Terminal dot segments lose URL path trailing slash and change relative redirects

[Timotty]

Potential issue

httpx.URL drops the trailing slash when the input path ends in /. or /... This changes the request target and where relative redirects resolve, even though RFC 3986 §5.2.4 preserves a trailing / after removing a terminal dot segment.

Minimal reproduction

import httpx

url = httpx.URL("https://example.com/x/y/..")
print(str(url))
print(url.raw_path)
print(url.join("child"))

Actual:

https://example.com/x
b'/x'
https://example.com/child

Expected after normalizing /x/y/.. to /x/:

https://example.com/x/
b'/x/'
https://example.com/x/child

This also reproduces for /x/. and /x/y/.. An in-process MockTransport redirect from /x/y/.. with Location: child requests /x then /child, instead of /x/ then /x/child.

Investigation

httpx/_urlparse.py:447-475, normalize_path(), removes terminal . and .. components without retaining the directory-ending slash. One possible localized fix is to append an empty component when an absolute path ends in /. or /..; regression tests can cover URL construction, .raw_path, .join() and redirects. Is this consistent with HTTPX's intended URL normalization behavior? If maintainers agree, I can submit a focused PR.

Verified against default-branch commit b5addb64f0161ff6bfe94c124ef76f6a1fba5254, HTTPX 0.28.1, Python 3.12.13 on Windows; checked open/closed issues and PRs for terminal dot segments and trailing slashes without finding this case.

AI disclosure: bug discovery assisted by Luna (timotty-responses/luna); reproduction and proposed fix reviewed with OpenCode (GPT-6 Sol). No PR has been published.

[Cha-Imaa]

Normalize first to preserve the trailing slash. Verified with HTTPX 0.28.1

from urllib.parse import urljoin
import httpx

url = httpx.URL(urljoin("https://example.com/", "/x/y/.."))
print(url.join("child"))

https://example.com/x/child

[GLec1er]

I checked your proposed trailing-slash correction on b5addb64f0161ff6bfe94c124ef76f6a1fba5254 (Python 3.11.8, macOS).

The distinction is supported by RFC 3986 §5.2.4, steps B/C: a terminal /. or /.. is replaced with /, with the preceding segment also removed for /... For the absolute paths in your report, appending an empty output component after processing the dot segments preserves that directory boundary:

if path.startswith("/") and path.endswith(("/.", "/..")):
    output.append("")

I added 58 local cases: 34 fail on the original checkout, and all 58 pass with this correction. Besides your examples, these cover normalization to the root, walking above the root, repeated slashes, keyword construction and copy_with(). Controls preserve existing behavior for encoded dot segments and names such as .file; query and fragment case is preserved too.

I also checked actual redirect handling through MockTransport, both synchronously and with AsyncClient under asyncio/Trio: /x/y/.. requests /x/, then a Location: child?Q=VaL#Frag resolves to /x/child?Q=VaL#Frag.

The full suite with just this local correction has 1,473 passed, 1 skipped, 2 failed. Both failures also occur on the unmodified base: test_download (Click deprecation warning) and test_write_timeout[trio] (async-generator cleanup warnings). I am not claiming a clean full CI run or complete RFC conformance beyond the checked cases.