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, 8 insertions, 4 deletions

diff --git a/core/bench_test.go b/core/bench_test.go
index 42d50a7b1..a154ccbb1 100644
--- a/core/bench_test.go
+++ b/core/bench_test.go
@@ -166,13 +166,17 @@ func benchInsertChain(b *testing.B, disk bool, gen func(int, *BlockGen)) {
 
 	// Generate a chain of b.N blocks using the supplied block
 	// generator function.
-	genesis := WriteGenesisBlockForTesting(db, GenesisAccount{benchRootAddr, benchRootFunds})
-	chain, _ := GenerateChain(params.TestChainConfig, genesis, db, b.N, gen)
+	gspec := Genesis{
+		Config: params.TestChainConfig,
+		Alloc:  GenesisAlloc{benchRootAddr: {Balance: benchRootFunds}},
+	}
+	genesis := gspec.MustCommit(db)
+	chain, _ := GenerateChain(gspec.Config, genesis, db, b.N, gen)
 
 	// Time the insertion of the new chain.
 	// State and blocks are stored in the same DB.
 	evmux := new(event.TypeMux)
-	chainman, _ := NewBlockChain(db, &params.ChainConfig{HomesteadBlock: new(big.Int)}, pow.FakePow{}, evmux, vm.Config{})
+	chainman, _ := NewBlockChain(db, gspec.Config, pow.FakePow{}, evmux, vm.Config{})
 	defer chainman.Stop()
 	b.ReportAllocs()
 	b.ResetTimer()
@@ -282,7 +286,7 @@ func benchReadChain(b *testing.B, full bool, count uint64) {
 		if err != nil {
 			b.Fatalf("error opening database at %v: %v", dir, err)
 		}
-		chain, err := NewBlockChain(db, testChainConfig(), pow.FakePow{}, new(event.TypeMux), vm.Config{})
+		chain, err := NewBlockChain(db, params.TestChainConfig, pow.FakePow{}, new(event.TypeMux), vm.Config{})
 		if err != nil {
 			b.Fatalf("error creating chain: %v", err)
 		}