net/connstats: make it modular (omittable)

Saves only 12 KB, but notably removes some deps on packages that future
changes can then eliminate entirely.

Updates #12614

Change-Id: Ibf830d3ee08f621d0a2011b1d4cd175427ef50df
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tailscaled/depaware-min.txt

@@ -134,7 +134,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/types/logger                                   from tailscale.com/appc+
         tailscale.com/types/logid                                    from tailscale.com/cmd/tailscaled+
         tailscale.com/types/mapx                                     from tailscale.com/ipn/ipnext
-        tailscale.com/types/netlogtype                               from tailscale.com/net/connstats
         tailscale.com/types/netmap                                   from tailscale.com/control/controlclient+
         tailscale.com/types/nettype                                  from tailscale.com/net/batching+
         tailscale.com/types/opt                                      from tailscale.com/control/controlknobs+
@@ -217,7 +216,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         golang.org/x/net/internal/socket                             from golang.org/x/net/icmp+
         golang.org/x/net/ipv4                                        from github.com/tailscale/wireguard-go/conn+
         golang.org/x/net/ipv6                                        from github.com/tailscale/wireguard-go/conn+
-        golang.org/x/sync/errgroup                                   from github.com/mdlayher/socket+
+        golang.org/x/sync/errgroup                                   from github.com/mdlayher/socket
         golang.org/x/sys/cpu                                         from github.com/tailscale/wireguard-go/tun+
         golang.org/x/sys/unix                                        from github.com/jsimonetti/rtnetlink/internal/unix+
         golang.org/x/term                                            from tailscale.com/logpolicy

cmd/tailscaled/depaware-minbox.txt

@@ -160,7 +160,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/types/logger                                   from tailscale.com/appc+
         tailscale.com/types/logid                                    from tailscale.com/cmd/tailscaled+
         tailscale.com/types/mapx                                     from tailscale.com/ipn/ipnext
-        tailscale.com/types/netlogtype                               from tailscale.com/net/connstats
         tailscale.com/types/netmap                                   from tailscale.com/control/controlclient+
         tailscale.com/types/nettype                                  from tailscale.com/net/batching+
         tailscale.com/types/opt                                      from tailscale.com/control/controlknobs+
@@ -245,7 +244,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         golang.org/x/net/internal/socket                             from golang.org/x/net/icmp+
         golang.org/x/net/ipv4                                        from github.com/tailscale/wireguard-go/conn+
         golang.org/x/net/ipv6                                        from github.com/tailscale/wireguard-go/conn+
-        golang.org/x/sync/errgroup                                   from github.com/mdlayher/socket+
+        golang.org/x/sync/errgroup                                   from github.com/mdlayher/socket
         golang.org/x/sys/cpu                                         from github.com/tailscale/wireguard-go/tun+
         golang.org/x/sys/unix                                        from github.com/jsimonetti/rtnetlink/internal/unix+
         golang.org/x/term                                            from tailscale.com/logpolicy

cmd/tailscaled/deps_test.go

@@ -243,6 +243,7 @@ func TestMinTailscaledNoCLI(t *testing.T) {
 		"golang.org/x/net/proxy",
 		"internal/socks",
 		"github.com/tailscale/peercred",
+		"tailscale.com/types/netlogtype",
 	}
 	deptest.DepChecker{
 		GOOS:   "linux",

feature/buildfeatures/feature_connstats_disabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build ts_omit_connstats
+
+package buildfeatures
+
+// HasConnStats is whether the binary was built with support for modular feature "Track per-packet connection statistics".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_connstats" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasConnStats = false

feature/buildfeatures/feature_connstats_enabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build !ts_omit_connstats
+
+package buildfeatures
+
+// HasConnStats is whether the binary was built with support for modular feature "Track per-packet connection statistics".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_connstats" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasConnStats = true

feature/featuretags/featuretags.go

@@ -130,7 +130,11 @@ var Features = map[FeatureTag]FeatureMeta{
 		Deps: []FeatureTag{"c2n"},
 	},
 	"completion": {Sym: "Completion", Desc: "CLI shell completion"},
-	"cloud":      {Sym: "Cloud", Desc: "detect cloud environment to learn instances IPs and DNS servers"},
+	"connstats": {
+		Sym:  "ConnStats",
+		Desc: "Track per-packet connection statistics",
+	},
+	"cloud": {Sym: "Cloud", Desc: "detect cloud environment to learn instances IPs and DNS servers"},
 	"dbus": {
 		Sym:                  "DBus",
 		Desc:                 "Linux DBus support",

net/connstats/stats.go

@@ -1,6 +1,8 @@
 // Copyright (c) Tailscale Inc & AUTHORS
 // SPDX-License-Identifier: BSD-3-Clause
 
+//go:build !ts_omit_connstats
+
 // Package connstats maintains statistics about connections
 // flowing through a TUN device (which operate at the IP layer).
 package connstats

net/connstats/stats_omit.go

@@ -0,0 +1,24 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build ts_omit_connstats
+
+package connstats
+
+import (
+	"context"
+	"net/netip"
+	"time"
+)
+
+type Statistics struct{}
+
+func NewStatistics(maxPeriod time.Duration, maxConns int, dump func(start, end time.Time, virtual, physical any)) *Statistics {
+	return &Statistics{}
+}
+
+func (s *Statistics) UpdateTxVirtual(b []byte)                                                {}
+func (s *Statistics) UpdateRxVirtual(b []byte)                                                {}
+func (s *Statistics) UpdateTxPhysical(src netip.Addr, dst netip.AddrPort, packets, bytes int) {}
+func (s *Statistics) UpdateRxPhysical(src netip.Addr, dst netip.AddrPort, packets, bytes int) {}
+func (s *Statistics) Shutdown(context.Context) error                                          { return nil }

net/tstun/wrap.go

@@ -973,8 +973,10 @@ func (t *Wrapper) Read(buffs [][]byte, sizes []int, offset int) (int, error) {
 			panic(fmt.Sprintf("short copy: %d != %d", n, len(data)-res.dataOffset))
 		}
 		sizes[buffsPos] = n
-		if stats := t.stats.Load(); stats != nil {
-			stats.UpdateTxVirtual(p.Buffer())
+		if buildfeatures.HasConnStats {
+			if stats := t.stats.Load(); stats != nil {
+				stats.UpdateTxVirtual(p.Buffer())
+			}
 		}
 		buffsPos++
 	}
@@ -1098,9 +1100,11 @@ func (t *Wrapper) injectedRead(res tunInjectedRead, outBuffs [][]byte, sizes []i
 		n, err = tun.GSOSplit(pkt, gsoOptions, outBuffs, sizes, offset)
 	}
 
-	if stats := t.stats.Load(); stats != nil {
-		for i := 0; i < n; i++ {
-			stats.UpdateTxVirtual(outBuffs[i][offset : offset+sizes[i]])
+	if buildfeatures.HasConnStats {
+		if stats := t.stats.Load(); stats != nil {
+			for i := 0; i < n; i++ {
+				stats.UpdateTxVirtual(outBuffs[i][offset : offset+sizes[i]])
+			}
 		}
 	}
 
@@ -1266,9 +1270,11 @@ func (t *Wrapper) Write(buffs [][]byte, offset int) (int, error) {
 }
 
 func (t *Wrapper) tdevWrite(buffs [][]byte, offset int) (int, error) {
-	if stats := t.stats.Load(); stats != nil {
-		for i := range buffs {
-			stats.UpdateRxVirtual((buffs)[i][offset:])
+	if buildfeatures.HasConnStats {
+		if stats := t.stats.Load(); stats != nil {
+			for i := range buffs {
+				stats.UpdateRxVirtual((buffs)[i][offset:])
+			}
 		}
 	}
 	return t.tdev.Write(buffs, offset)
@@ -1490,7 +1496,9 @@ func (t *Wrapper) Unwrap() tun.Device {
 // SetStatistics specifies a per-connection statistics aggregator.
 // Nil may be specified to disable statistics gathering.
 func (t *Wrapper) SetStatistics(stats *connstats.Statistics) {
-	t.stats.Store(stats)
+	if buildfeatures.HasConnStats {
+		t.stats.Store(stats)
+	}
 }
 
 var (

wgengine/magicsock/magicsock.go

@@ -1865,8 +1865,10 @@ func (c *Conn) receiveIP(b []byte, ipp netip.AddrPort, cache *epAddrEndpointCach
 	now := mono.Now()
 	ep.lastRecvUDPAny.StoreAtomic(now)
 	connNoted := ep.noteRecvActivity(src, now)
-	if stats := c.stats.Load(); stats != nil {
-		stats.UpdateRxPhysical(ep.nodeAddr, ipp, 1, geneveInclusivePacketLen)
+	if buildfeatures.HasConnStats {
+		if stats := c.stats.Load(); stats != nil {
+			stats.UpdateRxPhysical(ep.nodeAddr, ipp, 1, geneveInclusivePacketLen)
+		}
 	}
 	if src.vni.IsSet() && (connNoted || looksLikeInitiationMsg(b)) {
 		// connNoted is periodic, but we also want to verify if the peer is who
@@ -3743,7 +3745,9 @@ func (c *Conn) UpdateStatus(sb *ipnstate.StatusBuilder) {
 // SetStatistics specifies a per-connection statistics aggregator.
 // Nil may be specified to disable statistics gathering.
 func (c *Conn) SetStatistics(stats *connstats.Statistics) {
-	c.stats.Store(stats)
+	if buildfeatures.HasConnStats {
+		c.stats.Store(stats)
+	}
 }
 
 // SetHomeless sets whether magicsock should idle harder and not have a DERP

wgengine/netlog/netlog.go

@@ -19,6 +19,7 @@ import (
 	"sync"
 	"time"
 
+	"tailscale.com/feature/buildfeatures"
 	"tailscale.com/health"
 	"tailscale.com/logpolicy"
 	"tailscale.com/logtail"
@@ -130,20 +131,24 @@ func (nl *Logger) Startup(nodeID tailcfg.StableNodeID, nodeLogID, domainLogID lo
 	// can upload to the Tailscale log service, so stay below this limit.
 	const maxLogSize = 256 << 10
 	const maxConns = (maxLogSize - netlogtype.MaxMessageJSONSize) / netlogtype.MaxConnectionCountsJSONSize
-	nl.stats = connstats.NewStatistics(pollPeriod, maxConns, func(start, end time.Time, virtual, physical map[netlogtype.Connection]netlogtype.Counts) {
-		nl.mu.Lock()
-		addrs := nl.addrs
-		prefixes := nl.prefixes
-		nl.mu.Unlock()
-		recordStatistics(nl.logger, nodeID, start, end, virtual, physical, addrs, prefixes, logExitFlowEnabledEnabled)
-	})
+	if buildfeatures.HasConnStats {
+		nl.stats = connstats.NewStatistics(pollPeriod, maxConns, func(start, end time.Time, virtual, physical map[netlogtype.Connection]netlogtype.Counts) {
+			nl.mu.Lock()
+			addrs := nl.addrs
+			prefixes := nl.prefixes
+			nl.mu.Unlock()
+			recordStatistics(nl.logger, nodeID, start, end, virtual, physical, addrs, prefixes, logExitFlowEnabledEnabled)
+		})
+	}
 
 	// Register the connection tracker into the TUN device.
 	if tun == nil {
 		tun = noopDevice{}
 	}
 	nl.tun = tun
-	nl.tun.SetStatistics(nl.stats)
+	if buildfeatures.HasConnStats {
+		nl.tun.SetStatistics(nl.stats)
+	}
 
 	// Register the connection tracker into magicsock.
 	if sock == nil {