wgengine/netstack: add debug page for TCP forwarderandrew/netstack-forwarder-debug

To help in debugging issues with subnet routers in userspace mode–for
example, hitting the max inflight limit.

Updates tailscale/corp#12184

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: Idd922f4ae37695f6598a914c2d050574755ef309

2 files changed, 3 insertions, 1 deletions

diff --git a/cmd/tailscaled/depaware.txt b/cmd/tailscaled/depaware.txt
index 7d25abd2a..614369469 100644
--- a/cmd/tailscaled/depaware.txt
+++ b/cmd/tailscaled/depaware.txt
@@ -508,7 +508,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         hash/fnv                                                     from tailscale.com/wgengine/magicsock
         hash/maphash                                                 from go4.org/mem
         html                                                         from html/template+
-        html/template                                                from github.com/gorilla/csrf
+        html/template                                                from github.com/gorilla/csrf+
         io                                                           from archive/tar+
         io/fs                                                        from archive/tar+
         io/ioutil                                                    from github.com/aws/aws-sdk-go-v2/aws/protocol/query+
diff --git a/cmd/tailscaled/tailscaled.go b/cmd/tailscaled/tailscaled.go
index 8c4365548..3ca77dbf8 100644
--- a/cmd/tailscaled/tailscaled.go
+++ b/cmd/tailscaled/tailscaled.go
@@ -755,6 +755,8 @@ func newNetstack(logf logger.Logf, sys *tsd.System) (*netstack.Impl, error) {
 	// Only register debug info if we have a debug mux
 	if debugMux != nil {
 		expvar.Publish("netstack", ret.ExpVar())
+
+		debugMux.HandleFunc("/debug/netstack/tcp-forwarder", ret.DebugTCPForwarder)
 	}
 	return ret, nil
 }