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10 lines
1.1 KiB
Markdown
10 lines
1.1 KiB
Markdown
# Request-Reply
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The pattern of sending a message and receiving a response is encapsulated in most client libraries into a request method. Under the covers this method will publish a message with a unique reply-to subject and wait for the response before returning. In the older versions of some libraries a completely new reply-to subject is created each time. In newer versions, a subject hierarchy is used so that a single subscriber in the client library listens for a wildcard, and requests are sent with a unique child subject of a single subject.
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The primary difference between the request method and publishing with a reply-to is that the library is only going to accept one response, and in most libraries the request will be treated as a synchronous action. The library may provide a way to set the timeout. For example, updating the previous publish example we may request `time` with a one second timeout:
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!INCLUDE "../../_examples/request_reply.html"
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You can also build your own request-reply using publish-subscribe if you need a different semantic or timing.
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