How to trigger an API call when a message is sent to Azure service bus topic?

Question

I am working on Azure service bus topic. Following the documentation , created a sender and reciever code.

This is the sender code i am having,

const { ServiceBusClient } = require("@azure/service-bus");

const connectionString = "<SERVICE BUS NAMESPACE CONNECTION STRING>"
const topicName = "<TOPIC NAME>";

const messages = [
    { body: "Albert Einstein" },
    { body: "Werner Heisenberg" },
    { body: "Marie Curie" },
    { body: "Steven Hawking" },
    { body: "Isaac Newton" },
    { body: "Niels Bohr" },
    { body: "Michael Faraday" },
    { body: "Galileo Galilei" },
    { body: "Johannes Kepler" },
    { body: "Nikolaus Kopernikus" }
 ];

 async function main() {
    // create a Service Bus client using the connection string to the Service Bus namespace
    const sbClient = new ServiceBusClient(connectionString);

    // createSender() can also be used to create a sender for a queue.
    const sender = sbClient.createSender(topicName);

    try {
        // Tries to send all messages in a single batch.
        // Will fail if the messages cannot fit in a batch.
        // await sender.sendMessages(messages);

        // create a batch object
        let batch = await sender.createMessageBatch(); 
        for (let i = 0; i < messages.length; i++) {
            // for each message in the arry         

            // try to add the message to the batch
            if (!batch.tryAddMessage(messages[i])) {            
                // if it fails to add the message to the current batch
                // send the current batch as it is full
                await sender.sendMessages(batch);

                // then, create a new batch 
                batch = await sender.createMessageBatch();

                // now, add the message failed to be added to the previous batch to this batch
                if (!batch.tryAddMessage(messages[i])) {
                    // if it still can't be added to the batch, the message is probably too big to fit in a batch
                    throw new Error("Message too big to fit in a batch");
                }
            }
        }

        // Send the last created batch of messages to the topic
        await sender.sendMessages(batch);

        console.log(`Sent a batch of messages to the topic: ${topicName}`);

        // Close the sender
        await sender.close();
    } finally {
        await sbClient.close();
    }
}

// call the main function
main().catch((err) => {
    console.log("Error occurred: ", err);
    process.exit(1);
 });

This code is working fine, but instead of sending a batch of dummy data to the service bus topic i want to implement my use case here.

My use case is I will be using this sender code in a react front end application, where there is a node API call happening at the end of a form submission. So at the end of form submission, i will send that unique form ID to the topic and i need to somehow trigger the api call for that form id.

I am unable to connect the dots. How to do this?

Added reciever side code.

 const { delay, ServiceBusClient, ServiceBusMessage } = require("@azure/service-bus"); const axios = require("axios").default; const connectionString = "<ConnectionString>" const topicName = "<TopicName>"; const subscriptionName = "<Subscription>"; async function main() { // create a Service Bus client using the connection string to the Service Bus namespace const sbClient = new ServiceBusClient(connectionString); // createReceiver() can also be used to create a receiver for a queue. const receiver = sbClient.createReceiver(topicName, subscriptionName); // function to handle messages const myMessageHandler = async (messageReceived) => { console.log(`Received message: ${messageReceived.body}`); const response = axios({ method: 'post', url: 'http://localhost:8080/gitWrite?userprojectid=63874e2e3981e40a6f4e04a7', }); console.log(response); }; // function to handle any errors const myErrorHandler = async (error) => { console.log(error); }; // subscribe and specify the message and error handlers receiver.subscribe({ processMessage: myMessageHandler, processError: myErrorHandler }); // Waiting long enough before closing the sender to send messages await delay(5000); await receiver.close(); await sbClient.close(); } // call the main function main().catch((err) => { console.log("Error occurred: ", err); process.exit(1); });

Answer 1

While messages are published to a topic, they are recieved by subscriptions under the topic. You'll need to define one or more subscriptions to receive the messages. That's on the broker. For your code, you'll need a receiving code on the server-side/backend. Could be something like a node.js service or Azure Function. But a code that would receive from the subscription(s).

I would review the idea of publishing messages from the client side directly to Azure Service Bus. If the code is a React front end application, make sure the connection string is not embedded in resources or can be revealed.