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.

2 files changed, 28 insertions, 77 deletions

diff --git a/cmd/geth/chaincmd.go b/cmd/geth/chaincmd.go
index 6ea474a9c..2d121a611 100644
--- a/cmd/geth/chaincmd.go
+++ b/cmd/geth/chaincmd.go
@@ -17,6 +17,7 @@
 package main
 
 import (
+	"encoding/json"
 	"fmt"
 	"os"
 	"runtime"
@@ -110,17 +111,22 @@ func initGenesis(ctx *cli.Context) error {
 	stack := makeFullNode(ctx)
 	chaindb := utils.MakeChainDatabase(ctx, stack)
 
-	genesisFile, err := os.Open(genesisPath)
+	file, err := os.Open(genesisPath)
 	if err != nil {
 		utils.Fatalf("failed to read genesis file: %v", err)
 	}
-	defer genesisFile.Close()
+	defer file.Close()
 
-	block, err := core.WriteGenesisBlock(chaindb, genesisFile)
+	genesis := new(core.Genesis)
+	if err := json.NewDecoder(file).Decode(genesis); err != nil {
+		utils.Fatalf("invalid genesis file: %v", err)
+	}
+
+	_, hash, err := core.SetupGenesisBlock(chaindb, genesis)
 	if err != nil {
 		utils.Fatalf("failed to write genesis block: %v", err)
 	}
-	log.Info("Successfully wrote genesis state", "hash", block.Hash())
+	log.Info("Successfully wrote genesis state", "hash", hash)
 	return nil
 }
 
diff --git a/cmd/utils/flags.go b/cmd/utils/flags.go
index 38c90d801..478e08834 100644
--- a/cmd/utils/flags.go
+++ b/cmd/utils/flags.go
@@ -786,7 +786,6 @@ func RegisterEthService(ctx *cli.Context, stack *node.Node, extra []byte) {
 
 	ethConf := &eth.Config{
 		Etherbase:               MakeEtherbase(ks, ctx),
-		ChainConfig:             MakeChainConfig(ctx, stack),
 		FastSync:                ctx.GlobalBool(FastSyncFlag.Name),
 		LightMode:               ctx.GlobalBool(LightModeFlag.Name),
 		LightServ:               ctx.GlobalInt(LightServFlag.Name),
@@ -822,7 +821,6 @@ func RegisterEthService(ctx *cli.Context, stack *node.Node, extra []byte) {
 			ethConf.NetworkId = 3
 		}
 		ethConf.Genesis = core.DefaultTestnetGenesisBlock()
-
 	case ctx.GlobalBool(DevModeFlag.Name):
 		ethConf.Genesis = core.DevGenesisBlock()
 		if !ctx.GlobalIsSet(GasPriceFlag.Name) {
@@ -884,67 +882,6 @@ func SetupNetwork(ctx *cli.Context) {
 	params.TargetGasLimit = new(big.Int).SetUint64(ctx.GlobalUint64(TargetGasLimitFlag.Name))
 }
 
-// MakeChainConfig reads the chain configuration from the database in ctx.Datadir.
-func MakeChainConfig(ctx *cli.Context, stack *node.Node) *params.ChainConfig {
-	db := MakeChainDatabase(ctx, stack)
-	defer db.Close()
-
-	return MakeChainConfigFromDb(ctx, db)
-}
-
-// MakeChainConfigFromDb reads the chain configuration from the given database.
-func MakeChainConfigFromDb(ctx *cli.Context, db ethdb.Database) *params.ChainConfig {
-	// If the chain is already initialized, use any existing chain configs
-	config := new(params.ChainConfig)
-
-	genesis := core.GetBlock(db, core.GetCanonicalHash(db, 0), 0)
-	if genesis != nil {
-		storedConfig, err := core.GetChainConfig(db, genesis.Hash())
-		switch err {
-		case nil:
-			config = storedConfig
-		case core.ChainConfigNotFoundErr:
-			// No configs found, use empty, will populate below
-		default:
-			Fatalf("Could not make chain configuration: %v", err)
-		}
-	}
-	// set chain id in case it's zero.
-	if config.ChainId == nil {
-		config.ChainId = new(big.Int)
-	}
-	// Check whether we are allowed to set default config params or not:
-	//  - If no genesis is set, we're running either mainnet or testnet (private nets use `geth init`)
-	//  - If a genesis is already set, ensure we have a configuration for it (mainnet or testnet)
-	defaults := genesis == nil ||
-		(genesis.Hash() == params.MainNetGenesisHash && !ctx.GlobalBool(TestNetFlag.Name)) ||
-		(genesis.Hash() == params.TestNetGenesisHash && ctx.GlobalBool(TestNetFlag.Name))
-
-	if defaults {
-		if ctx.GlobalBool(TestNetFlag.Name) {
-			config = params.TestnetChainConfig
-		} else if ctx.GlobalBool(DevModeFlag.Name) {
-			config = params.AllProtocolChanges
-		} else {
-			// Homestead fork
-			config.HomesteadBlock = params.MainNetHomesteadBlock
-			// DAO fork
-			config.DAOForkBlock = params.MainNetDAOForkBlock
-			config.DAOForkSupport = true
-
-			// DoS reprice fork
-			config.EIP150Block = params.MainNetHomesteadGasRepriceBlock
-			config.EIP150Hash = params.MainNetHomesteadGasRepriceHash
-
-			// DoS state cleanup fork
-			config.EIP155Block = params.MainNetSpuriousDragon
-			config.EIP158Block = params.MainNetSpuriousDragon
-			config.ChainId = params.MainNetChainID
-		}
-	}
-	return config
-}
-
 func ChainDbName(ctx *cli.Context) string {
 	if ctx.GlobalBool(LightModeFlag.Name) {
 		return "lightchaindata"
@@ -968,26 +905,34 @@ func MakeChainDatabase(ctx *cli.Context, stack *node.Node) ethdb.Database {
 	return chainDb
 }
 
+func MakeGenesis(ctx *cli.Context) *core.Genesis {
+	var genesis *core.Genesis
+	switch {
+	case ctx.GlobalBool(TestNetFlag.Name):
+		genesis = core.DefaultTestnetGenesisBlock()
+	case ctx.GlobalBool(DevModeFlag.Name):
+		genesis = core.DevGenesisBlock()
+	}
+	return genesis
+}
+
 // MakeChain creates a chain manager from set command line flags.
 func MakeChain(ctx *cli.Context, stack *node.Node) (chain *core.BlockChain, chainDb ethdb.Database) {
 	var err error
 	chainDb = MakeChainDatabase(ctx, stack)
 
-	if ctx.GlobalBool(TestNetFlag.Name) {
-		_, err := core.WriteTestNetGenesisBlock(chainDb)
-		if err != nil {
-			Fatalf("Failed to write testnet genesis: %v", err)
-		}
-	}
-	chainConfig := MakeChainConfigFromDb(ctx, chainDb)
-
 	seal := pow.PoW(pow.FakePow{})
 	if !ctx.GlobalBool(FakePoWFlag.Name) {
 		seal = pow.NewFullEthash("", 1, 0, "", 1, 0)
 	}
-	chain, err = core.NewBlockChain(chainDb, chainConfig, seal, new(event.TypeMux), vm.Config{EnablePreimageRecording: ctx.GlobalBool(VMEnableDebugFlag.Name)})
+	config, _, err := core.SetupGenesisBlock(chainDb, MakeGenesis(ctx))
+	if err != nil {
+		Fatalf("%v", err)
+	}
+	vmcfg := vm.Config{EnablePreimageRecording: ctx.GlobalBool(VMEnableDebugFlag.Name)}
+	chain, err = core.NewBlockChain(chainDb, config, seal, new(event.TypeMux), vmcfg)
 	if err != nil {
-		Fatalf("Could not start chainmanager: %v", err)
+		Fatalf("Can't create BlockChain: %v", err)
 	}
 	return chain, chainDb
 }