Stop the topic '*' wildcard from matching across dots

[chuenchen309]

A topic binding using * matches routing keys with any number of words, not one — so queues receive messages they never bound.

TopicExchange's own docstring is the spec here:

The topic exchange routes messages based on words separated by dots, using wildcard characters * (any single word), and # (one or more words).

The bug

wildcards = {'*': r'.*?[^\.]',
             '#': r'.*?'}

* compiles to .*?[^\.] — "anything, then a non-dot". The intent reads as "one word, not ending in a dot", but the leading .*? is unconstrained and . matches dots, so only the final character is actually restricted. a.*.c becomes ^a\..*?[^\.]\.c$, which happily matches a.b.x.c.

Reproducer

Through the public API, no mocks — Connection('memory://'), a queue bound with a.*.c, three messages published:

binding 'a.*.c' received:
   - CONTROL: routing_key='a.b.c'      (one word — should arrive)
   - routing_key='a.b.x.c'             (two words — should NOT arrive)
   - routing_key='a.b.x.y.c'           (three words — should NOT arrive)

The control arrives correctly, so this is the wildcard specifically rather than a broken reproducer. The compiled patterns:

binding	current pattern	matches
a.*.c	^a\..*?[^\.]\.c$	a.b.c, a.b.x.c, a.b.x.y.c
*.b	^.*?[^\.]\.b$	a.b, a.x.b
*	^.*?[^\.]$	a, a.b

Scope

virtual/base.py:448 sets exchange_types = dict(STANDARD_EXCHANGE_TYPES) and no transport overrides it, so every virtual transport routes through this — redis, mongodb, filesystem, SQS, kafka, and so on. Real AMQP brokers route server-side and are unaffected.

The failure direction is over-delivery rather than loss: a queue silently processes messages outside its binding, which is why I'd call it more than cosmetic.

Fix

Compile * to a single dot-free word. # is untouched.

wildcards = {'*': r'[^\.]+',
             '#': r'.*?'}

I checked the boundaries explicitly — * still matches exactly one word and still rejects an empty word (a.*.c vs a..c) and an empty key, and a.#.c still matches both a.b.c and a.b.x.c.

On #

While here I noticed a.#.c doesn't match a.c, where AMQP defines # as zero or more words. I've deliberately left that alone: kombu's docstring says # is "one or more words", so the code matches its own documented contract, and changing it means restructuring the split/join rather than a wildcards entry. Happy to open a separate issue if you'd like it reconsidered.

Tests

Added one case to the existing test_Topic::test_lookup table — stock.us.nasdaq.tech must reach only the stock.# queue, not the stock.us.* one. It fails on main (Extra items in the left set: 'rBar') and passes with the fix.

There was no coverage for this: test_Topic and test_TopicMultibind only exercise stock.us.* against the single-word stock.us.nasdaq, so neither behaviour was pinned — no existing test changed.

Full unit suite, same command and tree both ways: 1184 passed with the fix vs. 1183 on main (the extra one is the new case). Failures are byte-identical between the two runs — 16 pre-existing ones in my sandbox (15 SQS, 1 pyro, both missing local credentials/deps), none attributable to this change. flake8 clean.

Disclosure

AI-assisted, and I'd rather say so plainly. The reproducer, the controls, the boundary table, the exchange_types scope check, and the main-vs-branch baseline diff are all things I ran and read myself rather than assumed. Happy to adjust scope or framing.

[Copilot]

Pull request overview

This PR fixes topic-exchange wildcard semantics in the virtual transport implementation so that * matches exactly one dot-delimited word (as documented), preventing unintended over-delivery to queues bound with patterns like a.*.c.

Changes:

• Update TopicExchange wildcard translation so * compiles to a single dot-free word regex ([^\.]+) instead of a cross-dot match.
• Add a unit test case ensuring stock.us.* does not match a longer routing key like stock.us.nasdaq.tech.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
kombu/transport/virtual/exchange.py	Fixes * wildcard regex so it cannot match across dot separators in virtual topic routing.
t/unit/transport/virtual/test_exchange.py	Adds coverage to prevent regressions for multi-word routing keys against * bindings.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.17%. Comparing base (e592de0) to head (fafff8e).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2568   +/-   ##
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  Coverage   83.17%   83.17%           
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  Files          79       79           
  Lines       10636    10636           
  Branches     1243     1243           
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  Hits         8846     8846           
  Misses       1584     1584           
  Partials      206      206           

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