324 lines
11 KiB
Go
324 lines
11 KiB
Go
// Copyright 2018 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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package network
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import (
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"context"
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"sync"
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"time"
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"github.com/ethereum/go-ethereum/log"
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"github.com/ethereum/go-ethereum/p2p/enode"
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"github.com/ethereum/go-ethereum/swarm/storage"
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)
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const (
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defaultSearchTimeout = 1 * time.Second
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// maximum number of forwarded requests (hops), to make sure requests are not
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// forwarded forever in peer loops
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maxHopCount uint8 = 20
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)
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// Time to consider peer to be skipped.
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// Also used in stream delivery.
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var RequestTimeout = 10 * time.Second
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type RequestFunc func(context.Context, *Request) (*enode.ID, chan struct{}, error)
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// Fetcher is created when a chunk is not found locally. It starts a request handler loop once and
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// keeps it alive until all active requests are completed. This can happen:
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// 1. either because the chunk is delivered
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// 2. or because the requester cancelled/timed out
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// Fetcher self destroys itself after it is completed.
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// TODO: cancel all forward requests after termination
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type Fetcher struct {
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protoRequestFunc RequestFunc // request function fetcher calls to issue retrieve request for a chunk
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addr storage.Address // the address of the chunk to be fetched
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offerC chan *enode.ID // channel of sources (peer node id strings)
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requestC chan uint8 // channel for incoming requests (with the hopCount value in it)
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searchTimeout time.Duration
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skipCheck bool
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ctx context.Context
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}
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type Request struct {
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Addr storage.Address // chunk address
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Source *enode.ID // nodeID of peer to request from (can be nil)
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SkipCheck bool // whether to offer the chunk first or deliver directly
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peersToSkip *sync.Map // peers not to request chunk from (only makes sense if source is nil)
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HopCount uint8 // number of forwarded requests (hops)
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}
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// NewRequest returns a new instance of Request based on chunk address skip check and
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// a map of peers to skip.
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func NewRequest(addr storage.Address, skipCheck bool, peersToSkip *sync.Map) *Request {
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return &Request{
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Addr: addr,
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SkipCheck: skipCheck,
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peersToSkip: peersToSkip,
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}
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}
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// SkipPeer returns if the peer with nodeID should not be requested to deliver a chunk.
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// Peers to skip are kept per Request and for a time period of RequestTimeout.
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// This function is used in stream package in Delivery.RequestFromPeers to optimize
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// requests for chunks.
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func (r *Request) SkipPeer(nodeID string) bool {
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val, ok := r.peersToSkip.Load(nodeID)
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if !ok {
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return false
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}
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t, ok := val.(time.Time)
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if ok && time.Now().After(t.Add(RequestTimeout)) {
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// deadline expired
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r.peersToSkip.Delete(nodeID)
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return false
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}
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return true
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}
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// FetcherFactory is initialised with a request function and can create fetchers
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type FetcherFactory struct {
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request RequestFunc
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skipCheck bool
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}
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// NewFetcherFactory takes a request function and skip check parameter and creates a FetcherFactory
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func NewFetcherFactory(request RequestFunc, skipCheck bool) *FetcherFactory {
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return &FetcherFactory{
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request: request,
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skipCheck: skipCheck,
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}
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}
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// New constructs a new Fetcher, for the given chunk. All peers in peersToSkip
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// are not requested to deliver the given chunk. peersToSkip should always
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// contain the peers which are actively requesting this chunk, to make sure we
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// don't request back the chunks from them.
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// The created Fetcher is started and returned.
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func (f *FetcherFactory) New(ctx context.Context, source storage.Address, peers *sync.Map) storage.NetFetcher {
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fetcher := NewFetcher(ctx, source, f.request, f.skipCheck)
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go fetcher.run(peers)
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return fetcher
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}
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// NewFetcher creates a new Fetcher for the given chunk address using the given request function.
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func NewFetcher(ctx context.Context, addr storage.Address, rf RequestFunc, skipCheck bool) *Fetcher {
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return &Fetcher{
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addr: addr,
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protoRequestFunc: rf,
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offerC: make(chan *enode.ID),
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requestC: make(chan uint8),
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searchTimeout: defaultSearchTimeout,
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skipCheck: skipCheck,
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ctx: ctx,
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}
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}
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// Offer is called when an upstream peer offers the chunk via syncing as part of `OfferedHashesMsg` and the node does not have the chunk locally.
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func (f *Fetcher) Offer(source *enode.ID) {
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// First we need to have this select to make sure that we return if context is done
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select {
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case <-f.ctx.Done():
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return
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default:
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}
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// This select alone would not guarantee that we return of context is done, it could potentially
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// push to offerC instead if offerC is available (see number 2 in https://golang.org/ref/spec#Select_statements)
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select {
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case f.offerC <- source:
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case <-f.ctx.Done():
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}
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}
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// Request is called when an upstream peer request the chunk as part of `RetrieveRequestMsg`, or from a local request through FileStore, and the node does not have the chunk locally.
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func (f *Fetcher) Request(hopCount uint8) {
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// First we need to have this select to make sure that we return if context is done
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select {
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case <-f.ctx.Done():
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return
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default:
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}
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if hopCount >= maxHopCount {
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log.Debug("fetcher request hop count limit reached", "hops", hopCount)
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return
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}
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// This select alone would not guarantee that we return of context is done, it could potentially
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// push to offerC instead if offerC is available (see number 2 in https://golang.org/ref/spec#Select_statements)
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select {
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case f.requestC <- hopCount + 1:
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case <-f.ctx.Done():
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}
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}
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// start prepares the Fetcher
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// it keeps the Fetcher alive within the lifecycle of the passed context
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func (f *Fetcher) run(peers *sync.Map) {
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var (
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doRequest bool // determines if retrieval is initiated in the current iteration
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wait *time.Timer // timer for search timeout
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waitC <-chan time.Time // timer channel
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sources []*enode.ID // known sources, ie. peers that offered the chunk
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requested bool // true if the chunk was actually requested
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hopCount uint8
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)
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gone := make(chan *enode.ID) // channel to signal that a peer we requested from disconnected
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// loop that keeps the fetching process alive
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// after every request a timer is set. If this goes off we request again from another peer
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// note that the previous request is still alive and has the chance to deliver, so
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// requesting again extends the search. ie.,
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// if a peer we requested from is gone we issue a new request, so the number of active
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// requests never decreases
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for {
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select {
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// incoming offer
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case source := <-f.offerC:
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log.Trace("new source", "peer addr", source, "request addr", f.addr)
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// 1) the chunk is offered by a syncing peer
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// add to known sources
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sources = append(sources, source)
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// launch a request to the source iff the chunk was requested (not just expected because its offered by a syncing peer)
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doRequest = requested
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// incoming request
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case hopCount = <-f.requestC:
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log.Trace("new request", "request addr", f.addr)
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// 2) chunk is requested, set requested flag
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// launch a request iff none been launched yet
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doRequest = !requested
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requested = true
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// peer we requested from is gone. fall back to another
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// and remove the peer from the peers map
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case id := <-gone:
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log.Trace("peer gone", "peer id", id.String(), "request addr", f.addr)
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peers.Delete(id.String())
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doRequest = requested
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// search timeout: too much time passed since the last request,
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// extend the search to a new peer if we can find one
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case <-waitC:
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log.Trace("search timed out: requesting", "request addr", f.addr)
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doRequest = requested
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// all Fetcher context closed, can quit
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case <-f.ctx.Done():
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log.Trace("terminate fetcher", "request addr", f.addr)
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// TODO: send cancellations to all peers left over in peers map (i.e., those we requested from)
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return
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}
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// need to issue a new request
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if doRequest {
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var err error
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sources, err = f.doRequest(gone, peers, sources, hopCount)
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if err != nil {
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log.Info("unable to request", "request addr", f.addr, "err", err)
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}
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}
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// if wait channel is not set, set it to a timer
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if requested {
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if wait == nil {
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wait = time.NewTimer(f.searchTimeout)
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defer wait.Stop()
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waitC = wait.C
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} else {
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// stop the timer and drain the channel if it was not drained earlier
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if !wait.Stop() {
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select {
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case <-wait.C:
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default:
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}
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}
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// reset the timer to go off after defaultSearchTimeout
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wait.Reset(f.searchTimeout)
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}
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}
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doRequest = false
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}
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}
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// doRequest attempts at finding a peer to request the chunk from
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// * first it tries to request explicitly from peers that are known to have offered the chunk
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// * if there are no such peers (available) it tries to request it from a peer closest to the chunk address
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// excluding those in the peersToSkip map
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// * if no such peer is found an error is returned
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//
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// if a request is successful,
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// * the peer's address is added to the set of peers to skip
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// * the peer's address is removed from prospective sources, and
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// * a go routine is started that reports on the gone channel if the peer is disconnected (or terminated their streamer)
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func (f *Fetcher) doRequest(gone chan *enode.ID, peersToSkip *sync.Map, sources []*enode.ID, hopCount uint8) ([]*enode.ID, error) {
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var i int
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var sourceID *enode.ID
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var quit chan struct{}
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req := &Request{
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Addr: f.addr,
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SkipCheck: f.skipCheck,
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peersToSkip: peersToSkip,
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HopCount: hopCount,
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}
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foundSource := false
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// iterate over known sources
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for i = 0; i < len(sources); i++ {
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req.Source = sources[i]
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var err error
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sourceID, quit, err = f.protoRequestFunc(f.ctx, req)
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if err == nil {
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// remove the peer from known sources
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// Note: we can modify the source although we are looping on it, because we break from the loop immediately
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sources = append(sources[:i], sources[i+1:]...)
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foundSource = true
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break
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}
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}
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// if there are no known sources, or none available, we try request from a closest node
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if !foundSource {
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req.Source = nil
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var err error
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sourceID, quit, err = f.protoRequestFunc(f.ctx, req)
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if err != nil {
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// if no peers found to request from
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return sources, err
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}
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}
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// add peer to the set of peers to skip from now
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peersToSkip.Store(sourceID.String(), time.Now())
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// if the quit channel is closed, it indicates that the source peer we requested from
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// disconnected or terminated its streamer
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// here start a go routine that watches this channel and reports the source peer on the gone channel
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// this go routine quits if the fetcher global context is done to prevent process leak
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go func() {
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select {
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case <-quit:
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gone <- sourceID
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case <-f.ctx.Done():
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}
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}()
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return sources, nil
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}
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