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Merge pull request #793 from karalabe/discovery-node-cache
p2p/discover: persistent node database
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// Contains the node database, storing previously seen nodes and any collected | ||
// metadata about them for QoS purposes. | ||
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package discover | ||
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import ( | ||
"bytes" | ||
"encoding/binary" | ||
"os" | ||
"sync" | ||
"time" | ||
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"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" | ||
) | ||
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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. | ||
) | ||
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// 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 | ||
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runner sync.Once // Ensures we can start at most one expirer | ||
quit chan struct{} // Channel to signal the expiring thread to stop | ||
} | ||
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// 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 | ||
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nodeDBDiscoverRoot = ":discover" | ||
nodeDBDiscoverPing = nodeDBDiscoverRoot + ":lastping" | ||
nodeDBDiscoverPong = nodeDBDiscoverRoot + ":lastpong" | ||
) | ||
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// 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) | ||
} | ||
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// 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 | ||
} | ||
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// 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))] | ||
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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 | ||
} | ||
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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 | ||
} | ||
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// 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...)...) | ||
} | ||
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// 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):]) | ||
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return id, field | ||
} | ||
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// 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 | ||
} | ||
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// 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)] | ||
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return db.lvl.Put(key, blob, nil) | ||
} | ||
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// 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 | ||
} | ||
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// 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) | ||
} | ||
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// 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() }) | ||
} | ||
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// 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) | ||
} | ||
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case <-db.quit: | ||
return | ||
} | ||
} | ||
} | ||
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// 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) | ||
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// Find discovered nodes that are older than the allowance | ||
it := db.lvl.NewIterator(nil, nil) | ||
defer it.Release() | ||
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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 | ||
} | ||
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// 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) | ||
} | ||
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// 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()) | ||
} | ||
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// 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) | ||
} | ||
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// 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()) | ||
} | ||
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// 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 | ||
} | ||
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// close flushes and closes the database files. | ||
func (db *nodeDB) close() { | ||
if db.seeder != nil { | ||
db.seeder.Release() | ||
} | ||
close(db.quit) | ||
db.lvl.Close() | ||
} |
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