Fix Blackhole implemention for e2e tests

Based on Fu Wei's idea discussed in the [issue](etcd-io#17737), we employ the blocking on L7 but without using external tools.

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.

We introduce an "HTTP proxy" for each peer, which will be proxying all the connections initiated from a peer to its peers.

The modified architecture will look something like this:
```
A -- A's HTTP proxy ----- B's (currently existing) proxy - B
     ^ newly introduced   ^ in the original codebase
```

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].

The main subtasks are
- set up an environment variable `FORWARD_PROXY`
- implement HTTP proxy by extending the existing proxy server code
- implement enable/disable of the HTTP proxy in the e2e test

The result is that for every peer, we will have the arch like this
```
A -- A's HTTP proxy (connections initiated from A will be forwarded from this proxy)
 |   ^ covers case (b)
 |
 --- A's (currently existing) proxy (advertised to other peers where the connection should come in from)
     ^ covers case (a)
```

- `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`

- I run into `context deadline exceeded` sometimes
```
    etcd_mix_versions_test.go:175:
                Error Trace:    /Users/henrybear327/go/src/etcd/tests/e2e/etcd_mix_versions_test.go:175
                                                        /Users/henrybear327/go/src/etcd/tests/e2e/blackhole_test.go:75
                                                        /Users/henrybear327/go/src/etcd/tests/e2e/blackhole_test.go:31
                Error:          Received unexpected error:
                                [/Users/henrybear327/go/src/etcd/bin/etcdctl --endpoints=http://localhost:20006 put key-0 value-0] match not found.  Set EXPECT_DEBUG for more info Errs: [unexpected exit code [1] after running [/Users/henrybear327/go/src/etcd/bin/etcdctl --endpoints=http://localhost:20006 put key-0 value-0]], last lines:
                                {"level":"warn","ts":"2024-05-05T23:02:36.809726+0800","logger":"etcd-client","caller":"v3@v3.6.0-alpha.0/retry_interceptor.go:65","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0x140001ee960/localhost:20006","method":"/etcdserverpb.KV/Put","attempt":0,"error":"rpc error: code = DeadlineExceeded desc = context deadline exceeded"}
                                Error: context deadline exceeded
                                 (expected "OK", got []). Try EXPECT_DEBUG=TRUE
                Test:           TestBlackholeByMockingPartitionLeader
                Messages:       failed to put "key-0", error: [/Users/henrybear327/go/src/etcd/bin/etcdctl --endpoints=http://localhost:20006 put key-0 value-0] match not found.  Set EXPECT_DEBUG for more info Errs: [unexpected exit code [1] after running [/Users/henrybear327/go/src/etcd/bin/etcdctl --endpoints=http://localhost:20006 put key-0 value-0]], last lines:
                                {"level":"warn","ts":"2024-05-05T23:02:36.809726+0800","logger":"etcd-client","caller":"v3@v3.6.0-alpha.0/retry_interceptor.go:65","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0x140001ee960/localhost:20006","method":"/etcdserverpb.KV/Put","attempt":0,"error":"rpc error: code = DeadlineExceeded desc = context deadline exceeded"}
                                Error: context deadline exceeded
                                 (expected "OK", got []). Try EXPECT_DEBUG=TRUE
```

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

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

client/pkg/transport/transport.go

@@ -18,6 +18,8 @@ import (
 	"context"
 	"net"
 	"net/http"
+	"net/url"
+	"os"
 	"strings"
 	"time"
 )
@@ -31,7 +33,17 @@ func NewTransport(info TLSInfo, dialtimeoutd time.Duration) (*http.Transport, er
 	}
 
 	t := &http.Transport{
-		Proxy: http.ProxyFromEnvironment,
+		Proxy: func(req *http.Request) (*url.URL, error) {
+			// according to the comment of http.ProxyFromEnvironment: if the
+			// proxy URL is "localhost" (with or without a port number),
+			// then a nil URL and nil error will be returned.
+			// Thus, we need to workaround this by manually setting an
+			// ENV named FORWARD_PROXY and parse the URL (which is a localhost in our case)
+			if forwardProxy, exists := os.LookupEnv("FORWARD_PROXY"); exists {
+				return url.Parse(forwardProxy)
+			}
+			return http.ProxyFromEnvironment(req)
+		},
 		DialContext: (&net.Dialer{
 			Timeout: dialtimeoutd,
 			// value taken from http.DefaultTransport

pkg/proxy/server.go

@@ -15,6 +15,8 @@
 package proxy
 
 import (
+	"bufio"
+	"bytes"
 	"context"
 	"fmt"
 	"io"
@@ -130,18 +132,21 @@ type Server interface {
 
 // ServerConfig defines proxy server configuration.
 type ServerConfig struct {
-	Logger        *zap.Logger
-	From          url.URL
-	To            url.URL
-	TLSInfo       transport.TLSInfo
-	DialTimeout   time.Duration
-	BufferSize    int
-	RetryInterval time.Duration
+	Logger         *zap.Logger
+	From           url.URL
+	To             url.URL
+	TLSInfo        transport.TLSInfo
+	DialTimeout    time.Duration
+	BufferSize     int
+	RetryInterval  time.Duration
+	IsForwardProxy bool
 }
 
 type server struct {
 	lg *zap.Logger
 
+	isForwardProxy bool
+
 	from     url.URL
 	fromPort int
 	to       url.URL
@@ -194,6 +199,8 @@ func NewServer(cfg ServerConfig) Server {
 	s := &server{
 		lg: cfg.Logger,
 
+		isForwardProxy: cfg.IsForwardProxy,
+
 		from: cfg.From,
 		to:   cfg.To,
 
@@ -216,10 +223,12 @@ func NewServer(cfg ServerConfig) Server {
 	if err == nil {
 		s.fromPort, _ = strconv.Atoi(fromPort)
 	}
-	var toPort string
-	_, toPort, err = net.SplitHostPort(cfg.To.Host)
-	if err == nil {
-		s.toPort, _ = strconv.Atoi(toPort)
+	if !s.isForwardProxy {
+		var toPort string
+		_, toPort, err = net.SplitHostPort(cfg.To.Host)
+		if err == nil {
+			s.toPort, _ = strconv.Atoi(toPort)
+		}
 	}
 
 	if s.dialTimeout == 0 {
@@ -239,8 +248,10 @@ func NewServer(cfg ServerConfig) Server {
 	if strings.HasPrefix(s.from.Scheme, "http") {
 		s.from.Scheme = "tcp"
 	}
-	if strings.HasPrefix(s.to.Scheme, "http") {
-		s.to.Scheme = "tcp"
+	if !s.isForwardProxy {
+		if strings.HasPrefix(s.to.Scheme, "http") {
+			s.to.Scheme = "tcp"
+		}
 	}
 
 	addr := fmt.Sprintf(":%d", s.fromPort)
@@ -273,7 +284,10 @@ func (s *server) From() string {
 }
 
 func (s *server) To() string {
-	return fmt.Sprintf("%s://%s", s.to.Scheme, s.to.Host)
+	if !s.isForwardProxy {
+		return fmt.Sprintf("%s://%s", s.to.Scheme, s.to.Host)
+	}
+	return ""
 }
 
 // TODO: implement packet reordering from multiple TCP connections
@@ -353,6 +367,40 @@ func (s *server) listenAndServe() {
 			continue
 		}
 
+		parseHeaderForDestination := func() string {
+			// the first request should always contain a CONNECT header field
+			// since we set the transport to forward the traffic to the proxy
+			buf := make([]byte, s.bufferSize)
+			var data []byte
+			if nr1, err := in.Read(buf); err != nil {
+				if err == io.EOF {
+					panic("No data available for forward proxy to work on")
+				}
+			} else {
+				data = buf[:nr1]
+			}
+
+			// attempt to parse for the HOST from the CONNECT request
+			var req *http.Request
+			if req, err = http.ReadRequest(bufio.NewReader(bytes.NewReader(data))); err != nil {
+				panic("Failed to parse header in forward proxy")
+			}
+
+			if req.Method == http.MethodConnect {
+				// make sure a reply is sent back to the client
+				connectResponse := &http.Response{
+					StatusCode: 200,
+					ProtoMajor: 1,
+					ProtoMinor: 1,
+				}
+				connectResponse.Write(in)
+
+				return req.URL.Host
+			}
+
+			panic("Wrong header type to start the connection")
+		}
+
 		var out net.Conn
 		if !s.tlsInfo.Empty() {
 			var tp *http.Transport
@@ -370,9 +418,19 @@ func (s *server) listenAndServe() {
 				}
 				continue
 			}
-			out, err = tp.DialContext(ctx, s.to.Scheme, s.to.Host)
+			if s.isForwardProxy {
+				dest := parseHeaderForDestination()
+				out, err = tp.DialContext(ctx, "tcp", dest)
+			} else {
+				out, err = tp.DialContext(ctx, s.to.Scheme, s.to.Host)
+			}
 		} else {
-			out, err = net.Dial(s.to.Scheme, s.to.Host)
+			if s.isForwardProxy {
+				dest := parseHeaderForDestination()
+				out, err = net.Dial("tcp", dest)
+			} else {
+				out, err = net.Dial(s.to.Scheme, s.to.Host)
+			}
 		}
 		if err != nil {
 			select {

tests/e2e/blackhole_test.go

@@ -51,17 +51,20 @@ func blackholeTestByMockingPartition(t *testing.T, clusterSize int, partitionLea
 		require.NoError(t, epc.Close(), "failed to close etcd cluster")
 	}()
 
-	leaderId := epc.WaitLeader(t)
-	mockPartitionNodeIndex := leaderId
+	leaderID := epc.WaitLeader(t)
+	mockPartitionNodeIndex := leaderID
 	if !partitionLeader {
-		mockPartitionNodeIndex = (leaderId + 1) % (clusterSize)
+		mockPartitionNodeIndex = (leaderID + 1) % (clusterSize)
 	}
 	partitionedMember := epc.Procs[mockPartitionNodeIndex]
 	// Mock partition
 	proxy := partitionedMember.PeerProxy()
+	forwardProxy := partitionedMember.PeerForwardProxy()
 	t.Logf("Blackholing traffic from and to member %q", partitionedMember.Config().Name)
 	proxy.BlackholeTx()
 	proxy.BlackholeRx()
+	forwardProxy.BlackholeTx()
+	forwardProxy.BlackholeRx()
 
 	t.Logf("Wait 5s for any open connections to expire")
 	time.Sleep(5 * time.Second)
@@ -81,6 +84,8 @@ func blackholeTestByMockingPartition(t *testing.T, clusterSize int, partitionLea
 	t.Logf("Unblackholing traffic from and to member %q", partitionedMember.Config().Name)
 	proxy.UnblackholeTx()
 	proxy.UnblackholeRx()
+	forwardProxy.UnblackholeTx()
+	forwardProxy.UnblackholeRx()
 
 	leaderEPC = epc.Procs[epc.WaitLeader(t)]
 	time.Sleep(5 * time.Second)

tests/framework/e2e/cluster.go

@@ -481,12 +481,13 @@ func (cfg *EtcdProcessClusterConfig) SetInitialOrDiscovery(serverCfg *EtcdServer
 func (cfg *EtcdProcessClusterConfig) EtcdServerProcessConfig(tb testing.TB, i int) *EtcdServerProcessConfig {
 	var curls []string
 	var curl string
-	port := cfg.BasePort + 5*i
+	port := cfg.BasePort + 6*i
 	clientPort := port
-	peerPort := port + 1
+	peerPort := port + 1 // the port that the peer actually listens on
 	metricsPort := port + 2
-	peer2Port := port + 3
+	peer2Port := port + 3 // the port that the peer advertises
 	clientHTTPPort := port + 4
+	forwardProxyPort := port + 5 // the port of the forward proxy
 
 	if cfg.Client.ConnectionType == ClientTLSAndNonTLS {
 		curl = clientURL(cfg.ClientScheme(), clientPort, ClientNonTLS)
@@ -499,6 +500,7 @@ func (cfg *EtcdProcessClusterConfig) EtcdServerProcessConfig(tb testing.TB, i in
 	peerListenURL := url.URL{Scheme: cfg.PeerScheme(), Host: fmt.Sprintf("localhost:%d", peerPort)}
 	peerAdvertiseURL := url.URL{Scheme: cfg.PeerScheme(), Host: fmt.Sprintf("localhost:%d", peerPort)}
 	var proxyCfg *proxy.ServerConfig
+	var forwardProxyCfg *proxy.ServerConfig
 	if cfg.PeerProxy {
 		if !cfg.IsPeerTLS {
 			panic("Can't use peer proxy without peer TLS as it can result in malformed packets")
@@ -509,6 +511,19 @@ func (cfg *EtcdProcessClusterConfig) EtcdServerProcessConfig(tb testing.TB, i in
 			To:     peerListenURL,
 			From:   peerAdvertiseURL,
 		}
+
+		// setup forward proxy
+		forwardProxyURL := url.URL{Scheme: cfg.PeerScheme(), Host: fmt.Sprintf("localhost:%d", forwardProxyPort)}
+		forwardProxyCfg = &proxy.ServerConfig{
+			Logger:         zap.NewNop(),
+			From:           forwardProxyURL,
+			IsForwardProxy: true,
+		}
+
+		if cfg.EnvVars == nil {
+			cfg.EnvVars = make(map[string]string)
+		}
+		cfg.EnvVars["FORWARD_PROXY"] = fmt.Sprintf("http://127.0.0.1:%d", forwardProxyPort)
 	}
 
 	name := fmt.Sprintf("%s-test-%d", testNameCleanRegex.ReplaceAllString(tb.Name(), ""), i)
@@ -631,6 +646,7 @@ func (cfg *EtcdProcessClusterConfig) EtcdServerProcessConfig(tb testing.TB, i in
 		GoFailPort:          gofailPort,
 		GoFailClientTimeout: cfg.GoFailClientTimeout,
 		Proxy:               proxyCfg,
+		ForwardProxy:        forwardProxyCfg,
 		LazyFSEnabled:       cfg.LazyFSEnabled,
 	}
 }

tests/framework/e2e/etcd_process.go

@@ -56,6 +56,7 @@ type EtcdProcess interface {
 	Close() error
 	Config() *EtcdServerProcessConfig
 	PeerProxy() proxy.Server
+	PeerForwardProxy() proxy.Server
 	Failpoints() *BinaryFailpoints
 	LazyFS() *LazyFS
 	Logs() LogsExpect
@@ -69,12 +70,13 @@ type LogsExpect interface {
 }
 
 type EtcdServerProcess struct {
-	cfg        *EtcdServerProcessConfig
-	proc       *expect.ExpectProcess
-	proxy      proxy.Server
-	lazyfs     *LazyFS
-	failpoints *BinaryFailpoints
-	donec      chan struct{} // closed when Interact() terminates
+	cfg          *EtcdServerProcessConfig
+	proc         *expect.ExpectProcess
+	proxy        proxy.Server
+	forwardProxy proxy.Server
+	lazyfs       *LazyFS
+	failpoints   *BinaryFailpoints
+	donec        chan struct{} // closed when Interact() terminates
 }
 
 type EtcdServerProcessConfig struct {
@@ -102,6 +104,7 @@ type EtcdServerProcessConfig struct {
 
 	LazyFSEnabled bool
 	Proxy         *proxy.ServerConfig
+	ForwardProxy  *proxy.ServerConfig
 }
 
 func NewEtcdServerProcess(t testing.TB, cfg *EtcdServerProcessConfig) (*EtcdServerProcess, error) {
@@ -159,6 +162,14 @@ func (ep *EtcdServerProcess) Start(ctx context.Context) error {
 		case err := <-ep.proxy.Error():
 			return err
 		}
+
+		ep.cfg.lg.Info("starting forward proxy...", zap.String("name", ep.cfg.Name), zap.String("from", ep.cfg.ForwardProxy.From.String()), zap.String("to", ep.cfg.ForwardProxy.To.String()))
+		ep.forwardProxy = proxy.NewServer(*ep.cfg.ForwardProxy)
+		select {
+		case <-ep.forwardProxy.Ready():
+		case err := <-ep.forwardProxy.Error():
+			return err
+		}
 	}
 	if ep.lazyfs != nil {
 		ep.cfg.lg.Info("starting lazyfs...", zap.String("name", ep.cfg.Name))
@@ -222,6 +233,13 @@ func (ep *EtcdServerProcess) Stop() (err error) {
 	}
 	ep.cfg.lg.Info("stopped server.", zap.String("name", ep.cfg.Name))
 	if ep.proxy != nil {
+		ep.cfg.lg.Info("stopping forward proxy...", zap.String("name", ep.cfg.Name))
+		err = ep.forwardProxy.Close()
+		ep.forwardProxy = nil
+		if err != nil {
+			return err
+		}
+
 		ep.cfg.lg.Info("stopping proxy...", zap.String("name", ep.cfg.Name))
 		err = ep.proxy.Close()
 		ep.proxy = nil
@@ -330,6 +348,10 @@ func (ep *EtcdServerProcess) PeerProxy() proxy.Server {
 	return ep.proxy
 }
 
+func (ep *EtcdServerProcess) PeerForwardProxy() proxy.Server {
+	return ep.forwardProxy
+}
+
 func (ep *EtcdServerProcess) LazyFS() *LazyFS {
 	return ep.lazyfs
 }

tests/robustness/failpoint/network.go

@@ -63,18 +63,21 @@ func (tb triggerBlackhole) Available(config e2e.EtcdProcessClusterConfig, proces
 
 func Blackhole(ctx context.Context, t *testing.T, member e2e.EtcdProcess, clus *e2e.EtcdProcessCluster, shouldWaitTillSnapshot bool) error {
 	proxy := member.PeerProxy()
+	forwardProxy := member.PeerForwardProxy()
 
-	// Blackholing will cause peers to not be able to use streamWriters registered with member
-	// but peer traffic is still possible because member has 'pipeline' with peers
-	// TODO: find a way to stop all traffic
 	t.Logf("Blackholing traffic from and to member %q", member.Config().Name)
 	proxy.BlackholeTx()
 	proxy.BlackholeRx()
+	forwardProxy.BlackholeTx()
+	forwardProxy.BlackholeRx()
 	defer func() {
 		t.Logf("Traffic restored from and to member %q", member.Config().Name)
 		proxy.UnblackholeTx()
 		proxy.UnblackholeRx()
+		forwardProxy.UnblackholeTx()
+		forwardProxy.UnblackholeRx()
 	}()
+
 	if shouldWaitTillSnapshot {
 		return waitTillSnapshot(ctx, t, clus, member)
 	}