`base_url` with a query string produces malformed request URLs

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Since Oct 26, 2026.

Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
52/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
python
Domain
api, backend

Research direction

Start in _client.py by reading _enforce_trailing_slash and _merge_url, focusing on their use of raw_path when base_url contains a query. Reproduce both examples, then confirm with maintainers whether query-bearing base URLs should be rejected or supported; done means tests cover both relative requests and params= without malformed or missing paths.

Written by the indexing model from the issue text.

Description

A base_url that contains a query string is not rejected, but every relative request built from it has a broken URL. Reproduced on httpx2 2.13.1:

import httpx2

client = httpx2.Client(base_url="https://example.com/api?key=k")
print(repr(client.base_url))
# URL('https://example.com/api?key=k/')

print(client.build_request("GET", "items").url)
# https://example.com/api?key=k/items

print(client.build_request("GET", "items", params={"b": "2"}).url)
# https://example.com/api?b=2

In the first request the path ends up inside the query (key becomes k/items). In the second the path items is lost entirely. No error is raised in either case, so the request silently goes to the wrong URL.

Cause

Both steps operate on raw_path, which includes the query:

  • _enforce_trailing_slash (_client.py) appends / to url.raw_path, so the slash lands after the query: /api?key=k/.
  • _merge_url builds self.base_url.raw_path + merge_url.raw_path.lstrip(b"/"), so the request path is appended after the query too.

The second case then loses the path because params= replaces the whole query (#905), and the query now holds the path.

Possible fixes

  1. Reject a base_url with a query string in the base_url setter, with a message pointing to params=.
  2. Support it: operate on path rather than raw_path in both places and merge the base query into the request's params.
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Merged PRs (30d)
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