How to send a file from cloud storage using response.sendFile in cloud functions?

Question

I'm trying to send a response back to a client using an http trigger from firebase cloud functions. When I sent the response using the file location from Cloud Storage, the sendFile method throws this error:

"path must be absolute or specify root to res.sendFile"

res.sendFile(obj.path(param1, param2, param3, param4));

obj.path(param1, param2, param3, param4) this builds a path to gs:// or an https:// with the params.

Then I decided to do this:

const rp = require("request-promise");

exports.fun = functions.https.onRequest( async (req, res) => {
let extResponse = await rp('firebase storage location');
          extResponse.pipe(res);
});

rp is now returning this error:

StatusCodeError: 403 - "{\n  \"error\": {\n    \"code\": 403,\n    \"message\": \"Permission denied. Could not perform this operation\"\n  }\n}"

This error is because cloud storage requires the request to be authenticated in order to let the service download the file from storage.

Is there a way to make this work and return the file back to the client?

Answer 1

sendFile won't work, because it doesn't understand URLs. It only understand files on the local filesystem. You should be using the Cloud Storage SDK for node to do this. Create a File object that points to the file you want to send, open up a read stream on it, then pipe the stream to the response:

const file = ... // whatever file you want to send
const readStream = file.createReadStream()
readStream.pipe(res)