Feature request : Function Outputs

[erkkikeranen]

While a HTTP triggered API is nice that returns a HTTP response, as a developer I would like to output some other stuff to db tables, queues, event hubs and what not automatically when I finish running of my function.

Similair to #83 (Function Inputs), we need an abstraction on outputs.

Ideas:

• Message(s) to Queue
• Write to DB table
• Post Event (future)
• Write to storage (S3/blob/..) (future)

First solution:

hedge.edn

 :api {"api2h" {:handler my_cool_function.core/handler-to-queue 
                :authorization :anonymous
                :outputs [{:type :queue
                                  :key "out1"
                                  :name "queue2"
                                  :connection "AzureWebJobsStorage"}
                                 {:type :queue
                                  :key "out2"
                                  :name "queue2"
                                  :connection "AzureWebJobsStorage"}]

handler signature change example:

(defn handler [req & {:keys [outputs]}
    (reset! (-> outputs :out1) "this value goes to queue1")
    ; obviously out2 is not set and thus not processed
)

Notes:

• outputs in this example is a map of {:out1 (atom nil) :out2 (atom nil)}. Keys correspond the :key names defined in hedge.edn
• an atom which value is nil is not processed in the output chain (outputs are optional in that sense during runtime)
• Azure runtime handles writing to outputs when context.done() is called for context.bindings. that are != null
• AWS handler must implement writing to outputs on exit
• You must be able to pass either one item or a vector of items i.e. "message" or ["message1" "message2"]
• Unhandled exception must not commit changes to outputs

Todo first solution:

• [x] Azure output to queue(s) (storage queue, servicebus queue, servicebus topic)
• [x] Azure output to table storage table (s) / Cosmos DB table (s)
• [ ] AWS output to queue (SNS - the Hedge queue implementation)
• [ ] AWS output to dynamodb table
• [ ] Documentation