filter.go

// Copyright 2019 The Waku Library Authors.
//
// The Waku library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The Waku library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty off
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the Waku library. If not, see <http://www.gnu.org/licenses/>.
//
// This software uses the go-ethereum library, which is licensed
// under the GNU Lesser General Public Library, version 3 or any later.

package waku

import (
	"crypto/ecdsa"
	"fmt"
	"sync"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/crypto"
	"github.com/ethereum/go-ethereum/log"
)

// MessageStore defines interface for temporary message store.
type MessageStore interface {
	Add(*ReceivedMessage) error
	Pop() ([]*ReceivedMessage, error)
}

// NewMemoryMessageStore returns pointer to an instance of the MemoryMessageStore.
func NewMemoryMessageStore() *MemoryMessageStore {
	return &MemoryMessageStore{
		messages: map[common.Hash]*ReceivedMessage{},
	}
}

// MemoryMessageStore stores massages in memory hash table.
type MemoryMessageStore struct {
	mu       sync.Mutex
	messages map[common.Hash]*ReceivedMessage
}

// Add adds message to store.
func (store *MemoryMessageStore) Add(msg *ReceivedMessage) error {
	store.mu.Lock()
	defer store.mu.Unlock()
	if _, exist := store.messages[msg.EnvelopeHash]; !exist {
		store.messages[msg.EnvelopeHash] = msg
	}
	return nil
}

// Pop returns all available messages and cleans the store.
func (store *MemoryMessageStore) Pop() ([]*ReceivedMessage, error) {
	store.mu.Lock()
	defer store.mu.Unlock()
	all := make([]*ReceivedMessage, 0, len(store.messages))
	for hash, msg := range store.messages {
		delete(store.messages, hash)
		all = append(all, msg)
	}
	return all, nil
}

// Filter represents a Waku message filter
type Filter struct {
	Src        *ecdsa.PublicKey  // Sender of the message
	KeyAsym    *ecdsa.PrivateKey // Private Key of recipient
	KeySym     []byte            // Key associated with the Topic
	Topics     [][]byte          // Topics to filter messages with
	PoW        float64           // Proof of work as described in the Waku spec
	AllowP2P   bool              // Indicates whether this filter is interested in direct peer-to-peer messages
	SymKeyHash common.Hash       // The Keccak256Hash of the symmetric key, needed for optimization
	id         string            // unique identifier

	Messages MessageStore
}

// Filters represents a collection of filters
type Filters struct {
	watchers map[string]*Filter

	topicMatcher     map[TopicType]map[*Filter]struct{} // map a topic to the filters that are interested in being notified when a message matches that topic
	allTopicsMatcher map[*Filter]struct{}               // list all the filters that will be notified of a new message, no matter what its topic is

	waku  *Waku
	mutex sync.RWMutex
}

// NewFilters returns a newly created filter collection
func NewFilters(w *Waku) *Filters {
	return &Filters{
		watchers:         make(map[string]*Filter),
		topicMatcher:     make(map[TopicType]map[*Filter]struct{}),
		allTopicsMatcher: make(map[*Filter]struct{}),
		waku:             w,
	}
}

// Install will add a new filter to the filter collection
func (fs *Filters) Install(watcher *Filter) (string, error) {
	if watcher.KeySym != nil && watcher.KeyAsym != nil {
		return "", fmt.Errorf("filters must choose between symmetric and asymmetric keys")
	}

	id, err := GenerateRandomID()
	if err != nil {
		return "", err
	}

	fs.mutex.Lock()
	defer fs.mutex.Unlock()

	if fs.watchers[id] != nil {
		return "", fmt.Errorf("failed to generate unique ID")
	}

	if watcher.expectsSymmetricEncryption() {
		watcher.SymKeyHash = crypto.Keccak256Hash(watcher.KeySym)
	}

	watcher.id = id
	fs.watchers[id] = watcher
	fs.addTopicMatcher(watcher)
	return id, err
}

// Uninstall will remove a filter whose id has been specified from
// the filter collection
func (fs *Filters) Uninstall(id string) bool {
	fs.mutex.Lock()
	defer fs.mutex.Unlock()
	if fs.watchers[id] != nil {
		fs.removeFromTopicMatchers(fs.watchers[id])
		delete(fs.watchers, id)
		return true
	}
	return false
}

// addTopicMatcher adds a filter to the topic matchers.
// If the filter's Topics array is empty, it will be tried on every topic.
// Otherwise, it will be tried on the topics specified.
func (fs *Filters) addTopicMatcher(watcher *Filter) {
	if len(watcher.Topics) == 0 {
		fs.allTopicsMatcher[watcher] = struct{}{}
	} else {
		for _, t := range watcher.Topics {
			topic := BytesToTopic(t)
			if fs.topicMatcher[topic] == nil {
				fs.topicMatcher[topic] = make(map[*Filter]struct{})
			}
			fs.topicMatcher[topic][watcher] = struct{}{}
		}
	}
}

// removeFromTopicMatchers removes a filter from the topic matchers
func (fs *Filters) removeFromTopicMatchers(watcher *Filter) {
	delete(fs.allTopicsMatcher, watcher)
	for _, topic := range watcher.Topics {
		delete(fs.topicMatcher[BytesToTopic(topic)], watcher)
	}
}

// getWatchersByTopic returns a slice containing the filters that
// match a specific topic
func (fs *Filters) getWatchersByTopic(topic TopicType) []*Filter {
	res := make([]*Filter, 0, len(fs.allTopicsMatcher))
	for watcher := range fs.allTopicsMatcher {
		res = append(res, watcher)
	}
	for watcher := range fs.topicMatcher[topic] {
		res = append(res, watcher)
	}
	return res
}

// Get returns a filter from the collection with a specific ID
func (fs *Filters) Get(id string) *Filter {
	fs.mutex.RLock()
	defer fs.mutex.RUnlock()
	return fs.watchers[id]
}

// NotifyWatchers notifies any filter that has declared interest
// for the envelope's topic.
func (fs *Filters) NotifyWatchers(env *Envelope, p2pMessage bool) {
	var msg *ReceivedMessage

	fs.mutex.RLock()
	defer fs.mutex.RUnlock()

	candidates := fs.getWatchersByTopic(env.Topic)
	for _, watcher := range candidates {
		if p2pMessage && !watcher.AllowP2P {
			log.Trace(fmt.Sprintf("msg [%x], filter [%s]: p2p messages are not allowed", env.Hash(), watcher.id))
			continue
		}

		var match bool
		if msg != nil {
			match = watcher.MatchMessage(msg)
		} else {
			match = watcher.MatchEnvelope(env)
			if match {
				msg = env.Open(watcher)
				if msg == nil {
					log.Trace("processing message: failed to open", "message", env.Hash().Hex(), "filter", watcher.id)
				}
			} else {
				log.Trace("processing message: does not match", "message", env.Hash().Hex(), "filter", watcher.id)
			}
		}

		if match && msg != nil {
			msg.P2P = p2pMessage
			log.Trace("processing message: decrypted", "hash", env.Hash().Hex())
			if watcher.Src == nil || IsPubKeyEqual(msg.Src, watcher.Src) {
				watcher.Trigger(msg)
			}
		}
	}
}

func (f *Filter) expectsAsymmetricEncryption() bool {
	return f.KeyAsym != nil
}

func (f *Filter) expectsSymmetricEncryption() bool {
	return f.KeySym != nil
}

// Trigger adds a yet-unknown message to the filter's list of
// received messages.
func (f *Filter) Trigger(msg *ReceivedMessage) {
	err := f.Messages.Add(msg)
	if err != nil {
		log.Error("failed to add msg into the filters store", "hash", msg.EnvelopeHash, "error", err)
	}
}

// Retrieve will return the list of all received messages associated
// to a filter.
func (f *Filter) Retrieve() []*ReceivedMessage {
	msgs, err := f.Messages.Pop()
	if err != nil {
		log.Error("failed to retrieve messages from filter store", "error", err)
		return nil
	}
	return msgs
}

// MatchMessage checks if the filter matches an already decrypted
// message (i.e. a Message that has already been handled by
// MatchEnvelope when checked by a previous filter).
// Topics are not checked here, since this is done by topic matchers.
func (f *Filter) MatchMessage(msg *ReceivedMessage) bool {
	if f.PoW > 0 && msg.PoW < f.PoW {
		return false
	}

	if f.expectsAsymmetricEncryption() && msg.isAsymmetricEncryption() {
		return IsPubKeyEqual(&f.KeyAsym.PublicKey, msg.Dst)
	} else if f.expectsSymmetricEncryption() && msg.isSymmetricEncryption() {
		return f.SymKeyHash == msg.SymKeyHash
	}
	return false
}

// MatchEnvelope checks if it's worth decrypting the message. If
// it returns `true`, client code is expected to attempt decrypting
// the message and subsequently call MatchMessage.
// Topics are not checked here, since this is done by topic matchers.
func (f *Filter) MatchEnvelope(envelope *Envelope) bool {
	return f.PoW <= 0 || envelope.pow >= f.PoW
}

// IsPubKeyEqual checks that two public keys are equal
func IsPubKeyEqual(a, b *ecdsa.PublicKey) bool {
	if !ValidatePublicKey(a) {
		return false
	} else if !ValidatePublicKey(b) {
		return false
	}
	// the curve is always the same, just compare the points
	return a.X.Cmp(b.X) == 0 && a.Y.Cmp(b.Y) == 0
}