Middlewares

Goose has provision for middlewares which can run before/after execution of a Job.

How Middlewares work?

• middleware-fn takes next as input
• It returns a function of arity 2
• Returned function takes opts & job as inputs
• Function calls next with opts & job
• Function can modify opts/job before proceeding, with utmost care
• Function may choose to act on the result of next or not call it altogether based on certain criteria

Practical applications of Middlewares

• Modify args of job pre-execution
• Use returned value of job post-execution
• Ignore exceptions thrown by job
• Extending Goose's functionalities as described in this issue

Usage

(defn my-middleware
  [next]
  (fn [opts job]
    ; Be careful when modifying fields of opts/job.
    (let [result (next opts job)]
      (log/info result))))

(w/start (assoc w/default-opts :middlewares my-middleware))

Nuances

• Middleware's time will be added to job execution time
• For client-side middlewares, you can wrap enqueuing function around your middleware

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