path: root/p2p/discover/database.go

// 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/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
    }
    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()
}