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, 140 insertions, 68 deletions

diff --git a/params/config.go b/params/config.go
index ee993fe4a..47d7c2ad0 100644
--- a/params/config.go
+++ b/params/config.go
@@ -23,39 +23,43 @@ import (
 	"github.com/ethereum/go-ethereum/common"
 )
 
-// MainnetChainConfig is the chain parameters to run a node on the main network.
-var MainnetChainConfig = &ChainConfig{
-	ChainId:        MainNetChainID,
-	HomesteadBlock: MainNetHomesteadBlock,
-	DAOForkBlock:   MainNetDAOForkBlock,
-	DAOForkSupport: true,
-	EIP150Block:    MainNetHomesteadGasRepriceBlock,
-	EIP150Hash:     MainNetHomesteadGasRepriceHash,
-	EIP155Block:    MainNetSpuriousDragon,
-	EIP158Block:    MainNetSpuriousDragon,
-}
-
-// TestnetChainConfig is the chain parameters to run a node on the test network.
-var TestnetChainConfig = &ChainConfig{
-	ChainId:        big.NewInt(3),
-	HomesteadBlock: big.NewInt(0),
-	DAOForkBlock:   nil,
-	DAOForkSupport: true,
-	EIP150Block:    big.NewInt(0),
-	EIP150Hash:     common.HexToHash("0x41941023680923e0fe4d74a34bdac8141f2540e3ae90623718e47d66d1ca4a2d"),
-	EIP155Block:    big.NewInt(10),
-	EIP158Block:    big.NewInt(10),
-}
-
-// AllProtocolChanges contains every protocol change (EIPs)
-// introduced and accepted by the Ethereum core developers.
-//
-// This configuration is intentionally not using keyed fields.
-// This configuration must *always* have all forks enabled, which
-// means that all fields must be set at all times. This forces
-// anyone adding flags to the config to also have to set these
-// fields.
-var AllProtocolChanges = &ChainConfig{big.NewInt(1337), big.NewInt(0), nil, false, big.NewInt(0), common.Hash{}, big.NewInt(0), big.NewInt(0)}
+var (
+	// MainnetChainConfig is the chain parameters to run a node on the main network.
+	MainnetChainConfig = &ChainConfig{
+		ChainId:        MainNetChainID,
+		HomesteadBlock: MainNetHomesteadBlock,
+		DAOForkBlock:   MainNetDAOForkBlock,
+		DAOForkSupport: true,
+		EIP150Block:    MainNetHomesteadGasRepriceBlock,
+		EIP150Hash:     MainNetHomesteadGasRepriceHash,
+		EIP155Block:    MainNetSpuriousDragon,
+		EIP158Block:    MainNetSpuriousDragon,
+	}
+
+	// TestnetChainConfig contains the chain parameters to run a node on the ropsten test network.
+	TestnetChainConfig = &ChainConfig{
+		ChainId:        big.NewInt(3),
+		HomesteadBlock: big.NewInt(0),
+		DAOForkBlock:   nil,
+		DAOForkSupport: true,
+		EIP150Block:    big.NewInt(0),
+		EIP150Hash:     common.HexToHash("0x41941023680923e0fe4d74a34bdac8141f2540e3ae90623718e47d66d1ca4a2d"),
+		EIP155Block:    big.NewInt(10),
+		EIP158Block:    big.NewInt(10),
+	}
+
+	// AllProtocolChanges contains every protocol change (EIPs)
+	// introduced and accepted by the Ethereum core developers.
+	// TestChainConfig is like AllProtocolChanges but has chain ID 1.
+	//
+	// This configuration is intentionally not using keyed fields.
+	// This configuration must *always* have all forks enabled, which
+	// means that all fields must be set at all times. This forces
+	// anyone adding flags to the config to also have to set these
+	// fields.
+	AllProtocolChanges = &ChainConfig{big.NewInt(1337), big.NewInt(0), nil, false, big.NewInt(0), common.Hash{}, big.NewInt(0), big.NewInt(0)}
+	TestChainConfig    = &ChainConfig{big.NewInt(1), big.NewInt(0), nil, false, big.NewInt(0), common.Hash{}, big.NewInt(0), big.NewInt(0)}
+)
 
 // ChainConfig is the core config which determines the blockchain settings.
 //
@@ -77,7 +81,7 @@ type ChainConfig struct {
 	EIP158Block *big.Int `json:"eip158Block"` // EIP158 HF block
 }
 
-// String implements the Stringer interface.
+// String implements the fmt.Stringer interface.
 func (c *ChainConfig) String() string {
 	return fmt.Sprintf("{ChainID: %v Homestead: %v DAO: %v DAOSupport: %v EIP150: %v EIP155: %v EIP158: %v}",
 		c.ChainId,
@@ -90,17 +94,26 @@ func (c *ChainConfig) String() string {
 	)
 }
 
-var (
-	TestChainConfig = &ChainConfig{big.NewInt(1), new(big.Int), new(big.Int), true, new(big.Int), common.Hash{}, new(big.Int), new(big.Int)}
-	TestRules       = TestChainConfig.Rules(new(big.Int))
-)
-
 // IsHomestead returns whether num is either equal to the homestead block or greater.
 func (c *ChainConfig) IsHomestead(num *big.Int) bool {
-	if c.HomesteadBlock == nil || num == nil {
-		return false
-	}
-	return num.Cmp(c.HomesteadBlock) >= 0
+	return isForked(c.HomesteadBlock, num)
+}
+
+// IsDAO returns whether num is either equal to the DAO fork block or greater.
+func (c *ChainConfig) IsDAOFork(num *big.Int) bool {
+	return isForked(c.DAOForkBlock, num)
+}
+
+func (c *ChainConfig) IsEIP150(num *big.Int) bool {
+	return isForked(c.EIP150Block, num)
+}
+
+func (c *ChainConfig) IsEIP155(num *big.Int) bool {
+	return isForked(c.EIP155Block, num)
+}
+
+func (c *ChainConfig) IsEIP158(num *big.Int) bool {
+	return isForked(c.EIP158Block, num)
 }
 
 // GasTable returns the gas table corresponding to the current phase (homestead or homestead reprice).
@@ -110,51 +123,110 @@ func (c *ChainConfig) GasTable(num *big.Int) GasTable {
 	if num == nil {
 		return GasTableHomestead
 	}
-
 	switch {
-	case c.EIP158Block != nil && num.Cmp(c.EIP158Block) >= 0:
+	case c.IsEIP158(num):
 		return GasTableEIP158
-	case c.EIP150Block != nil && num.Cmp(c.EIP150Block) >= 0:
+	case c.IsEIP150(num):
 		return GasTableHomesteadGasRepriceFork
 	default:
 		return GasTableHomestead
 	}
 }
 
-func (c *ChainConfig) IsEIP150(num *big.Int) bool {
-	if c.EIP150Block == nil || num == nil {
-		return false
+// CheckCompatible checks whether scheduled fork transitions have been imported
+// with a mismatching chain configuration.
+func (c *ChainConfig) CheckCompatible(newcfg *ChainConfig, height uint64) *ConfigCompatError {
+	bhead := new(big.Int).SetUint64(height)
+
+	// Iterate checkCompatible to find the lowest conflict.
+	var lasterr *ConfigCompatError
+	for {
+		err := c.checkCompatible(newcfg, bhead)
+		if err == nil || (lasterr != nil && err.RewindTo == lasterr.RewindTo) {
+			break
+		}
+		lasterr = err
+		bhead.SetUint64(err.RewindTo)
 	}
-	return num.Cmp(c.EIP150Block) >= 0
-
+	return lasterr
 }
 
-func (c *ChainConfig) IsEIP155(num *big.Int) bool {
-	if c.EIP155Block == nil || num == nil {
-		return false
+func (c *ChainConfig) checkCompatible(newcfg *ChainConfig, head *big.Int) *ConfigCompatError {
+	if isForkIncompatible(c.HomesteadBlock, newcfg.HomesteadBlock, head) {
+		return newCompatError("Homestead fork block", c.HomesteadBlock, newcfg.HomesteadBlock)
+	}
+	if isForkIncompatible(c.DAOForkBlock, newcfg.DAOForkBlock, head) {
+		return newCompatError("DAO fork block", c.DAOForkBlock, newcfg.DAOForkBlock)
 	}
-	return num.Cmp(c.EIP155Block) >= 0
+	if c.IsDAOFork(head) && c.DAOForkSupport != newcfg.DAOForkSupport {
+		return newCompatError("DAO fork support flag", c.DAOForkBlock, newcfg.DAOForkBlock)
+	}
+	if isForkIncompatible(c.EIP150Block, newcfg.EIP150Block, head) {
+		return newCompatError("EIP150 fork block", c.EIP150Block, newcfg.EIP150Block)
+	}
+	if isForkIncompatible(c.EIP155Block, newcfg.EIP155Block, head) {
+		return newCompatError("EIP155 fork block", c.EIP155Block, newcfg.EIP155Block)
+	}
+	if isForkIncompatible(c.EIP158Block, newcfg.EIP158Block, head) {
+		return newCompatError("EIP158 fork block", c.EIP158Block, newcfg.EIP158Block)
+	}
+	if c.IsEIP158(head) && !configNumEqual(c.ChainId, newcfg.ChainId) {
+		return newCompatError("EIP158 chain ID", c.EIP158Block, newcfg.EIP158Block)
+	}
+	return nil
+}
 
+// isForkIncompatible returns true if a fork scheduled at s1 cannot be rescheduled to
+// block s2 because head is already past the fork.
+func isForkIncompatible(s1, s2, head *big.Int) bool {
+	return (isForked(s1, head) || isForked(s2, head)) && !configNumEqual(s1, s2)
 }
 
-func (c *ChainConfig) IsEIP158(num *big.Int) bool {
-	if c.EIP158Block == nil || num == nil {
+// isForked returns whether a fork scheduled at block s is active at the given head block.
+func isForked(s, head *big.Int) bool {
+	if s == nil || head == nil {
 		return false
 	}
-	return num.Cmp(c.EIP158Block) >= 0
+	return s.Cmp(head) <= 0
+}
 
+func configNumEqual(x, y *big.Int) bool {
+	if x == nil {
+		return y == nil
+	}
+	if y == nil {
+		return x == nil
+	}
+	return x.Cmp(y) == 0
 }
 
-// Rules wraps ChainConfig and is merely syntatic sugar or can be used for functions
-// that do not have or require information about the block.
-//
-// Rules is a one time interface meaning that it shouldn't be used in between transition
-// phases.
-type Rules struct {
-	ChainId                                   *big.Int
-	IsHomestead, IsEIP150, IsEIP155, IsEIP158 bool
+// ConfigCompatError is raised if the locally-stored blockchain is initialised with a
+// ChainConfig that would alter the past.
+type ConfigCompatError struct {
+	What string
+	// block numbers of the stored and new configurations
+	StoredConfig, NewConfig *big.Int
+	// the block number to which the local chain must be rewound to correct the error
+	RewindTo uint64
+}
+
+func newCompatError(what string, storedblock, newblock *big.Int) *ConfigCompatError {
+	var rew *big.Int
+	switch {
+	case storedblock == nil:
+		rew = newblock
+	case newblock == nil || storedblock.Cmp(newblock) < 0:
+		rew = storedblock
+	default:
+		rew = newblock
+	}
+	err := &ConfigCompatError{what, storedblock, newblock, 0}
+	if rew != nil && rew.Sign() > 0 {
+		err.RewindTo = rew.Uint64() - 1
+	}
+	return err
 }
 
-func (c *ChainConfig) Rules(num *big.Int) Rules {
-	return Rules{ChainId: new(big.Int).Set(c.ChainId), IsHomestead: c.IsHomestead(num), IsEIP150: c.IsEIP150(num), IsEIP155: c.IsEIP155(num), IsEIP158: c.IsEIP158(num)}
+func (err *ConfigCompatError) Error() string {
+	return fmt.Sprintf("mismatching %s in database (have %d, want %d, rewindto %d)", err.What, err.StoredConfig, err.NewConfig, err.RewindTo)
 }