path: root/blockpool/section.go

package blockpool

import (
    "sync"
    "time"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/core/types"
)

/*
  section is the worker on each chain section in the block pool
  - remove the section if there are blocks missing after an absolute time
  - remove the section if there are maxIdleRounds of idle rounds of block requests with no response
  - periodically polls the chain section for missing blocks which are then requested from peers
  - registers the process controller on the peer so that if the peer is promoted as best peer the second time (after a disconnect of a better one), all active processes are switched back on unless they removed (inserted in blockchain, invalid or expired)
  - when turned off (if peer disconnects and new peer connects with alternative chain), no blockrequests are made but absolute expiry timer is ticking
  - when turned back on it recursively calls itself on the root of the next chain section
*/
type section struct {
    lock sync.RWMutex

    parent *section // connecting section back in time towards blockchain
    child  *section // connecting section forward in time

    top    *node // the topmost node = head node = youngest node within the chain section
    bottom *node // the bottom node = root node = oldest node within the chain section
    nodes  []*node

    peer       *peer
    parentHash common.Hash

    blockHashes []common.Hash

    poolRootIndex int

    bp *BlockPool

    controlC  chan *peer     // to (de)register the current best peer
    poolRootC chan *peer     // indicate connectedness to blockchain (well, known blocks)
    offC      chan bool      // closed if process terminated
    suicideC  chan bool      // initiate suicide on the section
    quitInitC chan bool      // to signal end of initialisation
    forkC     chan chan bool // freeze section process while splitting
    switchC   chan bool      // switching
    idleC     chan bool      // channel to indicate thai food
    processC  chan *node     //
    missingC  chan *node     //

    blocksRequestTimer      <-chan time.Time
    blockHashesRequestTimer <-chan time.Time
    suicideTimer            <-chan time.Time

    blocksRequests      int
    blockHashesRequests int

    blocksRequestsComplete      bool
    blockHashesRequestsComplete bool
    ready                       bool
    same                        bool
    initialised                 bool
    active                      bool

    step        int
    idle        int
    missing     int
    lastMissing int
    depth       int
    invalid     bool
    poolRoot    bool
}

//
func (self *BlockPool) newSection(nodes []*node) *section {
    sec := &section{
        bottom:        nodes[len(nodes)-1],
        top:           nodes[0],
        nodes:         nodes,
        poolRootIndex: len(nodes),
        bp:            self,
        controlC:      make(chan *peer),
        poolRootC:     make(chan *peer),
        offC:          make(chan bool),
    }

    for i, n := range nodes {
        entry := &entry{node: n, section: sec, index: &index{i}}
        self.set(n.hash, entry)
    }

    plog.DebugDetailf("[%s] setup section process", sectionhex(sec))

    go sec.run()
    return sec
}

func (self *section) addSectionToBlockChain(p *peer) {
    self.bp.wg.Add(1)
    go func() {

        self.lock.Lock()
        defer self.lock.Unlock()
        defer func() {
            self.bp.wg.Done()
        }()

        var nodes []*node
        var n *node
        var keys []common.Hash
        var blocks []*types.Block
        for self.poolRootIndex > 0 {
            n = self.nodes[self.poolRootIndex-1]
            n.lock.RLock()
            block := n.block
            n.lock.RUnlock()
            if block == nil {
                break
            }
            self.poolRootIndex--
            keys = append(keys, n.hash)
            blocks = append(blocks, block)
            nodes = append(nodes, n)
        }

        if len(blocks) == 0 {
            return
        }

        self.bp.lock.Lock()
        for _, key := range keys {
            delete(self.bp.pool, key)
        }
        self.bp.lock.Unlock()

        plog.Debugf("[%s] insert %v blocks [%v/%v] into blockchain", sectionhex(self), len(blocks), hex(blocks[0].Hash()), hex(blocks[len(blocks)-1].Hash()))
        err := self.bp.insertChain(blocks)
        if err != nil {
            self.invalid = true
            self.bp.peers.peerError(n.blockBy, ErrInvalidBlock, "%v", err)
            plog.Warnf("invalid block %x", n.hash)
            plog.Warnf("penalise peers %v (hash), %v (block)", n.hashBy, n.blockBy)

            // or invalid block and the entire chain needs to be removed
            self.removeChain()
        } else {
            // check tds
            self.bp.wg.Add(1)
            go func() {
                plog.DebugDetailf("checking td")
                self.bp.checkTD(nodes...)
                self.bp.wg.Done()
            }()
            // if all blocks inserted in this section
            // then need to try to insert blocks in child section
            if self.poolRootIndex == 0 {
                // if there is a child section, then recursively call itself:
                // also if section process is not terminated,
                // then signal blockchain connectivity with poolRootC
                if child := self.bp.getChild(self); child != nil {
                    select {
                    case <-child.offC:
                        plog.DebugDetailf("[%s] add complete child section [%s] to the blockchain", sectionhex(self), sectionhex(child))
                    case child.poolRootC <- p:
                        plog.DebugDetailf("[%s] add incomplete child section [%s] to the blockchain", sectionhex(self), sectionhex(child))
                    }
                    child.addSectionToBlockChain(p)
                } else {
                    plog.DebugDetailf("[%s] no child section in pool", sectionhex(self))
                }
                plog.DebugDetailf("[%s] section completely inserted to blockchain - remove", sectionhex(self))
                // complete sections are removed. if called from within section process,
                // this must run in its own go routine to avoid deadlock
                self.remove()
            }
        }

        self.bp.status.lock.Lock()
        if err == nil {
            headKey := blocks[0].ParentHash()
            height := self.bp.status.chain[headKey] + len(blocks)
            self.bp.status.chain[blocks[len(blocks)-1].Hash()] = height
            if height > self.bp.status.values.LongestChain {
                self.bp.status.values.LongestChain = height
            }
            delete(self.bp.status.chain, headKey)
        }
        self.bp.status.values.BlocksInChain += len(blocks)
        self.bp.status.values.BlocksInPool -= len(blocks)
        if err != nil {
            self.bp.status.badPeers[n.blockBy]++
        }
        self.bp.status.lock.Unlock()

    }()

}

func (self *section) run() {

    // absolute time after which sub-chain is killed if not complete (some blocks are missing)
    self.suicideC = make(chan bool)
    self.forkC = make(chan chan bool)
    self.suicideTimer = time.After(self.bp.Config.BlocksTimeout)

    // node channels for the section
    // container for missing block hashes
    var checking bool
    var ping = time.NewTicker(5 * time.Second)

LOOP:
    for !self.blockHashesRequestsComplete || !self.blocksRequestsComplete {

        select {
        case <-ping.C:
            var name = "no peer"
            if self.peer != nil {
                name = self.peer.id
            }
            plog.DebugDetailf("[%s] peer <%s> active: %v", sectionhex(self), name, self.active)

        // global quit from blockpool
        case <-self.bp.quit:
            break LOOP

        // pause for peer switching
        case <-self.switchC:
            self.switchC = nil

        case p := <-self.poolRootC:
            // signal on pool root channel indicates that the blockpool is
            // connected to the blockchain, insert the longest chain of blocks
            // ignored in idle mode to avoid inserting chain sections of non-live peers
            self.poolRoot = true
            // switch off hash requests in case they were on
            self.blockHashesRequestTimer = nil
            self.blockHashesRequestsComplete = true
            self.switchOn(p)

        // peer quit or demoted, put section in idle mode
        case <-self.idleC:
            // peer quit or demoted, put section in idle mode
            plog.Debugf("[%s] peer <%s> quit or demoted", sectionhex(self), self.peer.id)
            self.switchOff()
            self.idleC = nil

        // timebomb - if section is not complete in time, nuke the entire chain
        case <-self.suicideTimer:
            self.removeChain()
            plog.Debugf("[%s] timeout. (%v total attempts): missing %v/%v/%v...suicide", sectionhex(self), self.blocksRequests, self.missing, self.lastMissing, self.depth)
            self.suicideTimer = nil
            break LOOP

        // closing suicideC triggers section suicide: removes section nodes from pool and terminates section process
        case <-self.suicideC:
            plog.DebugDetailf("[%s] quit", sectionhex(self))
            break LOOP

        // alarm for checking blocks in the section
        case <-self.blocksRequestTimer:
            plog.DebugDetailf("[%s] alarm: block request time", sectionhex(self))
            self.processC = self.missingC

        // alarm for checking parent of the section or sending out hash requests
        case <-self.blockHashesRequestTimer:
            plog.DebugDetailf("[%s] alarm: hash request time", sectionhex(self))
            self.blockHashesRequest()

        // activate this section process with a peer
        case p := <-self.controlC:
            if p == nil {
                self.switchOff()
            } else {
                self.switchOn(p)
            }
            self.bp.wg.Done()
        // blocks the process until section is split at the fork
        case waiter := <-self.forkC:
            <-waiter
            self.initialised = false
            self.quitInitC = nil

        //
        case n, ok := <-self.processC:
            // channel closed, first iteration finished
            if !ok && !self.initialised {
                plog.DebugDetailf("[%s] section initalised: missing %v/%v/%v", sectionhex(self), self.missing, self.lastMissing, self.depth)
                self.initialised = true
                self.processC = nil
                // self.processC = make(chan *node, self.missing)
                self.checkRound()
                checking = false
                break
            }
            // plog.DebugDetailf("[%s] section proc step %v: missing %v/%v/%v", sectionhex(self), self.step, self.missing, self.lastMissing, self.depth)
            if !checking {
                self.step = 0
                self.missing = 0
                checking = true
            }
            self.step++

            n.lock.RLock()
            block := n.block
            n.lock.RUnlock()

            // if node has no block, request it (buffer it for batch request)
            // feed it to missingC channel for the next round
            if block == nil {
                pos := self.missing % self.bp.Config.BlockBatchSize
                if pos == 0 {
                    if self.missing != 0 {
                        self.bp.requestBlocks(self.blocksRequests, self.blockHashes[:])
                    }
                    self.blockHashes = self.bp.getHashSlice()
                }
                self.blockHashes[pos] = n.hash
                self.missing++
                self.missingC <- n
            } else {
                // checking for parent block
                if self.poolRoot {
                    // if node has got block (received via async AddBlock call from protocol)
                    if self.step == self.lastMissing {
                        // current root of the pool
                        plog.DebugDetailf("[%s] received block for current pool root %s", sectionhex(self), hex(n.hash))
                        self.addSectionToBlockChain(self.peer)
                    }
                } else {
                    if (self.parentHash == common.Hash{}) && n == self.bottom {
                        self.parentHash = block.ParentHash()
                        plog.DebugDetailf("[%s] got parent head block hash %s...checking", sectionhex(self), hex(self.parentHash))
                        self.blockHashesRequest()
                    }
                }
            }
            if self.initialised && self.step == self.lastMissing {
                plog.DebugDetailf("[%s] check if new blocks arrived (attempt %v): missing %v/%v/%v", sectionhex(self), self.blocksRequests, self.missing, self.lastMissing, self.depth)
                self.checkRound()
                checking = false
            }
        } // select
    } // for

    close(self.offC)
    if self.peer != nil {
        self.active = false
        self.bp.wg.Done()
    }

    plog.DebugDetailf("[%s] section process terminated: %v blocks retrieved (%v attempts), hash requests complete on root (%v attempts).", sectionhex(self), self.depth, self.blocksRequests, self.blockHashesRequests)

}

func (self *section) switchOn(newpeer *peer) {

    oldpeer := self.peer
    // reset switchC/switchC to current best peer
    self.idleC = newpeer.idleC
    self.switchC = newpeer.switchC
    self.peer = newpeer

    if oldpeer != newpeer {
        oldp := "no peer"
        newp := "no peer"
        if oldpeer != nil {
            oldp = oldpeer.id
        }
        if newpeer != nil {
            newp = newpeer.id
        }

        plog.DebugDetailf("[%s] active mode <%s> -> <%s>", sectionhex(self), oldp, newp)
    }

    // activate section with current peer
    if oldpeer == nil {
        self.bp.wg.Add(1)
        self.active = true

        if !self.blockHashesRequestsComplete {
            self.blockHashesRequestTimer = time.After(0)
        }
        if !self.blocksRequestsComplete {
            if !self.initialised {
                if self.quitInitC != nil {
                    <-self.quitInitC
                }
                self.missingC = make(chan *node, self.bp.Config.BlockHashesBatchSize)
                self.processC = make(chan *node, self.bp.Config.BlockHashesBatchSize)
                self.quitInitC = make(chan bool)

                self.step = 0
                self.missing = 0
                self.depth = len(self.nodes)
                self.lastMissing = self.depth

                self.feedNodes()
            } else {
                self.blocksRequestTimer = time.After(0)
            }
        }
    }
}

// put the section to idle mode
func (self *section) switchOff() {
    // active -> idle
    if self.peer != nil {
        oldp := "no peer"
        oldpeer := self.peer
        if oldpeer != nil {
            oldp = oldpeer.id
        }
        plog.DebugDetailf("[%s] idle mode peer <%s> -> <> (%v total attempts): missing %v/%v/%v", sectionhex(self), oldp, self.blocksRequests, self.missing, self.lastMissing, self.depth)

        self.active = false
        self.peer = nil
        // turn off timers
        self.blocksRequestTimer = nil
        self.blockHashesRequestTimer = nil

        if self.quitInitC != nil {
            <-self.quitInitC
            self.quitInitC = nil
        }
        self.processC = nil
        self.bp.wg.Done()
    }
}

// iterates through nodes of a section to feed processC
// used to initialise chain section
func (self *section) feedNodes() {
    // if not run at least once fully, launch iterator
    self.bp.wg.Add(1)
    go func() {
        self.lock.Lock()
        defer self.lock.Unlock()
        defer func() {
            self.bp.wg.Done()
        }()
        var n *node
    INIT:
        for _, n = range self.nodes {
            select {
            case self.processC <- n:
            case <-self.bp.quit:
                break INIT
            }
        }
        close(self.processC)
        close(self.quitInitC)
    }()
}

func (self *section) blockHashesRequest() {

    if self.switchC != nil {
        self.bp.chainLock.Lock()
        parentSection := self.parent

        if parentSection == nil {

            // only link to new parent if not switching peers
            // this protects against synchronisation issue where during switching
            // a demoted peer's fork will be chosen over the best peer's chain
            // because relinking the correct chain (activateChain) is overwritten here in
            // demoted peer's section process just before the section is put to idle mode
            if (self.parentHash != common.Hash{}) {
                if parent := self.bp.get(self.parentHash); parent != nil {
                    parentSection = parent.section
                    plog.DebugDetailf("[%s] blockHashesRequest: parent section [%s] linked\n", sectionhex(self), sectionhex(parentSection))
                    link(parentSection, self)
                } else {
                    if self.bp.hasBlock(self.parentHash) {
                        self.poolRoot = true
                        plog.DebugDetailf("[%s] blockHashesRequest: parentHash known ... inserting section in blockchain", sectionhex(self))
                        self.addSectionToBlockChain(self.peer)
                        self.blockHashesRequestTimer = nil
                        self.blockHashesRequestsComplete = true
                    }
                }
            }
        }
        self.bp.chainLock.Unlock()

        if !self.poolRoot {
            if parentSection != nil {
                //  activate parent section with this peer
                // but only if not during switch mode
                plog.DebugDetailf("[%s] parent section [%s] activated\n", sectionhex(self), sectionhex(parentSection))
                self.bp.activateChain(parentSection, self.peer, nil)
                // if not root of chain, switch off
                plog.DebugDetailf("[%s] parent found, hash requests deactivated (after %v total attempts)\n", sectionhex(self), self.blockHashesRequests)
                self.blockHashesRequestTimer = nil
                self.blockHashesRequestsComplete = true
            } else {
                self.blockHashesRequests++
                plog.DebugDetailf("[%s] hash request on root (%v total attempts)\n", sectionhex(self), self.blockHashesRequests)
                self.peer.requestBlockHashes(self.bottom.hash)
                self.blockHashesRequestTimer = time.After(self.bp.Config.BlockHashesRequestInterval)
            }
        }
    }
}

// checks number of missing blocks after each round of request and acts accordingly
func (self *section) checkRound() {
    if self.missing == 0 {
        // no missing blocks
        plog.DebugDetailf("[%s] section checked: got all blocks. process complete (%v total blocksRequests): missing %v/%v/%v", sectionhex(self), self.blocksRequests, self.missing, self.lastMissing, self.depth)
        self.blocksRequestsComplete = true
        self.blocksRequestTimer = nil
    } else {
        // some missing blocks
        plog.DebugDetailf("[%s] section checked: missing %v/%v/%v", sectionhex(self), self.missing, self.lastMissing, self.depth)
        self.blocksRequests++
        pos := self.missing % self.bp.Config.BlockBatchSize
        if pos == 0 {
            pos = self.bp.Config.BlockBatchSize
        }
        self.bp.requestBlocks(self.blocksRequests, self.blockHashes[:pos])

        // handle idle rounds
        if self.missing == self.lastMissing {
            // idle round
            if self.same {
                // more than once
                self.idle++
                // too many idle rounds
                if self.idle >= self.bp.Config.BlocksRequestMaxIdleRounds {
                    plog.DebugDetailf("[%s] block requests had %v idle rounds (%v total attempts): missing %v/%v/%v\ngiving up...", sectionhex(self), self.idle, self.blocksRequests, self.missing, self.lastMissing, self.depth)
                    self.removeChain()
                }
            } else {
                self.idle = 0
            }
            self.same = true
        } else {
            self.same = false
        }
        self.lastMissing = self.missing
        // put processC offline
        self.processC = nil
        self.blocksRequestTimer = time.After(self.bp.Config.BlocksRequestInterval)
    }
}

/*
 link connects two sections via parent/child fields
 creating a doubly linked list
 caller must hold BlockPool chainLock
*/
func link(parent *section, child *section) {
    if parent != nil {
        exChild := parent.child
        parent.child = child
        if exChild != nil && exChild != child {
            if child != nil {
                // if child is nil it is not a real fork
                plog.DebugDetailf("[%s] chain fork [%s] -> [%s]", sectionhex(parent), sectionhex(exChild), sectionhex(child))
            }
            exChild.parent = nil
        }
    }
    if child != nil {
        exParent := child.parent
        if exParent != nil && exParent != parent {
            if parent != nil {
                // if parent is nil it is not a real fork, but suicide delinking section
                plog.DebugDetailf("[%s] chain reverse fork [%s] -> [%s]", sectionhex(child), sectionhex(exParent), sectionhex(parent))
            }
            exParent.child = nil
        }
        child.parent = parent
    }
}

/*
  handle forks where connecting node is mid-section
  by splitting section at fork
  no splitting needed if connecting node is head of a section
  caller must hold chain lock
*/
func (self *BlockPool) splitSection(parent *section, entry *entry) {
    plog.DebugDetailf("[%s] split section at fork", sectionhex(parent))
    parent.deactivate()
    waiter := make(chan bool)
    parent.wait(waiter)
    chain := parent.nodes
    parent.nodes = chain[entry.index.int:]
    parent.top = parent.nodes[0]
    parent.poolRootIndex -= entry.index.int
    orphan := self.newSection(chain[0:entry.index.int])
    link(orphan, parent.child)
    close(waiter)
    orphan.deactivate()
}

func (self *section) wait(waiter chan bool) {
    self.forkC <- waiter
}

func (self *BlockPool) linkSections(nodes []*node, parent, child *section) (sec *section) {
    // if new section is created, link it to parent/child sections
    // and launch section process fetching block and further hashes
    if len(nodes) > 0 {
        sec = self.newSection(nodes)
        plog.Debugf("[%s]->[%s](%v)->[%s] new chain section", sectionhex(parent), sectionhex(sec), len(nodes), sectionhex(child))
        link(parent, sec)
        link(sec, child)
    } else {
        if parent != nil && child != nil {
            // now this can only happen if we allow response to hash request to include <from> hash
            // in this case we just link parent and child (without needing root block of child section)
            plog.Debugf("[%s]->[%s] connecting known sections", sectionhex(parent), sectionhex(child))
            link(parent, child)
        }
    }
    return
}

func (self *section) activate(p *peer) {
    self.bp.wg.Add(1)
    select {
    case <-self.offC:
        plog.DebugDetailf("[%s] completed section process. cannot activate for peer <%s>", sectionhex(self), p.id)
        self.bp.wg.Done()
    case self.controlC <- p:
        plog.DebugDetailf("[%s] activate section process for peer <%s>", sectionhex(self), p.id)
    }
}

func (self *section) deactivate() {
    self.bp.wg.Add(1)
    self.controlC <- nil
}

// removes this section exacly
func (self *section) remove() {
    select {
    case <-self.offC:
        close(self.suicideC)
        plog.DebugDetailf("[%s] remove: suicide", sectionhex(self))
    case <-self.suicideC:
        plog.DebugDetailf("[%s] remove: suicided already", sectionhex(self))
    default:
        plog.DebugDetailf("[%s] remove: suicide", sectionhex(self))
        close(self.suicideC)
    }
    self.unlink()
    self.bp.remove(self)
    plog.DebugDetailf("[%s] removed section.", sectionhex(self))

}

// remove a section and all its descendents from the pool
func (self *section) removeChain() {
    // need to get the child before removeSection delinks the section
    self.bp.chainLock.RLock()
    child := self.child
    self.bp.chainLock.RUnlock()

    plog.DebugDetailf("[%s] remove chain", sectionhex(self))
    self.remove()
    if child != nil {
        child.removeChain()
    }
}

// unlink a section from its parent/child
func (self *section) unlink() {
    // first delink from child and parent under chainlock
    self.bp.chainLock.Lock()
    link(nil, self)
    link(self, nil)
    self.bp.chainLock.Unlock()
}