eth/downloader: speed up tests by generating chain only once (#17916)

* core: speed up GenerateChain

Use a mock implementation of ChainReader instead of creating
and destroying a BlockChain object for each generated block.

* eth/downloader: speed up tests by generating chain only once

This change reworks the downloader tests so they share a common test
blockchain instead of generating a chain in every test. The tests are
roughly twice as fast now.

1 files changed, 28 insertions, 16 deletions

diff --git a/core/chain_makers.go b/core/chain_makers.go
index 0bc453fdf..e3a5537a4 100644
--- a/core/chain_makers.go
+++ b/core/chain_makers.go
@@ -33,12 +33,11 @@ import (
 // BlockGen creates blocks for testing.
 // See GenerateChain for a detailed explanation.
 type BlockGen struct {
-	i           int
-	parent      *types.Block
-	chain       []*types.Block
-	chainReader consensus.ChainReader
-	header      *types.Header
-	statedb     *state.StateDB
+	i       int
+	parent  *types.Block
+	chain   []*types.Block
+	header  *types.Header
+	statedb *state.StateDB
 
 	gasPool  *GasPool
 	txs      []*types.Transaction
@@ -138,7 +137,7 @@ func (b *BlockGen) AddUncle(h *types.Header) {
 // For index -1, PrevBlock returns the parent block given to GenerateChain.
 func (b *BlockGen) PrevBlock(index int) *types.Block {
 	if index >= b.i {
-		panic("block index out of range")
+		panic(fmt.Errorf("block index %d out of range (%d,%d)", index, -1, b.i))
 	}
 	if index == -1 {
 		return b.parent
@@ -154,7 +153,8 @@ func (b *BlockGen) OffsetTime(seconds int64) {
 	if b.header.Time.Cmp(b.parent.Header().Time) <= 0 {
 		panic("block time out of range")
 	}
-	b.header.Difficulty = b.engine.CalcDifficulty(b.chainReader, b.header.Time.Uint64(), b.parent.Header())
+	chainreader := &fakeChainReader{config: b.config}
+	b.header.Difficulty = b.engine.CalcDifficulty(chainreader, b.header.Time.Uint64(), b.parent.Header())
 }
 
 // GenerateChain creates a chain of n blocks. The first block's
@@ -174,14 +174,10 @@ func GenerateChain(config *params.ChainConfig, parent *types.Block, engine conse
 		config = params.TestChainConfig
 	}
 	blocks, receipts := make(types.Blocks, n), make([]types.Receipts, n)
+	chainreader := &fakeChainReader{config: config}
 	genblock := func(i int, parent *types.Block, statedb *state.StateDB) (*types.Block, types.Receipts) {
-		// TODO(karalabe): This is needed for clique, which depends on multiple blocks.
-		// It's nonetheless ugly to spin up a blockchain here. Get rid of this somehow.
-		blockchain, _ := NewBlockChain(db, nil, config, engine, vm.Config{}, nil)
-		defer blockchain.Stop()
-
-		b := &BlockGen{i: i, parent: parent, chain: blocks, chainReader: blockchain, statedb: statedb, config: config, engine: engine}
-		b.header = makeHeader(b.chainReader, parent, statedb, b.engine)
+		b := &BlockGen{i: i, chain: blocks, parent: parent, statedb: statedb, config: config, engine: engine}
+		b.header = makeHeader(chainreader, parent, statedb, b.engine)
 
 		// Mutate the state and block according to any hard-fork specs
 		if daoBlock := config.DAOForkBlock; daoBlock != nil {
@@ -201,7 +197,7 @@ func GenerateChain(config *params.ChainConfig, parent *types.Block, engine conse
 		}
 		if b.engine != nil {
 			// Finalize and seal the block
-			block, _ := b.engine.Finalize(b.chainReader, b.header, statedb, b.txs, b.uncles, b.receipts)
+			block, _ := b.engine.Finalize(chainreader, b.header, statedb, b.txs, b.uncles, b.receipts)
 
 			// Write state changes to db
 			root, err := statedb.Commit(config.IsEIP158(b.header.Number))
@@ -269,3 +265,19 @@ func makeBlockChain(parent *types.Block, n int, engine consensus.Engine, db ethd
 	})
 	return blocks
 }
+
+type fakeChainReader struct {
+	config  *params.ChainConfig
+	genesis *types.Block
+}
+
+// Config returns the chain configuration.
+func (cr *fakeChainReader) Config() *params.ChainConfig {
+	return cr.config
+}
+
+func (cr *fakeChainReader) CurrentHeader() *types.Header                            { return nil }
+func (cr *fakeChainReader) GetHeaderByNumber(number uint64) *types.Header           { return nil }
+func (cr *fakeChainReader) GetHeaderByHash(hash common.Hash) *types.Header          { return nil }
+func (cr *fakeChainReader) GetHeader(hash common.Hash, number uint64) *types.Header { return nil }
+func (cr *fakeChainReader) GetBlock(hash common.Hash, number uint64) *types.Block   { return nil }