Configuring Message Headers

In general, the source message header is propagated through the Micro-Integration to the target message header. When you configure the Micro-Integration, you can optionally configure mappings for the header information between the external system and the PubSub+event broker service.

If you want to map the source message header to a target message header, you do so using the Target Header Mappings step when you create a Micro-Integration or modify them after.

To specify the mappings, you must use the Spring Expression Language (SpEL). For examples to use SpEL expressions, see SpEL Examples for Target Header Mappings.

It's important to recognize that there are a set of common source and target message headers that you can use that are available for all Micro-Integration Types as well as specific message headers depending on the Micro-Integration Type you are using. For information about the message headers that are available, see:

• Common Reserved Message Headers
• Common and Vendor-Specific Dynamic Producer Destinations
• Amazon SNS Message Headers
• Amazon SQS Message Headers
• Azure Service Bus Message Headers
• Google Cloud Pub/Sub Message Headers
• IBM MQ Message Headers
• Solace Message Headers

SpEL Examples for Target Header Mappings

The following are examples that show how to use a SpEL expression in the fields for the Target Header Mappings step when you create a mapping between the source message header and the target message header. To fully utilize the mappings, you should have a good understanding of how to use SpEL expressions. For example, to access the header attributes or payload, you use the headers properties.

For more information about using Spring Expression Language (SpEL) expressions, see Spring Expression Language (SpEL). The following are how you would perform some header mapping operations:

• On the Target Header Mappings step, enter the following values to the following fields to map the Solace Correlation ID to the JMS correlation ID:
• Target Header Name:jms_correlationId
• Header Expression: headers.solace_correlationId

• On the Target Header Mappings step, enter the following values to map the to the following fields header ID with custom prefix called myprefix- to a custom header name called custom-message-id:

  • Target Header Name: custom-message-id
  • Header Expression: 'myprefix-' + headers.id

Common Reserved Message Headers

The following are reserved header spaces that are common to configure all Micro-Integrations:

• solace_

• scst_

• Any headers defined by the core Spring messaging framework. For more information, see Spring Integration: Message Headers.

Any headers with these prefixes (that are not defined by the Micro-Integration or any technology used by the Micro-Integration) may not be backwards compatible in future releases of this Micro-Integration.

Common and Vendor-Specific Dynamic Producer Destinations

To route messages to dynamic destinations at runtime, use the Configuring Message Headers described above to set the following headers. The following table contains both common and vendor-specific dynamic producer destinations.

Header Name	Type	Values	Applies To	Description
scst_targetDestination	string	Any valid destination name	Solace (PubSub+) JMS IBM MQ Amazon SQS Google Cloud Pub/Sub MQTT	Specifies the name of the dynamic destination to publish to. Setting this header overrides the configured destination.
solace_scst_targetDestinationType	string	(queue|topic)	Solace Amazon SQS Google Cloud Pub/Sub	Specifies the destination type of the dynamic destination. When unspecified, the configured or default destination type is used.
solace_connector_scst_targetDestinationType	string	(queue|topic)	JMS IBM MQ	Specifies the destination type of the dynamic destination. When unspecified, the configured or default destination type is used.
gcp_pubsub_topic	string	Any valid destination name	Google Cloud Pub/Sub	Specifies the name of the dynamic destination to publish to. Setting this header overrides the configured destination.

Amazon SNS Message Headers

To configure the common message headers for this Micro-Integration, see the following sections: 

• Solace Message Headers

• Common Reserved Message Headers

Amazon SQS Message Headers

To configure the common message headers for this Micro-Integration, see the following sections: 

• Solace Message Headers

• Common Reserved Message Headers

Azure Service Bus Message Headers

You can configure Azure Service Bus vendor-specific message headers using the following lists: 

• Dynamic Headers for Azure Service Bus

• Configuring Message Headers

Dynamic Headers for Azure Service Bus

Azure Service Bus supports Azure Service Bus partitioning and message sessions of the Azure Service Bus by setting the following headers:

Header Name	Type	Access	Description
azure_session_id	string	Read	Sets a session ID of a message in the message header.
azure_partition_key	string	Read	Sets a partition key in the message header.

The session ID has higher priority than the partition key. When both azure_partition_key and azure_session_id headers are set, the value of the session ID overwrites the value of the partition key.

To configure the common message headers for this Micro-Integration, see the following sections: 

• Solace Message Headers

• Common Reserved Message Headers

Google Cloud Pub/Sub Message Headers

You can configure Google Cloud Pub/Sub vendor-specific message headers using the following lists:

• Message Header Mappings for Google Cloud Pub/Sub

• Reserved Message Headers for Google Cloud Pub/Sub

Message Header Mappings for Google Cloud Pub/Sub

The following Google Cloud Pub/Sub  PubsubMessage attributes are mapped to the following message properties: 

Header Name	Type	Access	Description
gcp_pubsub_message_id	string	Read	The ID of the message, assigned by the Google Cloud Pub/Sub service when the message is published. See Google Cloud Pub/Sub PubsubMessage.getMessageId().
gcp_pubsub_publish_time	long(seconds)	Read	The time at which the message was published, populated by the Google Cloud Pub/Sub service when it receives the Publish call. See Google Cloud Pub/Sub PubsubMessage.getPublishTime().
gcp_pubsub_ordering_key	string	Read	The Google Cloud Pub/Sub message’s ordering key. See Google Cloud Pub/Sub PubsubMessage.getOrderingKey().

The following Solace message headers marked with Read access are automatically forwarded to Google Cloud Pub/Sub messages, while headers with Write access can be set using transformations.

Header Name	Type	Access	Description
solace_applicationMessageId	string	Read/Write	The application provided message ID.
solace_applicationMessageType	string	Read/Write	The application provided message type. This value is used by applications only.
solace_correlationId	string	Read/Write	The correlation ID for the message.
solace_dmqEligible	boolean	Write	Set the Solace message’s dmqEligible header.
solace_expiration	long	Write	Set the time at which the Solace message is set to expire.
solace_priority	int	Write	Set the Solace message’s priority.
solace_senderId	string	Read	The Sender ID for the Solace message.
solace_senderTimestamp	long	Read	The time at which the Solace message was published.
solace_sequenceNumber	string	Read	The application-defined sequence number set on the Solace message.

Reserved Message Headers for Google Cloud Pub/Sub

The following is a reserved header space that can be used with Google Cloud Pub/Sub:

• gcp_pubsub|goog

To configure the common message headers for this Micro-Integration, see the following sections: 

• Solace Message Headers

• Common Reserved Message Headers

IBM MQ Message Headers

You can configure IBM MQ vendor-specific message headers using the following lists:

• JMS Message Headers

• JMS Binder Headers

• Reserved Message Headers for IBM MQ

JMS Message Headers

You can use the following message headers to get and set JMS message properties for IBM MQ.

Header Name	Type	Access	Description
jms_correlationId	String	Read/Write	The correlation ID for the message.
jms_deliveryMode	int	Read	The delivery mode value specified for this message.
jms_destination	jakarta.jms.Destination	Read	The destination to which the message is being sent.
jms_expiration	long	Read	The time at which the JMS message is set to expire.
jms_messageId	String	Read	A value that uniquely identifies each message sent by a provider.
jms_priority	int	Read/Write	Specifies the message’s priority set on the send. When header is absent, JMS message is sent with default priority of 4.
jms_redelivered	boolean	Read	An indication of whether this message is being redelivered.
jms_replyTo	jakarta.jms.Destination	Read/Write	The Destination object to which a reply to this message should be sent.
jms_timestamp	long	Read	The time a message was handed off to a provider to be sent.
jms_timeToLive	long	Write	Specifies the message’s time to live set on the send. When header is absent, JMS message is sent with default timeToLive of 0 (zero means that a message never expires).
jms_type	String	Read/Write	The message type identifier supplied by the client when the message was sent.

JMS Binder Headers

The following are JMS Binder Headers.

Header Name	Type	Access	Description
jms_scst_nullPayload	boolean	Read	Specifies when the JMS message payload is null. Two cases exist: A JMS TextMessage with no message payload is received: The payload is converted to an empty String, and the jms_scst_nullPayload header is added. A JMS Message with no message payload is received: The payload is converted to an empty byte array, and the jms_scst_nullPayload header is added.

Reserved Message Headers for IBM MQ

The following is a reserved header space that can be used with IBM MQ:

• jms_|JMS_|JMSX

To configure the common message headers for this Micro-Integration, see the following sections: 

• Solace Message Headers

• Common Reserved Message Headers

Solace Message Headers

Solace headers exposed to the Micro-Integration are documented in the Spring Cloud Stream Binder for Solace PubSub+ documentation.