Parameter Resolver

Overview

The parameter resolver expands ${...} placeholders inside any nested string / list / dict structure. It is invoked automatically on every task before the user template touches it, so values flow seamlessly between actions.

Supported placeholders

Placeholder	Resolves to
`${var.NAME}`	The value passed to `register_variable` / `register_variables`.
`${env.NAME}`	Environment variable `NAME`.
`${csv.SOURCE.COLUMN}`	The next row from CSV source `SOURCE` (cycles by default).
`${faker.METHOD}`	Calls `Faker().METHOD()` (lazy import, optional dependency).
`${uuid()}`	A new UUID 4 string.
`${now()}`	Local time in ISO-8601 (seconds resolution).
`${randint(min, max)}`	Cryptographically-strong random int in `[min, max]`.

Unknown placeholders are left in place so missing data is visible during a dry run.

Registering data

from je_load_density import (
    register_variable, register_variables,
    register_csv_source, register_csv_sources,
)

register_variable("base", "https://api.example.com")
register_variables({"token": "abc", "tenant": "acme"})

register_csv_source("users", "users.csv")            # cycles
register_csv_sources([
    {"name": "products", "file_path": "products.csv", "cycle": False},
])

CSV files must have a header row. Each call to ${csv.name.col} returns the value at column col from the next row.

Action-JSON usage

The same APIs are available through the executor so an entire run can be parameterised from JSON:

{"load_density": [
  ["LD_register_variables", {"variables": {"base": "https://api.example.com"}}],
  ["LD_register_csv_sources", {"sources": [
    {"name": "users", "file_path": "users.csv"}
  ]}],
  ["LD_start_test", {
    "user_detail_dict": {"user": "fast_http_user"},
    "tasks": [{
      "method": "post",
      "request_url": "${var.base}/login",
      "json": {"email": "${csv.users.email}", "password": "${csv.users.password}"}
    }]
  }]
]}

Extracting values from responses

HTTP tasks may declare extract rules; matching values are written back into the resolver under the chosen variable name:

{
  "method": "post",
  "request_url": "${var.base}/login",
  "json": {"email": "u@example.com", "password": "secret"},
  "extract": [
    {"var": "auth_token", "from": "json_path", "path": "data.token"},
    {"var": "request_id", "from": "header", "name": "X-Request-Id"},
    {"var": "status", "from": "status_code"}
  ]
}

Subsequent tasks can read ${var.auth_token} straight from the resolver.

Clearing

Call parameter_resolver.clear() (or LD_clear_resolver) between runs to discard accumulated state.