timer-mq: A message queue with timers, written in Golang

Message queues are systems that transport messages from a source to a receiver. It is meant to achieve fault tolerance in highly distributed systems, through decoupling. TimerMQ is a Golang implementation of a message queue that supports adding a timeout before the message is sent. When the timeout expires, the message is sent to the receiver. The message may also be cancelled any time before the timeout expires.

How it works

1. Source sends a message to TimerMQ with a specified delayMs (0s by default, i.e., this behaves like a typical message queue)
2. TimerMQ returns a confirmation message with messageId for the newly created message.
3. If you cancel a message before its timeout expires, it is sent to a dead-letter queue and never makes its way to the receiver
4. When the timeout of a message expires (and if it hasn't been cancelled prior to that), the message is sent to the receiver.

Supported Commands

• PUSH <value> <args>: Pushes a string value into TimerMQ with default delay of 0ms. This method will return the message id id of the the pushed message
• GET <id>: Retrives a message with id. Returns an empty value if it does not exist.
• CANCEL <id>: Cancels the message with id id if it is scheduled to be published and has not expired yet.

Optional Args

When pushing a message into TimerMQ, you can set optional args modifying the behavior of the message

Optional Arg	Supported Commands	Description	Default
delayMs	PUSH	Sets a delay in milliseconds after which message will be pushed to TimerMQ. This message will be stored immediately if durable is true	0 ms
durable	PUSH	If true, the message will be stored in the persistence layer (in-memory, database, file, etc.)	false

Messages

Messages are a composite, atomic unit of transaction within TimerMQ. A message consists of a <COMMAND> and val specifying the action to be taken on val. This behavior may be modified by passing along optional args. Each message is separated by the newline characted (\n)

Each message sent to TimerMQ must be of the form:

<COMMAND> <val> <args>

val is then processed according to the specified COMMAND and args.

Once a message is passed, it cannot be modified.

TODO:

• If persistence is enabled, each message is stored in the specified persistence layer.
• If logging is enabled, each message is logged to the specified log stream.

As of today, TimerMQ operates using a simple message protocol over TCP. Support for other protocols such as MQTT and AMQP are in development.