les, les/flowcontrol: improved request serving and flow control (#18230)

This change

- implements concurrent LES request serving even for a single peer.
- replaces the request cost estimation method with a cost table based on
  benchmarks which gives much more consistent results. Until now the
  allowed number of light peers was just a guess which probably contributed
  a lot to the fluctuating quality of available service. Everything related
  to request cost is implemented in a single object, the 'cost tracker'. It
  uses a fixed cost table with a global 'correction factor'. Benchmark code
  is included and can be run at any time to adapt costs to low-level
  implementation changes.
- reimplements flowcontrol.ClientManager in a cleaner and more efficient
  way, with added capabilities: There is now control over bandwidth, which
  allows using the flow control parameters for client prioritization.
  Target utilization over 100 percent is now supported to model concurrent
  request processing. Total serving bandwidth is reduced during block
  processing to prevent database contention.
- implements an RPC API for the LES servers allowing server operators to
  assign priority bandwidth to certain clients and change prioritized
  status even while the client is connected. The new API is meant for
  cases where server operators charge for LES using an off-protocol mechanism.
- adds a unit test for the new client manager.
- adds an end-to-end test using the network simulator that tests bandwidth
  control functions through the new API.

les/freeclient_test.go

@@ -14,13 +14,12 @@
 // 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 light implements on-demand retrieval capable state and chain objects
-// for the Ethereum Light Client.
 package les
 
 import (
 	"fmt"
 	"math/rand"
+	"strconv"
 	"testing"
 	"time"
 
@@ -44,32 +43,38 @@ const testFreeClientPoolTicks = 500000
 
 func testFreeClientPool(t *testing.T, connLimit, clientCount int) {
 	var (
-		clock     mclock.Simulated
-		db        = ethdb.NewMemDatabase()
-		pool      = newFreeClientPool(db, connLimit, 10000, &clock)
-		connected = make([]bool, clientCount)
-		connTicks = make([]int, clientCount)
-		disconnCh = make(chan int, clientCount)
-	)
-	peerId := func(i int) string {
-		return fmt.Sprintf("test peer #%d", i)
-	}
-	disconnFn := func(i int) func() {
-		return func() {
+		clock       mclock.Simulated
+		db          = ethdb.NewMemDatabase()
+		connected   = make([]bool, clientCount)
+		connTicks   = make([]int, clientCount)
+		disconnCh   = make(chan int, clientCount)
+		peerAddress = func(i int) string {
+			return fmt.Sprintf("addr #%d", i)
+		}
+		peerId = func(i int) string {
+			return fmt.Sprintf("id #%d", i)
+		}
+		disconnFn = func(id string) {
+			i, err := strconv.Atoi(id[4:])
+			if err != nil {
+				panic(err)
+			}
 			disconnCh <- i
 		}
-	}
+		pool = newFreeClientPool(db, 1, 10000, &clock, disconnFn)
+	)
+	pool.setLimits(connLimit, uint64(connLimit))
 
 	// pool should accept new peers up to its connected limit
 	for i := 0; i < connLimit; i++ {
-		if pool.connect(peerId(i), disconnFn(i)) {
+		if pool.connect(peerAddress(i), peerId(i)) {
 			connected[i] = true
 		} else {
 			t.Fatalf("Test peer #%d rejected", i)
 		}
 	}
 	// since all accepted peers are new and should not be kicked out, the next one should be rejected
-	if pool.connect(peerId(connLimit), disconnFn(connLimit)) {
+	if pool.connect(peerAddress(connLimit), peerId(connLimit)) {
 		connected[connLimit] = true
 		t.Fatalf("Peer accepted over connected limit")
 	}
@@ -80,11 +85,11 @@ func testFreeClientPool(t *testing.T, connLimit, clientCount int) {
 
 		i := rand.Intn(clientCount)
 		if connected[i] {
-			pool.disconnect(peerId(i))
+			pool.disconnect(peerAddress(i))
 			connected[i] = false
 			connTicks[i] += tickCounter
 		} else {
-			if pool.connect(peerId(i), disconnFn(i)) {
+			if pool.connect(peerAddress(i), peerId(i)) {
 				connected[i] = true
 				connTicks[i] -= tickCounter
 			}
@@ -93,7 +98,7 @@ func testFreeClientPool(t *testing.T, connLimit, clientCount int) {
 		for {
 			select {
 			case i := <-disconnCh:
-				pool.disconnect(peerId(i))
+				pool.disconnect(peerAddress(i))
 				if connected[i] {
 					connTicks[i] += tickCounter
 					connected[i] = false
@@ -119,20 +124,21 @@ func testFreeClientPool(t *testing.T, connLimit, clientCount int) {
 	}
 
 	// a previously unknown peer should be accepted now
-	if !pool.connect("newPeer", func() {}) {
+	if !pool.connect("newAddr", "newId") {
 		t.Fatalf("Previously unknown peer rejected")
 	}
 
 	// close and restart pool
 	pool.stop()
-	pool = newFreeClientPool(db, connLimit, 10000, &clock)
+	pool = newFreeClientPool(db, 1, 10000, &clock, disconnFn)
+	pool.setLimits(connLimit, uint64(connLimit))
 
 	// try connecting all known peers (connLimit should be filled up)
 	for i := 0; i < clientCount; i++ {
-		pool.connect(peerId(i), func() {})
+		pool.connect(peerAddress(i), peerId(i))
 	}
 	// expect pool to remember known nodes and kick out one of them to accept a new one
-	if !pool.connect("newPeer2", func() {}) {
+	if !pool.connect("newAddr2", "newId2") {
 		t.Errorf("Previously unknown peer rejected after restarting pool")
 	}
 	pool.stop()