path: root/eth/gasprice/gasprice.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 gasprice

import (
    "context"
    "math/big"
    "sort"
    "sync"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/internal/ethapi"
    "github.com/ethereum/go-ethereum/params"
    "github.com/ethereum/go-ethereum/rpc"
)

var maxPrice = big.NewInt(500 * params.Shannon)

type Config struct {
    Blocks     int
    Percentile int
    Default    *big.Int
}

// Oracle recommends gas prices based on the content of recent
// blocks. Suitable for both light and full clients.
type Oracle struct {
    backend   ethapi.Backend
    lastHead  common.Hash
    lastPrice *big.Int
    cacheLock sync.RWMutex
    fetchLock sync.Mutex

    checkBlocks, maxEmpty, maxBlocks int
    percentile                       int
}

// NewOracle returns a new oracle.
func NewOracle(backend ethapi.Backend, params Config) *Oracle {
    blocks := params.Blocks
    if blocks < 1 {
        blocks = 1
    }
    percent := params.Percentile
    if percent < 0 {
        percent = 0
    }
    if percent > 100 {
        percent = 100
    }
    return &Oracle{
        backend:     backend,
        lastPrice:   params.Default,
        checkBlocks: blocks,
        maxEmpty:    blocks / 2,
        maxBlocks:   blocks * 5,
        percentile:  percent,
    }
}

// SuggestPrice returns the recommended gas price.
func (gpo *Oracle) SuggestPrice(ctx context.Context) (*big.Int, error) {
    gpo.cacheLock.RLock()
    lastHead := gpo.lastHead
    lastPrice := gpo.lastPrice
    gpo.cacheLock.RUnlock()

    head, _ := gpo.backend.HeaderByNumber(ctx, rpc.LatestBlockNumber)
    headHash := head.Hash()
    if headHash == lastHead {
        return lastPrice, nil
    }

    gpo.fetchLock.Lock()
    defer gpo.fetchLock.Unlock()

    // try checking the cache again, maybe the last fetch fetched what we need
    gpo.cacheLock.RLock()
    lastHead = gpo.lastHead
    lastPrice = gpo.lastPrice
    gpo.cacheLock.RUnlock()
    if headHash == lastHead {
        return lastPrice, nil
    }

    blockNum := head.Number.Uint64()
    ch := make(chan getBlockPricesResult, gpo.checkBlocks)
    sent := 0
    exp := 0
    var txPrices []*big.Int
    for sent < gpo.checkBlocks && blockNum > 0 {
        go gpo.getBlockPrices(ctx, blockNum, ch)
        sent++
        exp++
        blockNum--
    }
    maxEmpty := gpo.maxEmpty
    for exp > 0 {
        res := <-ch
        if res.err != nil {
            return lastPrice, res.err
        }
        exp--
        if len(res.prices) > 0 {
            txPrices = append(txPrices, res.prices...)
            continue
        }
        if maxEmpty > 0 {
            maxEmpty--
            continue
        }
        if blockNum > 0 && sent < gpo.maxBlocks {
            go gpo.getBlockPrices(ctx, blockNum, ch)
            sent++
            exp++
            blockNum--
        }
    }
    price := lastPrice
    if len(txPrices) > 0 {
        sort.Sort(bigIntArray(txPrices))
        price = txPrices[(len(txPrices)-1)*gpo.percentile/100]
    }
    if price.Cmp(maxPrice) > 0 {
        price = new(big.Int).Set(maxPrice)
    }

    gpo.cacheLock.Lock()
    gpo.lastHead = headHash
    gpo.lastPrice = price
    gpo.cacheLock.Unlock()
    return price, nil
}

type getBlockPricesResult struct {
    prices []*big.Int
    err    error
}

// getLowestPrice calculates the lowest transaction gas price in a given block
// and sends it to the result channel. If the block is empty, price is nil.
func (gpo *Oracle) getBlockPrices(ctx context.Context, blockNum uint64, ch chan getBlockPricesResult) {
    block, err := gpo.backend.BlockByNumber(ctx, rpc.BlockNumber(blockNum))
    if block == nil {
        ch <- getBlockPricesResult{nil, err}
        return
    }
    txs := block.Transactions()
    prices := make([]*big.Int, len(txs))
    for i, tx := range txs {
        prices[i] = tx.GasPrice()
    }
    ch <- getBlockPricesResult{prices, nil}
}

type bigIntArray []*big.Int

func (s bigIntArray) Len() int           { return len(s) }
func (s bigIntArray) Less(i, j int) bool { return s[i].Cmp(s[j]) < 0 }
func (s bigIntArray) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }