Request / Reply

Request / Reply in the sidebar sends a core NATS request: the message goes to a subject with a private reply inbox, and the first subscriber that answers wins. Use it to call a service, check that it is up, or look at what it returns. Nothing here goes through JetStream, and requests are not recorded in the publish history.

Send a request

1. Open Request / Reply in the sidebar, or press Cmd+K and pick Go to Request / Reply.
2. Enter a literal Subject, such as orders.validate or $SRV.PING. Wildcards are not allowed. Recent subjects and the literal patterns of your mappings show up as suggestions.
3. Pick a timeout: how long to wait for the first reply, from 500 ms to 60 s.
4. Write the payload, or leave it empty for a request without a body. Text that is not JSON is sent as plain text.
5. Add NATS headers if the service expects them.
6. Click Send Request, or press Cmd+Enter (Ctrl+Enter on Windows and Linux).

Dynamic values such as (listed under Dynamic value helpers in the editor toolbar) work in the subject, payload and header values. The last subject, payload, headers and timeout are kept as a draft until you disconnect.

The reply

The reply panel shows the round-trip time, the payload size, the inbox the reply arrived on, the payload as JSON, raw text or a hex dump, and the reply headers.

A reply that carries the Nats-Service-Error header, as services built on the NATS micro framework send, is flagged as a service error with its Nats-Service-Error-Code.

When no reply arrives, the panel tells you why:

• No responders: nothing is subscribed to the subject. NATS reports it at once instead of letting the request wait for the timeout.
• No reply within the timeout: something is subscribed but did not answer in time.
• No permission: your user may not publish to the subject or subscribe to its reply inbox; the panel names the missing permission.

Protobuf

When a subject mapping matches the request subject, the JSON payload is encoded to that Protobuf type before it is sent, with the mapping's framing and pinned schema, just like in the Publish tab. The editor completes fields at any depth and enum values, and offers an example message.

Replies arrive on an inbox subject, so no mapping applies to them. Pick the reply type in Decode as. If the request type ends in Request and the same source has a matching Response or Reply type, Natscope selects it for you. The choice is remembered per subject.

Templates

Templates and Save as template work as in the Publish tab. A template whose subject has wildcards is loaded with its saved wildcard values filled in.