Output bindings not registered

[JamieMagee]

I'm unable to get any output bindings to work when debugging locally using Azure Functions core tools. That includes using the example functions

Investigative information

n/a (Debugging locally)

Repro steps

Debug the function attached at the bottom of the bug report. context.bindings only contains 1 binding, but it should include 2: An input and an output. Both bindings are correctly defined in context.bindingDefinitions.

Trigger using curl localhost:7071/api/HttpTrigger

Related information

Environment

• Arch Linux
• Azure Functions core tools: 2.5.553

Source

{
  "bindings": [
    {
      "name": "req",
      "type": "httpTrigger",
      "direction": "in"
    },
    {
      "type": "http",
      "direction": "out",
      "name": "res"
    }
  ]
}

import { AzureFunction, Context } from '@azure/functions';

const index: AzureFunction = async function (context: Context): Promise<void> {
    
};

export default index;

[pragnagopa]

@JamieMagee - generated function.json looks right. Can you please explain what do you mean by

unable to get any output bindings to work

cc @mhoeger for follow up

[mhoeger]

@JamieMagee - I think what you're referring to is that the "bindings" object only contains the names and values of input / trigger type bindings. This is expected behavior as we've documented it (in our docs and in our TypeScript type definitions).

We do also say to set output through context.bindings (more info here), you can do it as follows:

import { AzureFunction, Context } from '@azure/functions';

const index: AzureFunction = async function (context: Context): Promise<void> {
    context.log('res' in context.bindings); // logs "false"
    context.log(context.bindings.res); // logs "undefined"
    context.bindings.res = {
        body: "hello, world",
        status: 200
    }
};

export default index;

Is the ask to change it so that the output binding key name is there with a starting value of "undefined"? So when you inspect the context object, you see that output bindings should be assigned to?

Another thing to note is that on context, there is a special http response object, "res", that sets http output in a way that is different from any other output binding type. If you look at the context.res object, you'll see it's already defined and has a few methods on it. This is to allow users to do "express-like" calls like context.res.send("hello world!"); (more here). Notice that it is scoped under "context" instead of "context.bindings", because it is treated as separate from the other dynamically generated output bindings (example of blob output).

Admittedly.... it is very confusing and not very intuitively organized.

Although we can't make a change in V2, can you tell us what your expectations were when you were trying to create an HTTP response? This is something we can improve in future major versions!

[ahmedelnably]

Closing as resolved