Improve TTL validation and handling in UMessageBuilder

src/main/java/org/eclipse/uprotocol/transport/builder/UMessageBuilder.java

@@ -106,16 +106,17 @@ public static UMessageBuilder notification(UUri source, UUri sink) {
      * @param source The URI that the sender of the request expects the response message at.
      * @param sink   The URI identifying the method to invoke.
      * @param ttl    The number of milliseconds after which the request should no longer be processed
-     * by the target service.
+     * by the target service. The given value is interpreted as an <em>unsigned</em> integer.
      * @return The builder.
      * @throws NullPointerException if the source or sink is {@code null}.
-     * @throws IllegalArgumentException if the ttl is less than or equal to 0.
+     * @throws IllegalArgumentException if the ttl is 0.
      */
     public static UMessageBuilder request(UUri source, UUri sink, int ttl) {
         Objects.requireNonNull(source, "source cannot be null.");
         Objects.requireNonNull(sink, "sink cannot be null.");
 
-        if (ttl <= 0) {
+        if (ttl == 0) {
+            // [impl->dsn~up-attributes-request-ttl~1]
             throw new IllegalArgumentException("ttl must be greater than 0.");
         }
         return new UMessageBuilder(
@@ -230,8 +231,15 @@ public UMessageBuilder withMessageId(UUID id) {
      * @param ttl The time-to-live in milliseconds. Note that the value is interpreted as an
      * <em>unsigned</em> integer. A value of 0 indicates that the message never expires.
      * @return The builder with the configured ttl.
+     * @throws IllegalArgumentException if the builder is used for creating an RPC message and the TTL is 0.
      */
     public UMessageBuilder withTtl(int ttl) {
+        if ((this.type == UMessageType.UMESSAGE_TYPE_REQUEST
+            || this.type == UMessageType.UMESSAGE_TYPE_RESPONSE)
+            && ttl == 0) {
+            // [impl->dsn~up-attributes-request-ttl~1]
+            throw new IllegalArgumentException("TTL of RPC messages must be greater than 0.");
+        }
         this.ttl = ttl;
         return this;
     }

src/main/java/org/eclipse/uprotocol/transport/validator/UAttributesValidator.java

@@ -147,6 +147,7 @@ public final void validateRpcTtl(UAttributes attributes) {
         int ttl = attributes.getTtl();
         // TTL is interpreted as an unsigned integer, so negative values are not possible
         if (ttl == 0) {
+            // [impl->dsn~up-attributes-request-ttl~1]
             throw new ValidationException("RPC message's TTL must not be 0");
         }
     }

src/main/java/org/eclipse/uprotocol/uuid/factory/UuidUtils.java

@@ -126,7 +126,7 @@ public static long getRemainingTime(UUID id, int ttl, Instant now) {
             throw new IllegalArgumentException("TTL must not be 0");
         }
         final long elapsedTime = getElapsedTime(id, now);
-        if (Long.compareUnsigned(elapsedTime, ttl) > 0) {
+        if (Long.compareUnsigned(elapsedTime, ttl) >= 0) {
             return 0; // Expired
         } else {
             return ttl - elapsedTime;

src/test/java/org/eclipse/uprotocol/transport/builder/UMessageBuilderTest.java

@@ -130,6 +130,7 @@ void assertBuilderPanics(
     }
 
     @Test
+    // [utest->dsn~up-attributes-request-ttl~1]
     void testRequestRejectsInvalidTtl() {
         assertThrows(
             IllegalArgumentException.class,
@@ -139,22 +140,25 @@ void testRequestRejectsInvalidTtl() {
 
     @ParameterizedTest
     @CsvSource(useHeadersInDisplayName = true, textBlock = """
-        commStatus, priority
-        NOT_FOUND,
+        commStatus, priority,              ttl
+        NOT_FOUND,  ,
         # // [utest->dsn~up-attributes-request-priority~1]
-        ,          UPRIORITY_UNSPECIFIED
+        ,          UPRIORITY_UNSPECIFIED,
         # // [utest->dsn~up-attributes-request-priority~1]
-        ,          UPRIORITY_CS0
+        ,          UPRIORITY_CS0,
         # // [utest->dsn~up-attributes-request-priority~1]
-        ,          UPRIORITY_CS1
+        ,          UPRIORITY_CS1,
         # // [utest->dsn~up-attributes-request-priority~1]
-        ,          UPRIORITY_CS2
+        ,          UPRIORITY_CS2,
         # // [utest->dsn~up-attributes-request-priority~1]
-        ,          UPRIORITY_CS3
+        ,          UPRIORITY_CS3,
+        # // [utest->dsn~up-attributes-request-ttl~1]
+        ,          ,                       0
         """)
     void testRequestMessageBuilderRejectsInvalidAttributes(
         UCode commStatus,
-        UPriority priority
+        UPriority priority,
+        Integer ttl
     ) {
         var builder = UMessageBuilder.request(UURI_DEFAULT, UURI_METHOD, 5000);
 
@@ -168,6 +172,11 @@ void testRequestMessageBuilderRejectsInvalidAttributes(
                 IllegalArgumentException.class,
                 () -> builder.withPriority(priority)
             );
+        } else if (ttl != null) {
+            assertThrows(
+                IllegalArgumentException.class,
+                () -> builder.withTtl(ttl)
+            );
         }
     }