1 files changed, 233 insertions, 0 deletions
diff --git a/p2p/discover/database.go b/p2p/discover/database.go
new file mode 100644
index 000000000..93a2ded24
--- /dev/null
+++ b/p2p/discover/database.go
@@ -0,0 +1,233 @@
+// Contains the node database, storing previously seen nodes and any collected
+// metadata about them for QoS purposes.
+
+package discover
+
+import (
+	"bytes"
+	"encoding/binary"
+	"os"
+	"time"
+
+	"github.com/ethereum/go-ethereum/rlp"
+	"github.com/syndtr/goleveldb/leveldb"
+	"github.com/syndtr/goleveldb/leveldb/storage"
+)
+
+// nodeDB stores all nodes we know about.
+type nodeDB struct {
+	lvl *leveldb.DB
+}
+
+// Schema layout for the node database
+var (
+	nodeDBVersionKey = []byte("version") // Version of the database to flush if changes
+	nodeDBStartupKey = []byte("startup") // Time when the node discovery started (seed selection)
+	nodeDBItemPrefix = []byte("n:")      // Identifier to prefix node entries with
+
+	nodeDBDiscoverRoot = ":discover"
+	nodeDBDiscoverPing = nodeDBDiscoverRoot + ":lastping"
+	nodeDBDiscoverBond = nodeDBDiscoverRoot + ":lastbond"
+)
+
+// 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) (*nodeDB, error) {
+	if path == "" {
+		return newMemoryNodeDB()
+	}
+	return newPersistentNodeDB(path)
+}
+
+// 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}, nil
+}
+
+// newPersistentNodeDB creates/opens a leveldb backed persistent node database,
+// also flushing its contents in case of a version mismatch.
+func newPersistentNodeDB(path string) (*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, Version)]
+
+	blob, err := db.Get(nodeDBVersionKey, nil)
+	switch err {
+	case leveldb.ErrNotFound:
+		// Version not found (i.e. empty cache), insert it
+		err = db.Put(nodeDBVersionKey, currentVer, nil)
+
+	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)
+		}
+	}
+	// Clean up in case of an error
+	if err != nil {
+		db.Close()
+		return nil, err
+	}
+	return &nodeDB{lvl: db}, nil
+}
+
+// key generates the leveldb key-blob from a node id and its particular field of
+// interest.
+func (db *nodeDB) key(id NodeID, field string) []byte {
+	return append(nodeDBItemPrefix, append(id[:], field...)...)
+}
+
+// splitKey tries to split a database key into a node id and a field part.
+func (db *nodeDB) 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
+}
+
+// fetchTime retrieves a time instance (encoded as a unix timestamp) associated
+// with a particular database key.
+func (db *nodeDB) fetchTime(key []byte) time.Time {
+	blob, err := db.lvl.Get(key, nil)
+	if err != nil {
+		return time.Time{}
+	}
+	var unix int64
+	if err := rlp.DecodeBytes(blob, &unix); err != nil {
+		return time.Time{}
+	}
+	return time.Unix(unix, 0)
+}
+
+// storeTime update a specific database entry to the current time instance as a
+// unix timestamp.
+func (db *nodeDB) storeTime(key []byte, instance time.Time) error {
+	blob, err := rlp.EncodeToBytes(instance.Unix())
+	if err != nil {
+		return err
+	}
+	return db.lvl.Put(key, blob, nil)
+}
+
+// startup retrieves the time instance when the bootstrapping last begun. Its
+// purpose is to prevent contacting potential seed nodes multiple times in the
+// same boot cycle.
+func (db *nodeDB) startup() time.Time {
+	return db.fetchTime(nodeDBStartupKey)
+}
+
+// updateStartup updates the bootstrap initiation time to the one specified.
+func (db *nodeDB) updateStartup(instance time.Time) error {
+	return db.storeTime(nodeDBStartupKey, instance)
+}
+
+// node retrieves a node with a given id from the database.
+func (db *nodeDB) node(id NodeID) *Node {
+	blob, err := db.lvl.Get(db.key(id, nodeDBDiscoverRoot), nil)
+	if err != nil {
+		return nil
+	}
+	node := new(Node)
+	if err := rlp.DecodeBytes(blob, node); err != nil {
+		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(db.key(node.ID, nodeDBDiscoverRoot), blob, 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 db.fetchTime(db.key(id, nodeDBDiscoverPing))
+}
+
+// updateLastPing updates the last time we tried contacting a remote node.
+func (db *nodeDB) updateLastPing(id NodeID, instance time.Time) error {
+	return db.storeTime(db.key(id, nodeDBDiscoverPing), instance)
+}
+
+// lastBond retrieves the time of the last successful bonding with a remote node.
+func (db *nodeDB) lastBond(id NodeID) time.Time {
+	return db.fetchTime(db.key(id, nodeDBDiscoverBond))
+}
+
+// updateLastBond updates the last time we successfully bound to a remote node.
+func (db *nodeDB) updateLastBond(id NodeID, instance time.Time) error {
+	return db.storeTime(db.key(id, nodeDBDiscoverBond), instance)
+}
+
+// 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 {
+	startup := db.startup()
+
+	it := db.lvl.NewIterator(nil, nil)
+	defer it.Release()
+
+	nodes := make([]*Node, 0, n)
+	for len(nodes) < n && it.Next() {
+		// Iterate until a discovery node is found
+		id, field := db.splitKey(it.Key())
+		if field != nodeDBDiscoverRoot {
+			continue
+		}
+		// Retrieve the last ping time, and if older than startup, query
+		lastPing := db.lastPing(id)
+		if lastPing.Before(startup) {
+			if node := db.node(id); node != nil {
+				nodes = append(nodes, node)
+			}
+		}
+	}
+	// Reset the startup time if no seeds were found
+	if len(nodes) == 0 {
+		db.updateStartup(time.Now())
+	}
+	return nodes
+}
+
+// close flushes and closes the database files.
+func (db *nodeDB) close() {
+	db.lvl.Close()
+}