les, light: LES/2 protocol version (#14970)

This PR implements the new LES protocol version extensions:

* new and more efficient Merkle proofs reply format (when replying to
  a multiple Merkle proofs request, we just send a single set of trie
  nodes containing all necessary nodes)
* BBT (BloomBitsTrie) works similarly to the existing CHT and contains
  the bloombits search data to speed up log searches
* GetTxStatusMsg returns the inclusion position or the
  pending/queued/unknown state of a transaction referenced by hash
* an optional signature of new block data (number/hash/td) can be
  included in AnnounceMsg to provide an option for "very light
  clients" (mobile/embedded devices) to skip expensive Ethash check
  and accept multiple signatures of somewhat trusted servers (still a
  lot better than trusting a single server completely and retrieving
  everything through RPC). The new client mode is not implemented in
  this PR, just the protocol extension.

les/bloombits.go

@@ -0,0 +1,84 @@
+// Copyright 2017 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 les
+
+import (
+	"time"
+
+	"github.com/ethereum/go-ethereum/common/bitutil"
+	"github.com/ethereum/go-ethereum/light"
+)
+
+const (
+	// bloomServiceThreads is the number of goroutines used globally by an Ethereum
+	// instance to service bloombits lookups for all running filters.
+	bloomServiceThreads = 16
+
+	// bloomFilterThreads is the number of goroutines used locally per filter to
+	// multiplex requests onto the global servicing goroutines.
+	bloomFilterThreads = 3
+
+	// bloomRetrievalBatch is the maximum number of bloom bit retrievals to service
+	// in a single batch.
+	bloomRetrievalBatch = 16
+
+	// bloomRetrievalWait is the maximum time to wait for enough bloom bit requests
+	// to accumulate request an entire batch (avoiding hysteresis).
+	bloomRetrievalWait = time.Microsecond * 100
+)
+
+// startBloomHandlers starts a batch of goroutines to accept bloom bit database
+// retrievals from possibly a range of filters and serving the data to satisfy.
+func (eth *LightEthereum) startBloomHandlers() {
+	for i := 0; i < bloomServiceThreads; i++ {
+		go func() {
+			for {
+				select {
+				case <-eth.shutdownChan:
+					return
+
+				case request := <-eth.bloomRequests:
+					task := <-request
+					task.Bitsets = make([][]byte, len(task.Sections))
+					compVectors, err := light.GetBloomBits(task.Context, eth.odr, task.Bit, task.Sections)
+					if err == nil {
+						for i, _ := range task.Sections {
+							if blob, err := bitutil.DecompressBytes(compVectors[i], int(light.BloomTrieFrequency/8)); err == nil {
+								task.Bitsets[i] = blob
+							} else {
+								task.Error = err
+							}
+						}
+					} else {
+						task.Error = err
+					}
+					request <- task
+				}
+			}
+		}()
+	}
+}
+
+const (
+	// bloomConfirms is the number of confirmation blocks before a bloom section is
+	// considered probably final and its rotated bits are calculated.
+	bloomConfirms = 256
+
+	// bloomThrottling is the time to wait between processing two consecutive index
+	// sections. It's useful during chain upgrades to prevent disk overload.
+	bloomThrottling = 100 * time.Millisecond
+)