// 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/crypto"
"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/errors"
"github.com/syndtr/goleveldb/leveldb/iterator"
"github.com/syndtr/goleveldb/leveldb/storage"
"github.com/syndtr/goleveldb/leveldb/util"
)
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.(*errors.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
}
node.sha = crypto.Sha3Hash(node.ID[:])
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
deleter := db.lvl.NewIterator(util.BytesPrefix(makeKey(id, "")), nil)
for deleter.Next() {
if err := db.lvl.Delete(deleter.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()
}
