How I Ported Netty’s MQTT Codec to t-io for Full MQTT 5 Support
This article details the process of adapting the Netty MQTT codec to the t‑io framework, covering the migration from MQTT 3.1.1 to MQTT 5, code adjustments, ByteBuf-to-ByteBuffer conversion, custom WriteBuffer handling, and the resulting client demonstrations.
1. Introduction
MQTT (Message Queuing Telemetry Transport) is a lightweight publish/subscribe messaging protocol released by IBM. The widely used versions are MQTT 3.1.1 (2014) and MQTT 5.0 (2018). Details of MQTT 5 features can be found at https://www.emqx.io/cn/mqtt/mqtt5.
2. mica-mqtt
To deepen understanding of MQTT, a project called mica-mqtt was built around September using t‑io. The MQTT encoding/decoding is based on Netty’s codec‑mqtt module, which at that time did not support MQTT 5. Netty’s codec‑mqtt is mature and used by many Java MQTT brokers. This article explains how the codec was ported to t‑io.
3. Migrating to MQTT 5
Two weeks ago Netty’s codec‑mqtt added MQTT 5 support, and I upgraded the code accordingly. The following steps show how it was done.
3.1 Copy source code
ObjectUtil.checkNotNullreplaced with Objects.requireNonNull. CharsetUtil.UTF_8 changed to StandardCharsets.UTF_8.
Reimplemented the toString method.
3.2 ByteBuf to ByteBuffer conversion
Netty parses protocols with ByteBuf, while t‑io uses ByteBuffer. The main task is converting between them. The method differences are: writeByte →
putwriteBytes→
putwriteShort→
putShortwriteInt→
putIntgetByte→
getgetBytes→
getgetShort→
getShortgetInt→
getInt3.3 Handling mqtt5 encodeProperties
Because ByteBuffer has a fixed length, I created a custom WriteBuffer to hold data during encoding, which is finally converted to a byte[]. The underlying implementation uses t‑io’s FastByteBuffer authored by biezhi.
4. Results (MQTT 5)
4.1 Using MQTTX client
4.2 Using mica-mqtt client
5. TODO
mica‑mqtt is currently experimental; contributions are welcome.
Bind topics.
Implement basic MQTT broker functionality.
Reference: ZBus can be used for messaging or internal clustering.
6. About t‑io
t‑io is a simple, high‑performance, low‑latency network middle‑platform that addresses pain points not solved by other frameworks, helping enterprises save labor costs.
Technical whitepaper: https://www.tiocloud.com/tio.pdf
t‑io IM (TanLiao) has a 14 k user group; join us!
Product brochure: https://www.tiocloud.com/tioim.pdf
7. Related Links
mica‑mqtt: https://gitee.com/596392912/mica-mqtt
t‑io: https://gitee.com/tywo45/t-io
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