Messages

Messages are the primary mechanism for communicating with other processes. The struct looks like this:

type Message struct {
    Timestamp time.Time
    Type      MessageType
    Forward   bool
    Value     interface{}
}

Message fields

• Timestamp: When the message was created (e.g. time.Now().UTC())
• Type: MessageType is just a string type for quick type-switching when processing the message
• Forward: If true, the message will be sent to all child nodes recursively. Otherwise, it will only be sent to the process’ direct children and no further.
• Value: Contains information fo be passed on. It will need to be type cast when received by the child processes.

Forwarding is neccessary for process life-cycle management. For instance, starting and stopping all processes. Most messages will not be forwarded. The Timestamp field is not strictly necessary.

Note: Setting the timestamp for every message will degrade performance.

MessageTypes

All messages must have a type in order to be processed. MessageTypes are simply const strings which identify the message’s purpose.

// MessageType helps enumerate message types
type MessageType string

Custom message types can be defined like so:

// TypeRandom is the message type for random numbers
const TypeRandom = dproc.MessageType("Random")

Built-in messages

There are only two built-in messages types. They are also forwarded to all children when using the default process. This informs all processes in the pipeline about the life-cycle state. For instance, starting and stopping the pipeline.

// Common message types
const (
	MessageTypeStart MessageType = "START"
	MessageTypeStop  MessageType = "STOP"
)

Handlers can also listen for these messages if additional initialization or clean-up is required, like opening/closing a file.