Transport metadata accompanying a delivered message.
readonly
topic: string
The topic the message arrived on.
readonly
optional
messageId: string
Broker-assigned message ID, when available.
readonly
optional
timestamp: Date
Delivery timestamp, when available.
readonly
optional
headers: Readonly<Record<string, string>>
Transport headers read from the delivered message. First-party brokers
populate this with {} when their transport carried no headers.