Publish

The term Publish in Pub/Sub refers to publishing data to topics.

Publishing messages

All pub/sub messages in Diffusion® are sent as updates to specific topics.

Topics have unique names, also referred to as topic paths. Topics work as a way of grouping and filtering the data that individual applications are sent, by allowing clients to select which topics to receive updates from.

Each topic can have an arbitrary number of subscribers; publishers can update topics even if there are no subscribers, and clients can pre-emptively subscribe to topic paths that don’t yet exist.

Topics can be added or removed dynamically.

Adding topics

You can create a topic via a client SDK or the REST API.

To add a topic:

Java and Android

session.feature(TopicControl.class).addTopic("my/topic/path", TopicType.JSON);

JavaScript

const result = await session.topics.add('my/topic/path', diffusion.topics.TopicType.JSON);

if (result.added) {
    console.log(`Topic "${result.topic}" has been successfully created`);
} else {
    console.log('Topic already exists.')
}

.NET

await session.TopicControl.AddTopicAsync("my/topic/path", TopicType.JSON);
WriteLine($"Topic has been added!");

static int on_topic_added(
        SESSION_T *session,
        TOPIC_ADD_RESULT_CODE result_code,
        void *context)
{
        return HANDLER_SUCCESS;
}


...


ADD_TOPIC_CALLBACK_T callback = {
        .on_topic_added_with_specification = on_topic_added
};
TOPIC_SPECIFICATION_T *specification = topic_specification_init(TOPIC_TYPE_JSON);

add_topic_from_specification(session, "my/topic/path", specification, callback);

Python

await session.topics.add_topic("my/topic/path", diffusion.datatypes.JSON)
print("Topic has been added!")

Apple

session.topicControl.addTopic(withPath: "my/topic/path", type: PTDiffusionTopicType.JSON) { (result, error) in
    print("Topic has been added!")
}

Adding topics is idempotent - that is, adding a topic to an existing path will succeed (as long as the topic properties are the same).

Publishing to a topic

Once a topic is created, you can publish an update to give it a value.

Topics must exist before you publish to them.

To publish to a topic:

Java and Android

session.feature(TopicUpdate.class).set("my/topic/path", JSON.class,
    Diffusion.dataTypes().json().fromJsonString("{\"hello\": \"world\"}"));

JavaScript

const jsonDataType = diffusion.datatypes.json();
const jsonValue = jsonDataType.from({
    hello : 'world'
});

await session.topicUpdate.set('my/topic/path', jsonDataType, jsonValue);
console.log('Topic has been updated');

.NET

var jsonValue = Diffusion.DataTypes.JSON.FromJSONString("{\"hello\": \"world\"}");

await session.TopicUpdate.SetAsync("my/topic/path", jsonValue);
WriteLine($"Topic has been updated!");

static int on_topic_update(void *context)
{
        return HANDLER_SUCCESS;
}


...


BUF_T *value_buf = buf_create();
write_diffusion_json_value("{\"hello\": \"world\"}", value_buf);

DIFFUSION_TOPIC_UPDATE_SET_PARAMS_T parameters = {
        .topic_path = "my/topic/path",
        .datatype = DATATYPE_JSON,
        .update = value_buf,
        .on_topic_update = on_topic_update
};

diffusion_topic_update_set(session, parameters);

Python

json_value = diffusion.datatypes.JSON({"hello": "world"})
await session.topics.set_topic("my/topic/path", json_value, diffusion.datatypes.JSON)
print("Topic has been updated")

Apple

let json_value = try! PTDiffusionJSON.init(jsonString: "{\"hello\": \"world\"}")
session.topicUpdate.setWithPath("my/topic/path", toJSONValue: json_value) { (error) in
    print("Topic has been updated!")
}