Create an event handler that receives and processes a Pub/Sub message event

Creates an event handler that receives and processes a Pub/Sub message event.

Explore further

For detailed documentation that includes this code sample, see the following:

• Develop event receivers

Code sample

C#

To authenticate to Eventarc, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

using CloudNative.CloudEvents;
using CloudNative.CloudEvents.AspNetCore;
using Google.Events.Protobuf.Cloud.PubSub.V1;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env, ILogger<Startup> logger)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        logger.LogInformation("Service is starting...");

        app.UseRouting();

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapPost("/", async context =>
            {
                var formatter = CloudEventFormatterAttribute.CreateFormatter(typeof(MessagePublishedData));
                var cloudEvent = await context.Request.ToCloudEventAsync(formatter);
                logger.LogInformation("Received CloudEvent\n" + GetEventLog(cloudEvent));

                var messagePublishedData = (MessagePublishedData) cloudEvent.Data;
                var pubSubMessage = messagePublishedData.Message;
                if (pubSubMessage == null)
                {
                    context.Response.StatusCode = 400;
                    await context.Response.WriteAsync("Bad request: Invalid Pub/Sub message format");
                    return;
                }

                var data = pubSubMessage.Data;
                logger.LogInformation($"Data: {data.ToBase64()}");

                var name = data.ToStringUtf8();
                logger.LogInformation($"Extracted name: {name}");

                var id = context.Request.Headers["ce-id"];
                await context.Response.WriteAsync($"Hello {name}! ID: {id}");
            });
        });
    }

    private string GetEventLog(CloudEvent cloudEvent)
    {
        return $"ID: {cloudEvent.Id}\n"
            + $"Source: {cloudEvent.Source}\n"
            + $"Type: {cloudEvent.Type}\n"
            + $"Subject: {cloudEvent.Subject}\n"
            + $"DataSchema: {cloudEvent.DataSchema}\n"
            + $"DataContentType: {cloudEvent.DataContentType}\n"
            + $"Time: {cloudEvent.Time?.UtcDateTime:yyyy-MM-dd'T'HH:mm:ss.fff'Z'}\n"
            + $"SpecVersion: {cloudEvent.SpecVersion}\n"
            + $"Data: {cloudEvent.Data}";
    }
}

Go

To authenticate to Eventarc, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

// Sample pubsub is a Cloud Run service which handles Pub/Sub messages.
package main

import (
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"os"
)

// PubSubMessage is the payload of a Pub/Sub event.
// See the documentation for more details:
// https://cloud.google.com/pubsub/docs/reference/rest/v1/PubsubMessage
type PubSubMessage struct {
	Message struct {
		Data []byte `json:"data,omitempty"`
		ID   string `json:"id"`
	} `json:"message"`
	Subscription string `json:"subscription"`
}

// HelloEventsPubSub receives and processes a Pub/Sub push message.
func HelloEventsPubSub(w http.ResponseWriter, r *http.Request) {
	var e PubSubMessage
	if err := json.NewDecoder(r.Body).Decode(&e); err != nil {
		http.Error(w, "Bad HTTP Request", http.StatusBadRequest)
		log.Printf("Bad HTTP Request: %v", http.StatusBadRequest)
		return
	}
	name := string(e.Message.Data)
	if name == "" {
		name = "World"
	}
	s := fmt.Sprintf("Hello, %s! ID: %s", name, string(r.Header.Get("Ce-Id")))
	log.Printf(s)
	fmt.Fprintln(w, s)
}

Java

To authenticate to Eventarc, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

import com.example.cloudrun.eventpojos.PubSubBody;
import java.util.Base64;
import java.util.Map;
import org.apache.commons.lang3.StringUtils;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestHeader;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class EventController {
  @RequestMapping(value = "/", method = RequestMethod.POST)
  public ResponseEntity<String> receiveMessage(
      @RequestBody PubSubBody body, @RequestHeader Map<String, String> headers) {
    // Get PubSub message from request body.
    PubSubBody.PubSubMessage message = body.getMessage();
    if (message == null) {
      String msg = "No Pub/Sub message received.";
      System.out.println(msg);
      return new ResponseEntity<>(msg, HttpStatus.BAD_REQUEST);
    }

    String data = message.getData();
    if (data == null || data.isEmpty()) {
      String msg = "Invalid Pub/Sub message format.";
      System.out.println(msg);
      return new ResponseEntity<>(msg, HttpStatus.BAD_REQUEST);
    }

    String name =
        !StringUtils.isEmpty(data) ? new String(Base64.getDecoder().decode(data)) : "World";
    String ceId = headers.getOrDefault("ce-id", "");
    String msg = String.format("Hello, %s! ID: %s", name, ceId);
    System.out.println(msg);
    return new ResponseEntity<>(msg, HttpStatus.OK);
  }
}

Node.js

To authenticate to Eventarc, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

const express = require('express');
const {
  toMessagePublishedData,
} = require('@google/events/cloud/pubsub/v1/MessagePublishedData');
const app = express();

app.use(express.json());
app.post('/', (req, res) => {
  if (!req.body) {
    const errorMessage = 'no Pub/Sub message received';
    res.status(400).send(`Bad Request: ${errorMessage}`);
    console.log(`Bad Request: ${errorMessage}`);
    return;
  }
  if (!req.body.message) {
    const errorMessage = 'invalid Pub/Sub message format';
    res.status(400).send(`Bad Request: ${errorMessage}`);
    console.log(`Bad Request: ${errorMessage}`);
    return;
  }
  // Cast to MessagePublishedEvent for IDE autocompletion
  const pubSubMessage = toMessagePublishedData(req.body);
  const name =
    pubSubMessage.message && pubSubMessage.message.data
      ? Buffer.from(pubSubMessage.message.data, 'base64').toString().trim()
      : 'World';

  const result = `Hello, ${name}! ID: ${req.get('ce-id') || ''}`;
  console.log(result);
  res.send(result);
});

module.exports = app;

Python

To authenticate to Eventarc, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

@app.route("/", methods=["POST"])
def index():
    data = request.get_json()
    if not data:
        msg = "no Pub/Sub message received"
        print(f"error: {msg}")
        return f"Bad Request: {msg}", 400

    if not isinstance(data, dict) or "message" not in data:
        msg = "invalid Pub/Sub message format"
        print(f"error: {msg}")
        return f"Bad Request: {msg}", 400

    pubsub_message = data["message"]

    name = "World"
    if isinstance(pubsub_message, dict) and "data" in pubsub_message:
        name = base64.b64decode(pubsub_message["data"]).decode("utf-8").strip()

    resp = f"Hello, {name}! ID: {request.headers.get('ce-id')}"
    print(resp)

    return (resp, 200)

Ruby

To authenticate to Eventarc, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

post "/" do
  request.body.rewind # in case someone already read it

  body = JSON.parse request.body.read
  data = Base64.decode64 body["message"]["data"]
  if data.empty?
    data = "World"
  end
  id = request.env["HTTP_CE_ID"]
  if request.has_header? "ce-id"
    id = request.get_header "ce-id"
  end

  result = "Hello #{data}! ID: #{id}"
  puts result
  result
end

What's next

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