core: more tests for sidechain import, fixes #19105 (#19113)

* blockchain: more tests for sidechain import, fixes #19105

* core/blockchain: rework import of pruned canon blocks and canon-prepended sidechains

* core/blockchain: minor clarity change

* core/blockchain: remove unused method

core/blockchain_test.go

@@ -1521,3 +1521,85 @@ func TestLowDiffLongChain(t *testing.T) {
 		header = chain.GetHeader(header.ParentHash, number-1)
 	}
 }
+
+// Tests that importing a sidechain (S), where
+// - S is sidechain, containing blocks [Sn...Sm]
+// - C is canon chain, containing blocks [G..Cn..Cm]
+// - A common ancestor is placed at prune-point + blocksBetweenCommonAncestorAndPruneblock
+// - The sidechain S is prepended with numCanonBlocksInSidechain blocks from the canon chain
+func testSideImport(t *testing.T, numCanonBlocksInSidechain, blocksBetweenCommonAncestorAndPruneblock int) {
+
+	// Generate a canonical chain to act as the main dataset
+	engine := ethash.NewFaker()
+	db := ethdb.NewMemDatabase()
+	genesis := new(Genesis).MustCommit(db)
+
+	// Generate and import the canonical chain
+	blocks, _ := GenerateChain(params.TestChainConfig, genesis, engine, db, 2*triesInMemory, nil)
+	diskdb := ethdb.NewMemDatabase()
+	new(Genesis).MustCommit(diskdb)
+	chain, err := NewBlockChain(diskdb, nil, params.TestChainConfig, engine, vm.Config{}, nil)
+	if err != nil {
+		t.Fatalf("failed to create tester chain: %v", err)
+	}
+	if n, err := chain.InsertChain(blocks); err != nil {
+		t.Fatalf("block %d: failed to insert into chain: %v", n, err)
+	}
+
+	lastPrunedIndex := len(blocks) - triesInMemory - 1
+	lastPrunedBlock := blocks[lastPrunedIndex]
+	firstNonPrunedBlock := blocks[len(blocks)-triesInMemory]
+
+	// Verify pruning of lastPrunedBlock
+	if chain.HasBlockAndState(lastPrunedBlock.Hash(), lastPrunedBlock.NumberU64()) {
+		t.Errorf("Block %d not pruned", lastPrunedBlock.NumberU64())
+	}
+	// Verify firstNonPrunedBlock is not pruned
+	if !chain.HasBlockAndState(firstNonPrunedBlock.Hash(), firstNonPrunedBlock.NumberU64()) {
+		t.Errorf("Block %d pruned", firstNonPrunedBlock.NumberU64())
+	}
+	// Generate the sidechain
+	// First block should be a known block, block after should be a pruned block. So
+	// canon(pruned), side, side...
+
+	// Generate fork chain, make it longer than canon
+	parentIndex := lastPrunedIndex + blocksBetweenCommonAncestorAndPruneblock
+	parent := blocks[parentIndex]
+	fork, _ := GenerateChain(params.TestChainConfig, parent, engine, db, 2*triesInMemory, func(i int, b *BlockGen) {
+		b.SetCoinbase(common.Address{2})
+	})
+	// Prepend the parent(s)
+	var sidechain []*types.Block
+	for i := numCanonBlocksInSidechain; i > 0; i-- {
+		sidechain = append(sidechain, blocks[parentIndex+1-i])
+	}
+	sidechain = append(sidechain, fork...)
+	_, err = chain.InsertChain(sidechain)
+	if err != nil {
+		t.Errorf("Got error, %v", err)
+	}
+	head := chain.CurrentBlock()
+	if got := fork[len(fork)-1].Hash(); got != head.Hash() {
+		t.Fatalf("head wrong, expected %x got %x", head.Hash(), got)
+	}
+}
+
+// Tests that importing a sidechain (S), where
+// - S is sidechain, containing blocks [Sn...Sm]
+// - C is canon chain, containing blocks [G..Cn..Cm]
+// - The common ancestor Cc is pruned
+// - The first block in S: Sn, is == Cn
+// That is: the sidechain for import contains some blocks already present in canon chain.
+// So the blocks are
+// [ Cn, Cn+1, Cc, Sn+3 ... Sm]
+//   ^    ^    ^  pruned
+func TestPrunedImportSide(t *testing.T) {
+	//glogger := log.NewGlogHandler(log.StreamHandler(os.Stdout, log.TerminalFormat(false)))
+	//glogger.Verbosity(3)
+	//log.Root().SetHandler(log.Handler(glogger))
+	testSideImport(t, 3, 3)
+	testSideImport(t, 3, -3)
+	testSideImport(t, 10, 0)
+	testSideImport(t, 1, 10)
+	testSideImport(t, 1, -10)
+}