Fix version comparison logic in update checker

jib-plugins-common/src/main/java/com/google/cloud/tools/jib/plugins/common/UpdateChecker.java

@@ -61,6 +61,57 @@ private static class VersionJsonTemplate implements JsonTemplate {
    * @param log {@link Consumer} used to log messages
    * @return a new {@link UpdateChecker}
    */
+
+  @VisibleForTesting
+   static int compareVersions(String v1, String v2) {
+    String[] p1 = v1.split("\\.");
+    String[] p2 = v2.split("\\.");
+
+    int len = Math.max(p1.length, p2.length);
+    for (int i = 0; i < len; i++) {
+      String s1 = i < p1.length ? p1[i] : "0";
+      String s2 = i < p2.length ? p2[i] : "0";
+
+      int n1 = parseNumericPrefix(s1);
+      int n2 = parseNumericPrefix(s2);
+
+      if (n1 != n2) {
+        return Integer.compare(n1, n2);
+      }
+
+      // Handle suffixes (e.g., "1-SNAPSHOT", "1-beta")
+      String suf1 = suffix(s1);
+      String suf2 = suffix(s2);
+
+      if (!suf1.equals(suf2)) {
+        if (suf1.isEmpty()) return 1;   // no suffix ⇒ stable release ⇒ newer
+        if (suf2.isEmpty()) return -1;  // suffix ⇒ prerelease ⇒ older
+        return suf1.compareTo(suf2);    // both have suffix ⇒ lexicographic
+      }
+    }
+    return 0;
+  }
+
+  private static int parseNumericPrefix(String s) {
+    int i = 0;
+    while (i < s.length() && Character.isDigit(s.charAt(i))) i++;
+    if (i == 0) return 0;
+    try {
+      return Integer.parseInt(s.substring(0, i));
+    } catch (NumberFormatException ex) {
+      return 0;
+    }
+  }
+
+  private static String suffix(String s) {
+    int i = 0;
+    while (i < s.length() && Character.isDigit(s.charAt(i))) i++;
+    return s.substring(i); // "" if no suffix
+  }
+
+
+
+
   public static Future<Optional<String>> checkForUpdate(
       ExecutorService executorService,
       String versionUrl,
@@ -118,10 +169,16 @@ static Optional<String> performUpdateCheck(
         Files.write(lastUpdateCheckTemp, Instant.now().toString().getBytes(StandardCharsets.UTF_8));
         Files.move(lastUpdateCheckTemp, lastUpdateCheck, StandardCopyOption.REPLACE_EXISTING);
 
-        if (currentVersion.equals(version.latest)) {
+        if (version.latest == null || version.latest.isEmpty()) {
           return Optional.empty();
         }
-        return Optional.of(version.latest);
+
+        if (compareVersions(currentVersion, version.latest) < 0) {
+          return Optional.of(version.latest); // only report if newer
+        }
+
+        return Optional.empty(); // otherwise equal or older
+
       } finally {
         httpClient.shutDown();
       }

jib-plugins-common/src/test/java/com/google/cloud/tools/jib/plugins/common/UpdateCheckerTest.java

@@ -62,6 +62,21 @@ public void setUp()
     configDir = temporaryFolder.getRoot().toPath();
   }
 
+  @Test
+  public void testCompareVersions() {
+    assertThat(UpdateChecker.compareVersions("3.5.0", "3.4.6")).isGreaterThan(0);
+    assertThat(UpdateChecker.compareVersions("3.4.6", "3.5.0")).isLessThan(0);
+    assertThat(UpdateChecker.compareVersions("3.5.0", "3.5.0")).isEqualTo(0);
+    assertThat(UpdateChecker.compareVersions("3.5", "3.5.0")).isEqualTo(0);
+    assertThat(UpdateChecker.compareVersions("3.5.1", "3.5")).isGreaterThan(0);
+    assertThat(UpdateChecker.compareVersions("1.0.0-SNAPSHOT", "1.0.0")).isLessThan(0);
+    assertThat(UpdateChecker.compareVersions("1.0.0-alpha", "1.0.0-beta")).isLessThan(0);
+    assertThat(UpdateChecker.compareVersions("1.0.0-beta", "1.0.0")).isLessThan(0);
+    assertThat(UpdateChecker.compareVersions("1.0.0", "1.0.0-alpha")).isGreaterThan(0);
+
+  }
+
+
   @After
   public void tearDown() throws IOException {
     testWebServer.close();