blockNumber) != nil {
-								fmt.Println("Error saving last import block", err)
-								os.Exit(1)
-							}
-							// export blockNumber to prometheus
-							gauge := prom.NewGauge(
-								prom.GaugeOpts{
-									Namespace: "hmy",
-									Subsystem: "blockchain",
-									Name:      "last_preimage_import",
-									Help:      "the last known block for which preimages were imported",
-								},
-							)
-							prometheus.PromRegistry().MustRegister(
-								gauge,
-							)
-							gauge.Set(float64(blockNumber))
-						}
-						// this is the last record
-						imported = blockNumber
-						break
-					}
-				}
-				key := ethCommon.HexToHash(record[0])
-				value := ethCommon.Hex2Bytes(record[1])
-				// validate
-				if crypto.Keccak256Hash(value) != key {
-					fmt.Println("Data mismatch: skipping", record)
-					continue
-				}
-				// add to database
-				rawdb.WritePreimages(
-					dbReader, map[ethCommon.Hash][]byte{
-						key: value,
-					},
-				)
-			}
-			// now, at this point, we will have to generate missing pre-images
-			if imported != 0 {
-				genStart, _ := rawdb.ReadPreImageStartBlock(dbReader)
-				genEnd, _ := rawdb.ReadPreImageEndBlock(dbReader)
-				current := chain.CurrentBlock().NumberU64()
-				toGenStart, toGenEnd := core.FindMissingRange(imported, genStart, genEnd, current)
-				if toGenStart != 0 && toGenEnd != 0 {
-					if err := core.GeneratePreimages(
-						chain, toGenStart, toGenEnd,
+			if err := core.ImportPreimages(
+				currentNode.Blockchain(),
+				hc.Preimage.ImportFrom,
 			); err != nil {
-						fmt.Println("Error generating", err)
+				fmt.Println("Error importing", err)
 				os.Exit(1)
 			}
-				}
-			}
 			os.Exit(0)
 		} else if exportPath := hc.Preimage.ExportTo; exportPath != "" {
 			if err := core.ExportPreimages(
@ -475,16 +397,23 @@ func setupNodeAndRun(hc harmonyconfig.HarmonyConfig) {
 			}
 			os.Exit(0)
 			// both must be set
-		} else if hc.Preimage.GenerateStart > 0 && hc.Preimage.GenerateEnd > 0 {
+		} else if hc.Preimage.GenerateStart > 0 {
 			chain := currentNode.Blockchain()
 			end := hc.Preimage.GenerateEnd
-			if number := chain.CurrentBlock().NumberU64(); number > end {
+			current := chain.CurrentBlock().NumberU64()
+			if end > current {
 				fmt.Printf(
 					"Cropping generate endpoint from %d to %d\n",
-					number, end,
+					end, current,
 				)
-				end = number
+				end = current
+			}
+
+			if end == 0 {
+				end = current
 			}
+
+			fmt.Println("Starting generation")
 			if err := core.GeneratePreimages(
 				chain,
 				hc.Preimage.GenerateStart, end,
@ -492,6 +421,7 @@ func setupNodeAndRun(hc harmonyconfig.HarmonyConfig) {
 				fmt.Println("Error generating", err)
 				os.Exit(1)
 			}
+			fmt.Println("Generation successful")
 			os.Exit(0)
 		}
 		os.Exit(0)
--- a/core/preimages.go
+++ b/core/preimages.go
@ -3,9 +3,12 @@ package core
 import (
 	"encoding/csv"
 	"fmt"
+	"io"
 	"os"
+	"strconv"

 	ethCommon "github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/crypto"
 	"github.com/harmony-one/harmony/api/service/prometheus"
 	"github.com/harmony-one/harmony/core/rawdb"
 	"github.com/harmony-one/harmony/core/state"
@ -14,6 +17,86 @@ import (
 	prom "github.com/prometheus/client_golang/prometheus"
 )

+// ImportPreimages is public so `main.go` can call it directly`
+func ImportPreimages(chain BlockChain, path string) error {
+	reader, err := os.Open(path)
+	if err != nil {
+		return fmt.Errorf("could not open file for reading: %s", err)
+	}
+	csvReader := csv.NewReader(reader)
+	dbReader := chain.ChainDb()
+	imported := uint64(0)
+	for {
+		record, err := csvReader.Read()
+		if err == io.EOF {
+			return fmt.Errorf("MyBlockNumber field missing, cannot proceed")
+		}
+		if err != nil {
+			return fmt.Errorf("could not read from reader: %s", err)
+		}
+		// this means the address is a number
+		if blockNumber, err := strconv.ParseUint(record[1], 10, 64); err == nil {
+			if record[0] == "MyBlockNumber" {
+				// set this value in database, and prometheus, if needed
+				prev, err := rawdb.ReadPreimageImportBlock(dbReader)
+				if err != nil {
+					return fmt.Errorf("no prior value found, overwriting: %s", err)
+				}
+				if blockNumber > prev {
+					if rawdb.WritePreimageImportBlock(dbReader, blockNumber) != nil {
+						return fmt.Errorf("error saving last import block: %s", err)
+					}
+					// export blockNumber to prometheus
+					gauge := prom.NewGauge(
+						prom.GaugeOpts{
+							Namespace: "hmy",
+							Subsystem: "blockchain",
+							Name:      "last_preimage_import",
+							Help:      "the last known block for which preimages were imported",
+						},
+					)
+					prometheus.PromRegistry().MustRegister(
+						gauge,
+					)
+					gauge.Set(float64(blockNumber))
+				}
+				// this is the last record
+				imported = blockNumber
+				break
+			}
+		}
+		key := ethCommon.HexToHash(record[0])
+		value := ethCommon.Hex2Bytes(record[1])
+		// validate
+		if crypto.Keccak256Hash(value) != key {
+			fmt.Println("Data mismatch: skipping", record)
+			continue
+		}
+		// add to database
+		_ = rawdb.WritePreimages(
+			dbReader, map[ethCommon.Hash][]byte{
+				key: value,
+			},
+		)
+	}
+	// now, at this point, we will have to generate missing pre-images
+	if imported != 0 {
+		genStart, _ := rawdb.ReadPreImageStartBlock(dbReader)
+		genEnd, _ := rawdb.ReadPreImageEndBlock(dbReader)
+		current := chain.CurrentBlock().NumberU64()
+		toGenStart, toGenEnd := FindMissingRange(imported, genStart, genEnd, current)
+		if toGenStart != 0 && toGenEnd != 0 {
+			if err := GeneratePreimages(
+				chain, toGenStart, toGenEnd,
+			); err != nil {
+				return fmt.Errorf("error generating: %s", err)
+			}
+		}
+	}
+
+	return nil
+}
+
 // ExportPreimages is public so `main.go` can call it directly`
 func ExportPreimages(chain BlockChain, path string) error {
 	// set up csv
@ -102,6 +185,8 @@ func GeneratePreimages(chain BlockChain, start, end uint64) error {
 	if start < 2 {
 		return fmt.Errorf("too low starting point %d", start)
 	}
+	fmt.Println("generating from", start, "to", end)
+
 	// fetch all the blocks, from start and end both inclusive
 	// then execute them - the execution will write the pre-images
 	// to disk and we are good to go
@ -111,15 +196,18 @@ func GeneratePreimages(chain BlockChain, start, end uint64) error {
 	var startingState *state.DB
 	var startingBlock *types.Block
 	for i := start - 1; i > 0; i-- {
+		fmt.Println("finding block number", i)
 		startingBlock = chain.GetBlockByNumber(i)
 		if startingBlock == nil {
+			fmt.Println("not found block number", i)
 			// rewound too much in snapdb, so exit loop
 			// although this is only designed for s2/s3 nodes in mind
 			// which do not have such a snapdb
 			break
 		}
+		fmt.Println("found block number", startingBlock.NumberU64(), startingBlock.Root().Hex())
 		state, err := chain.StateAt(startingBlock.Root())
-		if err == nil {
+		if err != nil {
 			continue
 		}
 		startingState = state
@ -131,18 +219,23 @@ func GeneratePreimages(chain BlockChain, start, end uint64) error {

 	// now execute block T+1 based on starting state
 	for i := startingBlock.NumberU64() + 1; i <= end; i++ {
+		if i%100000 == 0 {
+			fmt.Println("processing block", i)
+		}
 		block := chain.GetBlockByNumber(i)
 		if block == nil {
 			// because we have startingBlock we must have all following
 			return fmt.Errorf("block %d not found", i)
 		}
 		_, _, _, _, _, _, endingState, err := chain.Processor().Process(block, startingState, *chain.GetVMConfig(), false)
-		if err == nil {
+		if err != nil {
 			return fmt.Errorf("error executing block #%d: %s", i, err)
 		}
 		startingState = endingState
 	}
 	// force any pre-images in memory so far to go to disk, if they haven't already
+	fmt.Println("committing images")
+
 	if err := chain.CommitPreimages(); err != nil {
 		return fmt.Errorf("error committing preimages %s", err)
 	}
--- a/core/state_processor.go
+++ b/core/state_processor.go
@ -17,6 +17,8 @@
 package core

 import (
+	"encoding/binary"
+	"fmt"
 	"math/big"
 	"time"

@ -28,6 +30,7 @@ import (
 	"github.com/harmony-one/harmony/block"
 	consensus_engine "github.com/harmony-one/harmony/consensus/engine"
 	"github.com/harmony-one/harmony/consensus/reward"
+	"github.com/harmony-one/harmony/core/rawdb"
 	"github.com/harmony-one/harmony/core/state"
 	"github.com/harmony-one/harmony/core/types"
 	"github.com/harmony-one/harmony/core/vm"
@ -41,6 +44,11 @@ import (
 	"github.com/pkg/errors"
 )

+var (
+	ErrNoMigrationRequired = errors.New("No balance migration required")
+	ErrNoMigrationPossible = errors.New("No balance migration possible")
+)
+
 const (
 	resultCacheLimit = 64 // The number of cached results from processing blocks
 )
@ -128,6 +136,26 @@ func (p *StateProcessor) Process(
 		return nil, nil, nil, nil, 0, nil, statedb, err
 	}

+	processTxsAndStxs := true
+	cxReceipt, err := MayBalanceMigration(
+		gp, header, statedb, p.bc, p.config,
+	)
+	if err != nil {
+		if err == ErrNoMigrationPossible {
+			// ran out of accounts
+			processTxsAndStxs = false
+		}
+		if err != ErrNoMigrationRequired {
+			return nil, nil, nil, nil, 0, nil, statedb, err
+		}
+	} else {
+		if cxReceipt != nil {
+			outcxs = append(outcxs, cxReceipt)
+			// only 1 cx per block
+			processTxsAndStxs = false
+		}
+	}
+	if processTxsAndStxs {
 		startTime := time.Now()
 		// Iterate over and process the individual transactions
 		for i, tx := range block.Transactions() {
@ -164,7 +192,7 @@ func (p *StateProcessor) Process(
 			allLogs = append(allLogs, receipt.Logs...)
 		}
 		utils.Logger().Debug().Int64("elapsed time", time.Now().Sub(startTime).Milliseconds()).Msg("Process Staking Txns")
-
+	}
 	// incomingReceipts should always be processed
 	// after transactions (to be consistent with the block proposal)
 	for _, cx := range block.IncomingReceipts() {
@ -284,7 +312,7 @@ func ApplyTransaction(config *params.ChainConfig, bc ChainContext, author *commo
 	// Apply the transaction to the current state (included in the env)
 	result, err := ApplyMessage(vmenv, msg, gp)
 	if err != nil {
-		return nil, nil, nil, 0, err
+		return nil, nil, nil, 0, fmt.Errorf("apply failed from='%s' to='%s' balance='%s': %w", msg.From().Hex(), msg.To().Hex(), statedb.GetBalance(msg.From()).String(), err)
 	}
 	// Update the state with pending changes
 	var root []byte
@ -500,3 +528,161 @@ func MayShardReduction(bc ChainContext, statedb *state.DB, header *block.Header)
 	statedb.IntermediateRoot(bc.Config().IsS3(header.Epoch()))
 	return nil
 }
+
+func MayBalanceMigration(
+	gasPool *GasPool,
+	header *block.Header,
+	db *state.DB,
+	chain BlockChain,
+	config *params.ChainConfig,
+) (*types.CXReceipt, error) {
+	isMainnet := nodeconfig.GetDefaultConfig().GetNetworkType() == nodeconfig.Mainnet
+	if isMainnet {
+		if config.IsEpochBeforeHIP30(header.Epoch()) {
+			nxtShards := shard.Schedule.InstanceForEpoch(
+				new(big.Int).Add(header.Epoch(), common.Big1),
+			).NumShards()
+			if myShard := chain.ShardID(); myShard >= nxtShards {
+				// i need to send my balances to the destination shard
+				// however, i do not know when the next epoch will begin
+				// because only shard 0 can govern that
+				// so i will just generate one cross shard transaction
+				// in each block of the epoch. this epoch is defined by
+				// nxtShards = 2 and curShards = 4
+				parentRoot := chain.GetBlockByHash(
+					header.ParentHash(),
+				).Root() // for examining MPT at this root, should exist
+				cx, err := generateOneMigrationMessage(
+					db, parentRoot,
+					header.NumberU64(),
+					myShard, uint32(1), // dstShard is always 1
+				)
+				if err != nil {
+					return nil, err
+				}
+				if cx != nil {
+					gasPool.SubGas(params.TxGasXShard)
+					return cx, nil
+				}
+				// both err and cx are nil, which means we
+				// ran out of eligible accounts in MPT
+				return nil, ErrNoMigrationPossible
+			}
+		}
+	}
+	// for testing balance migration on devnet
+	isDevnet := nodeconfig.GetDefaultConfig().GetNetworkType() == nodeconfig.Devnet
+	isLocalnet := nodeconfig.GetDefaultConfig().GetNetworkType() == nodeconfig.Localnet
+	if isDevnet || isLocalnet {
+		if config.IsEpochBeforeHIP30(header.Epoch()) {
+			if myShard := chain.ShardID(); myShard != shard.BeaconChainShardID {
+				parentRoot := chain.GetBlockByHash(
+					header.ParentHash(),
+				).Root() // for examining MPT at this root, should exist
+				cx, err := generateOneMigrationMessage(
+					db, parentRoot,
+					header.NumberU64(),
+					myShard, shard.BeaconChainShardID, // dstShard
+				)
+				if err != nil {
+					return nil, err
+				}
+				if cx != nil {
+					gasPool.SubGas(params.TxGasXShard)
+					return cx, nil
+				}
+				return nil, ErrNoMigrationPossible
+			}
+		}
+	}
+
+	return nil, ErrNoMigrationRequired
+}
+
+func generateOneMigrationMessage(
+	statedb *state.DB,
+	parentRoot common.Hash,
+	number uint64,
+	myShard uint32,
+	dstShard uint32,
+) (*types.CXReceipt, error) {
+	// set up txHash prefix
+	txHash := make([]byte,
+		// 8 for uint64 block number
+		// 4 for uint32 shard id
+		8+4,
+	)
+	binary.LittleEndian.PutUint64(txHash[:8], number)
+	binary.LittleEndian.PutUint32(txHash[8:], myShard)
+	// open the trie, as of previous block.
+	// in this block we aren't processing transactions anyway.
+	trie, err := statedb.Database().OpenTrie(
+		parentRoot,
+	)
+	if err != nil {
+		return nil, err
+	}
+	// disk db, for use by rawdb
+	// this is same as blockchain.ChainDb
+	db := statedb.Database().DiskDB()
+	// start the iteration
+	accountIterator := trie.NodeIterator(nil)
+	// TODO: cache this iteration?
+	for accountIterator.Next(true) {
+		// leaf means leaf node of the MPT, which is an account
+		// the leaf key is the address
+		if accountIterator.Leaf() {
+			key := accountIterator.LeafKey()
+			preimage := rawdb.ReadPreimage(db, common.BytesToHash(key))
+			if len(preimage) == 0 {
+				return nil, errors.New(
+					fmt.Sprintf(
+						"cannot find preimage for %x", key,
+					),
+				)
+			}
+			address := common.BytesToAddress(preimage)
+			// skip blank address
+			if address == (common.Address{}) {
+				continue
+			}
+			// deserialize
+			var account state.Account
+			if err = rlp.DecodeBytes(accountIterator.LeafBlob(), &account); err != nil {
+				return nil, err
+			}
+			// skip contracts
+			if common.BytesToHash(account.CodeHash) != state.EmptyCodeHash {
+				continue
+			}
+			// skip anything with storage
+			if account.Root != state.EmptyRootHash {
+				continue
+			}
+			// skip no (or negative?) balance
+			if account.Balance.Cmp(common.Big0) <= 0 {
+				continue
+			}
+			// for safety, fetch the latest balance (again)
+			balance := statedb.GetBalance(address)
+			if balance.Cmp(common.Big0) <= 0 {
+				continue
+			}
+			// adds a journal entry (dirtied)
+			statedb.SubBalance(address, balance)
+			// create the receipt
+			res := &types.CXReceipt{
+				From:      address,
+				To:        &address,
+				ShardID:   myShard,
+				ToShardID: dstShard,
+				Amount:    balance,
+				TxHash:    common.BytesToHash(txHash),
+			}
+			// move from dirty to pending, same as b/w 2 txs
+			statedb.Finalise(true)
+			return res, nil
+		}
+	}
+	return nil, nil
+}
--- a/internal/params/config.go
+++ b/internal/params/config.go
@ -285,7 +285,7 @@ var (
 		LeaderRotationExternalBeaconLeaders:    big.NewInt(6),
 		FeeCollectEpoch:                        big.NewInt(2),
 		ValidatorCodeFixEpoch:                  big.NewInt(2),
-		HIP30Epoch:                             EpochTBD,
+		HIP30Epoch:                             big.NewInt(3),
 	}

 	// AllProtocolChanges ...
--- a/internal/params/protocol_params.go
+++ b/internal/params/protocol_params.go
@ -24,6 +24,8 @@ const (
 	CallNewAccountGas uint64 = 25000 // Paid for CALL when the destination address didn't exist prior.
 	// TxGas ...
 	TxGas uint64 = 21000 // Per transaction not creating a contract. NOTE: Not payable on data of calls between transactions.
+	// TxGasXShard
+	TxGasXShard uint64 = 23000 // Approximate cost for transferring native tokens across shards. Used in balance migration
 	// TxGasContractCreation ...
 	TxGasContractCreation uint64 = 53000 // Per transaction that creates a contract. NOTE: Not payable on data of calls between transactions.
 	// TxGasValidatorCreation ...
--- a/node/node.go
+++ b/node/node.go
@ -259,17 +259,34 @@ func addPendingTransactions(registry *registry.Registry, newTxs types.Transactio
 		bc            = registry.GetBlockchain()
 		txPool        = registry.GetTxPool()
 		poolTxs       = types.PoolTransactions{}
-		acceptCx = bc.Config().AcceptsCrossTx(bc.CurrentHeader().Epoch())
+		epoch         = bc.CurrentHeader().Epoch()
+		acceptCx      = bc.Config().AcceptsCrossTx(epoch)
+		isBeforeHIP30 = bc.Config().IsEpochBeforeHIP30(epoch)
+		nxtShards     = shard.Schedule.InstanceForEpoch(new(big.Int).Add(epoch, common.Big1)).NumShards()
 	)
 	for _, tx := range newTxs {
-		if tx.ShardID() != tx.ToShardID() && !acceptCx {
+		if tx.ShardID() != tx.ToShardID() {
+			if !acceptCx {
 				errs = append(errs, errors.WithMessage(errInvalidEpoch, "cross-shard tx not accepted yet"))
 				continue
 			}
+			if isBeforeHIP30 {
+				if tx.ToShardID() >= nxtShards {
+					errs = append(errs, errors.New("shards 2 and 3 are shutting down in the next epoch"))
+					continue
+				}
+			}
+		}
 		if tx.IsEthCompatible() && !bc.Config().IsEthCompatible(bc.CurrentBlock().Epoch()) {
 			errs = append(errs, errors.WithMessage(errInvalidEpoch, "ethereum tx not accepted yet"))
 			continue
 		}
+		if isBeforeHIP30 {
+			if bc.ShardID() >= nxtShards {
+				errs = append(errs, errors.New("shards 2 and 3 are shutting down in the next epoch"))
+				continue
+			}
+		}
 		poolTxs = append(poolTxs, tx)
 	}
 	errs = append(errs, registry.GetTxPool().AddRemotes(poolTxs)...)
--- a/node/node_newblock.go
+++ b/node/node_newblock.go
@ -200,7 +200,13 @@ func (node *Node) ProposeNewBlock(commitSigs chan []byte) (*types.Block, error)
 		utils.AnalysisEnd("proposeNewBlockChooseFromTxnPool")
 	}

-	// Prepare cross shard transaction receipts
+	// Prepare incoming cross shard transaction receipts
+	// These are accepted even during the epoch before hip-30
+	// because the destination shard only receives them after
+	// balance is deducted on source shard. to prevent this from
+	// being a significant problem, the source shards will stop
+	// accepting txs destined to the shards which are shutting down
+	// one epoch prior the shut down
 	receiptsList := node.proposeReceiptsProof()
 	if len(receiptsList) != 0 {
 		if err := node.Worker.CommitReceipts(receiptsList); err != nil {
--- a/node/worker/worker.go
+++ b/node/worker/worker.go
@ -150,6 +150,38 @@ func (w *Worker) CommitTransactions(
 		w.current.gasPool = new(core.GasPool).AddGas(w.current.header.GasLimit())
 	}

+	// if this is epoch for balance migration, no txs (or stxs)
+	// will be included in the block
+	// it is technically feasible for some to end up in the pool
+	// say, from the last epoch, but those will not be executed
+	// and no balance will be lost
+	// any cross-shard transfers destined to a shard being shut down
+	// will execute (since they are already spent on the source shard)
+	// but the balance will immediately be returned to shard 1
+	cx, err := core.MayBalanceMigration(
+		w.current.gasPool,
+		w.beacon.CurrentHeader(),
+		w.current.state,
+		w.chain,
+		w.chain.Config(),
+	)
+	if err != nil {
+		if err == core.ErrNoMigrationPossible {
+			// means we do not accept transactions from the network
+			return nil
+		}
+		if err != core.ErrNoMigrationRequired {
+			// this shard not migrating => ErrNoMigrationRequired
+			// any other error means exit this block
+			return err
+		}
+	} else {
+		if cx != nil {
+			w.current.outcxs = append(w.current.outcxs, cx)
+			return nil
+		}
+	}
+
 	// HARMONY TXNS
 	normalTxns := types.NewTransactionsByPriceAndNonce(w.current.signer, w.current.ethSigner, pendingNormal)

--- a/rpc/preimages.go
+++ b/rpc/preimages.go
@ -2,6 +2,7 @@ package rpc

 import (
 	"context"
+	"fmt"

 	"github.com/harmony-one/harmony/core"
 	"github.com/harmony-one/harmony/eth/rpc"
@ -23,7 +24,62 @@ func NewPreimagesAPI(hmy *hmy.Harmony, version string) rpc.API {
 	}
 }

-func (s *PreimagesService) Export(ctx context.Context, path string) error {
+func (s *PreimagesService) Export(_ context.Context, path string) error {
 	// these are by default not blocking
 	return core.ExportPreimages(s.hmy.BlockChain, path)
 }
+
+func (s *PreimagesService) Import(_ context.Context, path string) error {
+	// these are by default not blocking
+	return core.ImportPreimages(s.hmy.BlockChain, path)
+}
+func (s *PreimagesService) Generate(_ context.Context, start, end rpc.BlockNumber) error {
+	// earliestBlock: the number of blocks in the past where you can generate the preimage from the last block
+	earliestBlock := uint64(2)
+	currentBlockNum := s.hmy.CurrentBlock().NumberU64()
+
+	var startBlock uint64
+	switch start {
+	case rpc.EarliestBlockNumber:
+		startBlock = earliestBlock
+	case rpc.LatestBlockNumber:
+		startBlock = earliestBlock
+	case rpc.PendingBlockNumber:
+		startBlock = earliestBlock
+	default:
+		startBlock = uint64(start)
+	}
+
+	var endBlock = uint64(end)
+	switch end {
+	case rpc.EarliestBlockNumber:
+		endBlock = currentBlockNum
+	case rpc.LatestBlockNumber:
+		endBlock = currentBlockNum
+	case rpc.PendingBlockNumber:
+		endBlock = currentBlockNum
+	default:
+		endBlock = uint64(end)
+	}
+
+	fmt.Printf("Generating preimage from block %d to %d\n", startBlock, endBlock)
+
+	if number := currentBlockNum; number > endBlock {
+		fmt.Printf(
+			"Cropping generate endpoint from %d to %d\n",
+			endBlock, number,
+		)
+		endBlock = number
+	}
+
+	if startBlock >= endBlock {
+		fmt.Printf(
+			"Cropping generate startpoint from %d to %d\n",
+			startBlock, endBlock-earliestBlock,
+		)
+		startBlock = endBlock - earliestBlock
+	}
+
+	// these are by default not blocking
+	return core.GeneratePreimages(s.hmy.BlockChain, startBlock, endBlock)
+}
--- a/rpc/rpc.go
+++ b/rpc/rpc.go
@ -42,7 +42,7 @@ const (

 var (
 	// HTTPModules ..
-	HTTPModules = []string{"hmy", "hmyv2", "eth", "debug", "trace", netNamespace, netV1Namespace, netV2Namespace, web3Namespace, "explorer"}
+	HTTPModules = []string{"hmy", "hmyv2", "eth", "debug", "trace", netNamespace, netV1Namespace, netV2Namespace, web3Namespace, "explorer", "preimages"}
 	// WSModules ..
 	WSModules = []string{"hmy", "hmyv2", "eth", "debug", "trace", netNamespace, netV1Namespace, netV2Namespace, web3Namespace, "web3"}