Fix Blackhole implemention for e2e tests

Thanks to Fu Wei for the input regarding etcd-io#17938.

[Problem]

A peer will
(a) receive traffic from its peers
(b) initiate connections to its peers (via stream and pipeline).

Thus, the current mechanism of only blocking peer traffic via the peer's existing proxy is insufficient, since only scenario (a) is handled, and scenario (b) is not blocked at all.

[Main idea]

We introduce 1 shared "HTTP proxy" for all peers. All peers will be proxying all the connections through it.

The modified architecture will look something like this:
```
A -- shared HTTP proxy ----- B
     ^ newly introduced
```

By adding this HTTP proxy, we can block all in and out traffic that is initiated from a peer to others, without having to resort to external tools, such as iptables. It's verified that the blocking of traffic is complete, compared to previous solutions [2][3].

[Implementation]

The main subtasks are
- set up an environment variable `FORWARD_PROXY`, because go will not parse HTTP_PROXY and HTTPS_PROXY that is using localhost or 127.0.0.1, regardless if the port is present or not
- implement the shared HTTP proxy by extending the existing proxy server code
- remove existing proxy setup (the per-peer proxy)
- implement enable/disable of the HTTP proxy in the e2e test

[Testing]

- `make gofail-enable && make build && make gofail-disable && \
go test -timeout 60s -run ^TestBlackholeByMockingPartitionLeader$ go.etcd.io/etcd/tests/v3/e2e -v -count=1`
- `make gofail-enable && make build && make gofail-disable && \
go test -timeout 60s -run ^TestBlackholeByMockingPartitionFollower$ go.etcd.io/etcd/tests/v3/e2e -v -count=1`

[References]
[1] Tracking issue etcd-io#17737
[2] PR (V1) https://github.com/henrybear327/etcd/tree/fix/e2e_blackhole
[3] PR (V2) etcd-io#17891
[4] PR (V3) etcd-io#17938

Signed-off-by: Chun-Hung Tseng <henrybear327@gmail.com>

pkg/proxy/server.go

@@ -116,6 +116,11 @@ type Server interface {
 	// UnblackholeRx removes blackhole operation on "receiving".
 	UnblackholeRx()
 
+	// BlackholePeer drops all traffic coming in and out of the specified peer
+	BlackholePeer(url.URL)
+	// UnblackholePeer resumes all traffic coming in and out of the specified peer
+	UnblackholePeer(url.URL)
+
 	// PauseTx stops "forwarding" packets; "outgoing" traffic blocks.
 	PauseTx()
 	// UnpauseTx removes "forwarding" pause operation.
@@ -191,6 +196,11 @@ type server struct {
 
 	latencyRxMu sync.RWMutex
 	latencyRx   time.Duration
+
+	// TODO: add mutex
+	blackholeURL map[url.URL]struct{}
+	// TODO: add mutex, remove entries once the connection is closed
+	connectionMap map[net.Addr]url.URL
 }
 
 // NewServer returns a proxy implementation with no iptables/tc dependencies.
@@ -217,6 +227,9 @@ func NewServer(cfg ServerConfig) Server {
 		pauseAcceptc: make(chan struct{}),
 		pauseTxc:     make(chan struct{}),
 		pauseRxc:     make(chan struct{}),
+
+		blackholeURL:  make(map[url.URL]struct{}),
+		connectionMap: make(map[net.Addr]url.URL),
 	}
 
 	_, fromPort, err := net.SplitHostPort(cfg.From.Host)
@@ -395,6 +408,11 @@ func (s *server) listenAndServe() {
 				}
 				connectResponse.Write(in)
 
+				// maintain connection mapping
+				if s.isHTTPProxy {
+					s.connectionMap[in.RemoteAddr()] = ??? // FIXME: how to know which peer is sending out this traffic?
+				}
+
 				return req.URL.Host
 			}
 
@@ -465,11 +483,11 @@ func (s *server) listenAndServe() {
 	}
 }
 
-func (s *server) transmit(dst io.Writer, src io.Reader) {
+func (s *server) transmit(dst, src net.Conn) {
 	s.ioCopy(dst, src, proxyTx)
 }
 
-func (s *server) receive(dst io.Writer, src io.Reader) {
+func (s *server) receive(dst, src net.Conn) {
 	s.ioCopy(dst, src, proxyRx)
 }
 
@@ -480,7 +498,7 @@ const (
 	proxyRx
 )
 
-func (s *server) ioCopy(dst io.Writer, src io.Reader, ptype proxyType) {
+func (s *server) ioCopy(dst, src net.Conn, ptype proxyType) {
 	buf := make([]byte, s.bufferSize)
 	for {
 		nr1, err := src.Read(buf)
@@ -530,6 +548,25 @@ func (s *server) ioCopy(dst io.Writer, src io.Reader, ptype proxyType) {
 		default:
 			panic("unknown proxy type")
 		}
+
+		// blackhole by URL
+		switch ptype {
+		case proxyTx:
+			s.modifyTxMu.RLock()
+			if s.modifyTx != nil {
+				data = s.modifyTx(data)
+			}
+			s.modifyTxMu.RUnlock()
+		case proxyRx:
+			s.modifyRxMu.RLock()
+			if s.modifyRx != nil {
+				data = s.modifyRx(data)
+			}
+			s.modifyRxMu.RUnlock()
+		default:
+			panic("unknown proxy type")
+		}
+
 		nr2 := len(data)
 		switch ptype {
 		case proxyTx:
@@ -954,6 +991,14 @@ func (s *server) UnblackholeRx() {
 	)
 }
 
+func (s *server) BlackholePeer(peerURL url.URL) {
+	s.blackholeURL[peerURL] = struct{}{}
+}
+
+func (s *server) UnblackholePeer(peerURL url.URL) {
+	delete(s.blackholeURL, peerURL)
+}
+
 func (s *server) PauseTx() {
 	s.pauseTxMu.Lock()
 	s.pauseTxc = make(chan struct{})

tests/e2e/blackhole_test.go

@@ -44,7 +44,7 @@ func blackholeTestByMockingPartition(t *testing.T, clusterSize int, partitionLea
 		e2e.WithSnapshotCount(10),
 		e2e.WithSnapshotCatchUpEntries(10),
 		e2e.WithIsPeerTLS(true),
-		e2e.WithPeerProxy(true),
+		e2e.WithSingleHTTPProxy(true),
 	)
 	require.NoError(t, err, "failed to start etcd cluster: %v", err)
 	defer func() {
@@ -58,13 +58,8 @@ func blackholeTestByMockingPartition(t *testing.T, clusterSize int, partitionLea
 	}
 	partitionedMember := epc.Procs[mockPartitionNodeIndex]
 	// Mock partition
-	proxy := partitionedMember.PeerProxy()
-	httpProxy := partitionedMember.PeerHTTPProxy()
 	t.Logf("Blackholing traffic from and to member %q", partitionedMember.Config().Name)
-	proxy.BlackholeTx()
-	proxy.BlackholeRx()
-	httpProxy.BlackholeTx()
-	httpProxy.BlackholeRx()
+	epc.SingleHTTPProxyInstance.BlackholePeer(partitionedMember.Config().PeerURL)
 
 	t.Logf("Wait 5s for any open connections to expire")
 	time.Sleep(5 * time.Second)
@@ -82,10 +77,7 @@ func blackholeTestByMockingPartition(t *testing.T, clusterSize int, partitionLea
 	// Wait for some time to restore the network
 	time.Sleep(1 * time.Second)
 	t.Logf("Unblackholing traffic from and to member %q", partitionedMember.Config().Name)
-	proxy.UnblackholeTx()
-	proxy.UnblackholeRx()
-	httpProxy.UnblackholeTx()
-	httpProxy.UnblackholeRx()
+	epc.SingleHTTPProxyInstance.UnblackholePeer(partitionedMember.Config().PeerURL)
 
 	leaderEPC = epc.Procs[epc.WaitLeader(t)]
 	time.Sleep(5 * time.Second)

tests/framework/e2e/cluster.go

@@ -130,6 +130,8 @@ type EtcdProcessCluster struct {
 	Cfg     *EtcdProcessClusterConfig
 	Procs   []EtcdProcess
 	nextSeq int // sequence number of the next etcd process (if it will be required)
+
+	SingleHTTPProxyInstance proxy.Server
 }
 
 type EtcdProcessClusterConfig struct {
@@ -144,6 +146,9 @@ type EtcdProcessClusterConfig struct {
 	LazyFSEnabled       bool
 	PeerProxy           bool
 
+	SingleHTTPProxy     bool
+	SingleHTTPProxyPort int
+
 	// Process config
 
 	EnvVars map[string]string
@@ -184,6 +189,8 @@ func DefaultConfig() *EtcdProcessClusterConfig {
 		CN:          true,
 
 		ServerConfig: *embed.NewConfig(),
+
+		SingleHTTPProxyPort: 55688,
 	}
 	cfg.ServerConfig.InitialClusterToken = "new"
 	return cfg
@@ -371,6 +378,10 @@ func WithPeerProxy(enabled bool) EPClusterOption {
 	return func(c *EtcdProcessClusterConfig) { c.PeerProxy = enabled }
 }
 
+func WithSingleHTTPProxy(enabled bool) EPClusterOption {
+	return func(c *EtcdProcessClusterConfig) { c.SingleHTTPProxy = enabled }
+}
+
 // NewEtcdProcessCluster launches a new cluster from etcd processes, returning
 // a new EtcdProcessCluster once all nodes are ready to accept client requests.
 func NewEtcdProcessCluster(ctx context.Context, t testing.TB, opts ...EPClusterOption) (*EtcdProcessCluster, error) {
@@ -438,6 +449,20 @@ func StartEtcdProcessCluster(ctx context.Context, t testing.TB, epc *EtcdProcess
 		}
 	}
 
+	if cfg.SingleHTTPProxy && epc.SingleHTTPProxyInstance == nil {
+		cfg.Logger.Info("starting single HTTP proxy...", zap.String("name", cfg.ServerConfig.Name))
+		epc.SingleHTTPProxyInstance = proxy.NewServer(proxy.ServerConfig{
+			Logger:      zap.NewNop(),
+			From:        url.URL{Scheme: "tcp", Host: fmt.Sprintf("localhost:%d", cfg.SingleHTTPProxyPort)},
+			IsHTTPProxy: true,
+		})
+		select {
+		case <-epc.SingleHTTPProxyInstance.Ready():
+		case err := <-epc.SingleHTTPProxyInstance.Error():
+			return nil, err
+		}
+	}
+
 	return epc, nil
 }
 
@@ -501,6 +526,11 @@ func (cfg *EtcdProcessClusterConfig) EtcdServerProcessConfig(tb testing.TB, i in
 	peerAdvertiseURL := url.URL{Scheme: cfg.PeerScheme(), Host: fmt.Sprintf("localhost:%d", peerPort)}
 	var proxyCfg *proxy.ServerConfig
 	var httpProxyCfg *proxy.ServerConfig
+
+	if cfg.PeerProxy && cfg.SingleHTTPProxy {
+		panic("Can't only use PeerProxy and SingleHTTPProxy at the same time")
+	}
+
 	if cfg.PeerProxy {
 		if !cfg.IsPeerTLS {
 			panic("Can't use peer proxy without peer TLS as it can result in malformed packets")
@@ -524,6 +554,12 @@ func (cfg *EtcdProcessClusterConfig) EtcdServerProcessConfig(tb testing.TB, i in
 			cfg.EnvVars = make(map[string]string)
 		}
 		cfg.EnvVars["FORWARD_PROXY"] = fmt.Sprintf("http://127.0.0.1:%d", httpProxyPort)
+	} else if cfg.SingleHTTPProxy {
+		if !cfg.IsPeerTLS {
+			panic("Can't use peer proxy without peer TLS as it can result in malformed packets")
+		}
+
+		cfg.EnvVars["FORWARD_PROXY"] = fmt.Sprintf("http://127.0.0.1:%d", cfg.SingleHTTPProxyPort)
 	}
 
 	name := fmt.Sprintf("%s-test-%d", testNameCleanRegex.ReplaceAllString(tb.Name(), ""), i)
@@ -986,6 +1022,14 @@ func (epc *EtcdProcessCluster) Close() error {
 			err = cerr
 		}
 	}
+
+	if epc.SingleHTTPProxyInstance != nil {
+		epc.lg.Info("closing single HTTP Proxy...")
+		if err = epc.SingleHTTPProxyInstance.Close(); err != nil {
+			return err
+		}
+	}
+
 	epc.lg.Info("closed test cluster.")
 	return err
 }