control/controlhttp: quiet "forcing port 443" log spam

Minimal mitigation that doesn't do the full refactor that's probably
warranted.

Updates #15402

Change-Id: I79fd91de0e0661d25398f7d95563982ed1d11561
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

control/controlhttp/client.go

@@ -96,6 +96,9 @@ func (a *Dialer) httpsFallbackDelay() time.Duration {
 var _ = envknob.RegisterBool("TS_USE_CONTROL_DIAL_PLAN") // to record at init time whether it's in use
 
 func (a *Dialer) dial(ctx context.Context) (*ClientConn, error) {
+
+	a.logPort80Failure.Store(true)
+
 	// If we don't have a dial plan, just fall back to dialing the single
 	// host we know about.
 	useDialPlan := envknob.BoolDefaultTrue("TS_USE_CONTROL_DIAL_PLAN")
@@ -278,7 +281,9 @@ func (d *Dialer) forceNoise443() bool {
 		// This heuristic works around networks where port 80 is MITMed and
 		// appears to work for a bit post-Upgrade but then gets closed,
 		// such as seen in https://github.com/tailscale/tailscale/issues/13597.
-		d.logf("controlhttp: forcing port 443 dial due to recent noise dial")
+		if d.logPort80Failure.CompareAndSwap(true, false) {
+			d.logf("controlhttp: forcing port 443 dial due to recent noise dial")
+		}
 		return true
 	}
 

control/controlhttp/constants.go

@@ -6,6 +6,7 @@ package controlhttp
 import (
 	"net/http"
 	"net/url"
+	"sync/atomic"
 	"time"
 
 	"tailscale.com/health"
@@ -90,6 +91,11 @@ type Dialer struct {
 
 	proxyFunc func(*http.Request) (*url.URL, error) // or nil
 
+	// logPort80Failure is whether we should log about port 80 interceptions
+	// and forcing a port 443 dial. We do this only once per "dial" method
+	// which can result in many concurrent racing dialHost calls.
+	logPort80Failure atomic.Bool
+
 	// For tests only
 	drainFinished        chan struct{}
 	omitCertErrorLogging bool