whisper/whisperv6: PoW requirement (#15701)

New Whisper-level message introduced (PoW requirement),
corresponding logic added, plus some tests.

whisper/whisperv6/peer.go

@@ -18,6 +18,7 @@ package whisperv6
 
 import (
 	"fmt"
+	"math"
 	"time"
 
 	"github.com/ethereum/go-ethereum/common"
@@ -29,10 +30,12 @@ import (
 
 // peer represents a whisper protocol peer connection.
 type Peer struct {
-	host    *Whisper
-	peer    *p2p.Peer
-	ws      p2p.MsgReadWriter
-	trusted bool
+	host *Whisper
+	peer *p2p.Peer
+	ws   p2p.MsgReadWriter
+
+	trusted        bool
+	powRequirement float64
 
 	known *set.Set // Messages already known by the peer to avoid wasting bandwidth
 
@@ -42,12 +45,13 @@ type Peer struct {
 // newPeer creates a new whisper peer object, but does not run the handshake itself.
 func newPeer(host *Whisper, remote *p2p.Peer, rw p2p.MsgReadWriter) *Peer {
 	return &Peer{
-		host:    host,
-		peer:    remote,
-		ws:      rw,
-		trusted: false,
-		known:   set.New(),
-		quit:    make(chan struct{}),
+		host:           host,
+		peer:           remote,
+		ws:             rw,
+		trusted:        false,
+		powRequirement: 0.0,
+		known:          set.New(),
+		quit:           make(chan struct{}),
 	}
 }
 
@@ -152,7 +156,7 @@ func (p *Peer) broadcast() error {
 	envelopes := p.host.Envelopes()
 	bundle := make([]*Envelope, 0, len(envelopes))
 	for _, envelope := range envelopes {
-		if !p.marked(envelope) {
+		if !p.marked(envelope) && envelope.PoW() >= p.powRequirement {
 			bundle = append(bundle, envelope)
 		}
 	}
@@ -177,3 +181,8 @@ func (p *Peer) ID() []byte {
 	id := p.peer.ID()
 	return id[:]
 }
+
+func (p *Peer) notifyAboutPowRequirementChange(pow float64) error {
+	i := math.Float64bits(pow)
+	return p2p.Send(p.ws, powRequirementCode, i)
+}