HTTPX not flexible enough with preservation of HTTP method for 301 Moved Permanently redirect

[aebrahim]

Sadly, the specification for 301 is not strict enough, and says that the request method may be changed to GET (source). An external API provider that we call requires that the method be preserved, which is also the behavior used by tools like Postman.

I could not find a way to force HTTPX into this behavior. While HTTPX isn't doing anything wrong here per the standard, it would be nice to have an option called preserve_method_on_301_redirect or something to that effect. Another option would be a first-party wrapper to transparently follow redirects for this method, such as httpx.follow_301_redirects_preserving_method(client, response) which didn't seem as clean to me as an end-user of this library, but might be simpler to implement - I am not sure given that I'm not that familiar with httpx internals.

Here is a code block demonstrating our issue

"""Test httpx redirect behavior against the standard.

The standard is documented here:
https://developer.mozilla.org/en-US/docs/Web/HTTP/Redirections#permanent_redirections"""
import unittest
import respx
import httpx


class HttpxTest(unittest.TestCase):
    @respx.mock
    def test_308_preserves_method(self):
        """Ensure 308 permanent redirect preserves HTTP method."""

        client = httpx.Client(follow_redirects=True)

        intial_redirect = respx.post(
            "http://test.com/authenticate",
        ) % httpx.Response(status_code=308, headers={"location": "https://test.com/authenticate"})
        final_response = (
            respx.post(
                "https://test.com/authenticate",
            )
            % httpx.codes.OK
        )
        response = client.post("http://test.com/authenticate")
        self.assertEqual(response.status_code, 200)
        self.assertEqual(intial_redirect.call_count, 1)
        self.assertEqual(final_response.call_count, 1)

    @respx.mock
    def test_301_unspecified_behavior(self):
        """This follows the unspecified 301 behavior of the HTTP method."""

        client = httpx.Client(follow_redirects=True)

        intial_redirect = respx.post(
            "http://test.com/authenticate",
        ) % httpx.Response(status_code=301, headers={"location": "https://test.com/authenticate"})
        # It looks like httpx converts the method to a GET, which is valid, but
        # not always the behavior the server expects
        final_response = (
            respx.get(
                "https://test.com/authenticate",
            )
            % httpx.codes.METHOD_NOT_ALLOWED
        )
        response = client.post("http://test.com/authenticate")
        self.assertEqual(response.status_code, 405)
        self.assertEqual(intial_redirect.call_count, 1)
        self.assertEqual(final_response.call_count, 1)


if __name__ == "__main__":
    unittest.main()