Why is my kafkajs client (Node.js/express.js) throwing 'TypeError: topics.forEach is not a function' while fetching topics metadata?

Question

I'm trying to fetch my kafka brokers' topics' metadata using kafkajs admin client. I've written my server in Node.js + express.js.

This is my index.js file, which is the entrypoint of npm.

'use strict';

const express = require('express');
const bodyParser = require('body-parser');
const Admin = require('./Admin/create-admin-client');
const TopicMetaData = require('./Admin/topic-metadata-fetch');

const app = express();
app.use(bodyParser.urlencoded({ extended: false }));
app.use(bodyParser.json());

const adminConfig = new Admin({
    clientId: 'admin-client-4981',
    brokers: ['localhost:9092']
})

const admin = adminConfig.getAdmin();




.
..
...
// Handles the admin connection, disconnection, and other routes here
...
..
.




//This is where the error is
app.post('/api/v1/dev/admin/topicmetadata', (req, res) => {
    const topic = req.body;
    const topicmetadata = new TopicMetaData(admin);

    topicmetadata.setTopicConfig(topic);
    topicmetadata.commit(req, res);
});

app.listen(4040);

This is create-admin-client.js file, which retrieves admin object.

'use strict';

const { Kafka } = require('kafkajs');

class Admin {
    constructor(kafkaConfig) {
         this.kafka = new Kafka({
            clientId: kafkaConfig.clientId,
            brokers: kafkaConfig.brokers
        });
    }

    getAdmin() {
        return this.kafka.admin();
    };
}

module.exports = Admin;

This is the topics-metadata-fetch.js file, which fetches the topic's metadata.

'use strict';

class TopicMetaData {

    constructor(admin) {
        this.admin = admin;
    }

    setTopicConfig(topicConfig) {
        this.topic = topicConfig;
    }

    commit(req, res) {
        this.admin.fetchTopicMetadata({
            topics: this.topic
        })
        .then((topics) => {
            console.log("Topic MetaData Fetched Successfully!");
            res.status(200).send({
                topics
            });
        })
        .catch((err) => {
            console.error(err);
            res.status(500).send(err);
        })
    }
}

module.exports = TopicMetaData;

Whenever I send a POST request to fetch the metadata of a topic (example 'SERVICE-TYPES', I've created topic successfully), with the req.body as

{
    "topic": "SERVICE-TYPES",
    "partitions": [{
        "partitionErrorCode": 0,
        "partitionId": 0,
        "leader": 0,
        "replicas": [0],
        "isr": [0]
    }]
}

It return a TypeError: topics.forEach is not a function error. Where did I go wrong?

Answer 1

I found out that my http request body was supposed to be of the following structure:

{
    "topics": [{
        "topic": "SERVICE_TYPES",
        "partitions": [{
            "partitionErrorCode": 0,
            "partitionId": 0,
            "leader": 0,
            "replicas": [0],
            "isr": [0]
        }]
    }]
}

and my route handler should be like:

app.get('/api/v1/dev/admin/topicmetadata', (req, res) => {
        //topic should be array of the topics
        const topic = req.body.topics;
        const topicmetadata = new TopicMetaData(admin);

        topicmetadata.setTopicConfig(topic);
        topicmetadata.commit(req, res);
});

So I was passing down the wrong request body structure.