p2p: add optional SOCKS5 proxy support for outbound peer dials

- Add `UseProxy` field to `p2p.Config` and corresponding `--use-proxy` CLI flag.
- Implement proxy-aware `tcpDialer` (uses `golang.org/x/net/proxy` and attempts context-aware DialContext when supported).
- Wire `UseProxy` through `Server` to the dialer so peer dials can go via SOCKS5 proxy defined by `ALL_PROXY`/`all_proxy`.
- Minor debug `start.sh` for running geth with `--use-proxy`.

Signed-off-by: cloorc <[email protected]>

Author: cloorc

cmd/geth/main.go

@@ -126,6 +126,7 @@ var (
 		utils.NoDiscoverFlag,
 		utils.DiscoveryV4Flag,
 		utils.DiscoveryV5Flag,
+		utils.UseProxyFlag,
 		utils.LegacyDiscoveryV5Flag, // deprecated
 		utils.NetrestrictFlag,
 		utils.NodeKeyFileFlag,

cmd/utils/flags.go

@@ -873,6 +873,11 @@ var (
 		Category: flags.NetworkingCategory,
 		Value:    node.DefaultConfig.P2P.DiscoveryV5,
 	}
+	UseProxyFlag = &cli.BoolFlag{
+		Name:     "use-proxy",
+		Usage:    "Use SOCKS5 proxy from ALL_PROXY or all_proxy environment variable for peer connections",
+		Category: flags.NetworkingCategory,
+	}
 	NetrestrictFlag = &cli.StringFlag{
 		Name:     "netrestrict",
 		Usage:    "Restricts network communication to the given IP networks (CIDR masks)",
@@ -1379,6 +1384,7 @@ func SetP2PConfig(ctx *cli.Context, cfg *p2p.Config) {
 	if ctx.IsSet(DiscoveryV5Flag.Name) {
 		cfg.DiscoveryV5 = ctx.Bool(DiscoveryV5Flag.Name)
 	}
+	cfg.UseProxy = ctx.Bool(UseProxyFlag.Name)
 
 	if netrestrict := ctx.String(NetrestrictFlag.Name); netrestrict != "" {
 		list, err := netutil.ParseNetlist(netrestrict)

p2p/config.go

@@ -124,6 +124,9 @@ type Config struct {
 	// Logger is a custom logger to use with the p2p.Server.
 	Logger log.Logger `toml:"-"`
 
+	// If UseProxy is set to true, the server will use SOCKS5 proxy from ALL_PROXY or all_proxy environment variable for dialing peers.
+	UseProxy bool `toml:",omitempty"`
+
 	clock mclock.Clock
 }
 

p2p/dial.go

@@ -34,6 +34,7 @@ import (
 	"github.com/ethereum/go-ethereum/p2p/enode"
 	"github.com/ethereum/go-ethereum/p2p/enr"
 	"github.com/ethereum/go-ethereum/p2p/netutil"
+	"golang.org/x/net/proxy"
 )
 
 const (
@@ -63,11 +64,28 @@ type nodeResolver interface {
 
 // tcpDialer implements NodeDialer using real TCP connections.
 type tcpDialer struct {
-	d *net.Dialer
+	d        *net.Dialer
+	useProxy bool
 }
 
+// dialerWithContext is an interface implemented by proxy dialers that support context-aware dialing.
+// see proxy/direct#direct, proxy.SOCKS5() and internal/socks#Dialer.
+type dialerWithContext interface {
+	DialContext(ctx context.Context, network, address string) (net.Conn, error)
+}
+
+var proxyDialer = proxy.FromEnvironment()
+
 func (t tcpDialer) Dial(ctx context.Context, dest *enode.Node) (net.Conn, error) {
 	addr, _ := dest.TCPEndpoint()
+	if t.useProxy {
+		log.Debug("Dialing peer via proxy", "direct", proxyDialer == proxy.Direct, "addr", addr.String())
+		if v, ok := proxyDialer.(dialerWithContext); ok {
+			return v.DialContext(ctx, "tcp", addr.String())
+		} else {
+			log.Warn("Proxy dialer does not support context, falling back to direct", "addr", addr.String())
+		}
+	}
 	return t.d.DialContext(ctx, "tcp", addr.String())
 }
 

p2p/server.go

@@ -537,7 +537,7 @@ func (srv *Server) setupDialScheduler() {
 		config.resolver = srv.discv4
 	}
 	if config.dialer == nil {
-		config.dialer = tcpDialer{&net.Dialer{Timeout: defaultDialTimeout}}
+		config.dialer = tcpDialer{&net.Dialer{Timeout: defaultDialTimeout}, srv.UseProxy}
 	}
 	srv.dialsched = newDialScheduler(config, srv.discmix, srv.SetupConn)
 	for _, n := range srv.StaticNodes {