• Message Queue Client

This package provides an easy way to communicate with a message queue using our messaging protocol.

** Getting started Clone the repository and run =npm install=.

** Running tests The package.json includes scripts to run all tests. Just run =npm test=!

** The protocol The messaging protocol is built directly on top of TCP and follows the simple syntax of = =. Available keywords are as follows:

*** =SCHED= Adds a new task to the queue. Messages need to follow the syntax

#+BEGIN_SRC text SCHED [@] #+END_SRC

The =@= is optional and defines which listening service should execute the task. If not supplied, the task will be added to a =default= queue.

**** Examples #+BEGIN_SRC text SCHED { email: "[email protected]", message: "test message" }@EMAILSERVICE #+END_SRC

Schedules a task for services listening to the =EMAILSERVICE= queue. The task is encoded as a JSON object and contains an email address and a message. The data part does not have to be JSON as we will see in the next example. In the context of the studybear backend however, we will always encode tasks as JSON objects.

#+BEGIN_SRC text SCHED test #+END_SRC

This is more of a minimum working example. Schedules the task "test" for services listing to the =default= queue.

*** =ASK= Asks for a task from the queue. The full syntax is

#+BEGIN_SRC text ASK [service] #+END_SRC

Again, the =service= parameter is optional and the =default= queue is accessed if omitted. Prompts the messaging queue to respond with a =WANT?= message.

**** Examples

#+BEGIN_SRC text ASK EMAILSERVICE #+END_SRC

Asks for a new task from the =EMAILSERVICE= queue.

#+BEGIN_SRC text ASK #+END_SRC

Asks for a new task from the =default= queue.

*** =WANT?= Sent by the messaging queue to supply a task to a service. The full syntax is

#+BEGIN_SRC text WANT? #+END_SRC

The data represents the task, and is equivalent to the data in the =SCHED= message.

**** Examples

#+BEGIN_SRC text WANT? { email: "[email protected]" message: "test message" } #+END_SRC

Returns the same task we scheduled in the =SCHED= section.

*** =NOPE= Sent by the messaging queue to indicate that there are no available tasks in the requested queue.

*** =ACK= Confirms the acceptance of a =WANT?= message. The messaging queue assumes that the task will be done successfully and will remove it from the relevant queue. Should the receiving service fail in fulfilling the task, it has to be re =SCHED= uled.

*** =DCL= Declines the task. The messaging queue will skip it and move it to the back of the queue. Can be used to postpone tasks. ATTENTION the messaging queue will not respond with another =WANT?= message, the client needs to =ASK= again.

*** =DEL= Removes the task from the messaging queue. This may be useful if the task data is corrupted or not readable for some other reason. To avoid blocking the queue with tasks that will be =DCL= ined anyway, services can use =DEL= to remove them.

*** =END= Ends the communication and closes the socket.