TMC Comet support

A submodule of TMC server providing HTTP push support using cometd.

Protocol

Cometd's implementation of Bayeux is used as the transport. The following channels are defined.

• /broadcast/tmc/global/admin-msg
  • Publishes global messages from administrators, such as "maintenance window in 5 minutes".
  • Message payload: a string containing the message.
• /broadcast/tmc/global/course-updated
  • Published when a course is updated.
  • Message payload: a string containing the name of the course.
• /broadcast/tmc/user/<username>/review-available
  • Published when a review is available. The client should check the server for new reviews.
  • Message payload: {exercise_name: '...', url: '<url to view review as HTML>'}.

Clients authenticate by sending an ext parameter authentication containing the fields username, password and serverBaseUrl during handshake. Backends authorize by sending backendKey and serverBaseUrl. In both cases, serverBaseUrl should point to a TMC server instance. A fixed list of allowed server base URLs must be configured.

Configuration and running

Install an init script (for debian-based systems) using initscripts/install.sh [port]. The port defaults to 8080.

To run the server manually, do mvn -Dfi.helsinki.cs.tmc.comet.configFile=/path/to/file.properties jetty:start. The configuration file should not be world-readable and must have the following definitions.

• fi.helsinki.cs.tmc.comet.backendKey a secret that all backend servers use to authenticate when publishing messages.
• fi.helsinki.cs.tmc.comet.allowedServers a semicolon-separated list of server base URLs that are accepted and authenticated against. Terminating slashes don't matter.