// 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)
})
}
