Calling a Cloud Function from another Cloud Function

I am using a Cloud Function to call another Cloud Function on the free spark tier.

Is there a special way to call another Cloud Function? Or do you just use a standard http request?

I have tried calling the other function directly like so:

exports.purchaseTicket = functions.https.onRequest((req, res) => {    
  fetch('https://us-central1-functions-****.cloudfunctions.net/validate')
    .then(response => response.json())
    .then(json => res.status(201).json(json))
})

But I get the error

> FetchError: request to > https://us-central1-functions-****.cloudfunctions.net/validate > failed, reason: getaddrinfo ENOTFOUND > us-central1-functions-.cloudfunctions.net > us-central1-functions-.cloudfunctions.net:443

Which sounds like firebase is blocking the connection, despite it being a google owned, and therefore it shouldn't be locked

> the Spark plan only allows outbound network requests to Google owned > services.

How can I make use a Cloud Function to call another Cloud Function?

You don't need to go through the trouble of invoking some shared functionality via a whole new HTTPS call. You can simply abstract away the common bits of code into a regular javascript function that gets called by either one. For example, you could modify the template helloWorld function like this:

var functions = require('firebase-functions');

exports.helloWorld = functions.https.onRequest((request, response) => {
  common(response)
})

exports.helloWorld2 = functions.https.onRequest((request, response) => {
  common(response)
})

function common(response) {
  response.send("Hello from a regular old function!");
}

These two functions will do exactly the same thing, but with different endpoints.

To answer the question, you can do an https request to call another cloud function:

export const callCloudFunction = async (functionName: string, data: {} = {}) => {
	let url = `https://us-central1-${config.firebase.projectId}.cloudfunctions.net/${functionName}`
	await fetch(url, {
		method: 'POST',
		headers: {
			'Content-Type': 'application/json',
		},
		body: JSON.stringify({ data }),
	})
}

(Note we are using the npm package 'node-fetch' as our fetch implementation.)

And then simply call it:

callCloudFunction('search', { query: 'yo' })

There are legitimate reasons to do this. We used this to ping our search cloud function every minute and keep it running. This greatly lowers response latency for a few dollars a year.

It's possible to invoke another Google Cloud Function over HTTP by including an authorization token. It requires a primary HTTP request to calculate the token, which you then use when you call the actual Google Cloud Function that you want to run.

https://cloud.google.com/functions/docs/securing/authenticating#function-to-function

const {get} = require('axios');

// TODO(developer): set these values
const REGION = 'us-central1';
const PROJECT_ID = 'my-project-id';
const RECEIVING_FUNCTION = 'myFunction';

// Constants for setting up metadata server request
// See https://cloud.google.com/compute/docs/instances/verifying-instance-identity#request_signature
const functionURL = `https://${REGION}-${PROJECT_ID}.cloudfunctions.net/${RECEIVING_FUNCTION}`;
const metadataServerURL =
  'http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/identity?audience=';
const tokenUrl = metadataServerURL + functionURL;

exports.callingFunction = async (req, res) => {
  // Fetch the token
  const tokenResponse = await get(tokenUrl, {
    headers: {
      'Metadata-Flavor': 'Google',
    },
  });
  const token = tokenResponse.data;

  // Provide the token in the request to the receiving function
  try {
    const functionResponse = await get(functionURL, {
      headers: {Authorization: `bearer ${token}`},
    });
    res.status(200).send(functionResponse.data);
  } catch (err) {
    console.error(err);
    res.status(500).send('An error occurred! See logs for more details.');
  }
};

October 2021 Update: You should not need to do this from a local development environment, thank you Aman James for clarifying this

Despite of the question tag and other answers concern the javascript I want to share the python example as it reflects the title and also authentification aspect mentioned in the question.

Google Cloud Function provide REST API interface what incluse call method that can be used in another Cloud Function. Although the documentation mention using Google-provided client libraries there is still non one for Cloud Function on Python.

And instead you need to use general Google API Client Libraries. [This is the python one].3

Probably, the main difficulties while using this approach is an understanding of authentification process. Generally you need provide two things to build a client service: credentials ans scopes.

The simpliest way to get credentials is relay on Application Default Credentials (ADC) library. The rigth documentation about that are:

1. https://cloud.google.com/docs/authentication/production
2. https://github.com/googleapis/google-api-python-client/blob/master/docs/auth.md

The place where to get scopes is the each REST API function documentation page. Like, OAuth scope: https://www.googleapis.com/auth/cloud-platform

The complete code example of calling 'hello-world' clound fucntion is below. Before run:

1. Create default Cloud Function on GCP in your project.

• Keep and notice the default service account to use
• Keep the default body.

2. Notice the project_id, function name, location where you deploy function.
3. If you will call function outside Cloud Function environment (locally for instance) setup the environment variable GOOGLE_APPLICATION_CREDENTIALS according the doc mentioned above
4. If you will call actualy from another Cloud Function you don't need to configure credentials at all.

from googleapiclient.discovery import build
from googleapiclient.discovery_cache.base import Cache
import google.auth

import pprint as pp

def get_cloud_function_api_service():
    class MemoryCache(Cache):
        _CACHE = {}

        def get(self, url):
            return MemoryCache._CACHE.get(url)

        def set(self, url, content):
            MemoryCache._CACHE[url] = content

    scopes = ['https://www.googleapis.com/auth/cloud-platform']

    # If the environment variable GOOGLE_APPLICATION_CREDENTIALS is set,
    # ADC uses the service account file that the variable points to.
    #
    # If the environment variable GOOGLE_APPLICATION_CREDENTIALS isn't set,
    # ADC uses the default service account that Compute Engine, Google Kubernetes Engine, App Engine, Cloud Run,
    # and Cloud Functions provide
    #
    # see more on https://cloud.google.com/docs/authentication/production
    credentials, project_id = google.auth.default(scopes)

    service = build('cloudfunctions', 'v1', credentials=credentials, cache=MemoryCache())
    return service


google_api_service = get_cloud_function_api_service()
name = 'projects/{project_id}/locations/us-central1/functions/function-1'
body = {
    'data': '{ "message": "It is awesome, you are develop on Stack Overflow language!"}' # json passed as a string
}
result_call = google_api_service.projects().locations().functions().call(name=name, body=body).execute()
pp.pprint(result_call)
# expected out out is:
# {'executionId': '3h4c8cb1kwe2', 'result': 'It is awesome, you are develop on Stack Overflow language!'}

These suggestions don't seem to work anymore.

To get this to work for me, I made calls from the client side using httpsCallable and imported the requests into postman. There were some other links to https://firebase.google.com/docs/functions/callable-reference there were helpful. But determining where the information was available took a bit of figuring out.

I wrote everything down here as it takes a bit of explaining and some examples.

https://www.tiftonpartners.com/post/call-google-cloud-function-from-another-cloud-function

Here's an inline version for the 'url' might expire.

This 'should' work, it's not tested but based off of what I wrote and tested for my own application.

module.exports = function(name,context) {
    const {protocol,headers} = context.rawRequest;
    const host = headers['x-forwardedfor-host'] || headers.host;
    // there will be two different paths for
    // production and development
    const url = `${protocol}://${host}/${name}`;
    const method = 'post';    
    const auth = headers.authorization;
    
    return (...rest) => {
        const data = JSON.stringify({data:rest});
        const config = {
            method, url, data,
            headers: {
               'Content-Type': 'application/json',
               'Authorization': auth,
               'Connection': 'keep-alive',
               'Pragma': 'no-cache,
               'Cache-control': 'no-cache',
            }
        };
        try {
            const {data:{result}} = await axios(config);
            return result;        
        } catch(e) {
            throw e;
        }
    }
}

This is how you would call this function.

const crud = httpsCallable('crud',context);
return await crud('read',...data);

context you get from the google cloud entry point and is the most important piece, it contains the JWT token needed to make the subsequent call to your cloud function (in my example its crud)

To define the other httpsCallable endpoint you would write an export statement as follows

exports.crud = functions.https.onCall(async (data, context) => {})

It should work just like magic.

Hopefully this helps.

I found a combination of two of the methods works best

const anprURL = `https://${REGION}-${PROJECT_ID}.cloudfunctions.net/${RECEIVING_FUNCTION}`;
const metadataServerURL =
  'http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/identity?audience=';
const tokenUrl = metadataServerURL + anprURL;

// Fetch the token
const tokenResponse = await fetch(tokenUrl, {
    method: "GET"
    headers: {
      'Metadata-Flavor': 'Google',
    },
});

const token = await tokenResponse.text();

const functionResponse = await fetch(anprURL, {
    method: 'POST',
    headers: {
        "Authorization": `bearer ${token}`,
        'Content-Type': 'application/json',
    },
    body: JSON.stringify({"imageUrl": url}),
});

// Convert the response to text
const responseText = await functionResponse.text();

// Convert from text to json
const reponseJson = JSON.parse(responseText);

Extending the Shea Hunter Belsky's answer I would love to inform you that the call to the metatdata server of google to fetch the authorization token would not work from local machine