Add rest method to HttpUser - #3512

rest() / rest_() were only on FastHttpUser. People on the default HttpUser who test JSON APIs had to write the catch_response + json() + JSONDecodeError pattern themselves (see "REST/JSON APIs" in writing-a-locustfile.rst). k6 also makes JSON response checks first-class for its default HTTP client. This PR adds the same helpers to HttpUser.

PR #2274 moved rest from RestUser into FastHttpUser. I couldn't find any issue or discussion that says it should stay FastHttpUser-only.

What changed

• The rest/rest_ code (and _callstack_regex) moved unchanged out of FastHttpUser into a small RestMixin in locust/user/users.py. HttpUser and FastHttpUser both inherit from it.
  • FastHttpUser behaves exactly as before. The only edits to the moved code are typing: the yield type is now a generic parameter, and self.client is untyped inside the mixin.
• RestMixin is generic over the response type, so type checkers still see the right types:
  • FastHttpUser.rest() yields locust.contrib.fasthttp.RestResponseContextManager, as before.
  • HttpUser.rest() yields a new locust.clients.RestResponseContextManager, a ResponseContextManager with js: dict, mirroring the fasthttp one.
• Docs: rest/rest_ are now listed in the HttpUser API docs, and the REST sections in writing-a-locustfile.rst and increase-performance.rst say the method is available on both users.

Usage

from locust import HttpUser, task

class MyUser(HttpUser):
    @task
    def t(self):
        with self.rest("POST", "/api/items", json={"foo": 1}) as resp:
            assert resp.js["foo"] == 1, "unexpected foo,"

Testing

• Added TestHttpUserRest to locust/test/test_http.py:
  • test_rest_success and test_rest_fail mirror the tests in test_fasthttp.py.
  • New tests cover invalid JSON, a connection error (python-requests returns content=None there), an exception raised inside the with-block, and rest_ (timestamp query parameter and the ?_=... stats name).
• uv run pytest locust/test/test_http.py locust/test/test_fasthttp.py locust/test/test_locust_class.py locust/test/test_users.py: 155 passed, 1 failed. The failure is TestFastHttpSsl::test_ssl_request_insecure, which also fails on master in my local environment.
• uv run ruff check locust/ examples/, uv run ruff format --check, uv run mypy locust/: all clean.
• I ran mypy with reveal_type in a small locustfile to confirm the response types shown above, and checked that examples/rest.py type-checks the same as on master.
• sphinx-build renders locust.HttpUser.rest/rest_ and FastHttpUser.rest/rest_.

Claude Code helped write this change. I reviewed it.

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