Ignore unknown Http3Setting Identifier in Http3SettingsFrame (#360)

* According to the spec
https://www.rfc-editor.org/rfc/rfc9114.html#section-7.2.4-9 , endpoints
**must ignore unknown settings identifiers**. Netty’s previous behavior
incorrectly **stored** unknown settings values, which contradicts RFC
behaviour.
* A **HTTP/3 error code** was missing - H3_DATAGRAM_ERROR
* The **SETTINGS_H3_DATAGRAM (0x33)** identifier was not added.
* Prior behaviour fixed in
[https://github.com/netty/netty/pull/15835](https://github.com/netty/netty/pull/15835)
still allowed direct injection of unsupported settings; this PR
effectively deprecates that direct-settings behaviour completely.

---

* [x] **Ignore unknown HTTP/3 SETTINGS identifiers**

  * Updated parsing logic to skip unknown settings identifiers:

```java // When Non-Standard/Unknown settings identifier present -
Ignore if (Http3SettingIdentifier.fromId(key) == null) { return value; }
```

  * Unknown settings are **no longer stored** in `Http3Settings`.

  * Fully aligns with HTTP/3 specification behaviour.

* Effectively **deprecates the old direct-settings behavior**
introduced/fixed in PR #15835.

* [x] **Added missing HTTP/3 error codes**

  * Implemented the remaining H3 error codes defined in the RFC.
  * Ensures accurate error propagation and complete protocol support.

* [x] **Added `SETTINGS_H3_DATAGRAM (0x33)`**

  * Introduced the identifier:

    ```java SETTINGS_H3_DATAGRAM(0x33) ```

  * Added proper handling in both encoder and decoder paths.

* [x] **Added unit tests**

  * Tests covering:

    * Ignoring unknown setting identifiers
    * Correct handling of `SETTINGS_H3_DATAGRAM`
    * Verification of newly added error codes
    * Ensuring unknown settings do **not** appear in `Http3Settings`

---

* [x] Netty now **correctly ignores unknown HTTP/3 settings**, as
required by the specification.
* [x] `Http3Settings` no longer stores invalid or non-standard
identifiers.
* [x] Full support for **`SETTINGS_H3_DATAGRAM (0x33)`**.
* [x] Complete coverage of **HTTP/3 error codes**.
* [x] Added unit tests ensure long-term correctness.
* [x] Behaviour from PR #15835 is effectively superseded and corrected.

Fixes #[15908](netty/netty#15908) Port of
netty/netty#15909

Author: normanmaurer

src/main/java/io/netty/incubator/codec/http3/Http3ErrorCode.java

@@ -16,10 +16,20 @@
 package io.netty.incubator.codec.http3;
 
 /**
- * Different <a href="https://tools.ietf.org/html/draft-ietf-quic-http-32#section-8.1">HTTP3 error codes</a>.
+ * Different <a href="https://datatracker.ietf.org/doc/html/rfc9114#name-http-3-error-codes">HTTP3 error codes</a>.
  */
 public enum Http3ErrorCode {
 
+    /**
+     * Datagram or Capsule Protocol parse error
+     * <a href="https://www.rfc-editor.org/rfc/rfc9297.html#name-http-3-error-code">rfc9297</a>
+     * registered in IANA http3
+     * <a href="https://www.iana.org/assignments/http3-parameters/http3-parameters.xhtml#http3-parameters-error-codes"
+     * >
+     *     IANA Http3 Error Codes</a>
+     */
+    H3_DATAGRAM_ERROR(0x33),
+
     /**
      *  No error. This is used when the connection or stream needs to be closed, but there is no error to signal.
      */

src/main/java/io/netty/incubator/codec/http3/Http3SettingIdentifier.java

@@ -0,0 +1,124 @@
+/*
+ * Copyright 2025 The Netty Project
+ *
+ * The Netty Project licenses this file to you under the Apache License,
+ * version 2.0 (the "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at:
+ *
+ *   https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+package io.netty.incubator.codec.http3;
+
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.Map;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+public enum Http3SettingIdentifier {
+
+    /**
+     * QPACK maximum table capacity setting identifier (<b>0x1</b>).
+     * <p>
+     * Defined in <a href="https://datatracker.ietf.org/doc/html/rfc9204#section-5">
+     * RFC 9204, Section 5 (SETTINGS_QPACK_MAX_TABLE_CAPACITY)</a> and registered in
+     * the <a href="https://www.iana.org/assignments/http3-parameters/http3-parameters.xhtml#settings">
+     * HTTP/3 SETTINGS registry (IANA)</a>.
+     * <br>
+     * Controls the maximum size of the dynamic table used by QPACK.
+     */
+    HTTP3_SETTINGS_QPACK_MAX_TABLE_CAPACITY(0x1),
+
+    /**
+     * Maximum field section size setting identifier (<b>0x6</b>).
+     * <p>
+     * Defined in <a href="https://datatracker.ietf.org/doc/html/rfc9114#section-7.2.4.1">
+     * RFC 9114, Section 7.2.4.1 (SETTINGS_MAX_FIELD_SECTION_SIZE)</a> , also referenced
+     * in the <a href="https://datatracker.ietf.org/doc/html/rfc9114#section-7.2.4.1">
+     * HTTP/3 SETTINGS registry (RFC 9114, Section 7.2.4.1)</a> and registered in
+     * the <a href="https://www.iana.org/assignments/http3-parameters/http3-parameters.xhtml#settings">
+     * HTTP/3 SETTINGS registry (IANA)</a>.
+     * <br>
+     * Specifies the upper bound on the total size of HTTP field sections accepted by a peer.
+     */
+    HTTP3_SETTINGS_MAX_FIELD_SECTION_SIZE(0x6),
+
+    /**
+     * QPACK blocked streams setting identifier (<b>0x7</b>).
+     * <p>
+     * Defined in <a href="https://datatracker.ietf.org/doc/html/rfc9204#section-5">
+     * RFC 9204, Section 5 (SETTINGS_QPACK_BLOCKED_STREAMS)</a> and registered in
+     * the <a href="https://www.iana.org/assignments/http3-parameters/http3-parameters.xhtml#settings">
+     * HTTP/3 SETTINGS registry (IANA)</a>.
+     * <br>
+     * Indicates the maximum number of streams that can be blocked waiting for QPACK instructions.
+     */
+    HTTP3_SETTINGS_QPACK_BLOCKED_STREAMS(0x7),
+
+    /**
+     * ENABLE_CONNECT_PROTOCOL setting identifier (<b>0x8</b>).
+     * <p>
+     * Defined and registered in <a href="https://datatracker.ietf.org/doc/html/rfc9220#section-5">
+     * RFC 9220, Section 5 (IANA Considerations)</a> and registered in
+     * the <a href="https://www.iana.org/assignments/http3-parameters/http3-parameters.xhtml#settings">
+     * HTTP/3 SETTINGS registry (IANA)</a>.
+     * <br>
+     * Enables use of the CONNECT protocol in HTTP/3 when set to 1; disabled when 0.
+     */
+    HTTP3_SETTINGS_ENABLE_CONNECT_PROTOCOL(0x8),
+
+    /**
+     * ENABLE_H3_DATAGRAM setting identifier (<b>0x8</b>).
+     * <p>
+     * Defined and registered in <a href="https://datatracker.ietf.org/doc/html/rfc9297#name-http-3-setting">
+     * RFC 9220, Section 5 (IANA Considerations)</a> and registered in
+     * the <a href="https://www.iana.org/assignments/http3-parameters/http3-parameters.xhtml#settings">
+     * HTTP/3 SETTINGS registry (IANA)</a>.
+     * <br>
+     * Enables use of the CONNECT protocol in HTTP/3 when set to 1; disabled when 0.
+     */
+    HTTP3_SETTINGS_H3_DATAGRAM(0x33);
+
+    private final long id;
+
+    private static final Map<Long, Http3SettingIdentifier> LOOKUP = Collections.unmodifiableMap(
+            Arrays.stream(values())
+                    .collect(Collectors.toMap(
+                            Http3SettingIdentifier::id,
+                            Function.identity()
+                    ))
+    );
+
+    Http3SettingIdentifier(long id) {
+        this.id = id;
+    }
+
+    /**
+     * Returns the Identifier of {@link Http3SettingIdentifier}
+     * for example:
+     * SETTINGS_QPACK_MAX_TABLE_CAPACITY = 0x1 = 1 in the settings frame
+     * <br>
+     * @return long(represented as hexadecimal above) value of the Identifier
+     */
+    public long id() {
+        return id;
+    }
+
+    /**
+     * Returns {@link Http3SettingIdentifier}
+     * @param id
+     * @return {@link Http3SettingIdentifier} enum which represents @param id, null otherwise
+     */
+    @Nullable
+    public static Http3SettingIdentifier fromId(long id) {
+        return LOOKUP.get(id);
+    }
+}