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request-lifecycle.md

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Request Lifetime

Throughout a request's lifetime, Rack::Timeout keeps details about the request in env[Rack::Timeout::ENV_INFO_KEY], or, more explicitly, env["rack-timeout.info"].

The value of that entry is an instance of Rack::Timeout::RequestDetails, which is a Struct consisting of the following fields:

  • id: a unique ID per request. Either the value of the X-Request-ID header or a random ID generated internally.

  • wait: time in seconds since X-Request-Start at the time the request was initially seen by Rack::Timeout. Only set if X-Request-Start is present.

  • timeout: the final timeout value that was used or to be used, in seconds. For expired requests, that would be the wait_timeout, possibly with wait_overtime applied. In all other cases it's the service_timeout, potentially reduced to make up for time lost waiting. (See discussion regarding service_past_wait above, under the Wait Timeout section.)

  • service: set after a request completes (or times out). The time in seconds it took being processed. This is also updated while a request is still active, around every second, with the time taken so far.

  • state: the possible states, and their log level, are:

    • expired (ERROR): the request is considered too old and is skipped entirely. This happens when X-Request-Start is present and older than wait_timeout. When in this state, Rack::Timeout::RequestExpiryError is raised. See earlier discussion about the wait_overtime setting, too.

    • ready (INFO): this is the state a request is in right before it's passed down the middleware chain. Once it's being processed, it'll move on to active, and then on to timed_out and/or completed.

    • active (DEBUG): the request is being actively processed in the application thread. This is signaled repeatedly every ~1s until the request completes or times out.

    • timed_out (ERROR): the request ran for longer than the determined timeout and was aborted. Rack::Timeout::RequestTimeoutException is raised in the application when this occurs. This state is not the final one, completed will be set after the framework is done with it. (If the exception does bubble up, it's caught by rack-timeout and re-raised as Rack::Timeout::RequestTimeoutError, which descends from RuntimeError.)

    • completed (INFO): the request completed and Rack::Timeout is done with it. This does not mean the request completed successfully. Rack::Timeout does not concern itself with that. As mentioned just above, a timed out request will still end up with a completed state.