wgengine: start network logger in Userspace.Reconfig (#5908)

If the wgcfg.Config is specified with network logging arguments,
then Userspace.Reconfig starts up an asynchronous network logger,
which is shutdown either upon Userspace.Close or when Userspace.Reconfig
is called again without network logging or route arguments.

Signed-off-by: Joe Tsai <joetsai@digital-static.net>

wgengine/userspace.go

@@ -6,6 +6,7 @@ package wgengine
 
 import (
 	"bufio"
+	"context"
 	crand "crypto/rand"
 	"errors"
 	"fmt"
@@ -48,6 +49,7 @@ import (
 	"tailscale.com/wgengine/filter"
 	"tailscale.com/wgengine/magicsock"
 	"tailscale.com/wgengine/monitor"
+	"tailscale.com/wgengine/netlog"
 	"tailscale.com/wgengine/router"
 	"tailscale.com/wgengine/wgcfg"
 	"tailscale.com/wgengine/wgint"
@@ -84,6 +86,10 @@ const (
 // status (as long as there's activity). See docs on its use below.
 const statusPollInterval = 1 * time.Minute
 
+// networkLoggerUploadTimeout is the maximum timeout to wait when
+// shutting down the network logger as it uploads the last network log messages.
+const networkLoggerUploadTimeout = 5 * time.Second
+
 type userspaceEngine struct {
 	logf              logger.Logf
 	wgLogger          *wglog.Logger //a wireguard-go logging wrapper
@@ -145,6 +151,9 @@ type userspaceEngine struct {
 	// value of the ICMP identifer and sequence number concatenated.
 	icmpEchoResponseCallback map[uint32]func()
 
+	// networkLogger logs statistics about network connections.
+	networkLogger netlog.Logger
+
 	// Lock ordering: magicsock.Conn.mu, wgLock, then mu.
 }
 
@@ -872,6 +881,12 @@ func (e *userspaceEngine) Reconfig(cfg *wgcfg.Config, routerCfg *router.Config,
 	if !engineChanged && !routerChanged && listenPort == e.magicConn.LocalPort() && !isSubnetRouterChanged {
 		return ErrNoChanges
 	}
+	newLogIDs := cfg.NetworkLogging
+	oldLogIDs := e.lastCfgFull.NetworkLogging
+	netLogIDsNowValid := !newLogIDs.NodeID.IsZero() && !newLogIDs.DomainID.IsZero()
+	netLogIDsWasValid := !oldLogIDs.NodeID.IsZero() && !oldLogIDs.DomainID.IsZero()
+	netLogIDsChanged := netLogIDsNowValid && netLogIDsWasValid && newLogIDs != oldLogIDs
+	netLogRunning := netLogIDsNowValid && !routerCfg.Equal(&router.Config{})
 
 	// TODO(bradfitz,danderson): maybe delete this isDNSIPOverTailscale
 	// field and delete the resolver.ForwardLinkSelector hook and
@@ -921,8 +936,31 @@ func (e *userspaceEngine) Reconfig(cfg *wgcfg.Config, routerCfg *router.Config,
 		return err
 	}
 
+	// Shutdown the network logger because the IDs changed.
+	// Let it be started back up by subsequent logic.
+	if netLogIDsChanged && e.networkLogger.Running() {
+		e.logf("wgengine: Reconfig: shutting down network logger")
+		ctx, cancel := context.WithTimeout(context.Background(), networkLoggerUploadTimeout)
+		defer cancel()
+		if err := e.networkLogger.Shutdown(ctx); err != nil {
+			e.logf("wgengine: Reconfig: error shutting down network logger: %v", err)
+		}
+	}
+
+	// Startup the network logger.
+	// Do this before configuring the router so that we capture initial packets.
+	if netLogRunning && !e.networkLogger.Running() {
+		nid := cfg.NetworkLogging.NodeID
+		tid := cfg.NetworkLogging.DomainID
+		e.logf("wgengine: Reconfig: starting up network logger (node:%s tailnet:%s)", nid.Public(), tid.Public())
+		if err := e.networkLogger.Startup(nid, tid, e.tundev); err != nil {
+			e.logf("wgengine: Reconfig: error starting up network logger: %v", err)
+		}
+	}
+
 	if routerChanged {
 		e.logf("wgengine: Reconfig: configuring router")
+		e.networkLogger.ReconfigRoutes(routerCfg)
 		err := e.router.Set(routerCfg)
 		health.SetRouterHealth(err)
 		if err != nil {
@@ -939,6 +977,18 @@ func (e *userspaceEngine) Reconfig(cfg *wgcfg.Config, routerCfg *router.Config,
 		}
 	}
 
+	// Shutdown the network logger.
+	// Do this after configuring the router so that we capture final packets.
+	// This attempts to flush out any log messages and may block.
+	if !netLogRunning && e.networkLogger.Running() {
+		e.logf("wgengine: Reconfig: shutting down network logger")
+		ctx, cancel := context.WithTimeout(context.Background(), networkLoggerUploadTimeout)
+		defer cancel()
+		if err := e.networkLogger.Shutdown(ctx); err != nil {
+			e.logf("wgengine: Reconfig: error shutting down network logger: %v", err)
+		}
+	}
+
 	if isSubnetRouterChanged && e.birdClient != nil {
 		e.logf("wgengine: Reconfig: configuring BIRD")
 		var err error
@@ -1092,6 +1142,12 @@ func (e *userspaceEngine) Close() {
 		e.birdClient.Close()
 	}
 	close(e.waitCh)
+
+	ctx, cancel := context.WithTimeout(context.Background(), networkLoggerUploadTimeout)
+	defer cancel()
+	if err := e.networkLogger.Shutdown(ctx); err != nil {
+		e.logf("wgengine: Close: error shutting down network logger: %v", err)
+	}
 }
 
 func (e *userspaceEngine) Wait() {