イベント レシーバを開発する

このページでは、イベント レシーバ サービスを作成してデプロイする方法を説明します。ターゲット サービスは、イベントを含む HTTP リクエストを CloudEvents 形式で受信します。

イベント プロバイダ（ソース）は、以下のイベントタイプを提供できます。

• Google Cloud のソースから直接取得
• Cloud Audit Logs の使用
• サードパーティのソースの使用

イベント レシーバのレスポンス

レシーバ サービスが HTTP 2xx レスポンスを送信し、ルーターにイベントの受信成功を通知します。他の HTTP レスポンスはすべて配信エラーとして処理され、イベントが再送信されます。

オープンソース リポジトリ

すべてのイベントの HTTP 本文の構造は、CloudEvents GitHub リポジトリで入手できます。

リポジトリには、CloudEvents データを理解して、お使いのプログラミング言語で使用する際に役立つものが用意されています。

• CloudEvents データ ペイロード用の Google Protocol Buffer
• 生成された JSON スキーマ
• 公開 JSON スキーマ カタログ

クライアント ライブラリへのリンクも含まれます。

CloudEvents SDK ライブラリの使用

イベント レシーバ サービスは、CloudEvents SDK ライブラリを使用して作成できます。このライブラリは次の言語で利用できます。

• C#
• Go
• Java
• JavaScript
• Python
• Ruby

これはオープンソースのライブラリです。HTTP リクエストを言語固有の CloudEvents オブジェクトに簡単に変換できます。

サンプルのレシーバ ソースコード

Cloud Audit Logs

次のサンプルコードは、Cloud Run にデプロイされたサービスで Cloud Audit Logs を使用して Cloud Storage イベントを読み取る方法を示しています。

Python

@app.route("/", methods=["POST"])
def index():
    # Create a CloudEvent object from the incoming request
    event = from_http(request.headers, request.data)
    # Gets the GCS bucket name from the CloudEvent
    # Example: "storage.googleapis.com/projects/_/buckets/my-bucket"
    bucket = event.get("subject")

    print(f"Detected change in Cloud Storage bucket: {bucket}")
    return (f"Detected change in Cloud Storage bucket: {bucket}", 200)

Java

import io.cloudevents.CloudEvent;
import io.cloudevents.rw.CloudEventRWException;
import io.cloudevents.spring.http.CloudEventHttpUtils;
import org.springframework.http.HttpHeaders;
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, consumes = "application/json")
  public ResponseEntity<String> receiveMessage(
      @RequestBody String body, @RequestHeader HttpHeaders headers) {
    CloudEvent event;
    try {
      event =
          CloudEventHttpUtils.fromHttp(headers)
              .withData(headers.getContentType().toString(), body.getBytes())
              .build();
    } catch (CloudEventRWException e) {
      return new ResponseEntity<>(e.getMessage(), HttpStatus.BAD_REQUEST);
    }

    String ceSubject = event.getSubject();
    String msg = "Detected change in Cloud Storage bucket: " + ceSubject;
    System.out.println(msg);
    return new ResponseEntity<>(msg, HttpStatus.OK);
  }
}

Node.js

const express = require('express');
const app = express();

app.use(express.json());
app.post('/', (req, res) => {
  if (!req.header('ce-subject')) {
    return res
      .status(400)
      .send('Bad Request: missing required header: ce-subject');
  }

  console.log(
    `Detected change in Cloud Storage bucket: ${req.header('ce-subject')}`
  );
  return res
    .status(200)
    .send(
      `Detected change in Cloud Storage bucket: ${req.header('ce-subject')}`
    );
});

module.exports = app;

Go

// Processes CloudEvents containing Cloud Audit Logs for Cloud Storage
package main

import (
	"fmt"
	"log"
	"net/http"
	"os"

	cloudevent "github.com/cloudevents/sdk-go/v2"
)

// HelloEventsStorage receives and processes a Cloud Audit Log event with Cloud Storage data.
func HelloEventsStorage(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		http.Error(w, "Expected HTTP POST request with CloudEvent payload", http.StatusMethodNotAllowed)
		return
	}

	event, err := cloudevent.NewEventFromHTTPRequest(r)
	if err != nil {
		log.Printf("cloudevent.NewEventFromHTTPRequest: %v", err)
		http.Error(w, "Failed to create CloudEvent from request.", http.StatusBadRequest)
		return
	}
	s := fmt.Sprintf("Detected change in Cloud Storage bucket: %s", event.Subject())
	fmt.Fprintln(w, s)
}

C#

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 =>
            {
                logger.LogInformation("Handling HTTP POST");

                var ceSubject = context.Request.Headers["ce-subject"];
                logger.LogInformation($"ce-subject: {ceSubject}");

                if (string.IsNullOrEmpty(ceSubject))
                {
                    context.Response.StatusCode = 400;
                    await context.Response.WriteAsync("Bad Request: expected header Ce-Subject");
                    return;
                }

                await context.Response.WriteAsync($"GCS CloudEvent type: {ceSubject}");
            });
        });
    }
}

Pub/Sub

次のサンプルコードは、Cloud Run にデプロイされたサービスで Pub/Sub イベントを読み取る方法を示しています。

Python

@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)

Java

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

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;

Go

// 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)
}

C#

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}";
    }
}

次のステップ

• イベント プロバイダと宛先
• イベントルート