Add function calling to a Retell voice agent

// install the sdk: https://docs.retellai.com/get-started/sdk
import Retell from 'retell-sdk';

const retell = new Retell({ apiKey: "YOUR_API_KEY" });

const agentResponse = await retell.llm.update('your_llm_id', {
  general_tools: [
    {
      name: 'end_call',
      description: 'end the call if the customer has said goodbye',
      type: 'end_call',
    }
  ]
});

{
  "type": "object",
  "properties": {
    "city": {
      "type": "string",
      "description": "The city of the weather"
    }
  },
  "required": [
    "city"
  ]
}

{
  "call": {
    "call_type": "phone_call",
    "from_number": "+12137771234",
    "to_number": "+12137771235",
    "direction": "inbound",
    "call_id": "Jabr9TXYYJHfvl6Syypi88rdAHYHmcq6",
    "agent_id": "oBeDLoLOeuAbiuaMFXRtDOLriTJ5tSxD",
    "call_status": "registered",
    "metadata": {},
    "retell_llm_dynamic_variables": {
      "customer_name": "John Doe"
    },
    "opt_out_sensitive_data_storage": true
  },
  "name": "get_weather",
  "args": {
    "city": "New York"
  }
}

import { Retell } from "retell-sdk";
import express from "express";

const app = express();
// Use raw body for signature verification, not JSON.stringify(req.body).
app.use(express.raw({ type: "application/json" }));

app.post("/check-weather", async (req, res) => {
  const rawBody = req.body.toString("utf-8");
  const signature = req.headers["x-retell-signature"];
  if (
    typeof signature !== "string" ||
    !(await Retell.verify(rawBody, process.env.RETELL_API_KEY, signature))
  ) {
    console.error("Invalid signature");
    return;
  }
  const content = JSON.parse(rawBody);
  if (content.args.city === "New York") {
    return res.json("25f and sunny");
  } else {
    return res.json("20f and cloudy");
  }
});

from fastapi import FastAPI, Request
from fastapi.responses import JSONResponse
from retell import Retell

retell = Retell(api_key=os.environ["RETELL_API_KEY"])

@app.post("/webhook")
async def handle_webhook(request: Request):
    try:
        raw_body = (await request.body()).decode("utf-8")
        valid_signature = retell.verify(
            raw_body,
            api_key=str(os.environ["RETELL_API_KEY"]),
            signature=str(request.headers.get("X-Retell-Signature")),
        )
        if not valid_signature:
            print("Received Unauthorized")
            return JSONResponse(status_code=401, content={"message": "Unauthorized"})
        post_data = json.loads(raw_body)
        args = post_data["args"]
        if args["city"] == "New York":
            return JSONResponse(status_code=200, content={"result": "25f and sunny"})
        else:
            return JSONResponse(status_code=200, content={"result": "20f and cloudy"})
    except Exception as err:
        print(f"Error in webhook: {err}")
        return JSONResponse(
            status_code=500, content={"message": "Internal Server Error"}
        )