control/controlhttp: rename a param from addr to optAddr for clarity

And update docs.

Updates #cleanup
Updates #13597 (tangentially; noted this cleanup while debugging)

Change-Id: I62440294c78b0bb3f5673be10318dd89af1e1bfe
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

control/controlhttp/client.go

@@ -297,9 +297,11 @@ func (d *Dialer) clock() tstime.Clock {
 var debugNoiseDial = envknob.RegisterBool("TS_DEBUG_NOISE_DIAL")
 
 // dialHost connects to the configured Dialer.Hostname and upgrades the
-// connection into a controlbase.Conn. If addr is valid, then no DNS is used
-// and the connection will be made to the provided address.
-func (a *Dialer) dialHost(ctx context.Context, addr netip.Addr) (*ClientConn, error) {
+// connection into a controlbase.Conn.
+//
+// If optAddr is valid, then no DNS is used and the connection will be made to the
+// provided address.
+func (a *Dialer) dialHost(ctx context.Context, optAddr netip.Addr) (*ClientConn, error) {
 	// Create one shared context used by both port 80 and port 443 dials.
 	// If port 80 is still in flight when 443 returns, this deferred cancel
 	// will stop the port 80 dial.
@@ -330,11 +332,11 @@ func (a *Dialer) dialHost(ctx context.Context, addr netip.Addr) (*ClientConn, er
 	ch := make(chan tryURLRes) // must be unbuffered
 	try := func(u *url.URL) {
 		if debugNoiseDial() {
-			a.logf("trying noise dial (%v, %v) ...", u, addr)
+			a.logf("trying noise dial (%v, %v) ...", u, optAddr)
 		}
-		cbConn, err := a.dialURL(ctx, u, addr)
+		cbConn, err := a.dialURL(ctx, u, optAddr)
 		if debugNoiseDial() {
-			a.logf("noise dial (%v, %v) = (%v, %v)", u, addr, cbConn, err)
+			a.logf("noise dial (%v, %v) = (%v, %v)", u, optAddr, cbConn, err)
 		}
 		select {
 		case ch <- tryURLRes{u, cbConn, err}:
@@ -388,12 +390,15 @@ func (a *Dialer) dialHost(ctx context.Context, addr netip.Addr) (*ClientConn, er
 }
 
 // dialURL attempts to connect to the given URL.
-func (a *Dialer) dialURL(ctx context.Context, u *url.URL, addr netip.Addr) (*ClientConn, error) {
+//
+// If optAddr is valid, then no DNS is used and the connection will be made to the
+// provided address.
+func (a *Dialer) dialURL(ctx context.Context, u *url.URL, optAddr netip.Addr) (*ClientConn, error) {
 	init, cont, err := controlbase.ClientDeferred(a.MachineKey, a.ControlKey, a.ProtocolVersion)
 	if err != nil {
 		return nil, err
 	}
-	netConn, err := a.tryURLUpgrade(ctx, u, addr, init)
+	netConn, err := a.tryURLUpgrade(ctx, u, optAddr, init)
 	if err != nil {
 		return nil, err
 	}
@@ -439,19 +444,20 @@ var macOSScreenTime = health.Register(&health.Warnable{
 	ImpactsConnectivity: true,
 })
 
-// tryURLUpgrade connects to u, and tries to upgrade it to a net.Conn. If addr
-// is valid, then no DNS is used and the connection will be made to the
-// provided address.
+// tryURLUpgrade connects to u, and tries to upgrade it to a net.Conn.
+//
+// If optAddr is valid, then no DNS is used and the connection will be made to
+// the provided address.
 //
 // Only the provided ctx is used, not a.ctx.
-func (a *Dialer) tryURLUpgrade(ctx context.Context, u *url.URL, addr netip.Addr, init []byte) (_ net.Conn, retErr error) {
+func (a *Dialer) tryURLUpgrade(ctx context.Context, u *url.URL, optAddr netip.Addr, init []byte) (_ net.Conn, retErr error) {
 	var dns *dnscache.Resolver
 
 	// If we were provided an address to dial, then create a resolver that just
 	// returns that value; otherwise, fall back to DNS.
-	if addr.IsValid() {
+	if optAddr.IsValid() {
 		dns = &dnscache.Resolver{
-			SingleHostStaticResult: []netip.Addr{addr},
+			SingleHostStaticResult: []netip.Addr{optAddr},
 			SingleHost:             u.Hostname(),
 			Logf:                   a.Logf, // not a.logf method; we want to propagate nil-ness
 		}