Headers

Message headers are used in a variety of JetStream contexts, such de-duplication, auto-purging of messages, metadata from republished messages, and more.
Publish
Headers that can be set by a client when a message being published.
Name
Description
Example
Version
Nats-Msg-Id
Client-defined unique identifier for a message that will be used by the server apply de-duplication within the configured Duplicate Window.
9f01ccf0-8c34-4789-8688-231a2538a98b
2.2.0
Nats-Expected-Stream
Used to assert the published message is received by some expected stream.
my-stream
2.2.0
Nats-Expected-Last-Msg-Id
Used to apply optimistic concurrency control at the stream-level. The value is the last expected Nats-Msg-Id and the server will reject a publish if the current ID does not match.
9f01ccf0-8c34-4789-8688-231a2538a98b
2.2.0
Nats-Expected-Last-Sequence
Used to apply optimistic concurrency control at the stream-level. The value is the last expected sequence and the server will reject a publish if the current sequence does not match.
328
2.2.0
Nats-Expected-Last-Subject-Sequence
Used to apply optimistic concurrency control at the subject-level. The value is the last expected sequence and the server will reject a publish if the current sequence does not match for the message's subject.
38
2.3.1
Nats-Rollup
Used to apply a purge of all prior messages in the stream or at the subject-level.
all for stream, sub for subject
2.6.2
RePublish
Headers set messages that are republished.
Name
Description
Example
Version
Nats-Stream
Name of the stream the message was republished from.
Nats-Stream: my-stream
2.8.3
Nats-Subject
The original subject of the message.
events.mouse_clicked
2.8.3
Nats-Sequence
The original sequence of the message.
193
2.8.3
Nats-Last-Sequence
The last sequence of the message having the same subject, otherwise zero if this is the first message for the subject.
190
2.8.3
Nats-Time-Stamp
The original timestamp of the message.
2023-08-23T19:53:05.762416Z
2.10.0
Sources
Headers that are implicitly added to messages sourced from other streams.
Name
Description
Example
Version
Nats-Stream-Source
Specifies the origin stream name, the subject and the sequence number plus the subject filter and destination transform of the message being sourced.
my-stream
2.2.0
Headers-only
Headers added to messages when the consumer is configured to be "headers only" omitting the body.
Name
Description
Example
Version
Nats-Msg-Size
Indicates the message size in bytes.
1024
2.6.2
Mirror
Headers used for internal flow-control messages for a mirror.
Name
Description
Example
Version
Nats-Last-Consumer
​
​
2.2.1
Nats-Last-Stream
​
​
2.2.1
Nats-Consumer-Stalled
​
​
2.4.0
Nats-Response-Type
​
​
2.6.4

Name	Description	Example	Version
`Nats-Msg-Id`	Client-defined unique identifier for a message that will be used by the server apply de-duplication within the configured `Duplicate Window`.	`9f01ccf0-8c34-4789-8688-231a2538a98b`	2.2.0
`Nats-Expected-Stream`	Used to assert the published message is received by some expected stream.	`my-stream`	2.2.0
`Nats-Expected-Last-Msg-Id`	Used to apply optimistic concurrency control at the stream-level. The value is the last expected `Nats-Msg-Id` and the server will reject a publish if the current ID does not match.	`9f01ccf0-8c34-4789-8688-231a2538a98b`	2.2.0
`Nats-Expected-Last-Sequence`	Used to apply optimistic concurrency control at the stream-level. The value is the last expected sequence and the server will reject a publish if the current sequence does not match.	`328`	2.2.0
`Nats-Expected-Last-Subject-Sequence`	Used to apply optimistic concurrency control at the subject-level. The value is the last expected sequence and the server will reject a publish if the current sequence does not match for the message's subject.	`38`	2.3.1
`Nats-Rollup`	Used to apply a purge of all prior messages in the stream or at the subject-level.	`all` for stream, `sub` for subject	2.6.2

Name	Description	Example	Version
`Nats-Stream`	Name of the stream the message was republished from.	`Nats-Stream: my-stream`	2.8.3
`Nats-Subject`	The original subject of the message.	`events.mouse_clicked`	2.8.3
`Nats-Sequence`	The original sequence of the message.	`193`	2.8.3
`Nats-Last-Sequence`	The last sequence of the message having the same subject, otherwise zero if this is the first message for the subject.	`190`	2.8.3
`Nats-Time-Stamp`	The original timestamp of the message.	`2023-08-23T19:53:05.762416Z`	2.10.0

Name	Description	Example	Version
`Nats-Stream-Source`	Specifies the origin stream name, the subject and the sequence number plus the subject filter and destination transform of the message being sourced.	`my-stream`	2.2.0

Name	Description	Example	Version
`Nats-Msg-Size`	Indicates the message size in bytes.	`1024`	2.6.2

Name	Description	Example	Version
`Nats-Last-Consumer`			2.2.1
`Nats-Last-Stream`			2.2.1
`Nats-Consumer-Stalled`			2.4.0
`Nats-Response-Type`			2.6.4

Last modified 1d ago