path: root/swarm/storage/feed/handler.go

// Copyright 2018 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum 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 go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// 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 go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

// Handler is the API for feeds
// It enables creating, updating, syncing and retrieving feed updates and their data
package feed

import (
    "bytes"
    "context"
    "fmt"
    "sync"

    "github.com/dexon-foundation/dexon/swarm/storage/feed/lookup"

    "github.com/dexon-foundation/dexon/swarm/log"
    "github.com/dexon-foundation/dexon/swarm/storage"
)

type Handler struct {
    chunkStore *storage.NetStore
    HashSize   int
    cache      map[uint64]*cacheEntry
    cacheLock  sync.RWMutex
}

// HandlerParams pass parameters to the Handler constructor NewHandler
// Signer and TimestampProvider are mandatory parameters
type HandlerParams struct {
}

// hashPool contains a pool of ready hashers
var hashPool sync.Pool

// init initializes the package and hashPool
func init() {
    hashPool = sync.Pool{
        New: func() interface{} {
            return storage.MakeHashFunc(feedsHashAlgorithm)()
        },
    }
}

// NewHandler creates a new Swarm feeds API
func NewHandler(params *HandlerParams) *Handler {
    fh := &Handler{
        cache: make(map[uint64]*cacheEntry),
    }

    for i := 0; i < hasherCount; i++ {
        hashfunc := storage.MakeHashFunc(feedsHashAlgorithm)()
        if fh.HashSize == 0 {
            fh.HashSize = hashfunc.Size()
        }
        hashPool.Put(hashfunc)
    }

    return fh
}

// SetStore sets the store backend for the Swarm feeds API
func (h *Handler) SetStore(store *storage.NetStore) {
    h.chunkStore = store
}

// Validate is a chunk validation method
// If it looks like a feed update, the chunk address is checked against the userAddr of the update's signature
// It implements the storage.ChunkValidator interface
func (h *Handler) Validate(chunk storage.Chunk) bool {
    if len(chunk.Data()) < minimumSignedUpdateLength {
        return false
    }

    // check if it is a properly formatted update chunk with
    // valid signature and proof of ownership of the feed it is trying
    // to update

    // First, deserialize the chunk
    var r Request
    if err := r.fromChunk(chunk); err != nil {
        log.Debug("Invalid feed update chunk", "addr", chunk.Address(), "err", err)
        return false
    }

    // Verify signatures and that the signer actually owns the feed
    // If it fails, it means either the signature is not valid, data is corrupted
    // or someone is trying to update someone else's feed.
    if err := r.Verify(); err != nil {
        log.Debug("Invalid feed update signature", "err", err)
        return false
    }

    return true
}

// GetContent retrieves the data payload of the last synced update of the feed
func (h *Handler) GetContent(feed *Feed) (storage.Address, []byte, error) {
    if feed == nil {
        return nil, nil, NewError(ErrInvalidValue, "feed is nil")
    }
    feedUpdate := h.get(feed)
    if feedUpdate == nil {
        return nil, nil, NewError(ErrNotFound, "feed update not cached")
    }
    return feedUpdate.lastKey, feedUpdate.data, nil
}

// NewRequest prepares a Request structure with all the necessary information to
// just add the desired data and sign it.
// The resulting structure can then be signed and passed to Handler.Update to be verified and sent
func (h *Handler) NewRequest(ctx context.Context, feed *Feed) (request *Request, err error) {
    if feed == nil {
        return nil, NewError(ErrInvalidValue, "feed cannot be nil")
    }

    now := TimestampProvider.Now().Time
    request = new(Request)
    request.Header.Version = ProtocolVersion

    query := NewQueryLatest(feed, lookup.NoClue)

    feedUpdate, err := h.Lookup(ctx, query)
    if err != nil {
        if err.(*Error).code != ErrNotFound {
            return nil, err
        }
        // not finding updates means that there is a network error
        // or that the feed really does not have updates
    }

    request.Feed = *feed

    // if we already have an update, then find next epoch
    if feedUpdate != nil {
        request.Epoch = lookup.GetNextEpoch(feedUpdate.Epoch, now)
    } else {
        request.Epoch = lookup.GetFirstEpoch(now)
    }

    return request, nil
}

// Lookup retrieves a specific or latest feed update
// Lookup works differently depending on the configuration of `query`
// See the `query` documentation and helper functions:
// `NewQueryLatest` and `NewQuery`
func (h *Handler) Lookup(ctx context.Context, query *Query) (*cacheEntry, error) {

    timeLimit := query.TimeLimit
    if timeLimit == 0 { // if time limit is set to zero, the user wants to get the latest update
        timeLimit = TimestampProvider.Now().Time
    }

    if query.Hint == lookup.NoClue { // try to use our cache
        entry := h.get(&query.Feed)
        if entry != nil && entry.Epoch.Time <= timeLimit { // avoid bad hints
            query.Hint = entry.Epoch
        }
    }

    // we can't look for anything without a store
    if h.chunkStore == nil {
        return nil, NewError(ErrInit, "Call Handler.SetStore() before performing lookups")
    }

    var id ID
    id.Feed = query.Feed
    var readCount int

    // Invoke the lookup engine.
    // The callback will be called every time the lookup algorithm needs to guess
    requestPtr, err := lookup.Lookup(timeLimit, query.Hint, func(epoch lookup.Epoch, now uint64) (interface{}, error) {
        readCount++
        id.Epoch = epoch
        ctx, cancel := context.WithTimeout(ctx, defaultRetrieveTimeout)
        defer cancel()

        chunk, err := h.chunkStore.Get(ctx, id.Addr())
        if err != nil { // TODO: check for catastrophic errors other than chunk not found
            return nil, nil
        }

        var request Request
        if err := request.fromChunk(chunk); err != nil {
            return nil, nil
        }
        if request.Time <= timeLimit {
            return &request, nil
        }
        return nil, nil
    })
    if err != nil {
        return nil, err
    }

    log.Info(fmt.Sprintf("Feed lookup finished in %d lookups", readCount))

    request, _ := requestPtr.(*Request)
    if request == nil {
        return nil, NewError(ErrNotFound, "no feed updates found")
    }
    return h.updateCache(request)

}

// update feed updates cache with specified content
func (h *Handler) updateCache(request *Request) (*cacheEntry, error) {

    updateAddr := request.Addr()
    log.Trace("feed cache update", "topic", request.Topic.Hex(), "updateaddr", updateAddr, "epoch time", request.Epoch.Time, "epoch level", request.Epoch.Level)

    feedUpdate := h.get(&request.Feed)
    if feedUpdate == nil {
        feedUpdate = &cacheEntry{}
        h.set(&request.Feed, feedUpdate)
    }

    // update our rsrcs entry map
    feedUpdate.lastKey = updateAddr
    feedUpdate.Update = request.Update
    feedUpdate.Reader = bytes.NewReader(feedUpdate.data)
    return feedUpdate, nil
}

// Update publishes a feed update
// Note that a feed update cannot span chunks, and thus has a MAX NET LENGTH 4096, INCLUDING update header data and signature.
// This results in a max payload of `maxUpdateDataLength` (check update.go for more details)
// An error will be returned if the total length of the chunk payload will exceed this limit.
// Update can only check if the caller is trying to overwrite the very last known version, otherwise it just puts the update
// on the network.
func (h *Handler) Update(ctx context.Context, r *Request) (updateAddr storage.Address, err error) {

    // we can't update anything without a store
    if h.chunkStore == nil {
        return nil, NewError(ErrInit, "Call Handler.SetStore() before updating")
    }

    feedUpdate := h.get(&r.Feed)
    if feedUpdate != nil && feedUpdate.Epoch.Equals(r.Epoch) { // This is the only cheap check we can do for sure
        return nil, NewError(ErrInvalidValue, "A former update in this epoch is already known to exist")
    }

    chunk, err := r.toChunk() // Serialize the update into a chunk. Fails if data is too big
    if err != nil {
        return nil, err
    }

    // send the chunk
    h.chunkStore.Put(ctx, chunk)
    log.Trace("feed update", "updateAddr", r.idAddr, "epoch time", r.Epoch.Time, "epoch level", r.Epoch.Level, "data", chunk.Data())
    // update our feed updates map cache entry if the new update is older than the one we have, if we have it.
    if feedUpdate != nil && r.Epoch.After(feedUpdate.Epoch) {
        feedUpdate.Epoch = r.Epoch
        feedUpdate.data = make([]byte, len(r.data))
        feedUpdate.lastKey = r.idAddr
        copy(feedUpdate.data, r.data)
        feedUpdate.Reader = bytes.NewReader(feedUpdate.data)
    }

    return r.idAddr, nil
}

// Retrieves the feed update cache value for the given nameHash
func (h *Handler) get(feed *Feed) *cacheEntry {
    mapKey := feed.mapKey()
    h.cacheLock.RLock()
    defer h.cacheLock.RUnlock()
    feedUpdate := h.cache[mapKey]
    return feedUpdate
}

// Sets the feed update cache value for the given feed
func (h *Handler) set(feed *Feed, feedUpdate *cacheEntry) {
    mapKey := feed.mapKey()
    h.cacheLock.Lock()
    defer h.cacheLock.Unlock()
    h.cache[mapKey] = feedUpdate
}