From 9f8d192991c4f68fa14c91366722bbca601da117 Mon Sep 17 00:00:00 2001
From: Zsolt Felfoldi <zsfelfoldi@gmail.com>
Date: Fri, 14 Oct 2016 05:51:29 +0200
Subject: les: light client protocol and API

---
 eth/gasprice/lightprice.go | 160 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 160 insertions(+)
 create mode 100644 eth/gasprice/lightprice.go

(limited to 'eth/gasprice')

diff --git a/eth/gasprice/lightprice.go b/eth/gasprice/lightprice.go
new file mode 100644
index 000000000..ce075ff4e
--- /dev/null
+++ b/eth/gasprice/lightprice.go
@@ -0,0 +1,160 @@
+// Copyright 2015 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 (
+	"math/big"
+	"sort"
+	"sync"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/internal/ethapi"
+	"github.com/ethereum/go-ethereum/rpc"
+	"golang.org/x/net/context"
+)
+
+const (
+	LpoAvgCount     = 5
+	LpoMinCount     = 3
+	LpoMaxBlocks    = 20
+	LpoSelect       = 50
+	LpoDefaultPrice = 20000000000
+)
+
+// LightPriceOracle recommends gas prices based on the content of recent
+// blocks. Suitable for both light and full clients.
+type LightPriceOracle struct {
+	backend   ethapi.Backend
+	lastHead  common.Hash
+	lastPrice *big.Int
+	cacheLock sync.RWMutex
+	fetchLock sync.Mutex
+}
+
+// NewLightPriceOracle returns a new oracle.
+func NewLightPriceOracle(backend ethapi.Backend) *LightPriceOracle {
+	return &LightPriceOracle{
+		backend:   backend,
+		lastPrice: big.NewInt(LpoDefaultPrice),
+	}
+}
+
+// SuggestPrice returns the recommended gas price.
+func (self *LightPriceOracle) SuggestPrice(ctx context.Context) (*big.Int, error) {
+	self.cacheLock.RLock()
+	lastHead := self.lastHead
+	lastPrice := self.lastPrice
+	self.cacheLock.RUnlock()
+
+	head, _ := self.backend.HeaderByNumber(ctx, rpc.LatestBlockNumber)
+	headHash := head.Hash()
+	if headHash == lastHead {
+		return lastPrice, nil
+	}
+
+	self.fetchLock.Lock()
+	defer self.fetchLock.Unlock()
+
+	// try checking the cache again, maybe the last fetch fetched what we need
+	self.cacheLock.RLock()
+	lastHead = self.lastHead
+	lastPrice = self.lastPrice
+	self.cacheLock.RUnlock()
+	if headHash == lastHead {
+		return lastPrice, nil
+	}
+
+	blockNum := head.GetNumberU64()
+	chn := make(chan lpResult, LpoMaxBlocks)
+	sent := 0
+	exp := 0
+	var lps bigIntArray
+	for sent < LpoAvgCount && blockNum > 0 {
+		go self.getLowestPrice(ctx, blockNum, chn)
+		sent++
+		exp++
+		blockNum--
+	}
+	maxEmpty := LpoAvgCount - LpoMinCount
+	for exp > 0 {
+		res := <-chn
+		if res.err != nil {
+			return nil, res.err
+		}
+		exp--
+		if res.price != nil {
+			lps = append(lps, res.price)
+		} else {
+			if maxEmpty > 0 {
+				maxEmpty--
+			} else {
+				if blockNum > 0 && sent < LpoMaxBlocks {
+					go self.getLowestPrice(ctx, blockNum, chn)
+					sent++
+					exp++
+					blockNum--
+				}
+			}
+		}
+	}
+	price := lastPrice
+	if len(lps) > 0 {
+		sort.Sort(lps)
+		price = lps[(len(lps)-1)*LpoSelect/100]
+	}
+
+	self.cacheLock.Lock()
+	self.lastHead = headHash
+	self.lastPrice = price
+	self.cacheLock.Unlock()
+	return price, nil
+}
+
+type lpResult struct {
+	price *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 (self *LightPriceOracle) getLowestPrice(ctx context.Context, blockNum uint64, chn chan lpResult) {
+	block, err := self.backend.BlockByNumber(ctx, rpc.BlockNumber(blockNum))
+	if block == nil {
+		chn <- lpResult{nil, err}
+		return
+	}
+	txs := block.Transactions()
+	if len(txs) == 0 {
+		chn <- lpResult{nil, nil}
+		return
+	}
+	// find smallest gasPrice
+	minPrice := txs[0].GasPrice()
+	for i := 1; i < len(txs); i++ {
+		price := txs[i].GasPrice()
+		if price.Cmp(minPrice) < 0 {
+			minPrice = price
+		}
+	}
+	chn <- lpResult{minPrice, 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] }
-- 
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