Merge pull request #793 from karalabe/discovery-node-cache

p2p/discover: persistent node database

1 files changed, 304 insertions, 0 deletions

diff --git a/p2p/discover/database.go b/p2p/discover/database.go
new file mode 100644
index 000000000..d966a6ac1
--- /dev/null
+++ b/p2p/discover/database.go
@@ -0,0 +1,304 @@
+// Contains the node database, storing previously seen nodes and any collected
+// metadata about them for QoS purposes.
+
+package discover
+
+import (
+	"bytes"
+	"encoding/binary"
+	"os"
+	"sync"
+	"time"
+
+	"github.com/ethereum/go-ethereum/logger"
+	"github.com/ethereum/go-ethereum/logger/glog"
+	"github.com/ethereum/go-ethereum/rlp"
+	"github.com/syndtr/goleveldb/leveldb"
+	"github.com/syndtr/goleveldb/leveldb/iterator"
+	"github.com/syndtr/goleveldb/leveldb/storage"
+)
+
+var (
+	nodeDBNilNodeID      = NodeID{}       // Special node ID to use as a nil element.
+	nodeDBNodeExpiration = 24 * time.Hour // Time after which an unseen node should be dropped.
+	nodeDBCleanupCycle   = time.Hour      // Time period for running the expiration task.
+)
+
+// nodeDB stores all nodes we know about.
+type nodeDB struct {
+	lvl    *leveldb.DB       // Interface to the database itself
+	seeder iterator.Iterator // Iterator for fetching possible seed nodes
+
+	runner sync.Once     // Ensures we can start at most one expirer
+	quit   chan struct{} // Channel to signal the expiring thread to stop
+}
+
+// Schema layout for the node database
+var (
+	nodeDBVersionKey = []byte("version") // Version of the database to flush if changes
+	nodeDBItemPrefix = []byte("n:")      // Identifier to prefix node entries with
+
+	nodeDBDiscoverRoot = ":discover"
+	nodeDBDiscoverPing = nodeDBDiscoverRoot + ":lastping"
+	nodeDBDiscoverPong = nodeDBDiscoverRoot + ":lastpong"
+)
+
+// newNodeDB creates a new node database for storing and retrieving infos about
+// known peers in the network. If no path is given, an in-memory, temporary
+// database is constructed.
+func newNodeDB(path string, version int) (*nodeDB, error) {
+	if path == "" {
+		return newMemoryNodeDB()
+	}
+	return newPersistentNodeDB(path, version)
+}
+
+// newMemoryNodeDB creates a new in-memory node database without a persistent
+// backend.
+func newMemoryNodeDB() (*nodeDB, error) {
+	db, err := leveldb.Open(storage.NewMemStorage(), nil)
+	if err != nil {
+		return nil, err
+	}
+	return &nodeDB{
+		lvl:  db,
+		quit: make(chan struct{}),
+	}, nil
+}
+
+// newPersistentNodeDB creates/opens a leveldb backed persistent node database,
+// also flushing its contents in case of a version mismatch.
+func newPersistentNodeDB(path string, version int) (*nodeDB, error) {
+	// Try to open the cache, recovering any corruption
+	db, err := leveldb.OpenFile(path, nil)
+	if _, iscorrupted := err.(leveldb.ErrCorrupted); iscorrupted {
+		db, err = leveldb.RecoverFile(path, nil)
+	}
+	if err != nil {
+		return nil, err
+	}
+	// The nodes contained in the cache correspond to a certain protocol version.
+	// Flush all nodes if the version doesn't match.
+	currentVer := make([]byte, binary.MaxVarintLen64)
+	currentVer = currentVer[:binary.PutVarint(currentVer, int64(version))]
+
+	blob, err := db.Get(nodeDBVersionKey, nil)
+	switch err {
+	case leveldb.ErrNotFound:
+		// Version not found (i.e. empty cache), insert it
+		if err := db.Put(nodeDBVersionKey, currentVer, nil); err != nil {
+			db.Close()
+			return nil, err
+		}
+
+	case nil:
+		// Version present, flush if different
+		if !bytes.Equal(blob, currentVer) {
+			db.Close()
+			if err = os.RemoveAll(path); err != nil {
+				return nil, err
+			}
+			return newPersistentNodeDB(path, version)
+		}
+	}
+	return &nodeDB{
+		lvl:  db,
+		quit: make(chan struct{}),
+	}, nil
+}
+
+// makeKey generates the leveldb key-blob from a node id and its particular
+// field of interest.
+func makeKey(id NodeID, field string) []byte {
+	if bytes.Equal(id[:], nodeDBNilNodeID[:]) {
+		return []byte(field)
+	}
+	return append(nodeDBItemPrefix, append(id[:], field...)...)
+}
+
+// splitKey tries to split a database key into a node id and a field part.
+func splitKey(key []byte) (id NodeID, field string) {
+	// If the key is not of a node, return it plainly
+	if !bytes.HasPrefix(key, nodeDBItemPrefix) {
+		return NodeID{}, string(key)
+	}
+	// Otherwise split the id and field
+	item := key[len(nodeDBItemPrefix):]
+	copy(id[:], item[:len(id)])
+	field = string(item[len(id):])
+
+	return id, field
+}
+
+// fetchInt64 retrieves an integer instance associated with a particular
+// database key.
+func (db *nodeDB) fetchInt64(key []byte) int64 {
+	blob, err := db.lvl.Get(key, nil)
+	if err != nil {
+		return 0
+	}
+	val, read := binary.Varint(blob)
+	if read <= 0 {
+		return 0
+	}
+	return val
+}
+
+// storeInt64 update a specific database entry to the current time instance as a
+// unix timestamp.
+func (db *nodeDB) storeInt64(key []byte, n int64) error {
+	blob := make([]byte, binary.MaxVarintLen64)
+	blob = blob[:binary.PutVarint(blob, n)]
+
+	return db.lvl.Put(key, blob, nil)
+}
+
+// node retrieves a node with a given id from the database.
+func (db *nodeDB) node(id NodeID) *Node {
+	blob, err := db.lvl.Get(makeKey(id, nodeDBDiscoverRoot), nil)
+	if err != nil {
+		glog.V(logger.Detail).Infof("failed to retrieve node %v: %v", id, err)
+		return nil
+	}
+	node := new(Node)
+	if err := rlp.DecodeBytes(blob, node); err != nil {
+		glog.V(logger.Warn).Infof("failed to decode node RLP: %v", err)
+		return nil
+	}
+	return node
+}
+
+// updateNode inserts - potentially overwriting - a node into the peer database.
+func (db *nodeDB) updateNode(node *Node) error {
+	blob, err := rlp.EncodeToBytes(node)
+	if err != nil {
+		return err
+	}
+	return db.lvl.Put(makeKey(node.ID, nodeDBDiscoverRoot), blob, nil)
+}
+
+// ensureExpirer is a small helper method ensuring that the data expiration
+// mechanism is running. If the expiration goroutine is already running, this
+// method simply returns.
+//
+// The goal is to start the data evacuation only after the network successfully
+// bootstrapped itself (to prevent dumping potentially useful seed nodes). Since
+// it would require significant overhead to exactly trace the first successful
+// convergence, it's simpler to "ensure" the correct state when an appropriate
+// condition occurs (i.e. a successful bonding), and discard further events.
+func (db *nodeDB) ensureExpirer() {
+	db.runner.Do(func() { go db.expirer() })
+}
+
+// expirer should be started in a go routine, and is responsible for looping ad
+// infinitum and dropping stale data from the database.
+func (db *nodeDB) expirer() {
+	tick := time.Tick(nodeDBCleanupCycle)
+	for {
+		select {
+		case <-tick:
+			if err := db.expireNodes(); err != nil {
+				glog.V(logger.Error).Infof("Failed to expire nodedb items: %v", err)
+			}
+
+		case <-db.quit:
+			return
+		}
+	}
+}
+
+// expireNodes iterates over the database and deletes all nodes that have not
+// been seen (i.e. received a pong from) for some alloted time.
+func (db *nodeDB) expireNodes() error {
+	threshold := time.Now().Add(-nodeDBNodeExpiration)
+
+	// Find discovered nodes that are older than the allowance
+	it := db.lvl.NewIterator(nil, nil)
+	defer it.Release()
+
+	for it.Next() {
+		// Skip the item if not a discovery node
+		id, field := splitKey(it.Key())
+		if field != nodeDBDiscoverRoot {
+			continue
+		}
+		// Skip the node if not expired yet
+		if seen := db.lastPong(id); seen.After(threshold) {
+			continue
+		}
+		// Otherwise delete all associated information
+		prefix := makeKey(id, "")
+		for ok := it.Seek(prefix); ok && bytes.HasPrefix(it.Key(), prefix); ok = it.Next() {
+			if err := db.lvl.Delete(it.Key(), nil); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// lastPing retrieves the time of the last ping packet send to a remote node,
+// requesting binding.
+func (db *nodeDB) lastPing(id NodeID) time.Time {
+	return time.Unix(db.fetchInt64(makeKey(id, nodeDBDiscoverPing)), 0)
+}
+
+// updateLastPing updates the last time we tried contacting a remote node.
+func (db *nodeDB) updateLastPing(id NodeID, instance time.Time) error {
+	return db.storeInt64(makeKey(id, nodeDBDiscoverPing), instance.Unix())
+}
+
+// lastPong retrieves the time of the last successful contact from remote node.
+func (db *nodeDB) lastPong(id NodeID) time.Time {
+	return time.Unix(db.fetchInt64(makeKey(id, nodeDBDiscoverPong)), 0)
+}
+
+// updateLastPong updates the last time a remote node successfully contacted.
+func (db *nodeDB) updateLastPong(id NodeID, instance time.Time) error {
+	return db.storeInt64(makeKey(id, nodeDBDiscoverPong), instance.Unix())
+}
+
+// querySeeds retrieves a batch of nodes to be used as potential seed servers
+// during bootstrapping the node into the network.
+//
+// Ideal seeds are the most recently seen nodes (highest probability to be still
+// alive), but yet untried. However, since leveldb only supports dumb iteration
+// we will instead start pulling in potential seeds that haven't been yet pinged
+// since the start of the boot procedure.
+//
+// If the database runs out of potential seeds, we restart the startup counter
+// and start iterating over the peers again.
+func (db *nodeDB) querySeeds(n int) []*Node {
+	// Create a new seed iterator if none exists
+	if db.seeder == nil {
+		db.seeder = db.lvl.NewIterator(nil, nil)
+	}
+	// Iterate over the nodes and find suitable seeds
+	nodes := make([]*Node, 0, n)
+	for len(nodes) < n && db.seeder.Next() {
+		// Iterate until a discovery node is found
+		id, field := splitKey(db.seeder.Key())
+		if field != nodeDBDiscoverRoot {
+			continue
+		}
+		// Load it as a potential seed
+		if node := db.node(id); node != nil {
+			nodes = append(nodes, node)
+		}
+	}
+	// Release the iterator if we reached the end
+	if len(nodes) == 0 {
+		db.seeder.Release()
+		db.seeder = nil
+	}
+	return nodes
+}
+
+// close flushes and closes the database files.
+func (db *nodeDB) close() {
+	if db.seeder != nil {
+		db.seeder.Release()
+	}
+	close(db.quit)
+	db.lvl.Close()
+}