Managing Messages in the Solace C API

The following sections discuss how you can manage messages when you use the Solace C API.

Getting Message Properties

A client can obtain message properties from a created message before it is published or from a message the API receives from the event broker.

For a complete list of message properties that can be retrieved, see the Solace C API reference.

Some message properties, such as expiration, TTL and dead message queue eligibility, are only valid when used with guaranteed messages. See the relevant API reference documentation for more information.

To get message properties, use all solClient_msg_get*(...) functions. For example:

  • solClient_msg_getApplicationMsgType (solClient_opaqueMsg_pt msg_p, const char **msgType_p)

  • solClient_msg_getDeliveryMode (solClient_opaqueMsg_pt msg_p, solClient_uint32_t *mode_p)

  • solClient_msg_getSenderId (solClient_opaqueMsg_pt msg_p, const char **buf_p)

For a complete list of functions, see the Solace C API reference.

Setting Message Properties

A client can set message properties on a created message before it is published or on a message the API receives from the event broker.

For a complete list of message properties that can be set, see the Solace C API reference.

Some message properties, such as expiration, TTL and dead message queue eligibility, are only valid when used with guaranteed messages. See the relevant API reference documentation for more information.

To set message properties, use all solClient_msg_set*() functions. For example:

  • solClient_msg_setApplicationMsgType (solClient_opaqueMsg_pt msg_p, const char *msgType)

  • solClient_msg_setDeliveryMode (solClient_opaqueMsg_pt msg_p, solClient_uint32_t mode)

  • solClient_msg_setSenderId (solClient_opaqueMsg_pt msg_p, const char *buf_p)

For a complete list of functions, see the Solace C API reference.

Duplicating Messages

When using the Solace C API, a client can duplicate a message buffer, which allocates a new message that references the same data as the original. You can duplicate a created message or a received message.

The data is reference counted to indicate that two message buffers have pointers to the data.

Duplicating Messages Function

To duplicate a message, use the function solClient_msg_dup(...).

Displaying Messages

You can use the message dump utility to display the contents of a message in a human‑readable form. This utility function is provided as a programming aid to facilitate the development and testing of messaging applications. You can display the contents of a created message or a received message.

Displaying Message Contents

To display the contents of a message, use the function solClient_msg_dump(...).

The format of the generated output is:

<field>:                              <value>

For example, a message part, such as a message header field like SenderId, is displayed as:

SenderId:                             mySenderID

If a message part is present in the message, but it contains NULL or an empty string, the field is displayed (in this case, SenderID:) but no value is present. If a message part is not present, then no output is generated for that part. For example, if there is no SenderId header field, then no SenderId field or value is generated.

Freeing Messages

A client should free a message when it is finished with it so that the memory allocated to the message is freed. Clients should free outbound messages after publishing them, and free inbound messages after they finish processing them.

When the function successfully returns, the memory that was referenced by the freed message is no longer valid.

Freeing Messages Function

In general, a client does not need to free any message received from the Solace C API in a callback. However, to take ownership of messages received in a callback, a client can return SOLCLIENT_CALLBACK_TAKEMSG to the API. In this latter case, a client must free the message when it no longer needs it.

To free a message, use the function solClient_msg_free(solClient_opaqueMsg_pt * msg_p).