Message Composition

All of the different kinds of messages are classified by message types. For example, numeric variable data is typically sent in a NUMERIC_DATA type of message, and an operator warning is typically sent in a WARNING type of message. A SmartSockets application can use both the standard message types provided with SmartSockets, as well as user-defined message types.

A message (C type T_IPC_MSG) is composed of several parts or properties. The most important property is the message data. The other message properties are collectively referred to as the message header.


Arrival Timestamp	indicates the time the message was opened for reading.
Compression	is used to enable or disable compression for a message.
Correlation ID	is used for a message ID or an application-specific string.
Data	are the instructions or value part of a message.
Delivery Mode	is the level of guarantee when a message is sent through a connection.
Delivery Timeout	is the number of seconds specifying how long to wait for acknowledgment of delivery of a message sent through a connection.
Destination	is the name of where a message is going.
Expiration	indicates how long, in seconds, the message should be in existence.
Header String Encode	controls whether or not header strings are converted to four-byte integers when a message is sent through a connection.
Load Balancing Mode	is the method of delivery for publish-subscribe operations, which allows a message to be delivered to one or to all subscribing RTclients.
Message ID	uniquely identifies a SmartSockets message.
Num Fields	identifies how many fields are in a particular message.
Priority	is the level of importance of a message.
Read Only	controls whether or not a message can be modified.
Reference Count	is the number of independent references to a message.
Reply To	is the destination or subject where a reply to the messages should be sent.
Sender	is the name of the originator of a message.
Sender Timestamp	indicates the time the message was sent.
Sequence Number	uniquely identifies a message for guaranteed message delivery.
Type	is the kind of message being manipulated.
User-Defined Property	is a user-defined value that can be used for any purpose.

Figure 1 shows an example of a standard NUMERIC_DATA message. The data part of this example message is a series of variable name-value pairs (voltage = 33.4534, switch_pos = 0).