netsync: add checkHeadersList

diff --git a/netsync/manager.go b/netsync/manager.go
index d10188d..480eead 100644
--- a/netsync/manager.go
+++ b/netsync/manager.go
@@ -690,6 +690,47 @@ func (sm *SyncManager) current() bool {
 	return true
 }
 
+// checkHeadersList checks if the sync manager is in the initial block download
+// mode and returns if the given block hash is a checkpointed block and the
+// behavior flags for this block.  If the block is still under the checkpoint,
+// then it's given the fast-add flag.
+func (sm *SyncManager) checkHeadersList(blockHash *chainhash.Hash) (
+	bool, blockchain.BehaviorFlags) {
+
+	// Always return false and BFNone if we're not in ibd mode.
+	if !sm.headersFirstMode {
+		return false, blockchain.BFNone
+	}
+
+	isCheckpointBlock := false
+	behaviorFlags := blockchain.BFNone
+
+	// If we don't already know this is a valid header, return false and
+	// BFNone.
+	if !sm.chain.IsValidHeader(blockHash) {
+		return false, blockchain.BFNone
+	}
+
+	height, err := sm.chain.HeaderHeightByHash(*blockHash)
+	if err != nil {
+		return false, blockchain.BFNone
+	}
+
+	// Since findNextHeaderCheckpoint returns the next checkpoint after the
+	// passed height, we do a -1 to include the current block.
+	checkpoint := sm.findNextHeaderCheckpoint(height - 1)
+	if checkpoint == nil {
+		return false, blockchain.BFNone
+	}
+
+	behaviorFlags |= blockchain.BFFastAdd
+	if blockHash.IsEqual(checkpoint.Hash) {
+		isCheckpointBlock = true
+	}
+
+	return isCheckpointBlock, behaviorFlags
+}
+
 // handleBlockMsg handles block messages from all peers.
 func (sm *SyncManager) handleBlockMsg(bmsg *blockMsg) {
 	peer := bmsg.peer
diff --git a/netsync/manager_test.go b/netsync/manager_test.go
new file mode 100644
index 0000000..ee84cea
--- /dev/null
+++ b/netsync/manager_test.go
@@ -0,0 +1,228 @@
+package netsync
+
+import (
+	"bufio"
+	"bytes"
+	"encoding/hex"
+	"fmt"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/btcsuite/btcd/blockchain"
+	"github.com/btcsuite/btcd/btcutil"
+	"github.com/btcsuite/btcd/chaincfg"
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
+	"github.com/btcsuite/btcd/database"
+	_ "github.com/btcsuite/btcd/database/ffldb"
+	"github.com/btcsuite/btcd/mempool"
+	"github.com/btcsuite/btcd/peer"
+	"github.com/btcsuite/btcd/txscript"
+	"github.com/btcsuite/btcd/wire"
+	"github.com/stretchr/testify/require"
+)
+
+// noopPeerNotifier is a no-op implementation of PeerNotifier for tests.
+type noopPeerNotifier struct{}
+
+func (noopPeerNotifier) AnnounceNewTransactions([]*mempool.TxDesc)            {}
+func (noopPeerNotifier) UpdatePeerHeights(*chainhash.Hash, int32, *peer.Peer) {}
+func (noopPeerNotifier) RelayInventory(*wire.InvVect, interface{})            {}
+func (noopPeerNotifier) TransactionConfirmed(*btcutil.Tx)                     {}
+
+// dbSetup is used to create a new db with the genesis block already inserted.
+// It returns a teardown function the caller should invoke when done testing to
+// clean up.  The database is stored under t.TempDir() which is automatically
+// removed when the test finishes.
+func dbSetup(t *testing.T, params *chaincfg.Params) (database.DB, func(), error) {
+	dbPath := filepath.Join(t.TempDir(), "ffldb")
+	db, err := database.Create("ffldb", dbPath, params.Net)
+	if err != nil {
+		return nil, nil, fmt.Errorf("error creating db: %v", err)
+	}
+
+	teardown := func() {
+		db.Close()
+	}
+
+	return db, teardown, nil
+}
+
+// chainSetup is used to create a new db and chain instance with the genesis
+// block already inserted.  In addition to the new chain instance, it returns
+// a teardown function the caller should invoke when done testing to clean up.
+func chainSetup(t *testing.T, params *chaincfg.Params) (
+	*blockchain.BlockChain, func(), error) {
+
+	db, teardown, err := dbSetup(t, params)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	// Copy the chain params to ensure any modifications the tests do to
+	// the chain parameters do not affect the global instance.
+	paramsCopy := *params
+
+	// Deep-copy deployment starters/enders so that parallel tests don't
+	// race on the shared blockClock field written by SynchronizeClock.
+	for i := range paramsCopy.Deployments {
+		d := &paramsCopy.Deployments[i]
+		if s, ok := d.DeploymentStarter.(*chaincfg.MedianTimeDeploymentStarter); ok {
+			d.DeploymentStarter = chaincfg.NewMedianTimeDeploymentStarter(
+				s.StartTime())
+		}
+		if e, ok := d.DeploymentEnder.(*chaincfg.MedianTimeDeploymentEnder); ok {
+			d.DeploymentEnder = chaincfg.NewMedianTimeDeploymentEnder(
+				e.EndTime())
+		}
+	}
+
+	// Create the main chain instance.
+	chain, err := blockchain.New(&blockchain.Config{
+		DB:          db,
+		Checkpoints: paramsCopy.Checkpoints,
+		ChainParams: &paramsCopy,
+		TimeSource:  blockchain.NewMedianTime(),
+		SigCache:    txscript.NewSigCache(1000),
+	})
+	if err != nil {
+		teardown()
+		err := fmt.Errorf("failed to create chain instance: %v", err)
+		return nil, nil, err
+	}
+	return chain, teardown, nil
+}
+
+// loadHeaders loads headers from mainnet from 1 to 11.
+func loadHeaders(t *testing.T) []*wire.BlockHeader {
+	testFile := "blockheaders-mainnet-1-11.txt"
+	filename := filepath.Join("testdata/", testFile)
+
+	file, err := os.Open(filename)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	headers := make([]*wire.BlockHeader, 0, 10)
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		line := scanner.Text()
+		b, err := hex.DecodeString(line)
+		if err != nil {
+			t.Fatalf("failed to read block headers from file %v", testFile)
+		}
+
+		r := bytes.NewReader(b)
+		header := new(wire.BlockHeader)
+		header.Deserialize(r)
+
+		headers = append(headers, header)
+	}
+
+	return headers
+}
+
+func makeMockSyncManager(t *testing.T,
+	params *chaincfg.Params) (*SyncManager, func()) {
+
+	t.Helper()
+
+	chain, tearDown, err := chainSetup(t, params)
+	require.NoError(t, err)
+
+	sm, err := New(&Config{
+		PeerNotifier: noopPeerNotifier{},
+		Chain:        chain,
+		ChainParams:  params,
+	})
+	require.NoError(t, err)
+
+	return sm, tearDown
+}
+
+func TestCheckHeadersList(t *testing.T) {
+	// Set params to mainnet with a checkpoint at block 11.
+	params := chaincfg.MainNetParams
+	checkpointHeight := int32(11)
+	checkpointHash, err := chainhash.NewHashFromStr(
+		"0000000097be56d606cdd9c54b04d4747e957d3608abe69198c661f2add73073")
+	if err != nil {
+		t.Fatal(err)
+	}
+	params.Checkpoints = []chaincfg.Checkpoint{
+		{
+			Height: checkpointHeight,
+			Hash:   checkpointHash,
+		},
+	}
+
+	// Create mock SyncManager.
+	sm, tearDown := makeMockSyncManager(t, &params)
+	defer tearDown()
+
+	// Setup SyncManager with headers processed.
+	headers := loadHeaders(t)
+	for _, header := range headers {
+		isMainChain, err := sm.chain.ProcessBlockHeader(
+			header, blockchain.BFNone, false)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if !isMainChain {
+			t.Fatalf("expected block header %v to be in the main chain",
+				header.BlockHash())
+		}
+	}
+
+	tests := []struct {
+		hash              string
+		isCheckpointBlock bool
+		behaviorFlags     blockchain.BehaviorFlags
+	}{
+		{
+			hash:              chaincfg.MainNetParams.GenesisHash.String(),
+			isCheckpointBlock: false,
+			behaviorFlags:     blockchain.BFFastAdd,
+		},
+		{
+			// Block 10.
+			hash:              "000000002c05cc2e78923c34df87fd108b22221ac6076c18f3ade378a4d915e9",
+			isCheckpointBlock: false,
+			behaviorFlags:     blockchain.BFFastAdd,
+		},
+		{
+			// Block 11.
+			hash:              "0000000097be56d606cdd9c54b04d4747e957d3608abe69198c661f2add73073",
+			isCheckpointBlock: true,
+			behaviorFlags:     blockchain.BFFastAdd,
+		},
+		{
+			// Block 12.
+			hash:              "0000000027c2488e2510d1acf4369787784fa20ee084c258b58d9fbd43802b5e",
+			isCheckpointBlock: false,
+			behaviorFlags:     blockchain.BFNone,
+		},
+	}
+
+	for _, test := range tests {
+		hash, err := chainhash.NewHashFromStr(test.hash)
+		if err != nil {
+			t.Errorf("NewHashFromStr: %v", err)
+			continue
+		}
+
+		// Make sure that when the headers-first mode is off, we always get
+		// false and BFNone.
+		sm.headersFirstMode = false
+		isCheckpoint, gotFlags := sm.checkHeadersList(hash)
+		require.Equal(t, false, isCheckpoint)
+		require.Equal(t, blockchain.BFNone, gotFlags)
+
+		// Now check that the test values are correct.
+		sm.headersFirstMode = true
+		isCheckpoint, gotFlags = sm.checkHeadersList(hash)
+		require.Equal(t, test.isCheckpointBlock, isCheckpoint)
+		require.Equal(t, test.behaviorFlags, gotFlags)
+	}
+}
diff --git a/netsync/testdata/blockheaders-mainnet-1-11.txt b/netsync/testdata/blockheaders-mainnet-1-11.txt
new file mode 100644
index 0000000..27b5f18
--- /dev/null
+++ b/netsync/testdata/blockheaders-mainnet-1-11.txt
@@ -0,0 +1,11 @@
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+010000004860eb18bf1b1620e37e9490fc8a427514416fd75159ab86688e9a8300000000d5fdcc541e25de1c7a5addedf24858b8bb665c9f36ef744ee42c316022c90f9bb0bc6649ffff001d08d2bd61
+01000000bddd99ccfda39da1b108ce1a5d70038d0a967bacb68b6b63065f626a0000000044f672226090d85db9a9f2fbfe5f0f9609b387af7be5b7fbb7a1767c831c9e995dbe6649ffff001d05e0ed6d
+010000004944469562ae1c2c74d9a535e00b6f3e40ffbad4f2fda3895501b582000000007a06ea98cd40ba2e3288262b28638cec5337c1456aaf5eedc8e9e5a20f062bdf8cc16649ffff001d2bfee0a9
+0100000085144a84488ea88d221c8bd6c059da090e88f8a2c99690ee55dbba4e00000000e11c48fecdd9e72510ca84f023370c9a38bf91ac5cae88019bee94d24528526344c36649ffff001d1d03e477
+01000000fc33f596f822a0a1951ffdbf2a897b095636ad871707bf5d3162729b00000000379dfb96a5ea8c81700ea4ac6b97ae9a9312b2d4301a29580e924ee6761a2520adc46649ffff001d189c4c97
+010000008d778fdc15a2d3fb76b7122a3b5582bea4f21f5a0c693537e7a03130000000003f674005103b42f984169c7d008370967e91920a6a5d64fd51282f75bc73a68af1c66649ffff001d39a59c86
+010000004494c8cf4154bdcc0720cd4a59d9c9b285e4b146d45f061d2b6c967100000000e3855ed886605b6d4a99d5fa2ef2e9b0b164e63df3c4136bebf2d0dac0f1f7a667c86649ffff001d1c4b5666
+01000000c60ddef1b7618ca2348a46e868afc26e3efc68226c78aa47f8488c4000000000c997a5e56e104102fa209c6a852dd90660a20b2d9c352423edce25857fcd37047fca6649ffff001d28404f53
+010000000508085c47cc849eb80ea905cc7800a3be674ffc57263cf210c59d8d00000000112ba175a1e04b14ba9e7ea5f76ab640affeef5ec98173ac9799a852fa39add320cd6649ffff001d1e2de565
+01000000e915d9a478e3adf3186c07c61a22228b10fd87df343c92782ecc052c000000006e06373c80de397406dc3d19c90d71d230058d28293614ea58d6a57f8f5d32f8b8ce6649ffff001d173807f8