Improve BufferOptions (body, json_body)

[malud]

To further optimize the memory and cpu consumption we should determine an explicit usage of body or json_body content for its request context. We should skip parsing and converting to cty.Object if just the .body or .json_body gets passed without accessing any properties. Also the sequence usage of the mentioned root variables could just get piped to the next item.

[johakoch]

We could create a new BufferOption for JSON-parsing apart from BufferResponse (and BufferRequest?) and set this option in eval.MustBuffer().
The new option would be read in newBerespValues() and could be passed to parseRespBody() to help decide whether or not to parseJSONBytes().

However, looking at Test_StoreInvalidBackendResponse with its configuration testdata/integration/error_handler/06_couper.hcl:

server {
  api {
    endpoint "/anything" {
      proxy {
        backend {
          origin = "${env.COUPER_TEST_BACKEND_ADDR}"

          openapi {
            file = "02_schema.yaml"
          }
        }
      }
    }

    error_handler "backend_openapi_validation" {
      response {
        status = 418
          json_body = {
            req_path = backend_requests.default.path
            resp_status = backend_responses.default.status
            resp_json_body_query = backend_responses.default.json_body.Query
            resp_ct = backend_responses.default.headers.content-type
          }
      }
    }
  }
}

, the error handler gets its own BufferOpts, so the backend_responses.default.json_body.Query in the error_handler block does not affect the endpoint's BufferOpts to cause the response body to be JSON-parsed.

This test works, because both BufferOpts have BufferResponse set, the endpoint's because of the openapi block, the error_handler's because of a reference to json_body.

If we consider another configuration

server {
  api {
    endpoint "/anything" {
      request "r" {
        url = "https://blackhole.webpagetest.org/"
        backend {
          timeout = "1s"
        }
      }
      proxy {
        backend {
          origin = "https://httpbin.org"
        }
      }
    }

    error_handler "backend_timeout" {
      response {
        status = 418
        json_body = {
          resp_json_body_headers = backend_responses.default.json_body.headers
        }
      }
    }
  }
}

, the error handler's BufferOpts are BufferResponse (because of the reference to json_body), whereas the endpoint's are BufferNone. So the proxy response's body is not buffered, and resp_json_body_headers is null.

[johakoch]

blocked by #706

[johakoch]

We should skip parsing and converting to cty.Object if just the .body or .json_body gets passed without accessing any properties.

I agree on skipping the JSON-parsing with .body.
But .json_body is expected to be a JSON "thing". So we need to JSON-parse it.

json_body = {
  a = backend_responses.a.json_body
}