General API¶

A Backendless application can publish messages to Backendless for subsequent distribution to subscribers. A message must be published to a channel. Backendless supports unlimited number of channels per application. Channels can be used as a filtering mechanism - subscribers see the messages published only to the channel they subscribe to.

There is only one API for all types of message publishing. It supports the following scenarios:

Basic message publish
Publishing with headers - can be used for conditional delivery
Delayed publishing
Repeated publishing

Blocking API¶

Publishes a message to the default channel.

public MessageStatus Backendless.Messaging.Publish( object message )

Same as above, but publishes into the specified channel.

public MessageStatus Backendless.Messaging.Publish( object message,
                                                    string channelName )

Publishes a message to default channel. Message may have headers and/or subtopic defined in the publishOptions argument.

public MessageStatus Backendless.Messaging.Publish( object message, 
                                                    PublishOptions publishOptions )

Same as above, but publishes into the specified channel.

public MessageStatus Backendless.Messaging.Publish( object message, 
                                                    string channelName,
                                                    PublishOptions publishOptions )

Publishes a message to the default channel. Message may have headers and/or subtopic defined in the publishOptions argument. The deliveryOptions argument can be used to:

Publish the message at a later time (delayed publishing).
Specify that the message should be republished multiple times (repeated publishing).

public MessageStatus Backendless.Messaging.Publish( object message, 
                                                    PublishOptions publishOptions, 
                                                    DeliveryOptions deliveryOptions )

Same as above, but publishes into the specified channel.

public MessageStatus Backendless.Messaging.Publish( object message,
                                                    string channelName,
                                                    PublishOptions publishOptions,
                                                    DeliveryOptions deliveryOptions )

Non-Blocking API¶

The same set of methods is available for the asynchronous invocation. The difference in the method signatures is the AsyncCallback<MessageStatus> argument:

// Publishes message to "Default" channel.
public MessageStatus Backendless.Messaging.Publish( object message,
                                                    AsyncCallback<MessageStatus> publishResponder )

// Same as above, but published into the specified channel.
public MessageStatus Backendless.Messaging.Publish( object message,
                                                    string channelName,
                                                    AsyncCallback<MessageStatus> publishResponder )

// Publishes message to "Default" channel. Message may have headers and/or subtopic defined in the 
// publishOptions argument.
public MessageStatus Backendless.Messaging.Publish( object message, 
                                                    PublishOptions publishOptions,
                                                    AsyncCallback<MessageStatus> publishResponder )

// Same as above, but published into the specified channel.
public MessageStatus Backendless.Messaging.Publish( object message,
                                                    string channelName, 
                                                    PublishOptions publishOptions,
                                                    AsyncCallback<MessageStatus> publishResponder )

// Publishes message to "Default" channel. Message may have headers and/or subtopic 
// defined in the publishOptions argument. The deliveryOptions argument can be used to: 
// (1) designate the message as "push notification only" or both a push notification 
// and a pub/sub message; (2) publish the message at a later time (delayed publishing); 
// (3) specify that the message should be republished multiple times (repeated publishing).
public MessageStatus Backendless.Messaging.Publish( object message, 
                                                    PublishOptions publishOptions, 
                                                    DeliveryOptions deliveryOptions,
                                                    AsyncCallback<MessageStatus> publishResponder )

// Same as above, but published into the specified channel.
public MessageStatus Backendless.Messaging.Publish( object message,
                                                    string channelName,
                                                    PublishOptions publishOptions,
                                                    DeliveryOptions deliveryOptions,
                                                    AsyncCallback<MessageStatus> publishResponder )

where:

Argument	Description
`channelName`	Name of the channel to publish the message to. If the channel does not exist, Backendless automatically creates it.
`message`	Object to publish. The object can be of any data type - a primitive value, String, Date, a user-defined complex type, a collection or an array of these types.
`publishOptions`	An instance of `PublishOptions`. When provided may contain publisher ID (an arbitrary, application-specific string value identifying the publisher), subtopic value and/or a collection of headers. See the Delayed Publish and Repeated Publish sections for examples.
`deliveryOptions`	An instance of `DeliveryOptions`. When provides may specify options for message delivery such as: deliver as a push notification, delayed delivery or repeated delivery. See the Delayed Publish and Repeated Publish sections for examples.

Return value¶

Argument	Description
`MessageStatus`	A data structure which contains ID of the published message and the status of the publish operation. Available properties in the returned object include:

Status - status of the published message as defined in the BackendlessAPI.Messaging.PublishStatusEnum enumeration.

MessageId - an ID assigned to the message by the backend (the ID is needed to cancel the message).

ErrorMessage - When the message Status is returned as PublishStatusEnum.FAILED, the corresponding error message is available through the ErrorMessage property.

Errors¶

The following errors may occur during the message publishing API call. See the Error Handling section for details on how to retrieve the error code when the server returns an error:

Error Code	Description
5003	Invalid `repeatExpiresAt` date in delivery options.
5007	User does not have the permission to publish messages
5030	Invalid `publishAt` date in the delivery options.

Codeless Reference¶

pubsub_api_basic_publish_1

where:

Argument	Description
`channel name`	Name of the channel where a message must be published to.
`subtopic name`	The subtopic of the message allows developers to designate and filter messages by subtopic name. For instance, if a messaging application has a group and a few subgroups, all messages sent to the main group can be marked with this subtopic name which can be used to route messages to the appropriate subgroups depending on the context.
`message`	The contents of the message that must be published to a channel.
`headers`	Message headers is a collection of `name/value` pairs. A subscriber can set a filter expressed as an SQL "where clause" query (called selector) which Backendless uses to determine whether a message should be delivered to the subscriber. When the query matches the published data in message headers, message is delivered to the corresponding subscriber. For more information see the Conditional Delivery section of this guide.
`publish at`	Must be a Unix Timestamp, which is the number of milliseconds since the Epoch (January 1st, 1970 at UTC). Note that if you want to specify the number of seconds instead of milliseconds, you must multiply the number by `1000` or add three trailing zeroes to your number (e.g. `(1681324179 * 1000)` or `1681324179000`.
`return result`	When this box is checked, the operation returns an object containing the status of the message delivery and a unique message identifier.

Returns an object containing the status of the message delivery and a unique message identifier:

// Sample object  

{  
    "errorMessage":null,  
    "messageId":"message:FCBD8BF1-A45D-4564-B449-3C91D4896987",  
    "status":"published"  
}

For examples refer to the following topics: