path: root/swarm/storage/netstore.go

// Copyright 2016 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/>.

package storage

import (
    "context"
    "encoding/hex"
    "fmt"
    "sync"
    "sync/atomic"
    "time"

    "github.com/ethereum/go-ethereum/p2p/enode"
    "github.com/ethereum/go-ethereum/swarm/log"
    lru "github.com/hashicorp/golang-lru"
)

type (
    NewNetFetcherFunc func(ctx context.Context, addr Address, peers *sync.Map) NetFetcher
)

type NetFetcher interface {
    Request(ctx context.Context, hopCount uint8)
    Offer(ctx context.Context, source *enode.ID)
}

// NetStore is an extension of local storage
// it implements the ChunkStore interface
// on request it initiates remote cloud retrieval using a fetcher
// fetchers are unique to a chunk and are stored in fetchers LRU memory cache
// fetchFuncFactory is a factory object to create a fetch function for a specific chunk address
type NetStore struct {
    mu                sync.Mutex
    store             SyncChunkStore
    fetchers          *lru.Cache
    NewNetFetcherFunc NewNetFetcherFunc
    closeC            chan struct{}
}

var fetcherTimeout = 2 * time.Minute // timeout to cancel the fetcher even if requests are coming in

// NewNetStore creates a new NetStore object using the given local store. newFetchFunc is a
// constructor function that can create a fetch function for a specific chunk address.
func NewNetStore(store SyncChunkStore, nnf NewNetFetcherFunc) (*NetStore, error) {
    fetchers, err := lru.New(defaultChunkRequestsCacheCapacity)
    if err != nil {
        return nil, err
    }
    return &NetStore{
        store:             store,
        fetchers:          fetchers,
        NewNetFetcherFunc: nnf,
        closeC:            make(chan struct{}),
    }, nil
}

// Put stores a chunk in localstore, and delivers to all requestor peers using the fetcher stored in
// the fetchers cache
func (n *NetStore) Put(ctx context.Context, ch Chunk) error {
    n.mu.Lock()
    defer n.mu.Unlock()

    // put to the chunk to the store, there should be no error
    err := n.store.Put(ctx, ch)
    if err != nil {
        return err
    }

    // if chunk is now put in the store, check if there was an active fetcher and call deliver on it
    // (this delivers the chunk to requestors via the fetcher)
    if f := n.getFetcher(ch.Address()); f != nil {
        f.deliver(ctx, ch)
    }
    return nil
}

// Get retrieves the chunk from the NetStore DPA synchronously.
// It calls NetStore.get, and if the chunk is not in local Storage
// it calls fetch with the request, which blocks until the chunk
// arrived or context is done
func (n *NetStore) Get(rctx context.Context, ref Address) (Chunk, error) {
    chunk, fetch, err := n.get(rctx, ref)
    if err != nil {
        return nil, err
    }
    if chunk != nil {
        return chunk, nil
    }
    return fetch(rctx)
}

func (n *NetStore) BinIndex(po uint8) uint64 {
    return n.store.BinIndex(po)
}

func (n *NetStore) Iterator(from uint64, to uint64, po uint8, f func(Address, uint64) bool) error {
    return n.store.Iterator(from, to, po, f)
}

// FetchFunc returns nil if the store contains the given address. Otherwise it returns a wait function,
// which returns after the chunk is available or the context is done
func (n *NetStore) FetchFunc(ctx context.Context, ref Address) func(context.Context) error {
    chunk, fetch, _ := n.get(ctx, ref)
    if chunk != nil {
        return nil
    }
    return func(ctx context.Context) error {
        _, err := fetch(ctx)
        return err
    }
}

// Close chunk store
func (n *NetStore) Close() {
    close(n.closeC)
    n.store.Close()
    // TODO: loop through fetchers to cancel them
}

// get attempts at retrieving the chunk from LocalStore
// If it is not found then using getOrCreateFetcher:
//     1. Either there is already a fetcher to retrieve it
//     2. A new fetcher is created and saved in the fetchers cache
// From here on, all Get will hit on this fetcher until the chunk is delivered
// or all fetcher contexts are done.
// It returns a chunk, a fetcher function and an error
// If chunk is nil, the returned fetch function needs to be called with a context to return the chunk.
func (n *NetStore) get(ctx context.Context, ref Address) (Chunk, func(context.Context) (Chunk, error), error) {
    n.mu.Lock()
    defer n.mu.Unlock()

    chunk, err := n.store.Get(ctx, ref)
    if err != nil {
        if err != ErrChunkNotFound {
            log.Debug("Received error from LocalStore other than ErrNotFound", "err", err)
        }
        // The chunk is not available in the LocalStore, let's get the fetcher for it, or create a new one
        // if it doesn't exist yet
        f := n.getOrCreateFetcher(ref)
        // If the caller needs the chunk, it has to use the returned fetch function to get it
        return nil, f.Fetch, nil
    }

    return chunk, nil, nil
}

// getOrCreateFetcher attempts at retrieving an existing fetchers
// if none exists, creates one and saves it in the fetchers cache
// caller must hold the lock
func (n *NetStore) getOrCreateFetcher(ref Address) *fetcher {
    if f := n.getFetcher(ref); f != nil {
        return f
    }

    // no fetcher for the given address, we have to create a new one
    key := hex.EncodeToString(ref)
    // create the context during which fetching is kept alive
    ctx, cancel := context.WithTimeout(context.Background(), fetcherTimeout)
    // destroy is called when all requests finish
    destroy := func() {
        // remove fetcher from fetchers
        n.fetchers.Remove(key)
        // stop fetcher by cancelling context called when
        // all requests cancelled/timedout or chunk is delivered
        cancel()
    }
    // peers always stores all the peers which have an active request for the chunk. It is shared
    // between fetcher and the NewFetchFunc function. It is needed by the NewFetchFunc because
    // the peers which requested the chunk should not be requested to deliver it.
    peers := &sync.Map{}

    fetcher := newFetcher(ref, n.NewNetFetcherFunc(ctx, ref, peers), destroy, peers, n.closeC)
    n.fetchers.Add(key, fetcher)

    return fetcher
}

// getFetcher retrieves the fetcher for the given address from the fetchers cache if it exists,
// otherwise it returns nil
func (n *NetStore) getFetcher(ref Address) *fetcher {
    key := hex.EncodeToString(ref)
    f, ok := n.fetchers.Get(key)
    if ok {
        return f.(*fetcher)
    }
    return nil
}

// RequestsCacheLen returns the current number of outgoing requests stored in the cache
func (n *NetStore) RequestsCacheLen() int {
    return n.fetchers.Len()
}

// One fetcher object is responsible to fetch one chunk for one address, and keep track of all the
// peers who have requested it and did not receive it yet.
type fetcher struct {
    addr        Address       // address of chunk
    chunk       Chunk         // fetcher can set the chunk on the fetcher
    deliveredC  chan struct{} // chan signalling chunk delivery to requests
    cancelledC  chan struct{} // chan signalling the fetcher has been cancelled (removed from fetchers in NetStore)
    netFetcher  NetFetcher    // remote fetch function to be called with a request source taken from the context
    cancel      func()        // cleanup function for the remote fetcher to call when all upstream contexts are called
    peers       *sync.Map     // the peers which asked for the chunk
    requestCnt  int32         // number of requests on this chunk. If all the requests are done (delivered or context is done) the cancel function is called
    deliverOnce *sync.Once    // guarantees that we only close deliveredC once
}

// newFetcher creates a new fetcher object for the fiven addr. fetch is the function which actually
// does the retrieval (in non-test cases this is coming from the network package). cancel function is
// called either
//     1. when the chunk has been fetched all peers have been either notified or their context has been done
//     2. the chunk has not been fetched but all context from all the requests has been done
// The peers map stores all the peers which have requested chunk.
func newFetcher(addr Address, nf NetFetcher, cancel func(), peers *sync.Map, closeC chan struct{}) *fetcher {
    cancelOnce := &sync.Once{} // cancel should only be called once
    return &fetcher{
        addr:        addr,
        deliveredC:  make(chan struct{}),
        deliverOnce: &sync.Once{},
        cancelledC:  closeC,
        netFetcher:  nf,
        cancel: func() {
            cancelOnce.Do(func() {
                cancel()
            })
        },
        peers: peers,
    }
}

// Fetch fetches the chunk synchronously, it is called by NetStore.Get is the chunk is not available
// locally.
func (f *fetcher) Fetch(rctx context.Context) (Chunk, error) {
    atomic.AddInt32(&f.requestCnt, 1)
    defer func() {
        // if all the requests are done the fetcher can be cancelled
        if atomic.AddInt32(&f.requestCnt, -1) == 0 {
            f.cancel()
        }
    }()

    // The peer asking for the chunk. Store in the shared peers map, but delete after the request
    // has been delivered
    peer := rctx.Value("peer")
    if peer != nil {
        f.peers.Store(peer, time.Now())
        defer f.peers.Delete(peer)
    }

    // If there is a source in the context then it is an offer, otherwise a request
    sourceIF := rctx.Value("source")

    hopCount, _ := rctx.Value("hopcount").(uint8)

    if sourceIF != nil {
        var source enode.ID
        if err := source.UnmarshalText([]byte(sourceIF.(string))); err != nil {
            return nil, err
        }
        f.netFetcher.Offer(rctx, &source)
    } else {
        f.netFetcher.Request(rctx, hopCount)
    }

    // wait until either the chunk is delivered or the context is done
    select {
    case <-rctx.Done():
        return nil, rctx.Err()
    case <-f.deliveredC:
        return f.chunk, nil
    case <-f.cancelledC:
        return nil, fmt.Errorf("fetcher cancelled")
    }
}

// deliver is called by NetStore.Put to notify all pending requests
func (f *fetcher) deliver(ctx context.Context, ch Chunk) {
    f.deliverOnce.Do(func() {
        f.chunk = ch
        // closing the deliveredC channel will terminate ongoing requests
        close(f.deliveredC)
    })
}