feat: Validate string format 'hostname'

Author: thced

src/main/java/com/retailsvc/http/validate/DefaultValidator.java

@@ -47,6 +47,11 @@ private record FormatCheck(Predicate<String> isValid, String message) {}
 
   private static final Pattern EMAIL = Pattern.compile("^[^\\s@]+@[^\\s@]+\\.[^\\s@]+$");
 
+  private static final Pattern HOSTNAME =
+      Pattern.compile(
+          "^(?=.{1,253}$)([a-zA-Z0-9]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)"
+              + "(\\.[a-zA-Z0-9]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$");
+
   private static final Map<String, FormatCheck> FORMAT_CHECKS =
       Map.ofEntries(
           Map.entry("uuid", new FormatCheck(DefaultValidator::isUuid, "not a valid uuid")),
@@ -57,7 +62,10 @@ private record FormatCheck(Predicate<String> isValid, String message) {}
           Map.entry("uri", new FormatCheck(DefaultValidator::isUri, "not a valid uri")),
           Map.entry(
               "uri-reference",
-              new FormatCheck(DefaultValidator::isUriReference, "not a valid uri-reference")));
+              new FormatCheck(DefaultValidator::isUriReference, "not a valid uri-reference")),
+          Map.entry(
+              "hostname",
+              new FormatCheck(s -> HOSTNAME.matcher(s).matches(), "not a valid hostname")));
 
   private final Function<String, Schema> refResolver;
   private final ConcurrentMap<String, Pattern> compiledPatterns = new ConcurrentHashMap<>();

src/test/java/com/retailsvc/http/validate/StringIntegerNumberTest.java

@@ -103,6 +103,19 @@ void stringFormatUriReference() {
         .isEqualTo("format");
   }
 
+  @Test
+  void stringFormatHostname() {
+    StringSchema s = new StringSchema(Set.of(TypeName.STRING), null, null, null, "hostname", null);
+    assertThatCode(() -> v.validate("example.com", s, "/v")).doesNotThrowAnyException();
+    assertThatCode(() -> v.validate("a.b.c.example", s, "/v")).doesNotThrowAnyException();
+    assertThatThrownBy(() -> v.validate("-leading-hyphen.com", s, "/v"))
+        .extracting(t -> ((ValidationException) t).error().keyword())
+        .isEqualTo("format");
+    assertThatThrownBy(() -> v.validate("invalid host name", s, "/v"))
+        .extracting(t -> ((ValidationException) t).error().keyword())
+        .isEqualTo("format");
+  }
+
   @Test
   void integerWithMinMax() {
     IntegerSchema s =