How can I create an instance of builtin Pulsar Function using the Pulsar REST API?

[oneebhkhan]

I am trying to create an instance of a builtin Pulsar Function using the Pulsar REST API.
However, I am coming across an issue where I get the following error:
400: {"reason":"Function package is not provided"}
I am using a multi-part upload for the REST request and the entire point of using a builtin function is so that I can avoid having to specify the function package.

[lhotari]

when using a builtin function, it's necessary to pass builtin://<function name> in the jar key of function config.

Something like this (example using curl):

cat >/tmp/functionconfig.json <<EOF
{
  "tenant": "public",
  "namespace": "default",
  "name": "myfunction",
  "jar": "builtin://builtin-function-name",
  "runtime": "JAVA",
  "inputs": [
    "public/default/input-topic"
  ],
  "output": "public/default/output-topic",
  "autoAck": true,
  "parallelism": 1
}
EOF

curl -H "Authorization: Bearer $(cat token)" -v -X POST \
  -F "functionConfig=@/tmp/functionconfig.json;type=application/json" \
  http://pulsar-function-worker:6750/admin/v3/functions/public/default/myfunction

It's not related to this question, but to expand the curl example to cover uploading of a jar/nar file, this is the way curl can be used to create functions from a jar/nar file:

cat >/tmp/functionconfig.json <<EOF
{
  "tenant": "public",
  "namespace": "default",
  "name": "myfunction",
  "className": "MyFunction",
  "runtime": "JAVA",
  "inputs": [
    "public/default/input-topic"
  ],
  "output": "public/default/output-topic",
  "autoAck": true,
  "parallelism": 1
}
EOF

curl -H "Authorization: Bearer $(cat token)" -v -X POST \
  -F "functionConfig=@/tmp/functionconfig.json;type=application/json" \
  -F "data=@function.jar;type=application/octet-stream" \
  http://pulsar-function-worker:6750/admin/v3/functions/public/default/myfunction