Durable Subscription

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What is a Durable Subscription?

"A durable subscription saves messages for an inactive subscriber and delivers these saved messages when the subscriber reconnects. In this way, a subscriber will not lose any messages even though it disconnected. A durable subscription has no effect on the behaviour of the subscriber or the messaging system while the subscriber is active (e.g., connected). A connected subscriber acts the same whether its subscription is durable or non-durable. The difference is in how the messaging system behaves when the subscriber is disconnected." -- http://www.eaipatterns.com/DurableSubscription.html

Why Should I use One?

You may occasionally disconnect from the Datafeeds service - your client may crash, you may experience connectivity problems or you might simply need to reboot a machine. A durable subscription stops you losing messages when you're not connected:

  • The TD and Train Movements feeds are high-volume, and if you disconnect for even a minute, you can lose a lot of data
  • The VSTP feed contains new schedules, and if you miss one of these, you can't track that train
  • The TSR feed has a handful of messages on a Friday morning (when the Weekly Operating Notice is published)

The Time-to-Live (TTL) on messages is 5 minutes. As long as you reconnect within 5 minutes from your last connection, on your next connection, you will receive all messages that you may have missed whilst your client was offline.

How do I Request a Durable Subscription?

You don't need to rewrite your client! Just do these three things:

  • When you send a CONNECT frame, send a client-id in the header. Set this to the email address you use to subscribe - this makes it easy to identify who the durable subscriber belongs to
  • When you send a SUBSCRIBE frame, send a activemq.subscriptionName header. Set this to a unique string for each feed - for example, the hostname of your subscriber and the feed name, e.g. "prodbox-vstp"
  • Each time you receive a message, send an ACK so the service knows you've received it

If your client disconnects and reconnects, the service will automatically send all queued messages when you reconnect.

Network Rail Open Data Feeds
Data Feeds About the Feeds Account States Durable Subscriptions Example Code ( PHP / C# / Java / Ruby / Node.js) • Advanced UsesFAQ Release Notes
Train Movements Train Movements Feed Train Activation Train Cancellation Train Movement Train Reinstatement Change of Origin Change of Identity Change of Location TSPEED Field Planned Cancellations Cancellation Codes
TD TD Feed C-Class Messages S-Class Messages Train Describers TD Berths
TSR TSR Feed Route Codes
SCHEDULE SCHEDULE Feed Schedule and Location Records Association Records CIF Codes How Scheduling Works Allowances
Reference Data Reference Data Feed TOC Codes CIF Codes Delay Attribution Codes Identifying Locations (STANOX, TIPLOC, NLC and 3-Alpha Codes) STANOX Geographical Areas Train Planning data