[DISSCUSS] RIP-13 RocketMQ-RPC

[Eason Chen <qq...@gmail.com>]

RIP 13 RocketMQ RPC

Status

   - Current State: Proposed
   - Authors: EasonChen
   - Shepherds: [author](qqeasonchen)
   - Mailing List discussion:
   - Pull Request: #PR_NUMBER
   - Released: <relased_version>

Background & Motivation

RPC is a powerful technique for constructing distributed, client-server
based applications. Many companies use MQ system to constructing their
service bus, especially in financial industry. We need to implement a RPC
client based on MQ system ourselves because MQ system doesn’t support RPC
naturally. In current version of rocketmq project, producer client only
support to send a message to broker and cannot wait a response message
replied from consumer. We wish RocketMQ can provide a RPC client implement
to help developers building their applications conveniently and effectively.

Goals

   - What problem is this proposal designed to solve?

(1) Design and implement a RPC interface based on RocketMQ Producer, which
support send a message and then wait a response message replied from
consumer.

(2) Design and Implement a consumer which can automatic or manually send a
reply message.

(3) Enable broker to push a message to an explicit producer.



   - To what degree should we solve the problem?

We wish developers can use RocketMQ easily to constructing their
distributed applications which need RPC call.

Non-Goals

   - What problem is this proposal NOT designed to solve?

In this phase, this rip only support a usable RPC call in most common
scenarios.

   - Are there any limits of this proposal?

Users may need to tune some client and broker’s configurations to achieve a
better performance.

Changes

Architecture

We plan to add RPC implement into client and broker modules. In client
modules, we will add a RPC interface into DefaultMQProducer, and add reply
logic into DefaultMQPushConsumer. In broker modules, we will add a
processor to push reply message from consumer to explicit producer.

Interface Design/Change

   - Method signature changes

Plan to add interfaces as follow:

Message request(final Message msg, final long timeout) throws
MQClientException, RemotingException, MQBrokerException,
InterruptedException;



Message request(final Message msg, final SendCallback sendCallback, final
long timeout) throws MQClientException, RemotingException,
InterruptedException;



Message request(final Message msg, final MessageQueueSelector selector,
final Object arg, final long timeout) throws MQClientException,
RemotingException, MQBrokerException, InterruptedException;



Message request(final Message msg, final MessageQueueSelector selector,
final Object arg, final SendCallback sendCallback, final long timeout)
throws MQClientException, RemotingException, InterruptedException;



Message request(final Message msg, final MessageQueue mq, final long
timeout) throws MQClientException, RemotingException, MQBrokerException,
InterruptedException;



Message request(final Message msg, final MessageQueue mq, final
SendCallback sendCallback, long timeout) throws MQClientException,
RemotingException, InterruptedException;



   - Method behavior changes

No issue

   - CLI command changes

No issue

   - Log format or content changes

No issue

 Compatibility, Deprecation, and Migration Plan

   - No issue

Implementation Outline

We will implement the proposed changes by *1* phases.

Phase 1

   1. Implement RPC feature in Producer
   2. Implement RPC feature in Consumer
   3. Implement RPC feature in Broker