python-ipware 4.1.0

The first 4.x release on PyPI. 4.0.0 was tagged internally but never published, so this
release carries everything since 3.0.0: a pluggable algorithm router with a new default
engine, a better best-match for the client IP, tighter trusted-proxy matching, and a much
larger test suite. Existing code keeps working: from python_ipware import IpWare is
unchanged.

Upgrade in one minute

• Python 3.9 or newer is required (3.7 and 3.8 are end of life). Tested on 3.9–3.14 and PyPy.
• The default engine is now modern. For normal, well-formed headers it returns the same
  address as 3.x. It differs where 3.x picked a worse address, see below.
• Need the exact 3.x behavior? IpWare(algorithm="legacy") runs the frozen v3 algorithm.
• proxy_list is stricter. A complete IP entry now matches exactly, not as a prefix. If you
  relied on "1.2.3.4" also matching 1.2.3.45, use a CIDR or a prefix ending in ..
• Misconfiguration now raises ValueError when IpWare(...) is created instead of silently
  trusting the wrong thing: an empty proxy_list entry, a bare string instead of a list, a non-IP
  entry, or a negative / non-integer proxy_count.

What changed since 3.0.0

Algorithm router

IpWare(algorithm="auto" | "modern" | "legacy"). auto (the default) resolves to modern.
legacy keeps the v3 algorithm byte for byte, validated by the original v3 test suite.

Best match for the client IP (modern)

• Every address is ranked: public > private > link-local > loopback. Unspecified, 0.0.0.0/8,
  multicast, broadcast and reserved addresses are never returned. (Python reports multicast as
  global, so 3.x could return 224.0.0.1 as the client.)
• Without proxy settings, the first public hop of a chain wins, not just the first hop:
  10.0.0.1, 177.139.233.139 now yields 177.139.233.139. With leftmost=False the chain is
  scanned from the right. That public hop may be an upstream proxy; set proxy_count or
  proxy_list when you must identify private (intranet / VPN) clients.
• With proxy_count / proxy_list, the client position is fixed exactly as in 3.x, and
  trusted_route is now True for private clients behind trusted proxies too.

Parsing (modern)

• RFC 7239 Forwarded is parsed by its for= value, quote-aware, including for="[2001:db8::1]:4711".
• IPv4-mapped (::ffff:1.2.3.4) and NAT64 (64:ff9b::1.2.3.4) addresses unwrap to plain IPv4.
• Malformed tokens are rejected instead of truncated: [::1, [::1]junk, 1.2.3.4:abc, 1.2.3.4:70000.
• Header names match case-insensitively (- and _ equivalent), so lowercase keys such as AWS
  Lambda's work. The dash spelling always wins, whatever the dict order, so a client-sent
  x_forwarded_for cannot shadow the proxy's x-forwarded-for.
• Non-string header values are skipped instead of crashing.

Trusted proxies (modern)

• proxy_list entries: a CIDR network (IPv4 or IPv6, by membership), a complete IP
  (exact), or an IP prefix matched on whole octets / groups ("10.1" matches 10.1.x.x, not
  10.100.x.x). IPv6 entries ignore case and leading zeros.
• IPv4-mapped and NAT64 CIDR entries (::ffff:10.0.0.0/104) match the unwrapped IPv4 hops.

Default headers (modern)

Added, in order of arrival: True-Client-IP, Fastly-Client-IP, Fly-Client-IP, App Engine
X-AppEngine-User-IP, Azure X-Client-IP, Azure Front Door X-Azure-ClientIP, DigitalOcean
DO-Connecting-IP, Envoy X-Envoy-External-Address. Headers released earlier never move; new
ones sit just above REMOTE_ADDR, so an upgrade never lets a new header outrank one that already
resolved your requests.

Packaging and CI

• PEP 621 pyproject.toml with the Hatchling backend; the version lives in __version__.py.
• CI runs the test matrix, then builds, then publishes on v* tags via PyPI trusted publishing.

Tests

182 tests. The modern engine has 100% line and branch coverage, checked by an exhaustive matrix
against an independent reference model, a never-worse-than-legacy differential over the whole
matrix, formatting-invariance and fuzz runs, and mutation checks. The original v3 suite passes on
both engines.

Thanks

@griffi-gh (#26, CIDR proxy entries), @mdalp (#23, Fly.io), @iloveitaly (#24, #25).

Full details: CHANGELOG.md.