Azure Function outgoing storage queue binding not available on context

Question

I have a really simple Azure Function with the sole purpose of taking all messages included in a blob and put those messages on a storage queue.

I'm running Functions 2.x, the function is written in JavaScript and I've registered a blob trigger and an output binding for storage queues.

The problem I'm having is that the output binding isn't available in ctx.bindings in my function. I'm using a named output binding, because I will have multiple output bindings. When I change the output binding name to $return and return my data, the messages are written to the queue as expected, but when I set a different name the binding doesn't show up in the context. I can however see the binding definition in ctx.bindingDefinitions.

I'm running the code locally with Azure Function Host, with the proper extensions installed.

My code goes like this:

import { Context } from '@azure/functions'

export async function run(ctx: Context , content: string): Promise<void> {
  try {
    const data = JSON.parse(content)

    if (!ctx.bindings[data.queue]) {
      throw new Error(`No output binding defined for queue '${data.queue}'`)
    }

    ctx.bindings[data.queue] = [...data.messages]
  } catch (e) {
    return Promise.reject(e)
  }
}

And my function.json:

{
  "disabled": false,
  "bindings": [
   {
    "name": "content",
    "type": "blobTrigger",
    "direction": "in",
    "path": "message-batches/{filename}.txt"
   },
   {
      "type": "queue",
      "direction": "out",
      "name": "message",
      "queueName": "message",
      "connection": "AZURE_STORAGE_CONNECTION_STRING"
    }
  ],
  "scriptFile": "index.js"
 }

My incoming content binding is available as ctx.bindings.content. I'm thinking I might be missing something trivial here, but what could be the reason for the binding not to show up under ctx.bindings?

Jerry Liu Jerry Liu · Accepted Answer · 2019-02-15T07:35:36

The output binding is not available in Context.bindings until it's populated with content at runtime.

If we want to check the existence of output definition, turn to Context.bindingDefinitions.

let flag:boolean = false;

for (let bindingDefinition of ctx.bindingDefinitions) {
    if(bindingDefinition.name == data.queue) {
        flag = true;
        break;
    }
}

if(!flag){
    throw new Error(`No output binding defined for queue '${data.queue}'`)
}

Azure Function outgoing storage queue binding not available on context

1 Answers