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C++ 上的主题消息传递

基于其发布/订阅的模式，FCM 主题消息传递功能可让您将消息发送至已经选择加入特定主题的多台设备。您根据需要撰写主题消息，FCM 负责确定发布路径并将消息可靠地传送至正确的设备。

例如，某个本地潮汐预报应用的用户可选择加入“潮汐警报”主题，并接收关于特定区域最佳海水捕鱼条件的通知。体育应用的用户可以订阅他们心仪球队的实时比分自动更新。

关于主题，请注意以下事项：

  • 主题消息传递最适合传递天气或其他可通过公开途径获得的信息。
  • 主题消息的优化重心是吞吐量而非延迟。要将消息快速安全地传送到单台设备或小规模设备组，应将消息定位至注册令牌，而非主题。
  • 如果您需要向每个用户的多台设备发送消息，请考虑为这些用例使用设备组消息传递。
  • 主题消息传递不限制每个主题的订阅数。但是，FCM 在这些方面有强制性限制：
    • 一个应用实例不可订阅超过 2000 个主题。
    • 如果您正在使用批量导入来订阅应用实例，则每次请求仅限订阅 1000 个应用实例。
    • 每个项目新订阅频率的速率受限。如果您在短时间内发送过多订阅请求，FCM 服务器将给出 429 RESOURCE_EXHAUSTED（“已超出配额”）响应。使用指数退避重试。

为客户端应用订阅主题

要订阅主题，请从您的应用调用 ::firebase::messaging::Subscribe。这会向 FCM 后端发出一个异步请求，并为该客户端订阅指定主题。

::firebase::messaging::Subscribe("example");

如果一开始订阅请求失败，FCM 会重试，直至能够成功订阅该主题。每次应用启动时，FCM 会确保所有已请求的主题都已订阅。

若要退订，可调用 ::firebase::messaging::Unsubscribe，FCM 即会在后台中退订相关主题。

在服务器上管理主题订阅

利用 Firebase Admin SDK 和 Google Instance ID API，您可以从服务器端执行基本的主题管理任务。如果有客户端应用实例的注册令牌，您还可以使用服务器逻辑批量订阅和退订这些实例。

您可以为客户端应用实例订阅任何现有主题，也可创建新主题。当您使用 API 为客户端应用订阅新主题（您的 Firebase 项目中尚不存在的名称）时，系统会在 FCM 中使用这个名称创建一个新主题，随后任何客户端都可订阅该主题。

使用 Firebase Admin SDK 订阅和退订主题

您可以将注册令牌列表传递给 Firebase Admin SDK 订阅方法，以便为相应的设备订阅主题：

Node.js

// These registration tokens come from the client FCM SDKs.
var registrationTokens = [
  'YOUR_REGISTRATION_TOKEN_1',
  // ...
  'YOUR_REGISTRATION_TOKEN_n'
];

// Subscribe the devices corresponding to the registration tokens to the
// topic.
admin.messaging().subscribeToTopic(registrationTokens, topic)
  .then(function(response) {
    // See the MessagingTopicManagementResponse reference documentation
    // for the contents of response.
    console.log('Successfully subscribed to topic:', response);
  })
  .catch(function(error) {
    console.log('Error subscribing to topic:', error);
  });

Java

// These registration tokens come from the client FCM SDKs.
List<String> registrationTokens = Arrays.asList(
    "YOUR_REGISTRATION_TOKEN_1",
    // ...
    "YOUR_REGISTRATION_TOKEN_n"
);

// Subscribe the devices corresponding to the registration tokens to the
// topic.
TopicManagementResponse response = FirebaseMessaging.getInstance().subscribeToTopic(
    registrationTokens, topic);
// See the TopicManagementResponse reference documentation
// for the contents of response.
System.out.println(response.getSuccessCount() + " tokens were subscribed successfully");

Python

# These registration tokens come from the client FCM SDKs.
registration_tokens = [
    'YOUR_REGISTRATION_TOKEN_1',
    # ...
    'YOUR_REGISTRATION_TOKEN_n',
]

# Subscribe the devices corresponding to the registration tokens to the
# topic.
response = messaging.subscribe_to_topic(registration_tokens, topic)
# See the TopicManagementResponse reference documentation
# for the contents of response.
print(response.success_count, 'tokens were subscribed successfully')

Go

// These registration tokens come from the client FCM SDKs.
registrationTokens := []string{
	"YOUR_REGISTRATION_TOKEN_1",
	// ...
	"YOUR_REGISTRATION_TOKEN_n",
}

// Subscribe the devices corresponding to the registration tokens to the
// topic.
response, err := client.SubscribeToTopic(ctx, registrationTokens, topic)
if err != nil {
	log.Fatalln(err)
}
// See the TopicManagementResponse reference documentation
// for the contents of response.
fmt.Println(response.SuccessCount, "tokens were subscribed successfully")

利用 Admin FCM API，您还可以通过将注册令牌传递给相应的方法来为设备退订主题：

Node.js

// These registration tokens come from the client FCM SDKs.
var registrationTokens = [
  'YOUR_REGISTRATION_TOKEN_1',
  // ...
  'YOUR_REGISTRATION_TOKEN_n'
];

// Unsubscribe the devices corresponding to the registration tokens from
// the topic.
admin.messaging().unsubscribeFromTopic(registrationTokens, topic)
  .then(function(response) {
    // See the MessagingTopicManagementResponse reference documentation
    // for the contents of response.
    console.log('Successfully unsubscribed from topic:', response);
  })
  .catch(function(error) {
    console.log('Error unsubscribing from topic:', error);
  });

Java

// These registration tokens come from the client FCM SDKs.
List<String> registrationTokens = Arrays.asList(
    "YOUR_REGISTRATION_TOKEN_1",
    // ...
    "YOUR_REGISTRATION_TOKEN_n"
);

// Unsubscribe the devices corresponding to the registration tokens from
// the topic.
TopicManagementResponse response = FirebaseMessaging.getInstance().unsubscribeFromTopic(
    registrationTokens, topic);
// See the TopicManagementResponse reference documentation
// for the contents of response.
System.out.println(response.getSuccessCount() + " tokens were unsubscribed successfully");

Python

# These registration tokens come from the client FCM SDKs.
registration_tokens = [
    'YOUR_REGISTRATION_TOKEN_1',
    # ...
    'YOUR_REGISTRATION_TOKEN_n',
]

# Unubscribe the devices corresponding to the registration tokens from the
# topic.
response = messaging.unsubscribe_from_topic(registration_tokens, topic)
# See the TopicManagementResponse reference documentation
# for the contents of response.
print(response.success_count, 'tokens were unsubscribed successfully')

Go

// These registration tokens come from the client FCM SDKs.
registrationTokens := []string{
	"YOUR_REGISTRATION_TOKEN_1",
	// ...
	"YOUR_REGISTRATION_TOKEN_n",
}

// Unsubscribe the devices corresponding to the registration tokens from
// the topic.
response, err := client.UnsubscribeFromTopic(ctx, registrationTokens, topic)
if err != nil {
	log.Fatalln(err)
}
// See the TopicManagementResponse reference documentation
// for the contents of response.
fmt.Println(response.SuccessCount, "tokens were unsubscribed successfully")

subscribeToTopic() 和 unsubscribeFromTopic() 方法会返回一个包含 FCM 响应的对象。无论请求中指定的注册令牌的数量为何，返回类型的格式都是相同的。

如果出现错误（身份验证失败、令牌或主题无效等），这些方法会返回错误。如需错误代码的完整列表（包括说明和解决步骤），请参阅 Admin FCM API 错误。

使用 Instance ID API 订阅和退订主题

Google Instance ID API 可用于进行以下主题管理任务：

接收和处理主题消息

FCM 传送主题消息的方式与处理其他下游消息的方式相同。

通过重写 ::firebase::messaging::Listener::OnMessage 方法，您可以根据收到的消息执行操作并获取消息数据：

void OnMessage(const ::firebase::messaging::Message& message) {
  LogMessage(TAG, "From: %s", message.from.c_str());
  LogMessage(TAG, "Message ID: %s", message.message_id.c_str());
}

构建发送请求

您创建一个主题后，可以通过两种方法向主题发送消息：一是在客户端为客户端应用实例订阅主题，二是通过服务器 API。在后端的发送逻辑中，按如下所示指定所需的主题名称：

Node.js

// The topic name can be optionally prefixed with "/topics/".
var topic = 'highScores';

var message = {
  data: {
    score: '850',
    time: '2:45'
  },
  topic: topic
};

// Send a message to devices subscribed to the provided topic.
admin.messaging().send(message)
  .then((response) => {
    // Response is a message ID string.
    console.log('Successfully sent message:', response);
  })
  .catch((error) => {
    console.log('Error sending message:', error);
  });

Java

// The topic name can be optionally prefixed with "/topics/".
String topic = "highScores";

// See documentation on defining a message payload.
Message message = Message.builder()
    .putData("score", "850")
    .putData("time", "2:45")
    .setTopic(topic)
    .build();

// Send a message to the devices subscribed to the provided topic.
String response = FirebaseMessaging.getInstance().send(message);
// Response is a message ID string.
System.out.println("Successfully sent message: " + response);
FirebaseMessagingSnippets.java

Python

# The topic name can be optionally prefixed with "/topics/".
topic = 'highScores'

# See documentation on defining a message payload.
message = messaging.Message(
    data={
        'score': '850',
        'time': '2:45',
    },
    topic=topic,
)

# Send a message to the devices subscribed to the provided topic.
response = messaging.send(message)
# Response is a message ID string.
print('Successfully sent message:', response)
cloud_messaging.py

Go

// The topic name can be optionally prefixed with "/topics/".
topic := "highScores"

// See documentation on defining a message payload.
message := &messaging.Message{
	Data: map[string]string{
		"score": "850",
		"time":  "2:45",
	},
	Topic: topic,
}

// Send a message to the devices subscribed to the provided topic.
response, err := client.Send(ctx, message)
if err != nil {
	log.Fatalln(err)
}
// Response is a message ID string.
fmt.Println("Successfully sent message:", response)
messaging.go

C#

// The topic name can be optionally prefixed with "/topics/".
var topic = "highScores";

// See documentation on defining a message payload.
var message = new Message()
{
    Data = new Dictionary<string, string>()
    {
        { "score", "850" },
        { "time", "2:45" },
    },
    Topic = topic,
};

// Send a message to the devices subscribed to the provided topic.
string response = await FirebaseMessaging.DefaultInstance.SendAsync(message);
// Response is a message ID string.
Console.WriteLine("Successfully sent message: " + response);

REST

POST https://fcm.googleapis.com/v1/projects/myproject-b5ae1/messages:send HTTP/1.1

Content-Type: application/json
Authorization: Bearer ya29.ElqKBGN2Ri_Uz...HnS_uNreA
{
  "message":{
    "topic" : "foo-bar",
    "notification" : {
      "body" : "This is a Firebase Cloud Messaging Topic Message!",
      "title" : "FCM Message"
      }
   }
}

cURL 命令：

curl -X POST -H "Authorization: Bearer ya29.ElqKBGN2Ri_Uz...HnS_uNreA" -H "Content-Type: application/json" -d '{
  "message": {
    "topic" : "foo-bar",
    "notification": {
      "body": "This is a Firebase Cloud Messaging Topic Message!",
      "title": "FCM Message"
    }
  }
}' https://fcm.googleapis.com/v1/projects/myproject-b5ae1/messages:send HTTP/1.1

要向主题组合发送消息，请指定一个条件，即指定目标主题的布尔表达式。例如，以下条件会将消息发送至已订阅 TopicA 以及 TopicB 或 TopicC 的设备：

"'TopicA' in topics && ('TopicB' in topics || 'TopicC' in topics)"

FCM 首先对括号中的所有条件求值，然后从左至右对表达式求值。在上述表达式中，只订阅某个单一主题的用户将不会接收到消息。同样地，未订阅 TopicA 的用户也不会接收到消息。下列组合将会接收到消息：

  • TopicA 和 TopicB
  • TopicA 和 TopicC

您最多可以在条件表达式中包括五个主题。

向条件发送消息：

Node.js

// Define a condition which will send to devices which are subscribed
// to either the Google stock or the tech industry topics.
var condition = "'stock-GOOG' in topics || 'industry-tech' in topics";

// See documentation on defining a message payload.
var message = {
  notification: {
    title: '$GOOG up 1.43% on the day',
    body: '$GOOG gained 11.80 points to close at 835.67, up 1.43% on the day.'
  },
  condition: condition
};

// Send a message to devices subscribed to the combination of topics
// specified by the provided condition.
admin.messaging().send(message)
  .then((response) => {
    // Response is a message ID string.
    console.log('Successfully sent message:', response);
  })
  .catch((error) => {
    console.log('Error sending message:', error);
  });

Java

// Define a condition which will send to devices which are subscribed
// to either the Google stock or the tech industry topics.
String condition = "'stock-GOOG' in topics || 'industry-tech' in topics";

// See documentation on defining a message payload.
Message message = Message.builder()
    .setNotification(new Notification(
        "$GOOG up 1.43% on the day",
        "$GOOG gained 11.80 points to close at 835.67, up 1.43% on the day."))
    .setCondition(condition)
    .build();

// Send a message to devices subscribed to the combination of topics
// specified by the provided condition.
String response = FirebaseMessaging.getInstance().send(message);
// Response is a message ID string.
System.out.println("Successfully sent message: " + response);
FirebaseMessagingSnippets.java

Python

# Define a condition which will send to devices which are subscribed
# to either the Google stock or the tech industry topics.
condition = "'stock-GOOG' in topics || 'industry-tech' in topics"

# See documentation on defining a message payload.
message = messaging.Message(
    notification=messaging.Notification(
        title='$GOOG up 1.43% on the day',
        body='$GOOG gained 11.80 points to close at 835.67, up 1.43% on the day.',
    ),
    condition=condition,
)

# Send a message to devices subscribed to the combination of topics
# specified by the provided condition.
response = messaging.send(message)
# Response is a message ID string.
print('Successfully sent message:', response)
cloud_messaging.py

Go

// Define a condition which will send to devices which are subscribed
// to either the Google stock or the tech industry topics.
condition := "'stock-GOOG' in topics || 'industry-tech' in topics"

// See documentation on defining a message payload.
message := &messaging.Message{
	Data: map[string]string{
		"score": "850",
		"time":  "2:45",
	},
	Condition: condition,
}

// Send a message to devices subscribed to the combination of topics
// specified by the provided condition.
response, err := client.Send(ctx, message)
if err != nil {
	log.Fatalln(err)
}
// Response is a message ID string.
fmt.Println("Successfully sent message:", response)
messaging.go

C#

// Define a condition which will send to devices which are subscribed
// to either the Google stock or the tech industry topics.
var condition = "'stock-GOOG' in topics || 'industry-tech' in topics";

// See documentation on defining a message payload.
var message = new Message()
{
    Notification = new Notification()
    {
        Title = "$GOOG up 1.43% on the day",
        Body = "$GOOG gained 11.80 points to close at 835.67, up 1.43% on the day.",
    },
    Condition = condition,
};

// Send a message to devices subscribed to the combination of topics
// specified by the provided condition.
string response = await FirebaseMessaging.DefaultInstance.SendAsync(message);
// Response is a message ID string.
Console.WriteLine("Successfully sent message: " + response);

REST

POST https://fcm.googleapis.com/v1/projects/myproject-b5ae1/messages:send HTTP/1.1

Content-Type: application/json
Authorization: Bearer ya29.ElqKBGN2Ri_Uz...HnS_uNreA
{
   "message":{
    "condition": "'dogs' in topics || 'cats' in topics",
    "notification" : {
      "body" : "This is a Firebase Cloud Messaging Topic Message!",
      "title" : "FCM Message",
    }
  }
}

cURL 命令：

curl -X POST -H "Authorization: Bearer ya29.ElqKBGN2Ri_Uz...HnS_uNreA" -H "Content-Type: application/json" -d '{
  "notification": {
    "title": "FCM Message",
    "body": "This is a Firebase Cloud Messaging Topic Message!",
  },
  "condition": "'dogs' in topics || 'cats' in topics"
}' https://fcm.googleapis.com/v1/projects/myproject-b5ae1/messages:send HTTP/1.1

后续步骤