path: root/p2p/discover/cache.go

// Contains the discovery cache, storing previously seen nodes to act as seed
// servers during bootstrapping the network.

package discover

import (
    "bytes"
    "encoding/binary"
    "net"
    "os"

    "github.com/ethereum/go-ethereum/rlp"
    "github.com/syndtr/goleveldb/leveldb"
    "github.com/syndtr/goleveldb/leveldb/storage"
)

// Cache stores all nodes we know about.
type Cache struct {
    db *leveldb.DB
}

// Cache version to allow dumping old data if it changes.
var cacheVersionKey = []byte("pv")

// NewMemoryCache creates a new in-memory peer cache without a persistent backend.
func NewMemoryCache() (*Cache, error) {
    db, err := leveldb.Open(storage.NewMemStorage(), nil)
    if err != nil {
        return nil, err
    }
    return &Cache{db: db}, nil
}

// NewPersistentCache creates/opens a leveldb backed persistent peer cache, also
// flushing its contents in case of a version mismatch.
func NewPersistentCache(path string) (*Cache, 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(cacheVersionKey, nil)
    switch err {
    case leveldb.ErrNotFound:
        // Version not found (i.e. empty cache), insert it
        err = db.Put(cacheVersionKey, 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 NewPersistentCache(path)
        }
    }
    // Clean up in case of an error
    if err != nil {
        db.Close()
        return nil, err
    }
    return &Cache{db: db}, nil
}

// get retrieves a node with a given id from the seed da
func (c *Cache) get(id NodeID) *Node {
    blob, err := c.db.Get(id[:], nil)
    if err != nil {
        return nil
    }
    node := new(Node)
    if err := rlp.DecodeBytes(blob, node); err != nil {
        return nil
    }
    return node
}

// list retrieves a batch of nodes from the database.
func (c *Cache) list(n int) []*Node {
    it := c.db.NewIterator(nil, nil)
    defer it.Release()

    nodes := make([]*Node, 0, n)
    for i := 0; i < n && it.Next(); i++ {
        var id NodeID
        copy(id[:], it.Key())

        if node := c.get(id); node != nil {
            nodes = append(nodes, node)
        }
    }
    return nodes
}

// update inserts - potentially overwriting - a node in the seed database.
func (c *Cache) update(node *Node) error {
    blob, err := rlp.EncodeToBytes(node)
    if err != nil {
        return err
    }
    return c.db.Put(node.ID[:], blob, nil)
}

// add inserts a new node into the seed database.
func (c *Cache) add(id NodeID, addr *net.UDPAddr, tcpPort uint16) *Node {
    node := &Node{
        ID:       id,
        IP:       addr.IP,
        DiscPort: addr.Port,
        TCPPort:  int(tcpPort),
    }
    c.update(node)

    return node
}

// delete removes a node from the database.
func (c *Cache) delete(id NodeID) error {
    return c.db.Delete(id[:], nil)
}

// Close flushes and closes the database files.
func (c *Cache) Close() {
    c.db.Close()
}