Reuse message across tag validation

Author: anisaoshafi

internal/api/client.go

@@ -13,6 +13,7 @@ import (
 
 	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
 
+	"github.com/localstack/lstk/internal/config"
 	"github.com/localstack/lstk/internal/log"
 	"github.com/localstack/lstk/internal/version"
 )
@@ -313,7 +314,7 @@ func (c *PlatformClient) GetLicense(ctx context.Context, licReq *LicenseRequest)
 		if strings.Contains(detail, "licensing.license.format") {
 			return nil, &LicenseError{
 				Status:  statusCode,
-				Message: "unsupported image tag — check the tag in your config file",
+				Message: config.UnsupportedTagMessage(),
 				Detail:  detail,
 			}
 		}

internal/config/containers.go

@@ -1,6 +1,7 @@
 package config
 
 import (
+	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -112,6 +113,15 @@ func (c *ContainerConfig) VolumeDir() (string, error) {
 	return filepath.Join(cacheDir, "lstk", "volume", c.Name()), nil
 }
 
+func UnsupportedTagMessage() string {
+	y, m, _ := time.Now().Date()
+	m--
+	if m == 0 {
+		m, y = 12, y-1
+	}
+	return fmt.Sprintf("unsupported image tag — try a tag like %q or \"latest\" in your config file", fmt.Sprintf("%d.%d", y, int(m)))
+}
+
 // zeroPaddedMonthTagRe matches calendar-versioned tags where the month is zero-padded
 // (e.g. "2026.04", "2026.04.1-amd64"), which the license API does not accept.
 var zeroPaddedMonthTagRe = regexp.MustCompile(`^(\d{4}\.)0([1-9].*)$`)
@@ -120,22 +130,12 @@ var zeroPaddedMonthTagRe = regexp.MustCompile(`^(\d{4}\.)0([1-9].*)$`)
 // must not start with a dot or hyphen; max 128 characters.
 var validTagRe = regexp.MustCompile(`^[a-zA-Z0-9_][a-zA-Z0-9._-]*$`)
 
-// prevMonthExample returns the previous calendar month as a tag example, e.g. "2026.4".
-func prevMonthExample() string {
-	y, m, _ := time.Now().Date()
-	m--
-	if m == 0 {
-		m, y = 12, y-1
-	}
-	return fmt.Sprintf("%d.%d", y, int(m))
-}
-
 func validateTag(tag string) error {
 	if tag == "" {
 		return nil
 	}
 	if len(tag) > 128 || !validTagRe.MatchString(tag) || zeroPaddedMonthTagRe.MatchString(tag) {
-		return fmt.Errorf("tag %q is not supported — try a tag like %q or \"latest\" in your config file", tag, prevMonthExample())
+		return errors.New(UnsupportedTagMessage())
 	}
 	return nil
 }

internal/config/containers_test.go

@@ -54,7 +54,7 @@ func TestValidate_ZeroPaddedMonthTag_IsRejected(t *testing.T) {
 	for _, tag := range []string{"2026.04", "2026.04.1", "2026.04.0-amd64", "2026.01", "2026.09.2"} {
 		t.Run(tag, func(t *testing.T) {
 			c := &ContainerConfig{Type: EmulatorAWS, Port: "4566", Tag: tag}
-			assert.ErrorContains(t, c.Validate(), "not supported")
+			assert.ErrorContains(t, c.Validate(), "unsupported")
 		})
 	}
 }
@@ -72,7 +72,7 @@ func TestValidate_InvalidDockerTag_IsRejected(t *testing.T) {
 		t.Run(tag, func(t *testing.T) {
 			c := &ContainerConfig{Type: EmulatorAWS, Port: "4566", Tag: tag}
 			err := c.Validate()
-			assert.ErrorContains(t, err, "not supported")
+			assert.ErrorContains(t, err, "unsupported")
 		})
 	}
 }