urljoining an empty query string doesn't clear query string

[thetorpedodog]

BPO	32779
Nosy	@orsenthil, @asvetlov, @thetorpedodog, @iritkatriel
PRs	gh-76960: Fix urljoining with an empty query string. #5645

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2018-02-06.04:48:49.412>
labels = ['type-bug', 'library', '3.9', '3.10', '3.11']
title = "urljoining an empty query string doesn't clear query string"
updated_at = <Date 2021-05-28.14:36:47.327>
user = 'https://github.com/thetorpedodog'

bugs.python.org fields:

activity = <Date 2021-05-28.14:36:47.327>
actor = 'pfish'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2018-02-06.04:48:49.412>
creator = 'pfish'
dependencies = []
files = []
hgrepos = []
issue_num = 32779
keywords = ['patch']
message_count = 7.0
messages = ['311704', '311937', '312201', '312223', '394648', '394649', '394664']
nosy_count = 4.0
nosy_names = ['orsenthil', 'asvetlov', 'pfish', 'iritkatriel']
pr_nums = ['5645']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue32779'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

Linked PRs

• gh-76960: Fix urljoin() and urldefrag() for URIs with empty components #123273

[thetorpedodog]

urljoining with '?' will not clear a query string:

ACTUAL:
>>> import urllib.parse
>>> urllib.parse.urljoin('http://a/b/c?d=e', '?')
'http://a/b/c?d=e'

EXPECTED:
'http://a/b/c' (optionally, with a ? at the end)

WhatWG's URL standard expects a relative URL consisting of only a ? to replace a query string:

https://url.spec.whatwg.org/#relative-state

Seen in versions 3.6 and 2.7, but probably also affects later versions.

[thetorpedodog]

I'm working on a patch for this and can have one up in the next week or so, once I get the CLA signed and other boxes ticked. I'm new to the Github process but hopefully it will be a good start for the discussion.

[asvetlov]

Python follows not WhatWG but RFC.
https://tools.ietf.org/html/rfc3986#section-5.2.2 is proper definition for url joining algorithm.

[thetorpedodog]

In this case, the RFC is mismatched from the actual behaviour of browsers (as described and codified by WhatWG). It was surprising to me that urljoin() didn't do what I percieved as "the right thing" (and I expect other users would too).

I would personally expect urljoin to do "the thing that everybody else does". Is there a sensible way to reduce this mismatch?

For reference, Java's stdlib does what I would expect here:

URI base = URI.create("https://example.com/?a=b");
URI rel = base.resolve("?");
System.out.println(rel);

https://example.com/?

[iritkatriel]

The relevant part in the RFC pseudo code is

 if defined(R.query) then
 T.query = R.query;
 else
 T.query = Base.query;
 endif;

which is implemented in urljoin as:

 if not query:
 query = bquery

Is this correct? Should the code not say "if query is not None"?
(I can't see in the RFC a definition of defined()).

[iritkatriel]

Sorry, urlparse returns '' rather than None when there is no query.
So we indeed need to check something like
if '?' not in url:
or what's in Paul's patch.

However, my main point was to question whether fixing this is actually in contradiction with the RFC.

[thetorpedodog]

Reading more into this, from section 5.2,1:

A component is undefined if its associated delimiter does not appear in the URI reference

So you could say that since there is a '?', the query component is *defined*, but *empty*. This would mean that assigning the target query to be '' has the desired effect as implemented by browsers and other languages' standard libraries.

[orsenthil]

Yes, this a bug with urljoin in Python.

I compared the behavior against Ruby, and Golang.

require 'uri'

base_url = 'https://www.example.com/?a=b'
relative_url = '?'

url = URI.join(base_url, relative_url).to_s

puts url

Output:

https://www.example.com/?

And go's https://pkg.go.dev/net/url@go1.19beta1#URL.ResolveReference, ResolveReference resolves a URI reference to an absolute URI from an absolute base URI u, per RFC 3986 Section 5.2.

package main

import (
	"fmt"
	"net/url"
)

func main() {
	base, _ := url.Parse("https://example.com/?a=b")
	u, _ := url.Parse("?")
	fmt.Println(base.ResolveReference(u))
}

https://example.com/?

In python

Python 3.12.0a7+ (heads/main:4898415df7, Apr 20 2023, 16:46:44) [GCC 11.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import urllib.parse
>>> urllib.parse.urljoin("http://www.example.com/?a/b","?")
'http://www.example.com/?a/b'

We can treat this as bug and fix it. However, there are very high chances that people are relying on the current no-op behavior, and this change in behavior can cause frameworks to break. This sounds a bit costly to me.