$status var in responses

[lennyburdette]

---

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[router-perf]

CI performance tests

• connectors-const - Connectors stress test that runs with a constant number of users
• const - Basic stress test that runs with a constant number of users
• demand-control-instrumented - A copy of the step test, but with demand control monitoring and metrics enabled
• demand-control-uninstrumented - A copy of the step test, but with demand control monitoring enabled
• enhanced-signature - Enhanced signature enabled
• events - Stress test for events with a lot of users and deduplication ENABLED
• events_big_cap_high_rate - Stress test for events with a lot of users, deduplication enabled and high rate event with a big queue capacity
• events_big_cap_high_rate_callback - Stress test for events with a lot of users, deduplication enabled and high rate event with a big queue capacity using callback mode
• events_callback - Stress test for events with a lot of users and deduplication ENABLED in callback mode
• events_without_dedup - Stress test for events with a lot of users and deduplication DISABLED
• events_without_dedup_callback - Stress test for events with a lot of users and deduplication DISABLED using callback mode
• extended-reference-mode - Extended reference mode enabled
• large-request - Stress test with a 1 MB request payload
• no-tracing - Basic stress test, no tracing
• reload - Reload test over a long period of time at a constant rate of users
• step-jemalloc-tuning - Clone of the basic stress test for jemalloc tuning
• step-local-metrics - Field stats that are generated from the router rather than FTV1
• step-with-prometheus - A copy of the step test with the Prometheus metrics exporter enabled
• step - Basic stress test that steps up the number of users over time
• xlarge-request - Stress test with 10 MB request payload
• xxlarge-request - Stress test with 100 MB request payload

[benjamn]

This looks good, though it needs a rebase and I have a couple inline comments below.

[benjamn]

Does it make sense to default $status to Value::Number(200.into()) in this map? That way we'd be guaranteed it's always defined, and JSONSelection strings that mention $status can still function even if there's no HTTP response involved.

[lennyburdette]

that's interesting, but i think it's better to have an apply_to error if you try to use $status in a body selection, headers, or URLs. that's certainly a mistake, and it'd be weird to let customers emit 200s in strange places.

we should probably also validate which variables are available in the different selections. i'll make a ticket for that.

[pubmodmatt]

The fact that KnownVariable::Status maps to None here points to something missing here. We're reusing the Variable and VariableType definitions from the URL template code, which doesn't seem right, and doesn't capture a key distinction, which is request vs response variables - status only makes sense in a response context. We've already had bugs here, where $context was passed in where it wasn't supported. I'd like to see some better type definitions around variables which clarify where they can be used and prevent mistakes where a variable is passed in somewhere it isn't supported at the code level, and also enable validations at the user level that they are only referencing variables where they are supported. This doesn't necessarily need to be solved in this PR, but it does come up here as it's really unclear without additional context why this one variable maps to None here.

[lennyburdette]

yeah that's a good point. i'll make a ticket