chore: simplify ConnectInfo interface (#29)

dialer.go

@@ -130,14 +130,10 @@ func (d *Dialer) Dial(ctx context.Context, instance string, opts ...DialOption)
 	if err != nil {
 		return nil, err
 	}
-	ipAddrs, tlsCfg, err := i.ConnectInfo(ctx)
+	addr, tlsCfg, err := i.ConnectInfo(ctx, cfg.ipType)
 	if err != nil {
 		return nil, err
 	}
-	addr, ok := ipAddrs[cfg.ipType]
-	if !ok {
-		return nil, fmt.Errorf("instance '%s' does not have IP of type '%s'", instance, cfg.ipType)
-	}
 	addr = net.JoinHostPort(addr, serverProxyPort)
 
 	conn, err := proxy.Dial(ctx, "tcp", addr)

internal/cloudsql/instance.go

@@ -154,16 +154,22 @@ func NewInstance(instance string, client *sqladmin.Service, key *rsa.PrivateKey,
 	return i, nil
 }
 
-// ConnectInfo returns a map of IP types and a TLS config that can be used to connect to a Cloud SQL instance.
-func (i *Instance) ConnectInfo(ctx context.Context) (map[string]string, *tls.Config, error) {
+// ConnectInfo returns an IP address specified by ipType (i.e., public or
+// private) and a TLS config that can be used to connect to a Cloud SQL
+// instance.
+func (i *Instance) ConnectInfo(ctx context.Context, ipType string) (string, *tls.Config, error) {
 	i.resultGuard.RLock()
 	res := i.cur
 	i.resultGuard.RUnlock()
 	err := res.Wait(ctx)
 	if err != nil {
-		return nil, nil, err
+		return "", nil, err
 	}
-	return res.md.ipAddrs, res.tlsCfg, nil
+	addr, ok := res.md.ipAddrs[ipType]
+	if !ok {
+		return "", nil, fmt.Errorf("instance '%s' does not have IP of type '%s'", i, ipType)
+	}
+	return addr, res.tlsCfg, nil
 }
 
 // ForceRefresh triggers an immediate refresh operation to be scheduled and used for future connection attempts.

internal/cloudsql/instance_test.go

@@ -94,7 +94,7 @@ func TestConnectInfo(t *testing.T) {
 		t.Fatalf("failed to initialize Instance: %v", err)
 	}
 
-	_, _, err = im.ConnectInfo(ctx)
+	_, _, err = im.ConnectInfo(ctx, PublicIP)
 	if err != nil {
 		t.Fatalf("failed to retrieve connect info: %v", err)
 	}
@@ -127,8 +127,14 @@ func TestRefreshTimeout(t *testing.T) {
 		t.Fatalf("failed to initialize Instance: %v", err)
 	}
 
-	_, _, err = im.ConnectInfo(ctx)
+	_, _, err = im.ConnectInfo(ctx, PublicIP)
 	if !errors.Is(err, context.DeadlineExceeded) {
 		t.Fatalf("failed to retrieve connect info: %v", err)
 	}
+
+	// when client asks for wrong IP address type
+	gotAddr, _, err := im.ConnectInfo(ctx, PrivateIP)
+	if err == nil {
+		t.Fatalf("expected ConnectInfo to fail but returned IP address = %v", gotAddr)
+	}
 }