snowflake/broker/ipc.go

package main

import (
	"container/heap"
	"encoding/hex"
	"fmt"
	"log"

	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/v2/common/bridgefingerprint"
	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/v2/common/constants"
	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/v2/common/util"

	"github.com/prometheus/client_golang/prometheus"
	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/v2/common/messages"
)

const (
	ClientTimeout = constants.BrokerClientTimeout
	ProxyTimeout  = 10

	NATUnknown      = "unknown"
	NATRestricted   = "restricted"
	NATUnrestricted = "unrestricted"
)

type IPC struct {
	ctx *BrokerContext
}

func (i *IPC) Debug(_ interface{}, response *string) error {
	var unknowns int
	var natRestricted, natUnrestricted, natUnknown int
	proxyTypes := make(map[string]int)

	i.ctx.snowflakeLock.Lock()
	s := fmt.Sprintf("current snowflakes available: %d\n", len(i.ctx.idToSnowflake))
	for _, snowflake := range i.ctx.idToSnowflake {
		if messages.KnownProxyTypes[snowflake.proxyType] {
			proxyTypes[snowflake.proxyType]++
		} else {
			unknowns++
		}

		switch snowflake.natType {
		case NATRestricted:
			natRestricted++
		case NATUnrestricted:
			natUnrestricted++
		default:
			natUnknown++
		}

	}
	i.ctx.snowflakeLock.Unlock()

	for pType, num := range proxyTypes {
		s += fmt.Sprintf("\t%s proxies: %d\n", pType, num)
	}
	s += fmt.Sprintf("\tunknown proxies: %d", unknowns)

	s += fmt.Sprintf("\nNAT Types available:")
	s += fmt.Sprintf("\n\trestricted: %d", natRestricted)
	s += fmt.Sprintf("\n\tunrestricted: %d", natUnrestricted)
	s += fmt.Sprintf("\n\tunknown: %d", natUnknown)

	*response = s
	return nil
}

func (i *IPC) ProxyPolls(arg messages.Arg, response *[]byte) error {
	sid, proxyType, natType, clients, relayPattern, relayPatternSupported, err := messages.DecodeProxyPollRequestWithRelayPrefix(arg.Body)
	if err != nil {
		return messages.ErrBadRequest
	}

	if !relayPatternSupported {
		i.ctx.metrics.IncrementCounter("proxy-poll-without-relay-url")
		i.ctx.metrics.promMetrics.ProxyPollWithoutRelayURLExtensionTotal.With(prometheus.Labels{"nat": natType, "type": proxyType}).Inc()
	} else {
		i.ctx.metrics.IncrementCounter("proxy-poll-with-relay-url")
		i.ctx.metrics.promMetrics.ProxyPollWithRelayURLExtensionTotal.With(prometheus.Labels{"nat": natType, "type": proxyType}).Inc()
	}

	if !i.ctx.CheckProxyRelayPattern(relayPattern, !relayPatternSupported) {
		i.ctx.metrics.IncrementCounter("proxy-poll-rejected-relay-url")
		i.ctx.metrics.promMetrics.ProxyPollRejectedForRelayURLExtensionTotal.With(prometheus.Labels{"nat": natType, "type": proxyType}).Inc()

		b, err := messages.EncodePollResponseWithRelayURL("", false, "", "", "incorrect relay pattern")
		*response = b
		if err != nil {
			return messages.ErrInternal
		}
		return nil
	}

	// Log geoip stats
	remoteIP := arg.RemoteAddr
	if err != nil {
		log.Println("Warning: cannot process proxy IP: ", err.Error())
	} else {
		i.ctx.metrics.UpdateProxyStats(remoteIP, proxyType, natType)
	}

	var b []byte

	// Wait for a client to avail an offer to the snowflake, or timeout if nil.
	offer := i.ctx.RequestOffer(sid, proxyType, natType, clients)

	if offer == nil {
		i.ctx.metrics.IncrementCounter("proxy-idle")
		i.ctx.metrics.promMetrics.ProxyPollTotal.With(prometheus.Labels{"nat": natType, "status": "idle"}).Inc()

		b, err = messages.EncodePollResponse("", false, "")
		if err != nil {
			return messages.ErrInternal
		}

		*response = b
		return nil
	}

	i.ctx.metrics.promMetrics.ProxyPollTotal.With(prometheus.Labels{"nat": natType, "status": "matched"}).Inc()
	var relayURL string
	bridgeFingerprint, err := bridgefingerprint.FingerprintFromBytes(offer.fingerprint)
	if err != nil {
		return messages.ErrBadRequest
	}
	if info, err := i.ctx.bridgeList.GetBridgeInfo(bridgeFingerprint); err != nil {
		return err
	} else {
		relayURL = info.WebSocketAddress
	}
	b, err = messages.EncodePollResponseWithRelayURL(string(offer.sdp), true, offer.natType, relayURL, "")
	if err != nil {
		return messages.ErrInternal
	}
	*response = b

	return nil
}

func sendClientResponse(resp *messages.ClientPollResponse, response *[]byte) error {
	data, err := resp.EncodePollResponse()
	if err != nil {
		log.Printf("error encoding answer")
		return messages.ErrInternal
	} else {
		*response = []byte(data)
		return nil
	}
}

func (i *IPC) ClientOffers(arg messages.Arg, response *[]byte) error {

	req, err := messages.DecodeClientPollRequest(arg.Body)
	if err != nil {
		return sendClientResponse(&messages.ClientPollResponse{Error: err.Error()}, response)
	}

	// If we couldn't extract the remote IP from the rendezvous method
	// pull it from the offer SDP
	remoteAddr := arg.RemoteAddr
	if remoteAddr == "" {
		sdp, err := util.DeserializeSessionDescription(req.Offer)
		if err == nil {
			candidateAddrs := util.GetCandidateAddrs(sdp.SDP)
			if len(candidateAddrs) > 0 {
				remoteAddr = candidateAddrs[0].String()
			}
		}
	}

	offer := &ClientOffer{
		natType: req.NAT,
		sdp:     []byte(req.Offer),
	}

	fingerprint, err := hex.DecodeString(req.Fingerprint)
	if err != nil {
		return sendClientResponse(&messages.ClientPollResponse{Error: err.Error()}, response)
	}

	BridgeFingerprint, err := bridgefingerprint.FingerprintFromBytes(fingerprint)
	if err != nil {
		return sendClientResponse(&messages.ClientPollResponse{Error: err.Error()}, response)
	}

	if _, err := i.ctx.GetBridgeInfo(BridgeFingerprint); err != nil {
		return sendClientResponse(
			&messages.ClientPollResponse{Error: err.Error()},
			response,
		)
	}

	offer.fingerprint = BridgeFingerprint.ToBytes()

	snowflake := i.matchSnowflake(offer.natType)
	if snowflake != nil {
		snowflake.offerChannel <- offer
	} else {
		i.ctx.metrics.UpdateClientStats(remoteAddr, arg.RendezvousMethod, offer.natType, "denied")
		resp := &messages.ClientPollResponse{Error: messages.StrNoProxies}
		return sendClientResponse(resp, response)
	}

	// Wait for the answer to be returned on the channel or timeout.
	select {
	case answer := <-snowflake.answerChannel:
		i.ctx.metrics.UpdateClientStats(remoteAddr, arg.RendezvousMethod, offer.natType, "matched")
		resp := &messages.ClientPollResponse{Answer: answer}
		err = sendClientResponse(resp, response)
	case <-arg.Context.Done():
		i.ctx.metrics.UpdateClientStats(remoteAddr, arg.RendezvousMethod, offer.natType, "timeout")
		resp := &messages.ClientPollResponse{Error: messages.StrTimedOut}
		err = sendClientResponse(resp, response)
	}

	i.ctx.snowflakeLock.Lock()
	i.ctx.metrics.promMetrics.AvailableProxies.With(prometheus.Labels{"nat": snowflake.natType, "type": snowflake.proxyType}).Dec()
	delete(i.ctx.idToSnowflake, snowflake.id)
	i.ctx.snowflakeLock.Unlock()

	return err
}

func (i *IPC) matchSnowflake(natType string) *Snowflake {
	i.ctx.snowflakeLock.Lock()
	defer i.ctx.snowflakeLock.Unlock()

	// Proiritize known restricted snowflakes for unrestricted clients
	if natType == NATUnrestricted && i.ctx.restrictedSnowflakes.Len() > 0 {
		return heap.Pop(i.ctx.restrictedSnowflakes).(*Snowflake)
	}

	if i.ctx.snowflakes.Len() > 0 {
		return heap.Pop(i.ctx.snowflakes).(*Snowflake)
	}

	return nil
}

func (i *IPC) ProxyAnswers(arg messages.Arg, response *[]byte) error {
	answer, id, err := messages.DecodeAnswerRequest(arg.Body)
	if err != nil || answer == "" {
		return messages.ErrBadRequest
	}

	var success = true
	i.ctx.snowflakeLock.Lock()
	snowflake, ok := i.ctx.idToSnowflake[id]
	i.ctx.snowflakeLock.Unlock()
	if !ok || snowflake == nil {
		// The snowflake took too long to respond with an answer, so its client
		// disappeared / the snowflake is no longer recognized by the Broker.
		success = false
	}

	b, err := messages.EncodeAnswerResponse(success)
	if err != nil {
		log.Printf("Error encoding answer: %s", err.Error())
		return messages.ErrInternal
	}
	*response = b

	if success {
		snowflake.answerChannel <- answer
	}

	return nil
}