Publish/subscribe local messages

The following example recipe allows the component to publish to all topics.

The following example Java application demonstrates how to use the publish/subscribe IPC service to publish messages to other components.

/* Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 * SPDX-License-Identifier: Apache-2.0 */

package com.example.ipc.pubsub;

import software.amazon.awssdk.aws.greengrass.GreengrassCoreIPCClient;
import software.amazon.awssdk.aws.greengrass.model.*;
import software.amazon.awssdk.eventstreamrpc.EventStreamRPCConnection;

import java.nio.charset.StandardCharsets;
import java.util.Optional;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

public class PubSubPublisher {

    public static void main(String[] args) {
        String message = "Hello from the pub/sub publisher (Java).";
        String topic = "test/topic/java";

        try (EventStreamRPCConnection eventStreamRPCConnection = IPCUtils.getEventStreamRpcConnection()) {
            GreengrassCoreIPCClient ipcClient = new GreengrassCoreIPCClient(eventStreamRPCConnection);

            while (true) {
                PublishToTopicRequest publishRequest = new PublishToTopicRequest();
                PublishMessage publishMessage = new PublishMessage();
                BinaryMessage binaryMessage = new BinaryMessage();
                binaryMessage.setMessage(message.getBytes(StandardCharsets.UTF_8));
                publishMessage.setBinaryMessage(binaryMessage);
                publishRequest.setPublishMessage(publishMessage);
                publishRequest.setTopic(topic);
                CompletableFuture<PublishToTopicResponse> futureResponse = ipcClient
                        .publishToTopic(publishRequest, Optional.empty()).getResponse();

                try {
                    futureResponse.get(10, TimeUnit.SECONDS);
                    System.out.println("Successfully published to topic: " + topic);
                } catch (TimeoutException e) {
                    System.err.println("Timeout occurred while publishing to topic: " + topic);
                } catch (ExecutionException e) {
                    if (e.getCause() instanceof UnauthorizedError) {
                        System.err.println("Unauthorized error while publishing to topic: " + topic);
                    } else {
                        System.err.println("Execution exception while publishing to topic: " + topic);
                    }
                    throw e;
                }
                Thread.sleep(5000);
            }
        } catch (InterruptedException e) {
            System.out.println("Publisher interrupted.");
        } catch (Exception e) {
            System.err.println("Exception occurred when using IPC.");
            e.printStackTrace();
            System.exit(1);
        }
    }
}

The following example recipe allows the component to subscribe to all topics.

The following example Java application demonstrates how to use the publish/subscribe IPC service to subscribe to messages to other components.

/* Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 * SPDX-License-Identifier: Apache-2.0 */

package com.example.ipc.pubsub;

import software.amazon.awssdk.aws.greengrass.GreengrassCoreIPCClient;
import software.amazon.awssdk.aws.greengrass.SubscribeToTopicResponseHandler;
import software.amazon.awssdk.aws.greengrass.model.SubscribeToTopicRequest;
import software.amazon.awssdk.aws.greengrass.model.SubscribeToTopicResponse;
import software.amazon.awssdk.aws.greengrass.model.SubscriptionResponseMessage;
import software.amazon.awssdk.aws.greengrass.model.UnauthorizedError;
import software.amazon.awssdk.eventstreamrpc.EventStreamRPCConnection;
import software.amazon.awssdk.eventstreamrpc.StreamResponseHandler;

import java.nio.charset.StandardCharsets;
import java.util.Optional;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

public class PubSubSubscriber {

    public static void main(String[] args) {
        String topic = "test/topic/java";

        try (EventStreamRPCConnection eventStreamRPCConnection = IPCUtils.getEventStreamRpcConnection()) {
            GreengrassCoreIPCClient ipcClient = new GreengrassCoreIPCClient(eventStreamRPCConnection);

            SubscribeToTopicRequest subscribeRequest = new SubscribeToTopicRequest();
            subscribeRequest.setTopic(topic);
            SubscribeToTopicResponseHandler operationResponseHandler = ipcClient
                    .subscribeToTopic(subscribeRequest, Optional.of(new SubscribeResponseHandler()));
            CompletableFuture<SubscribeToTopicResponse> futureResponse = operationResponseHandler.getResponse();

            try {
                futureResponse.get(10, TimeUnit.SECONDS);
                System.out.println("Successfully subscribed to topic: " + topic);
            } catch (TimeoutException e) {
                System.err.println("Timeout occurred while subscribing to topic: " + topic);
                throw e;
            } catch (ExecutionException e) {
                if (e.getCause() instanceof UnauthorizedError) {
                    System.err.println("Unauthorized error while subscribing to topic: " + topic);
                } else {
                    System.err.println("Execution exception while subscribing to topic: " + topic);
                }
                throw e;
            }

            // Keep the main thread alive, or the process will exit.
            try {
                while (true) {
                    Thread.sleep(10000);
                }
            } catch (InterruptedException e) {
                System.out.println("Subscribe interrupted.");
            }
        } catch (Exception e) {
            System.err.println("Exception occurred when using IPC.");
            e.printStackTrace();
            System.exit(1);
        }
    }

    private static class SubscribeResponseHandler implements StreamResponseHandler<SubscriptionResponseMessage> {

        @Override
        public void onStreamEvent(SubscriptionResponseMessage subscriptionResponseMessage) {
            try {
                String message = new String(subscriptionResponseMessage.getBinaryMessage()
                        .getMessage(), StandardCharsets.UTF_8);
                System.out.println("Received new message: " + message);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        @Override
        public boolean onStreamError(Throwable error) {
            System.err.println("Received a stream error.");
            error.printStackTrace();
            return false; // Return true to close stream, false to keep stream open.
        }

        @Override
        public void onStreamClosed() {
            System.out.println("Subscribe to topic stream closed.");
        }
    }
}

The following example recipe allows the component to publish to all topics.

The following example Python application demonstrates how to use the publish/subscribe IPC service to publish messages to other components.

import concurrent.futures
import sys
import time
import traceback

import awsiot.greengrasscoreipc
from awsiot.greengrasscoreipc.model import (
    PublishToTopicRequest,
    PublishMessage,
    BinaryMessage,
    UnauthorizedError
)

                    
topic = "test/topic/python"
message = "Hello from the pub/sub publisher (Python)."
TIMEOUT = 10

try:
    ipc_client = awsiot.greengrasscoreipc.connect()

    while True:
        request = PublishToTopicRequest()
        request.topic = topic
        publish_message = PublishMessage()
        publish_message.binary_message = BinaryMessage()
        publish_message.binary_message.message = bytes(message, "utf-8")
        request.publish_message = publish_message
        operation = ipc_client.new_publish_to_topic()
        operation.activate(request)
        future_response = operation.get_response()

        try:
            future_response.result(TIMEOUT)
            print('Successfully published to topic: ' + topic)
        except concurrent.futures.TimeoutError:
            print('Timeout occurred while publishing to topic: ' + topic, file=sys.stderr)
        except UnauthorizedError as e:
            print('Unauthorized error while publishing to topic: ' + topic, file=sys.stderr)
            raise e
        except Exception as e:
            print('Exception while publishing to topic: ' + topic, file=sys.stderr)
            raise e
        time.sleep(5)
except InterruptedError:
    print('Publisher interrupted.')
except Exception:
    print('Exception occurred when using IPC.', file=sys.stderr)
    traceback.print_exc()
    exit(1)

The following example recipe allows the component to subscribe to all topics.

The following example Python application demonstrates how to use the publish/subscribe IPC service to subscribe to messages to other components.

import concurrent.futures
import sys
import time
import traceback

import awsiot.greengrasscoreipc
import awsiot.greengrasscoreipc.client as client
from awsiot.greengrasscoreipc.model import (
    SubscribeToTopicRequest,
    SubscriptionResponseMessage,
    UnauthorizedError
)

topic = "test/topic/python"
TIMEOUT = 10

                    
class StreamHandler(client.SubscribeToTopicStreamHandler):
    def __init__(self):
        super().__init__()

    def on_stream_event(self, event: SubscriptionResponseMessage) -> None:
        try:
            message = str(event.binary_message.message, "utf-8")
            print("Received new message: " + message)
        except:
            traceback.print_exc()

    def on_stream_error(self, error: Exception) -> bool:
        print("Received a stream error.", file=sys.stderr)
        traceback.print_exc()
        return False  # Return True to close stream, False to keep stream open.

    def on_stream_closed(self) -> None:
        print('Subscribe to topic stream closed.')


try:
    ipc_client = awsiot.greengrasscoreipc.connect()

    request = SubscribeToTopicRequest()
    request.topic = topic
    handler = StreamHandler()
    operation = ipc_client.new_subscribe_to_topic(handler)
    operation.activate(request)
    future_response = operation.get_response()
    
    try:
        future_response.result(TIMEOUT)
        print('Successfully subscribed to topic: ' + topic)
    except concurrent.futures.TimeoutError as e:
        print('Timeout occurred while subscribing to topic: ' + topic, file=sys.stderr)
        raise e
    except UnauthorizedError as e:
        print('Unauthorized error while subscribing to topic: ' + topic, file=sys.stderr)
        raise e
    except Exception as e:
        print('Exception while subscribing to topic: ' + topic, file=sys.stderr)
        raise e

    # Keep the main thread alive, or the process will exit.
    try:
        while True:
            time.sleep(10)
    except InterruptedError:
        print('Subscribe interrupted.')
except Exception:
    print('Exception occurred when using IPC.', file=sys.stderr)
    traceback.print_exc()
    exit(1)

The following example recipe allows the component to publish to all topics.

The following example C++ application demonstrates how to use the publish/subscribe IPC service to publish messages to other components.

#include <iostream>

#include <aws/crt/Api.h>
#include <aws/greengrass/GreengrassCoreIpcClient.h>

using namespace Aws::Crt;
using namespace Aws::Greengrass;

class IpcClientLifecycleHandler : public ConnectionLifecycleHandler {
    void OnConnectCallback() override {
        std::cout << "OnConnectCallback" << std::endl;
    }

    void OnDisconnectCallback(RpcError error) override {
        std::cout << "OnDisconnectCallback: " << error.StatusToString() << std::endl;
        exit(-1);
    }

    bool OnErrorCallback(RpcError error) override {
        std::cout << "OnErrorCallback: " << error.StatusToString() << std::endl;
        return true;
    }
};

int main() {
    String message("Hello from the pub/sub publisher (C++).");
    String topic("test/topic/cpp");
    int timeout = 10;

    ApiHandle apiHandle(g_allocator);
    Io::EventLoopGroup eventLoopGroup(1);
    Io::DefaultHostResolver socketResolver(eventLoopGroup, 64, 30);
    Io::ClientBootstrap bootstrap(eventLoopGroup, socketResolver);
    IpcClientLifecycleHandler ipcLifecycleHandler;
    GreengrassCoreIpcClient ipcClient(bootstrap);
    auto connectionStatus = ipcClient.Connect(ipcLifecycleHandler).get();
    if (!connectionStatus) {
        std::cerr << "Failed to establish IPC connection: " << connectionStatus.StatusToString() << std::endl;
        exit(-1);
    }

    while (true) {
        PublishToTopicRequest request;
        Vector<uint8_t> messageData({message.begin(), message.end()});
        BinaryMessage binaryMessage;
        binaryMessage.SetMessage(messageData);
        PublishMessage publishMessage;
        publishMessage.SetBinaryMessage(binaryMessage);
        request.SetTopic(topic);
        request.SetPublishMessage(publishMessage);

        auto operation = ipcClient.NewPublishToTopic();
        auto activate = operation->Activate(request, nullptr);
        activate.wait();

        auto responseFuture = operation->GetResult();
        if (responseFuture.wait_for(std::chrono::seconds(timeout)) == std::future_status::timeout) {
            std::cerr << "Operation timed out while waiting for response from Greengrass Core." << std::endl;
            exit(-1);
        }

        auto response = responseFuture.get();
        if (response) {
            std::cout << "Successfully published to topic: " << topic << std::endl;
        } else {
            // An error occurred.
            std::cout << "Failed to publish to topic: " << topic << std::endl;
            auto errorType = response.GetResultType();
            if (errorType == OPERATION_ERROR) {
                auto *error = response.GetOperationError();
                std::cout << "Operation error: " << error->GetMessage().value() << std::endl;
            } else {
                std::cout << "RPC error: " << response.GetRpcError() << std::endl;
            }
            exit(-1);
        }

        std::this_thread::sleep_for(std::chrono::seconds(5));
    }

    return 0;
}

The following example recipe allows the component to subscribe to all topics.

The following example C++ application demonstrates how to use the publish/subscribe IPC service to subscribe to messages to other components.

#include <iostream>

#include <aws/crt/Api.h>
#include <aws/greengrass/GreengrassCoreIpcClient.h>

using namespace Aws::Crt;
using namespace Aws::Greengrass;

class SubscribeResponseHandler : public SubscribeToTopicStreamHandler {
    public:
        virtual ~SubscribeResponseHandler() {}

    private:
        void OnStreamEvent(SubscriptionResponseMessage *response) override {
            auto jsonMessage = response->GetJsonMessage();
            if (jsonMessage.has_value() && jsonMessage.value().GetMessage().has_value()) {
                auto messageString = jsonMessage.value().GetMessage().value().View().WriteReadable();
                std::cout << "Received new message: " << messageString << std::endl;
            } else {
                auto binaryMessage = response->GetBinaryMessage();
                if (binaryMessage.has_value() && binaryMessage.value().GetMessage().has_value()) {
                    auto messageBytes = binaryMessage.value().GetMessage().value();
                    std::string messageString(messageBytes.begin(), messageBytes.end());
                    std::cout << "Received new message: " << messageString << std::endl;
                }
            }
        }

        bool OnStreamError(OperationError *error) override {
            std::cout << "Received an operation error: ";
            if (error->GetMessage().has_value()) {
                std::cout << error->GetMessage().value();
            }
            std::cout << std::endl;
            return false; // Return true to close stream, false to keep stream open.
        }

        void OnStreamClosed() override {
            std::cout << "Subscribe to topic stream closed." << std::endl;
        }
};

class IpcClientLifecycleHandler : public ConnectionLifecycleHandler {
    void OnConnectCallback() override {
        std::cout << "OnConnectCallback" << std::endl;
    }

    void OnDisconnectCallback(RpcError error) override {
        std::cout << "OnDisconnectCallback: " << error.StatusToString() << std::endl;
        exit(-1);
    }

    bool OnErrorCallback(RpcError error) override {
        std::cout << "OnErrorCallback: " << error.StatusToString() << std::endl;
        return true;
    }
};

int main() {
    String topic("test/topic/cpp");
    int timeout = 10;

    ApiHandle apiHandle(g_allocator);
    Io::EventLoopGroup eventLoopGroup(1);
    Io::DefaultHostResolver socketResolver(eventLoopGroup, 64, 30);
    Io::ClientBootstrap bootstrap(eventLoopGroup, socketResolver);
    IpcClientLifecycleHandler ipcLifecycleHandler;
    GreengrassCoreIpcClient ipcClient(bootstrap);
    auto connectionStatus = ipcClient.Connect(ipcLifecycleHandler).get();
    if (!connectionStatus) {
        std::cerr << "Failed to establish IPC connection: " << connectionStatus.StatusToString() << std::endl;
        exit(-1);
    }

    SubscribeToTopicRequest request;
    request.SetTopic(topic);
    auto streamHandler = MakeShared<SubscribeResponseHandler>(DefaultAllocator());
    auto operation = ipcClient.NewSubscribeToTopic(streamHandler);
    auto activate = operation->Activate(request, nullptr);
    activate.wait();

    auto responseFuture = operation->GetResult();
    if (responseFuture.wait_for(std::chrono::seconds(timeout)) == std::future_status::timeout) {
        std::cerr << "Operation timed out while waiting for response from Greengrass Core." << std::endl;
        exit(-1);
    }

    auto response = responseFuture.get();
    if (response) {
        std::cout << "Successfully subscribed to topic: " << topic << std::endl;
    } else {
        // An error occurred.
        std::cout << "Failed to subscribe to topic: " << topic << std::endl;
        auto errorType = response.GetResultType();
        if (errorType == OPERATION_ERROR) {
            auto *error = response.GetOperationError();
            std::cout << "Operation error: " << error->GetMessage().value() << std::endl;
        } else {
            std::cout << "RPC error: " << response.GetRpcError() << std::endl;
        }
        exit(-1);
    }

    // Keep the main thread alive, or the process will exit.
    while (true) {
        std::this_thread::sleep_for(std::chrono::seconds(10));
    }

    operation->Close();
    return 0;
}