Set up the WhatsApp Echo Bot

Before you start, make sure to register and sign into an AWS development account.

1. Open the AWS Lambda console. AWS operates in several regional data centers and this example is set up in the US East (N. Virginia) us-east-1 region. So the actual link is https://us-east-1.console.aws.amazon.com/lambda/home.
2. Click Create Function > Author from scratch and create your function. For this example, we have added and/or selected the following options:
   • Function name: cloudEcho
   • Runtime: Node.js 16.x, since we're implementing Javascript-based Lambda function
   • Execution role: Create a new role with basic Lambda permissions
   • Advanced Settings: Enable function URL has been checked and Auth type was set to None.
   The Advanced Settings look like this:
3. Click Create Function.
4. Once the function is created, you are redirected to the function page. There, you can see the following information:
   • The function's URL ending in .lambda-url.AWS_REGION.on.aws/. Save that for later use.
   • The Code source tab for that function.
5. Inside your function's Code Source, you need to add code that does the following:
   • Only accepts GET and POST requests
   • Verifies using the GETrequest described here.
   • Replies to the message based on the message payload structure described here.
   The code sample to be copied and pasted is:

   const https = require("https");
   
   exports.handler = async (event)  => {
     const VERIFY_TOKEN = "Set_your_verify_token_value_here";
     const WHATSAPP_TOKEN = "Paste_whatsapp_access_token_here";
   
     let response;
     if (event?.requestContext?.http?.method === "GET") {
       // https://developers.facebook.com/docs/graph-api/webhooks/getting-started#verification-requests
       // to learn more about GET request for webhook verification
       let queryParams = event?.queryStringParameters;
       if (queryParams != null) {
         const mode = queryParams["hub.mode"];
         if (mode == "subscribe") {
           const verifyToken = queryParams["hub.verify_token"];
           if (verifyToken == VERIFY_TOKEN) {
             let challenge = queryParams["hub.challenge"];
             response = {
                 "statusCode": 200,
                 "body": parseInt(challenge),
                 "isBase64Encoded": false
             };
           } else {
             const responseBody = "Error, wrong validation token";
             response = {
                 "statusCode": 403,
                 "body": JSON.stringify(responseBody),
                 "isBase64Encoded": false
             };
           }
         } else {
             const responseBody = "Error, wrong mode";
             response = {
                 "statusCode": 403,
                 "body": JSON.stringify(responseBody),
                 "isBase64Encoded": false
           };
         }
       }
       else {
         const responseBody = "Error, no query parameters";
         response = {
             "statusCode": 403,
             "body": JSON.stringify(responseBody),
             "isBase64Encoded": false
         };
       }
     } else if (event?.requestContext?.http?.method === "POST") {
       // process POST request (WhatsApp chat messages)
       // https://developers.facebook.com/docs/whatsapp/cloud-api/webhooks/payload-examples#text-messages
       // to learn about WhatsApp text message payload structure
       let body = JSON.parse(event.body)
       let entries = body.entry;
       for (let entry of entries) {
         for (let change of entry.changes) {
           let value = change.value;
           if(value != null) {
             let phone_number_id = value.metadata.phone_number_id;
             if (value.messages != null) {
               for (let message of value.messages) {
                 if (message.type === 'text') {
                   let from = message.from;
                   let message_body = message.text.body;
                   let reply_message = "Ack from AWS lambda: " + message_body;
                   sendReply(phone_number_id, WHATSAPP_TOKEN, from, reply_message);
                   const responseBody = "Done";
                   response = {
                       "statusCode": 200,
                       "body": JSON.stringify(responseBody),
                       "isBase64Encoded": false
                   };
                 }
               }
             }
           }
         }
       }
     } else {
       const responseBody = "Unsupported method";
       response = {
           "statusCode": 403,
           "body": JSON.stringify(responseBody),
           "isBase64Encoded": false
       };
     }
     
     return response;
   }
   
   const sendReply = (phone_number_id, whatsapp_token, to, reply_message) => {
     let json = {
       messaging_product: "whatsapp",
       to: to,
       text: { body: reply_message },
     };
     let data = JSON.stringify(json);
     let path = "/v12.0/"+phone_number_id+"/messages?access_token="+whatsapp_token;
     let options = {
       host: "graph.facebook.com",
       path: path,
       method: "POST",
       headers: { "Content-Type": "application/json" }
     };
     let callback = (response) => {
       let str = "";
       response.on("data", (chunk) => {
         str += chunk;
       });
       response.on("end", () => {
       });
     };
     let req = https.request(options, callback);
     req.on("error", (e) => {});
     req.write(data);
     req.end();
   }
   
6. Once you paste the code, you will see the Changes not deployed banner pop up. Do not deploy your function yet! We need to set verify token and access token before that.

1. Open Meta for Developers > My Apps and select the app you have created while following the getting started workflow. Click WhatsApp > Getting started.
2. Copy the temporary access token:
   

1. Paste the access token into your Lambda function. Then, set up the VERIFY_TOKEN field in your Lambda function. For this example, we're using blue_panda.
2. Click Deploy.

1. Open Meta for Developers > My Apps and select the app you have created while following the getting started workflow. Click WhatsApp > Configuration > Configure a webhook.
2. Under Callback URL, paste your Lambda function URL (this is the URL that was generated immediately after the function was created). Under Verify Token, paste the token you created after pasting your access token (for our example, we're using blue_panda):
3. Click Verify and Save.
4. Once verification is successful, click Manage back in the Configuration page:
5. A new dialog module opens up with all available objects you can subscribe to. Click Subscribe for the messages object. Then, click Done.
6. You are done setting up the echo bot! Now, when you send a message to the API number on WhatsApp, it should send back your message in the following format "Ack from AWS lambda: {your message}".