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.

3 files changed, 27 insertions, 22 deletions

diff --git a/les/backend.go b/les/backend.go
index 3cab75f33..d656cf41f 100644
--- a/les/backend.go
+++ b/les/backend.go
@@ -18,7 +18,6 @@
 package les
 
 import (
-	"errors"
 	"fmt"
 	"time"
 
@@ -74,15 +73,19 @@ func New(ctx *node.ServiceContext, config *eth.Config) (*LightEthereum, error) {
 	if err != nil {
 		return nil, err
 	}
-	if err := eth.SetupGenesisBlock(&chainDb, config); err != nil {
-		return nil, err
+	chainConfig, genesisHash, genesisErr := core.SetupGenesisBlock(chainDb, config.Genesis)
+	if _, isCompat := genesisErr.(*params.ConfigCompatError); genesisErr != nil && !isCompat {
+		return nil, genesisErr
 	}
+	log.Info("Initialised chain configuration", "config", chainConfig)
+
 	odr := NewLesOdr(chainDb)
 	relay := NewLesTxRelay()
 	eth := &LightEthereum{
 		odr:            odr,
 		relay:          relay,
 		chainDb:        chainDb,
+		chainConfig:    chainConfig,
 		eventMux:       ctx.EventMux,
 		accountManager: ctx.AccountManager,
 		pow:            eth.CreatePoW(ctx, config),
@@ -91,17 +94,16 @@ func New(ctx *node.ServiceContext, config *eth.Config) (*LightEthereum, error) {
 		solcPath:       config.SolcPath,
 	}
 
-	if config.ChainConfig == nil {
-		return nil, errors.New("missing chain config")
-	}
-	eth.chainConfig = config.ChainConfig
 	eth.blockchain, err = light.NewLightChain(odr, eth.chainConfig, eth.pow, eth.eventMux)
 	if err != nil {
-		if err == core.ErrNoGenesis {
-			return nil, fmt.Errorf(`Genesis block not found. Please supply a genesis block with the "--genesis /path/to/file" argument`)
-		}
 		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)
+	}
 
 	eth.txPool = light.NewTxPool(eth.chainConfig, eth.eventMux, eth.blockchain, eth.relay)
 	if eth.protocolManager, err = NewProtocolManager(eth.chainConfig, config.LightMode, config.NetworkId, eth.eventMux, eth.pow, eth.blockchain, nil, chainDb, odr, relay); err != nil {
diff --git a/les/helper_test.go b/les/helper_test.go
index 3e8ce57b6..f37bec80e 100644
--- a/les/helper_test.go
+++ b/les/helper_test.go
@@ -134,28 +134,31 @@ func testRCL() RequestCostList {
 // channels for different events.
 func newTestProtocolManager(lightSync bool, blocks int, generator func(int, *core.BlockGen)) (*ProtocolManager, ethdb.Database, *LesOdr, error) {
 	var (
-		evmux       = new(event.TypeMux)
-		pow         = new(pow.FakePow)
-		db, _       = ethdb.NewMemDatabase()
-		genesis     = core.WriteGenesisBlockForTesting(db, core.GenesisAccount{Address: testBankAddress, Balance: testBankFunds})
-		chainConfig = &params.ChainConfig{HomesteadBlock: big.NewInt(0)} // homestead set to 0 because of chain maker
-		odr         *LesOdr
-		chain       BlockChain
+		evmux = new(event.TypeMux)
+		pow   = new(pow.FakePow)
+		db, _ = ethdb.NewMemDatabase()
+		gspec = core.Genesis{
+			Config: params.TestChainConfig,
+			Alloc:  core.GenesisAlloc{testBankAddress: {Balance: testBankFunds}},
+		}
+		genesis = gspec.MustCommit(db)
+		odr     *LesOdr
+		chain   BlockChain
 	)
 
 	if lightSync {
 		odr = NewLesOdr(db)
-		chain, _ = light.NewLightChain(odr, chainConfig, pow, evmux)
+		chain, _ = light.NewLightChain(odr, gspec.Config, pow, evmux)
 	} else {
-		blockchain, _ := core.NewBlockChain(db, chainConfig, pow, evmux, vm.Config{})
-		gchain, _ := core.GenerateChain(chainConfig, genesis, db, blocks, generator)
+		blockchain, _ := core.NewBlockChain(db, gspec.Config, pow, evmux, vm.Config{})
+		gchain, _ := core.GenerateChain(gspec.Config, genesis, db, blocks, generator)
 		if _, err := blockchain.InsertChain(gchain); err != nil {
 			panic(err)
 		}
 		chain = blockchain
 	}
 
-	pm, err := NewProtocolManager(chainConfig, lightSync, NetworkId, evmux, pow, chain, nil, db, odr, nil)
+	pm, err := NewProtocolManager(gspec.Config, lightSync, NetworkId, evmux, pow, chain, nil, db, odr, nil)
 	if err != nil {
 		return nil, nil, nil, err
 	}
diff --git a/les/server.go b/les/server.go
index 04bfa0292..5957add36 100644
--- a/les/server.go
+++ b/les/server.go
@@ -45,7 +45,7 @@ type LesServer struct {
 }
 
 func NewLesServer(eth *eth.Ethereum, config *eth.Config) (*LesServer, error) {
-	pm, err := NewProtocolManager(config.ChainConfig, false, config.NetworkId, eth.EventMux(), eth.Pow(), eth.BlockChain(), eth.TxPool(), eth.ChainDb(), nil, nil)
+	pm, err := NewProtocolManager(eth.BlockChain().Config(), false, config.NetworkId, eth.EventMux(), eth.Pow(), eth.BlockChain(), eth.TxPool(), eth.ChainDb(), nil, nil)
 	if err != nil {
 		return nil, err
 	}