core: refactor genesis handling

This commit solves several issues concerning the genesis block:

* Genesis/ChainConfig loading was handled by cmd/geth code. This left
  library users in the cold. They could specify a JSON-encoded
  string and overwrite the config, but didn't get any of the additional
  checks performed by geth.
* Decoding and writing of genesis JSON was conflated in
  WriteGenesisBlock. This made it a lot harder to embed the genesis
  block into the forthcoming config file loader. This commit changes
  things so there is a single Genesis type that represents genesis
  blocks. All uses of Write*Genesis* are changed to use the new type
  instead.
* If the chain config supplied by the user was incompatible with the
  current chain (i.e. the chain had already advanced beyond a scheduled
  fork), it got overwritten. This is not an issue in practice because
  previous forks have always had the highest total difficulty. It might
  matter in the future though. The new code reverts the local chain to
  the point of the fork when upgrading configuration.

The change to genesis block data removes compression library
dependencies from package core.

1 files changed, 25 insertions, 62 deletions

diff --git a/eth/backend.go b/eth/backend.go
index ef951a6c2..b8df98976 100644
--- a/eth/backend.go
+++ b/eth/backend.go
@@ -18,11 +18,9 @@
 package eth
 
 import (
-	"errors"
 	"fmt"
 	"math/big"
 	"regexp"
-	"strings"
 	"sync"
 	"time"
 
@@ -60,15 +58,17 @@ var (
 )
 
 type Config struct {
-	ChainConfig *params.ChainConfig // chain configuration
+	// The genesis block, which is inserted if the database is empty.
+	// If nil, the Ethereum main net block is used.
+	Genesis *core.Genesis
 
-	NetworkId  int    // Network ID to use for selecting peers to connect to
-	Genesis    string // Genesis JSON to seed the chain database with
-	FastSync   bool   // Enables the state download based fast synchronisation algorithm
-	LightMode  bool   // Running in light client mode
-	LightServ  int    // Maximum percentage of time allowed for serving LES requests
-	LightPeers int    // Maximum number of LES client peers
-	MaxPeers   int    // Maximum number of global peers
+	NetworkId int // Network ID to use for selecting peers to connect to
+
+	FastSync   bool // Enables the state download based fast synchronisation algorithm
+	LightMode  bool // Running in light client mode
+	LightServ  int  // Maximum percentage of time allowed for serving LES requests
+	LightPeers int  // Maximum number of LES client peers
+	MaxPeers   int  // Maximum number of global peers
 
 	SkipBcVersionCheck bool // e.g. blockchain export
 	DatabaseCache      int
@@ -100,9 +100,6 @@ type Config struct {
 	GpobaseCorrectionFactor int
 
 	EnablePreimageRecording bool
-
-	TestGenesisBlock *types.Block   // Genesis block to seed the chain database with (testing only!)
-	TestGenesisState ethdb.Database // Genesis state to seed the database with (testing only!)
 }
 
 type LesServer interface {
@@ -155,11 +152,15 @@ func New(ctx *node.ServiceContext, config *Config) (*Ethereum, error) {
 		return nil, err
 	}
 	stopDbUpgrade := upgradeSequentialKeys(chainDb)
-	if err := SetupGenesisBlock(&chainDb, config); err != nil {
-		return nil, err
+	chainConfig, genesisHash, genesisErr := core.SetupGenesisBlock(chainDb, config.Genesis)
+	if _, ok := genesisErr.(*params.ConfigCompatError); genesisErr != nil && !ok {
+		return nil, genesisErr
 	}
+	log.Info("Initialised chain configuration", "config", chainConfig)
+
 	eth := &Ethereum{
 		chainDb:        chainDb,
+		chainConfig:    chainConfig,
 		eventMux:       ctx.EventMux,
 		accountManager: ctx.AccountManager,
 		pow:            CreatePoW(ctx, config),
@@ -184,33 +185,18 @@ func New(ctx *node.ServiceContext, config *Config) (*Ethereum, error) {
 		core.WriteBlockChainVersion(chainDb, core.BlockChainVersion)
 	}
 
-	// load the genesis block or write a new one if no genesis
-	// block is prenent in the database.
-	genesis := core.GetBlock(chainDb, core.GetCanonicalHash(chainDb, 0), 0)
-	if genesis == nil {
-		genesis, err = core.WriteDefaultGenesisBlock(chainDb)
-		if err != nil {
-			return nil, err
-		}
-		log.Warn("Wrote default Ethereum genesis block")
-	}
-
-	if config.ChainConfig == nil {
-		return nil, errors.New("missing chain config")
-	}
-	core.WriteChainConfig(chainDb, genesis.Hash(), config.ChainConfig)
-
-	eth.chainConfig = config.ChainConfig
-
-	log.Info("Initialised chain configuration", "config", eth.chainConfig)
-
-	eth.blockchain, err = core.NewBlockChain(chainDb, eth.chainConfig, eth.pow, eth.EventMux(), vm.Config{EnablePreimageRecording: config.EnablePreimageRecording})
+	vmConfig := vm.Config{EnablePreimageRecording: config.EnablePreimageRecording}
+	eth.blockchain, err = core.NewBlockChain(chainDb, eth.chainConfig, eth.pow, eth.eventMux, vmConfig)
 	if err != nil {
-		if err == core.ErrNoGenesis {
-			return nil, fmt.Errorf(`No chain found. Please initialise a new chain using the "init" subcommand.`)
-		}
 		return nil, err
 	}
+	// Rewind the chain in case of an incompatible config upgrade.
+	if compat, ok := genesisErr.(*params.ConfigCompatError); ok {
+		log.Warn("Rewinding chain to upgrade configuration", "err", compat)
+		eth.blockchain.SetHead(compat.RewindTo)
+		core.WriteChainConfig(chainDb, genesisHash, chainConfig)
+	}
+
 	newPool := core.NewTxPool(eth.chainConfig, eth.EventMux(), eth.blockchain.State, eth.blockchain.GasLimit)
 	eth.txPool = newPool
 
@@ -255,29 +241,6 @@ func CreateDB(ctx *node.ServiceContext, config *Config, name string) (ethdb.Data
 	return db, err
 }
 
-// SetupGenesisBlock initializes the genesis block for an Ethereum service
-func SetupGenesisBlock(chainDb *ethdb.Database, config *Config) error {
-	// Load up any custom genesis block if requested
-	if len(config.Genesis) > 0 {
-		block, err := core.WriteGenesisBlock(*chainDb, strings.NewReader(config.Genesis))
-		if err != nil {
-			return err
-		}
-		log.Info("Successfully wrote custom genesis block", "hash", block.Hash())
-	}
-	// Load up a test setup if directly injected
-	if config.TestGenesisState != nil {
-		*chainDb = config.TestGenesisState
-	}
-	if config.TestGenesisBlock != nil {
-		core.WriteTd(*chainDb, config.TestGenesisBlock.Hash(), config.TestGenesisBlock.NumberU64(), config.TestGenesisBlock.Difficulty())
-		core.WriteBlock(*chainDb, config.TestGenesisBlock)
-		core.WriteCanonicalHash(*chainDb, config.TestGenesisBlock.Hash(), config.TestGenesisBlock.NumberU64())
-		core.WriteHeadBlockHash(*chainDb, config.TestGenesisBlock.Hash())
-	}
-	return nil
-}
-
 // CreatePoW creates the required type of PoW instance for an Ethereum service
 func CreatePoW(ctx *node.ServiceContext, config *Config) pow.PoW {
 	switch {