fix(asyncio): reject connection URLs missing the scheme separator

[Arunendra21]

Summary

The async parse_url in redis/asyncio/connection.py validated the URL scheme with urlparse(url).scheme, which accepts a URL that has a valid scheme name but is missing the :// separator, for example redis:foo.bar.com:12345. In that case urlparse reports the scheme as redis with an empty netloc, so the function returned partial kwargs (no host/port) and the async client silently connected to the default host instead of raising.

The sync parse_url in redis/connection.py already guards against this up front and has a dedicated test (test_invalid_scheme_raises_error_when_double_slash_missing), but the async copy did not, so redis.from_url("redis:foo.bar.com:12345") and redis.asyncio.from_url("redis:foo.bar.com:12345") behaved differently.

Changes

• Add the same up-front scheme check that the sync version uses, so a URL missing the redis://, rediss://, or unix:// prefix raises ValueError with the same message. The now-unreachable trailing else branch is removed, matching the structure of the sync implementation.
• Add test_invalid_scheme_raises_error_when_double_slash_missing to the async connection-pool URL-parsing tests, mirroring the existing sync test.

Testing

Verified that async parse_url / ConnectionPool.from_url now raises for redis:foo.bar.com:12345, localhost, and http://localhost, while valid redis://, rediss://, and unix:// URLs (including host, port, db, and querystring options) still parse exactly as before. The sync and async implementations now return matching results for these inputs.

---

Note

Low Risk
Localized URL validation at pool creation; behavior change only for previously mis-parsed or non-canonical scheme strings.

Overview
Connection URL parsing is tightened in both redis/connection.py and redis/asyncio/connection.py so invalid or ambiguous URLs fail fast with the same ValueError message.

parse_url now requires a case-insensitive redis://, rediss://, or unix:// prefix (RFC 3986 schemes). That rejects strings like redis:foo.bar.com:12345 where urlparse would treat redis as the scheme but leave no host—async previously could return partial kwargs and connect to defaults instead of raising. The async path is aligned with the sync guard and drops the redundant post-parse else branch.

Tests add coverage for the missing-:// case on async (mirroring sync) and for uppercase REDIS://, REDISS://, and UNIX:// on both clients.

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Behavior change (for release notes)

While aligning the sync and async parsers and addressing review feedback, the checks are now case-insensitive per RFC 3986. As a result the sync redis.from_url() now also accepts uppercase schemes such as REDIS://, REDISS://, and UNIX:// (the urlparse-based async parser already accepted these). This is a released-behavior change for the sync parser worth noting in the release notes; the missing-separator case (e.g. redis:foo.bar.com:12345) is still rejected.

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[Arunendra21]

Good catch, thanks. Updated the check to normalize the scheme case with url.lower().startswith((...)), so REDIS://, Rediss://, and UNIX:// are accepted again while the missing-separator case (e.g. redis:foo.bar.com:12345) still raises. Applied the same change to the sync parse_url so the two stay consistent, and added an uppercase-scheme test to both.

[petyaslavova]

Hey @Arunendra21, thank you for your contribution!

Two items before merge:

1. Please extend the uppercase coverage to REDISS:// (asserting SSLConnection) and UNIX:// (asserting UnixDomainSocketConnection) in both tests/test_connection_pool.py and tests/test_asyncio/test_connection_pool.py. Case-insensitive acceptance is new for the sync parser, and the TLS variant is the one worth pinning with a test.
2. Please mention in the PR description that sync from_url now accepts uppercase schemes — it is a released-behavior change we want captured in the release notes.

[Arunendra21]

Thanks @petyaslavova! Both addressed:

1. Extended test_uppercase_scheme_is_accepted in both tests/test_connection_pool.py and tests/test_asyncio/test_connection_pool.py to also assert REDISS:// → SSLConnection and UNIX:// → UnixDomainSocketConnection.
2. Added a "Behavior change (for release notes)" section to the PR description noting that sync from_url now accepts uppercase schemes, while the missing-separator case is still rejected.