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发布/订阅本地消息
发布/订阅 (pubsub) 消息使您能够向主题发送和接收消息。组件可以将消息发布到主题以向其他组件发送消息。然后,订阅该主题的组件可以对它们接收的消息执行操作。
您不能使用发布/订购IPC 服务发布或订阅Amazon IoT CoreMQT。有关如何通过Amazon IoT CoreMQTT,请参阅发布/订阅Amazon IoT CoreMQTT 消息.
Authorization
要在自定义组件中使用本地发布/订阅消息,必须定义允许组件向主题发送和接收消息的授权策略。有关定义授权策略的信息,请参阅授权组件执行 IPC 操作.
发布/订阅消息的授权策略具有以下属性。
IPC 服务标识符: aws.greengrass.ipc.pubsub
操作 | 说明 | 资源 |
---|---|---|
|
允许组件向指定的主题发布消息。 |
主题字符串,如 |
|
允许组件订阅您指定主题的消息。 |
主题字符串,如 |
|
允许组件发布和订阅您指定主题的消息。 |
主题字符串,如 |
例 授权策略示例
以下示例授权策略允许组件发布和订阅所有主题。
{ "accessControl": { "aws.greengrass.ipc.pubsub": { "
com.example.MyLocalPubSubComponent
:pubsub:1": { "policyDescription": "Allows access to publish/subscribe to all topics.", "operations": [ "aws.greengrass#PublishToTopic", "aws.greengrass#SubscribeToTopic" ], "resources": [ "*" ] } } } }
PublishToTopic
向一个主题发布消息。
Request
该操作的请求包含以下参数:
topic
-
要向其发布消息的主题。
publishMessage
-
要发布的消息。这个对象,
PublishMessage
包含以下信息。您必须指定jsonMessage
和binaryMessage
.jsonMessage
-
(可选)JSON 消息。这个对象,
JsonMessage
包含以下信息:message
-
作为对象的 JSON 消息。
binaryMessage
-
(可选)二进制消息。这个对象,
BinaryMessage
包含以下信息:message
-
二进制消息作为 Blob。
此操作在其响应中不提供任何信息。
Examples
以下示例演示如何在自定义组件代码中调用此操作。
SubscribeToTopic
订阅主题的消息。
此操作是订阅事件消息流的订阅操作。要使用此操作,请使用处理事件消息、错误和流关闭的函数定义流响应处理程序。有关更多信息,请参阅 订阅 IPC 事件流。
事件消息类型: SubscriptionResponseMessage
Request
该操作的请求包含以下参数:
topic
-
订阅的主题。
注意 本主题不支持 MQTT 主题通配符 (
#
和+
)。
Response
此操作的响应包含以下信息:
topicName
-
向其发布消息的主题。
messages
-
消息流。这个对象,
SubscriptionResponseMessage
包含以下信息。每条消息都包含jsonMessage
或者binaryMessage
.jsonMessage
-
(可选)JSON 消息。这个对象,
JsonMessage
包含以下信息:message
-
作为对象的 JSON 消息。
binaryMessage
-
(可选)二进制消息。这个对象,
BinaryMessage
包含以下信息:message
-
二进制消息作为 Blob。
Examples
以下示例演示如何在自定义组件代码中调用此操作。
Examples
使用以下示例了解如何在组件中使用发布/订阅 IPC 服务。
以下示例配方允许组件发布到所有主题。
下面的 Java 应用程序示例演示了如何使用发布/订阅 IPC 服务将消息发布到其他组件。
/* 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); } } }
以下示例配方允许组件订阅所有主题。
下面的 Java 应用程序示例演示了如何使用发布/订阅 IPC 服务来订阅其他组件的消息。
/* 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."); } } }
以下示例配方允许组件发布到所有主题。
下面的 Python 应用程序示例演示了如何使用发布/订阅 IPC 服务将消息发布到其他组件。
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) futureResponse = operation.get_response() try: futureResponse.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)
以下示例配方允许组件订阅所有主题。
下面的 Python 应用程序示例演示了如何使用发布/订阅 IPC 服务来订阅其他组件的消息。
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) future = operation.activate(request) try: future.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)
以下示例配方允许组件发布到所有主题。
以下示例 C++ 应用程序演示了如何使用发布/订阅 IPC 服务将消息发布到其他组件。
#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); PublishToTopicOperation 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; }
以下示例配方允许组件订阅所有主题。
以下示例 C++ 应用程序演示了如何使用发布/订阅 IPC 服务来订阅其他组件的消息。
#include <iostream> #include <aws/crt/Api.h> #include <aws/greengrass/GreengrassCoreIpcClient.h> using namespace Aws::Crt; using namespace Aws::Greengrass; class SubscribeResponseHandler : public SubscribeToTopicStreamHandler { 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); SubscribeResponseHandler streamHandler; SubscribeToTopicOperation 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; }