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OpenMessaging Extension Header

The OpenMessaging Specification defines the core fields of for messaging and
streaming, which can meet the needs of most common message middleware message transmissions, but there are still many fields related to the message domain, and are also well known to many developers, but not produced by every message. but not so much commonly used as the fields in OpenMessaging Specification, but these fields are still very meaningful and can help message middleware achieve more features and improve its visibility.

So we officially defined some of the following attributes in extensionHeader:

storeTimestamp

  • Type: Long
  • Description: when the durability The timestamp that a message stored by server. when a message is stored by the server, this field will be set with the current timestamp of the server.
    It is represented as a long value which is defined as the difference, measured in milliseconds, between this time and midnight, January 1, 1970 UTC.
  • Constraints: OPTIONAL

storeHost

  • Type: String
  • Description: The host info of the server that stores this message. when a message is stored by the server, this field will be set with the host info of server.
  • Constraints: OPTIONAL

correlationId

  • Type: String
  • Description: A client can use the correlationId header field to link one message with another. A typical use is to link a response message with its request message.
  • Constraints: OPTIONAL

messageKey

  • Type: String
  • Description: This key that specifies that a message belongs to a specific message group, and this key can be used for the server to shard or dispatch messages.
  • Constraints: OPTIONAL

delayTime

  • Type: Long
  • Description: The message will be delivered after delayTime milliseconds starting from bornTimeStamp .
    When this filed isn't set explicitly, this means this message should be delivered immediately.
  • Constraints: OPTIONAL

expireTime

  • Type: Long
  • Description: This field represents the discard time of the message, if an undelivered message's expireTime is reached, the message would be destroyed. If an earlier timestamp is set than expireTime or isn't set , that means the message will not be expired.
    It is represented as a long value which is defined as the difference, measured in milliseconds, between this time and midnight, January 1, 1970 UTC.
  • Constraints: OPTIONAL

traceId

  • Type: String
  • Description: This identifier represents a global and unique identification, to associate key events in the whole lifecycle of a message, like sent by who, stored at where, and received by who. And, the messaging system only plays exchange role in a distributed system in most cases, so the TraceID can be used to trace the whole call link with other parts in the whole system.
  • Constraints: OPTIONAL

transactionId

  • Type: String
  • Description: This field is used in transactional message, and it can be used to trace a transaction. So the same transactionId will be appeared not only in prepare message, but also in commit message, and consumer received message also contains this field.
  • Constraints: OPTIONAL

deliveryCount

  • Type: Integer
  • Description: This field indicates the times of the message was delivered, when a consumer consumes a message failed, it will be resend to the server for consume it later. and this field records the consumed times during the consume process.
  • Constraints: OPTIONAL

priority

  • Type: Integer
  • Description: OpenMessaging defines a ten level priority value with 1 as the lowest priority and 10 as the highest, and the default priority is 5. The priority beyond this region will be ignored.
    OpenMessaging does not require or provide any guarantee that the message should be delivered in priority order strictly, but the vendor should provide a best effort to deliver expedited messages ahead of normal messages.
  • Constraints: OPTIONAL

partition

  • Type: Integer
  • Description: This field in extension header contains the partition of target destination which the message is being sent. When a Message is set with this value, this message will be delivered to specified partition, but the premise is that the implementation of the server side is dependent on the partition or a queue-like storage mechanism.
  • Constraints: OPTIONAL