Demand Control: Calculate actual cost for a response

[tninesling]

Introduces a third method to CostCalculator which scores the cost of a GraphQL response.

The first stage of scoring a response is to zip it together with the request. The initial implementation does not use the request fields, but this will be required to support custom cost. In that case, we will need to check the corresponding request field definition to see if a custom cost needs to be applied to a particular response field. This information is stored in a counterpart to serde_json::Value, which is called TypedValue. This TypedValue enum pairs each JSON value with the corresponding apollo_compiler::executable::Field.

Once the response values are paired with their corresponding fields, it is simple to traverse the JSON structure, taking query or schema directives into account.

Implements ROUTER-175

Checklist

Complete the checklist (and note appropriate exceptions) before the PR is marked ready-for-review.

• Changes are compatible¹
• Documentation² completed
• Performance impact assessed and acceptable
• Tests added and passing³
  • Unit Tests
  • Integration Tests
  • Manual Tests

Exceptions

Note any exceptions here

Notes

Footnotes

1. It may be appropriate to bring upcoming changes to the attention of other (impacted) groups. Please endeavour to do this before seeking PR approval. The mechanism for doing this will vary considerably, so use your judgement as to how and when to do this. ↩

2. Configuration is an important part of many changes. Where applicable please try to document configuration examples. ↩

3. Tick whichever testing boxes are applicable. If you are adding Manual Tests, please document the manual testing (extensively) in the Exceptions. ↩

[router-perf]

CI performance tests

• reload - Reload test over a long period of time at a constant rate of users
• 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_without_dedup_callback - Stress test for events with a lot of users and deduplication DISABLED using callback mode
• large-request - Stress test with a 1 MB request payload
• const - Basic stress test that runs with a constant number of users
• no-graphos - Basic stress test, no GraphOS.
• step-jemalloc-tuning - Clone of the basic stress test for jemalloc tuning
• events - Stress test for events with a lot of users and deduplication ENABLED
• events_callback - Stress test for events with a lot of users and deduplication ENABLED in callback mode
• 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_without_dedup - Stress test for events with a lot of users and deduplication DISABLED
• xxlarge-request - Stress test with 100 MB request payload
• xlarge-request - Stress test with 10 MB request payload
• step - Basic stress test that steps up the number of users over time

[github-actions]

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