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"
    "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()
}