package dht import ( "crypto/sha1" "encoding/binary" "time" "github.com/bradfitz/iter" ) // Manages creation and validation of tokens issued to querying nodes. type tokenServer struct { // Something only we know that peers can't guess, so they can't deduce valid tokens. secret []byte // How long between token changes. interval time.Duration // How many intervals may pass between the current interval, and one used to generate a token before it is invalid. maxIntervalDelta int timeNow func() time.Time } func (me tokenServer) CreateToken(addr Addr) string { return me.createToken(addr, me.getTimeNow()) } func (me tokenServer) createToken(addr Addr, t time.Time) string { h := sha1.New() ip := addr.IP().To16() if len(ip) != 16 { panic(ip) } h.Write(ip) ti := t.UnixNano() / int64(me.interval) var b [8]byte binary.BigEndian.PutUint64(b[:], uint64(ti)) h.Write(b[:]) h.Write(me.secret) return string(h.Sum(nil)) } func (me *tokenServer) ValidToken(token string, addr Addr) bool { t := me.getTimeNow() for range iter.N(me.maxIntervalDelta + 1) { if me.createToken(addr, t) == token { return true } t = t.Add(-me.interval) } return false } func (me *tokenServer) getTimeNow() time.Time { if me.timeNow == nil { return time.Now() } return me.timeNow() }