Messages

Message[+P, +H] is a sealed trait hierarchy with two orthogonal dimensions:

Direction: Message.Outbound (for sending) / Message.Inbound (received from queue)
Shape: Message.IsPlain (payload only) / Message.HasHeaders (payload + headers)

Outbound messages (sending)

Message.Outbound.Plain[P] — payload only
Message.Outbound.WithHeaders[P, H] — payload + headers

Inbound messages (reading)

Message.Inbound.Plain[P] — payload only
Message.Inbound.WithHeaders[P, H] — payload + headers

Inbound messages expose the following fields:

Field	Type	Description
`id`	`MessageId`	PGMQ-assigned message identifier
`readCount`	`Int`	Number of times the message has been delivered
`enqueuedAt`	`OffsetDateTime`	When the message was inserted
`lastReadAt`	`Option[OffsetDateTime]`	When the message was last delivered; `None` if never read
`visibleAt`	`OffsetDateTime`	When the message becomes visible again (end of current visibility timeout)
`payload`	`P`	Decoded payload

Message.HasHeaders (both inbound and outbound) additionally exposes headers: H.

Sending

Wrap your payload in an Outbound case class:

// Plain message
client.send(queue, Message.Outbound.Plain(order))

// With headers
case class OrderHeaders(region: String, priority: Int)
client.send(queue, Message.Outbound.WithHeaders(order, OrderHeaders("eu", 1)))

// Batch send
client.sendBatch(queue, orders.map(Message.Outbound.Plain(_)))

Reading with Headers

val messages: F[List[Message.Inbound[OrderCreated, OrderHeaders]]] =
  client.read[OrderCreated, OrderHeaders](queue, 30.secondsVisibility, 10.messages)

Reading without headers ignores any headers present:

val messages: F[List[Message.Inbound.Plain[OrderCreated]]] =
  client.read[OrderCreated](queue, 30.secondsVisibility, 10.messages)

Warning

Both the payload type P and the headers type H need PgmqEncoder/PgmqDecoder instances in scope. Make sure your JSON codec bridge import covers both types.

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