兄弟连区块链教程以太坊源码分析downloader-peer源码分析，区块链行业正逐渐褪去发展之初的浮躁、回归理性，表面上看相关人才需求与身价似乎正在回落。但事实上，正是初期泡沫的渐退，让人们更多的关注点放在了区块链真正的技术之上。
peer模块包含了downloader使用的peer节点，封装了吞吐量，是否空闲，并记录了之前失败的信息。
peer
// peerConnection represents an active peer from which hashes and blocks are retrieved.
type peerConnection struct {
id string // Unique identifier of the peer
headerIdle int32 // Current header activity state of the peer (idle = 0, active = 1) 当前的header获取的工作状态。
blockIdle int32 // Current block activity state of the peer (idle = 0, active = 1) 当前的区块获取的工作状态
receiptIdle int32 // Current receipt activity state of the peer (idle = 0, active = 1) 当前的收据获取的工作状态
stateIdle int32 // Current node data activity state of the peer (idle = 0, active = 1) 当前节点状态的工作状态
headerThroughput float64 // Number of headers measured to be retrievable per second //记录每秒能够接收多少个区块头的度量值
blockThroughput float64 // Number of blocks (bodies) measured to be retrievable per second //记录每秒能够接收多少个区块的度量值
receiptThroughput float64 // Number of receipts measured to be retrievable per second 记录每秒能够接收多少个收据的度量值
stateThroughput float64 // Number of node data pieces measured to be retrievable per second 记录每秒能够接收多少个账户状态的度量值
rtt time.Duration // Request round trip time to track responsiveness (QoS) 请求回应时间
headerStarted time.Time // Time instance when the last header fetch was started 记录最后一个header fetch的请求时间
blockStarted time.Time // Time instance when the last block (body) fetch was started
receiptStarted time.Time // Time instance when the last receipt fetch was started
stateStarted time.Time // Time instance when the last node data fetch was started
lacking map[common.Hash]struct{} // Set of hashes not to request (didn't have previously) 记录的Hash值不会去请求，一般是因为之前的请求失败
peer Peer // eth的peer
version int // Eth protocol version number to switch strategies
log log.Logger // Contextual logger to add extra infos to peer logs
lock sync.RWMutex}
FetchXXX
FetchHeaders FetchBodies等函数 主要调用了eth.peer的功能来进行发送数据请求。
// FetchHeaders sends a header retrieval request to the remote peer.
func (p *peerConnection) FetchHeaders(from uint64, count int) error {
// Sanity check the protocol version
if p.version = maxLackingHashes {
for drop := range p.lacking {
delete(p.lacking, drop)
break
}
}
p.lacking[hash] = struct{}{}
}
// Lacks retrieves whether the hash of a blockchain item is on the peers lacking
// list (i.e. whether we know that the peer does not have it).
func (p *peerConnection) Lacks(hash common.Hash) bool {
p.lock.RLock()
defer p.lock.RUnlock()
_, ok := p.lacking[hash]
return ok
}peerSet
// peerSet represents the collection of active peer participating in the chain
// download procedure.
type peerSet struct {
peers map[string]*peerConnection
newPeerFeed event.Feed
peerDropFeed event.Feed
lock sync.RWMutex}
Register 和 UnRegister
// Register injects a new peer into the working set, or returns an error if the
// peer is already known.
//
// The method also sets the starting throughput values of the new peer to the
// average of all existing peers, to give it a realistic chance of being used
// for data retrievals.
func (ps peerSet) Register(p peerConnection) error {
// Retrieve the current median RTT as a sane default
p.rtt = ps.medianRTT()
// Register the new peer with some meaningful defaults
ps.lock.Lock()
if _, ok := ps.peers[p.id]; ok {
ps.lock.Unlock()
return errAlreadyRegistered
}
if len(ps.peers) > 0 {
p.headerThroughput, p.blockThroughput, p.receiptThroughput, p.stateThroughput = 0, 0, 0, 0
for _, peer := range ps.peers {
peer.lock.RLock()
p.headerThroughput += peer.headerThroughput
p.blockThroughput += peer.blockThroughput
p.receiptThroughput += peer.receiptThroughput
p.stateThroughput += peer.stateThroughput
peer.lock.RUnlock()
}
p.headerThroughput /= float64(len(ps.peers))
p.blockThroughput /= float64(len(ps.peers))
p.receiptThroughput /= float64(len(ps.peers))
p.stateThroughput /= float64(len(ps.peers))
}
ps.peers[p.id] = p
ps.lock.Unlock()
ps.newPeerFeed.Send(p)
return nil}
// Unregister removes a remote peer from the active set, disabling any further
// actions to/from that particular entity.
func (ps *peerSet) Unregister(id string) error {
ps.lock.Lock()
p, ok := ps.peers[id]
if !ok {
defer ps.lock.Unlock()
return errNotRegistered
}
delete(ps.peers, id)
ps.lock.Unlock()
ps.peerDropFeed.Send(p)
return nil}
XXXIdlePeers
// HeaderIdlePeers retrieves a flat list of all the currently header-idle peers
// within the active peer set, ordered by their reputation.
func (ps peerSet) HeaderIdlePeers() ([]peerConnection, int) {
idle := func(p *peerConnection) bool {
return atomic.LoadInt32(&p.headerIdle) == 0
}
throughput := func(p *peerConnection) float64 {
p.lock.RLock()
defer p.lock.RUnlock()
return p.headerThroughput
}
return ps.idlePeers(62, 64, idle, throughput)}
// idlePeers retrieves a flat list of all currently idle peers satisfying the
// protocol version constraints, using the provided function to check idleness.
// The resulting set of peers are sorted by their measure throughput.
func (ps peerSet) idlePeers(minProtocol, maxProtocol int, idleCheck func(peerConnection) bool, throughput func(peerConnection) float64) ([]peerConnection, int) {
ps.lock.RLock()
defer ps.lock.RUnlock()
idle, total := make([]*peerConnection, 0, len(ps.peers)), 0
for _, p := range ps.peers { //首先抽取idle的peer
if p.version >= minProtocol && p.version 0 {
median = time.Duration(rtts[len(rtts)/2]) // Median of our connected peers (maintain even like this some baseline qos)
}
// Restrict the RTT into some QoS defaults, irrelevant of true RTT
if median rttMaxEstimate {
median = rttMaxEstimate
}
return median}
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