all: use cmpx.Or where it made sense

I left a few out where writing it explicitly was better
for various reasons.

Updates #8296

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

cmd/derper/depaware.txt

@@ -125,6 +125,7 @@ tailscale.com/cmd/derper dependencies: (generated by github.com/tailscale/depawa
    W    tailscale.com/util/clientmetric                              from tailscale.com/net/tshttpproxy
         tailscale.com/util/cloudenv                                  from tailscale.com/hostinfo+
    W    tailscale.com/util/cmpver                                    from tailscale.com/net/tshttpproxy
+        tailscale.com/util/cmpx                                      from tailscale.com/cmd/derper+
    L 💣 tailscale.com/util/dirwalk                                   from tailscale.com/metrics
         tailscale.com/util/dnsname                                   from tailscale.com/hostinfo+
         tailscale.com/util/httpm                                     from tailscale.com/client/tailscale

cmd/derper/derper.go

@@ -33,6 +33,7 @@ import (
 	"tailscale.com/net/stun"
 	"tailscale.com/tsweb"
 	"tailscale.com/types/key"
+	"tailscale.com/util/cmpx"
 )
 
 var (
@@ -436,11 +437,7 @@ func defaultMeshPSKFile() string {
 }
 
 func rateLimitedListenAndServeTLS(srv *http.Server) error {
-	addr := srv.Addr
-	if addr == "" {
-		addr = ":https"
-	}
-	ln, err := net.Listen("tcp", addr)
+	ln, err := net.Listen("tcp", cmpx.Or(srv.Addr, ":https"))
 	if err != nil {
 		return err
 	}

cmd/get-authkey/main.go

@@ -16,6 +16,7 @@ import (
 
 	"golang.org/x/oauth2/clientcredentials"
 	"tailscale.com/client/tailscale"
+	"tailscale.com/util/cmpx"
 )
 
 func main() {
@@ -39,10 +40,7 @@ func main() {
 		log.Fatal("at least one tag must be specified")
 	}
 
-	baseURL := os.Getenv("TS_BASE_URL")
-	if baseURL == "" {
-		baseURL = "https://api.tailscale.com"
-	}
+	baseURL := cmpx.Or(os.Getenv("TS_BASE_URL"), "https://api.tailscale.com")
 
 	credentials := clientcredentials.Config{
 		ClientID:     clientID,

cmd/tailscale/cli/cli_test.go

@@ -22,6 +22,7 @@ import (
 	"tailscale.com/tstest"
 	"tailscale.com/types/persist"
 	"tailscale.com/types/preftype"
+	"tailscale.com/util/cmpx"
 	"tailscale.com/version/distro"
 )
 
@@ -719,10 +720,7 @@ func TestPrefsFromUpArgs(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			var warnBuf tstest.MemLogger
-			goos := tt.goos
-			if goos == "" {
-				goos = "linux"
-			}
+			goos := cmpx.Or(tt.goos, "linux")
 			st := tt.st
 			if st == nil {
 				st = new(ipnstate.Status)

cmd/tailscale/cli/web.go

@@ -29,6 +29,7 @@ import (
 	"tailscale.com/ipn"
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/tailcfg"
+	"tailscale.com/util/cmpx"
 	"tailscale.com/util/groupmember"
 	"tailscale.com/version/distro"
 )
@@ -155,10 +156,7 @@ func runWeb(ctx context.Context, args []string) error {
 // urlOfListenAddr parses a given listen address into a formatted URL
 func urlOfListenAddr(addr string) string {
 	host, port, _ := net.SplitHostPort(addr)
-	if host == "" {
-		host = "127.0.0.1"
-	}
-	return fmt.Sprintf("http://%s", net.JoinHostPort(host, port))
+	return fmt.Sprintf("http://%s", net.JoinHostPort(cmpx.Or(host, "127.0.0.1"), port))
 }
 
 // authorize returns the name of the user accessing the web UI after verifying

cmd/tailscale/depaware.txt

@@ -114,6 +114,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
         tailscale.com/util/clientmetric                              from tailscale.com/net/netcheck+
         tailscale.com/util/cloudenv                                  from tailscale.com/net/dnscache+
    W    tailscale.com/util/cmpver                                    from tailscale.com/net/tshttpproxy
+        tailscale.com/util/cmpx                                      from tailscale.com/cmd/tailscale/cli+
    L 💣 tailscale.com/util/dirwalk                                   from tailscale.com/metrics
         tailscale.com/util/dnsname                                   from tailscale.com/cmd/tailscale/cli+
         tailscale.com/util/groupmember                               from tailscale.com/cmd/tailscale/cli

cmd/tailscaled/depaware.txt

@@ -308,6 +308,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/util/clientmetric                              from tailscale.com/control/controlclient+
         tailscale.com/util/cloudenv                                  from tailscale.com/net/dns/resolver+
   LW    tailscale.com/util/cmpver                                    from tailscale.com/net/dns+
+        tailscale.com/util/cmpx                                      from tailscale.com/derp/derphttp+
      💣 tailscale.com/util/deephash                                  from tailscale.com/ipn/ipnlocal+
    L 💣 tailscale.com/util/dirwalk                                   from tailscale.com/metrics+
         tailscale.com/util/dnsname                                   from tailscale.com/hostinfo+

derp/derphttp/derphttp_client.go

@@ -40,6 +40,7 @@ import (
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/key"
 	"tailscale.com/types/logger"
+	"tailscale.com/util/cmpx"
 )
 
 // Client is a DERP-over-HTTP client.
@@ -654,10 +655,7 @@ func (c *Client) dialNode(ctx context.Context, n *tailcfg.DERPNode) (net.Conn, e
 					// Start v4 dial
 				}
 			}
-			dst := dstPrimary
-			if dst == "" {
-				dst = n.HostName
-			}
+			dst := cmpx.Or(dstPrimary, n.HostName)
 			port := "443"
 			if n.DERPPort != 0 {
 				port = fmt.Sprint(n.DERPPort)

ipn/ipnlocal/dnsconfig_test.go

@@ -16,6 +16,7 @@ import (
 	"tailscale.com/types/dnstype"
 	"tailscale.com/types/netmap"
 	"tailscale.com/util/cloudenv"
+	"tailscale.com/util/cmpx"
 	"tailscale.com/util/dnsname"
 )
 
@@ -308,10 +309,7 @@ func TestDNSConfigForNetmap(t *testing.T) {
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			verOS := tt.os
-			if verOS == "" {
-				verOS = "linux"
-			}
+			verOS := cmpx.Or(tt.os, "linux")
 			var log tstest.MemLogger
 			got := dnsConfigForNetmap(tt.nm, tt.prefs.View(), log.Logf, verOS)
 			if !reflect.DeepEqual(got, tt.want) {

ipn/ipnlocal/local.go

@@ -71,6 +71,7 @@ import (
 	"tailscale.com/types/preftype"
 	"tailscale.com/types/ptr"
 	"tailscale.com/types/views"
+	"tailscale.com/util/cmpx"
 	"tailscale.com/util/deephash"
 	"tailscale.com/util/dnsname"
 	"tailscale.com/util/mak"
@@ -3932,10 +3933,7 @@ func (b *LocalBackend) setNetMapLocked(nm *netmap.NetworkMap) {
 	b.dialer.SetNetMap(nm)
 	var login string
 	if nm != nil {
-		login = nm.UserProfiles[nm.User].LoginName
-		if login == "" {
-			login = "<missing-profile>"
-		}
+		login = cmpx.Or(nm.UserProfiles[nm.User].LoginName, "<missing-profile>")
 	}
 	b.netMap = nm
 	if login != b.activeLogin {

ipn/ipnlocal/serve_test.go

@@ -16,6 +16,7 @@ import (
 	"testing"
 
 	"tailscale.com/ipn"
+	"tailscale.com/util/cmpx"
 )
 
 func TestExpandProxyArg(t *testing.T) {
@@ -140,10 +141,7 @@ func TestGetServeHandler(t *testing.T) {
 				},
 				TLS: &tls.ConnectionState{ServerName: serverName},
 			}
-			port := tt.port
-			if port == 0 {
-				port = 443
-			}
+			port := cmpx.Or(tt.port, 443)
 			req = req.WithContext(context.WithValue(req.Context(), serveHTTPContextKey{}, &serveHTTPContext{
 				DestPort: port,
 			}))

net/dnscache/messagecache.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/golang/groupcache/lru"
 	"golang.org/x/net/dns/dnsmessage"
+	"tailscale.com/util/cmpx"
 )
 
 // MessageCache is a cache that works at the DNS message layer,
@@ -59,10 +60,7 @@ func (c *MessageCache) Flush() {
 // pruneLocked prunes down the cache size to the configured (or
 // default) max size.
 func (c *MessageCache) pruneLocked() {
-	max := c.cacheSizeSet
-	if max == 0 {
-		max = 500
-	}
+	max := cmpx.Or(c.cacheSizeSet, 500)
 	for c.cache.Len() > max {
 		c.cache.RemoveOldest()
 	}

net/netcheck/netcheck.go

@@ -42,6 +42,7 @@ import (
 	"tailscale.com/types/opt"
 	"tailscale.com/types/ptr"
 	"tailscale.com/util/clientmetric"
+	"tailscale.com/util/cmpx"
 	"tailscale.com/util/mak"
 )
 
@@ -450,10 +451,9 @@ func makeProbePlan(dm *tailcfg.DERPMap, ifState *interfaces.State, last *Report)
 				do6 = false
 			}
 			n := reg.Nodes[try%len(reg.Nodes)]
-			prevLatency := last.RegionLatency[reg.RegionID] * 120 / 100
-			if prevLatency == 0 {
-				prevLatency = defaultActiveRetransmitTime
-			}
+			prevLatency := cmpx.Or(
+				last.RegionLatency[reg.RegionID]*120/100,
+				defaultActiveRetransmitTime)
 			delay := time.Duration(try) * prevLatency
 			if try > 1 {
 				delay += time.Duration(try) * 50 * time.Millisecond
@@ -1589,10 +1589,7 @@ func (rs *reportState) runProbe(ctx context.Context, dm *tailcfg.DERPMap, probe
 // proto is 4 or 6
 // If it returns nil, the node is skipped.
 func (c *Client) nodeAddr(ctx context.Context, n *tailcfg.DERPNode, proto probeProto) (ap netip.AddrPort) {
-	port := n.STUNPort
-	if port == 0 {
-		port = 3478
-	}
+	port := cmpx.Or(n.STUNPort, 3478)
 	if port < 0 || port > 1<<16-1 {
 		return
 	}

tsweb/tsweb.go

@@ -27,6 +27,7 @@ import (
 	"tailscale.com/net/tsaddr"
 	"tailscale.com/tsweb/varz"
 	"tailscale.com/types/logger"
+	"tailscale.com/util/cmpx"
 	"tailscale.com/util/vizerror"
 )
 
@@ -144,10 +145,7 @@ func (h Port80Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		// Redirect authorized user to the debug handler.
 		path = "/debug/"
 	}
-	host := h.FQDN
-	if host == "" {
-		host = r.Host
-	}
+	host := cmpx.Or(h.FQDN, r.Host)
 	target := "https://" + host + path
 	http.Redirect(w, r, target, http.StatusFound)
 }

tsweb/varz/varz.go

@@ -18,6 +18,7 @@ import (
 	"time"
 
 	"tailscale.com/metrics"
+	"tailscale.com/util/cmpx"
 	"tailscale.com/version"
 )
 
@@ -96,16 +97,10 @@ func writePromExpVar(w io.Writer, prefix string, kv expvar.KeyValue) {
 
 	switch v := kv.Value.(type) {
 	case *expvar.Int:
-		if typ == "" {
-			typ = "counter"
-		}
-		fmt.Fprintf(w, "# TYPE %s %s\n%s %v\n", name, typ, name, v.Value())
+		fmt.Fprintf(w, "# TYPE %s %s\n%s %v\n", name, cmpx.Or(typ, "counter"), name, v.Value())
 		return
 	case *expvar.Float:
-		if typ == "" {
-			typ = "gauge"
-		}
-		fmt.Fprintf(w, "# TYPE %s %s\n%s %v\n", name, typ, name, v.Value())
+		fmt.Fprintf(w, "# TYPE %s %s\n%s %v\n", name, cmpx.Or(typ, "gauge"), name, v.Value())
 		return
 	case *metrics.Set:
 		v.Do(func(kv expvar.KeyValue) {

util/linuxfw/nftables.go

@@ -16,6 +16,7 @@ import (
 	"github.com/josharian/native"
 	"golang.org/x/sys/unix"
 	"tailscale.com/types/logger"
+	"tailscale.com/util/cmpx"
 )
 
 // DebugNetfilter prints debug information about netfilter rules to the
@@ -52,27 +53,18 @@ func DebugNetfilter(logf logger.Logf) error {
 			for _, ex := range rule.Exprs {
 				switch v := ex.(type) {
 				case *expr.Meta:
-					key := metaKeyNames[v.Key]
-					if key == "" {
-						key = "UNKNOWN"
-					}
+					key := cmpx.Or(metaKeyNames[v.Key], "UNKNOWN")
 					logf("netfilter:     Meta: key=%s source_register=%v register=%d", key, v.SourceRegister, v.Register)
 
 				case *expr.Cmp:
-					op := cmpOpNames[v.Op]
-					if op == "" {
-						op = "UNKNOWN"
-					}
+					op := cmpx.Or(cmpOpNames[v.Op], "UNKNOWN")
 					logf("netfilter:     Cmp: op=%s register=%d data=%s", op, v.Register, formatMaybePrintable(v.Data))
 
 				case *expr.Counter:
 					// don't print
 
 				case *expr.Verdict:
-					kind := verdictNames[v.Kind]
-					if kind == "" {
-						kind = "UNKNOWN"
-					}
+					kind := cmpx.Or(verdictNames[v.Kind], "UNKNOWN")
 					logf("netfilter:     Verdict: kind=%s data=%s", kind, v.Chain)
 
 				case *expr.Target: