ipfs, libp2p DHT

DHT Message Handling

• FindNode
• Ping
• GetValue
• PutValue
• AddProvider
• GetProvider

putValue/getValue is used by IPNS namespace system. Data format is like:

/pk/encoded(key+value)  :   timestamp
/ipns/encoded(key+value)  :   timestamp

Provider is the DHT k/v system. Data format:

/provider/encoded(key)/encoded(value)   :   encoded(unixnano)
example: /providers/CIQIF7JNQBSUDCM4ZDQWGNFQFCATUJHDRKVLLAV7XWM7CKIU7C6LVEY/CIQEWHPUHMAV572SCJNKBRDA2KSS4M7KV2U24OJD3TO3OSE2BWVUXFY

func (dht *IpfsDHT) handlerForMsgType(t pb.Message_MessageType) dhtHandler {
	switch t {
	case pb.Message_FIND_NODE:
		return dht.handleFindPeer
	case pb.Message_PING:
		return dht.handlePing
	}
	if dht.enableValues {
		switch t {
		case pb.Message_GET_VALUE:
			return dht.handleGetValue
		case pb.Message_PUT_VALUE:
			return dht.handlePutValue
		}
	}
	if dht.enableProviders {
		switch t {
		case pb.Message_ADD_PROVIDER:
			return dht.handleAddProvider
		case pb.Message_GET_PROVIDERS:
			return dht.handleGetProviders
		}
	}
	return nil
}

handleAddProvider

func (dht *IpfsDHT) handleGetProviders(ctx context.Context, p peer.ID, pmes *pb.Message) (_ *pb.Message, _err error) {
	ctx = logger.Start(ctx, "handleGetProviders")
	defer func() { logger.FinishWithErr(ctx, _err) }()
	logger.SetTag(ctx, "peer", p)

	resp := pb.NewMessage(pmes.GetType(), pmes.GetKey(), pmes.GetClusterLevel())
	key := pmes.GetKey()
	if len(key) > 80 {
		return nil, fmt.Errorf("handleGetProviders key size too large")
	}
	logger.SetTag(ctx, "key", key)

	// debug logging niceness.
	reqDesc := fmt.Sprintf("%s handleGetProviders(%s, %s): ", dht.self, p, key)
	logger.Debugf("%s begin", reqDesc)
	defer logger.Debugf("%s end", reqDesc)

	// check if we have this value, to add ourselves as provider.
	//providersKeyPrefix + base32.RawStdEncoding.EncodeToString(k)
	has, err := dht.datastore.Has(convertToDsKey(key))
	if err != nil && err != ds.ErrNotFound {
		logger.Debugf("unexpected datastore error: %v\n", err)
		has = false
	}

	// setup providers
	providers := dht.providers.GetProviders(ctx, key)
	if has {
		providers = append(providers, dht.self)
		logger.Debugf("%s have the value. added self as provider", reqDesc)
	}

	if len(providers) > 0 {
		// TODO: pstore.PeerInfos should move to core (=> peerstore.AddrInfos).
		infos := pstore.PeerInfos(dht.peerstore, providers)
		resp.ProviderPeers = pb.PeerInfosToPBPeers(dht.host.Network(), infos)
		logger.Debugf("%s have %d providers: %s", reqDesc, len(providers), infos)
	}

	// Also send closer peers.
	closer := dht.betterPeersToQuery(pmes, p, dht.bucketSize)
	if closer != nil {
		// TODO: pstore.PeerInfos should move to core (=> peerstore.AddrInfos).
		infos := pstore.PeerInfos(dht.peerstore, closer)
		resp.CloserPeers = pb.PeerInfosToPBPeers(dht.host.Network(), infos)
		logger.Debugf("%s have %d closer peers: %s", reqDesc, len(closer), infos)
	}

	return resp, nil
}

handleGetProvider

See flow chart:

ProviderManager.GetProvider

Send getProv message to pm worker

func (pm *ProviderManager) GetProviders(ctx context.Context, k []byte) []peer.ID {
	gp := &getProv{
		k:    k,
		resp: make(chan []peer.ID, 1), // buffered to prevent sender from blocking
	}
	select {
	case <-ctx.Done():
		return nil
	case pm.getprovs <- gp:
	}
	select {
	case <-ctx.Done():
		return nil
	case peers := <-gp.resp:
		return peers
	}
}

pm will od getProvSet and eventually respond with getProv.resp

func (pm *ProviderManager) getProvSet(k []byte) (*providerSet, error) {
	// look up in the LRU cache at first
	cached, ok := pm.providers.Get(string(k))
	if ok {
		return cached.(*providerSet), nil
	}

	// otherwise, load from data store
	pset, err := loadProvSet(pm.dstore, k)
	if err != nil {
		return nil, err
	}

	if len(pset.providers) > 0 {
		pm.providers.Add(string(k), pset)
	}
	return pset, nil
}

func loadProvSet(dstore ds.Datastore, k []byte) (*providerSet, error) {
	// query the prefix, get the hit list
	res, err := dstore.Query(dsq.Query{Prefix: mkProvKey(k)})
	...
	...

Then we got the values sharing the same key, in other words, the PeerID list serving the same CID.

hanldePutValue

handleGetValue