fix: NO_PROXY should support IPv4, IPv6 and localhost

[HearyShen]

Closes #2660

The get_environment_proxies function in _utils.py is responsible for parsing and mounting proxy info from system environment.

httpx/httpx/_utils.py

Lines 229 to 264 in 4b5a92e

	def get_environment_proxies() -> typing.Dict[str, typing.Optional[str]]:
	"""Gets proxy information from the environment"""
	# urllib.request.getproxies() falls back on System
	# Registry and Config for proxies on Windows and macOS.
	# We don't want to propagate non-HTTP proxies into
	# our configuration such as 'TRAVIS_APT_PROXY'.
	proxy_info = getproxies()
	mounts: typing.Dict[str, typing.Optional[str]] = {}
	for scheme in ("http", "https", "all"):
	if proxy_info.get(scheme):
	hostname = proxy_info[scheme]
	mounts[f"{scheme}://"] = (
	hostname if "://" in hostname else f"http://{hostname}"
	)
	no_proxy_hosts = [host.strip() for host in proxy_info.get("no", "").split(",")]
	for hostname in no_proxy_hosts:
	# See https://curl.haxx.se/libcurl/c/CURLOPT_NOPROXY.html for details
	# on how names in `NO_PROXY` are handled.
	if hostname == "*":
	# If NO_PROXY=* is used or if "*" occurs as any one of the comma
	# separated hostnames, then we should just bypass any information
	# from HTTP_PROXY, HTTPS_PROXY, ALL_PROXY, and always ignore
	# proxies.
	return {}
	elif hostname:
	# NO_PROXY=.google.com is marked as "all://*.google.com,
	# which disables "www.google.com" but not "google.com"
	# NO_PROXY=google.com is marked as "all://*google.com,
	# which disables "www.google.com" and "google.com".
	# (But not "wwwgoogle.com")
	mounts[f"all://*{hostname}"] = None
	return mounts

For env no_proxy, according to CURLOPT_NOPROXY explained, it should support domains, IPv4, IPv6 and the localhost. However, current get_environment_proxies function implementation only supports domains correctly as it always adds wildcard * in front of the hostname.

I encountered error when my environment no_proxy includes IPv6 address like ::1. It is wrongly transformed into all://*::1 and causes urlparse error since the _urlparse.py parses the :1 as port.

To fix this issue, I looked into this repo and suggest handling the no_proxy hostnames as domains, IPv4, IPv6 and the localhost seperately. I have updated the get_environment_proxies function in _utils.py and tested it.

Replies and discussions are welcomed!

[tomchristie]

Nicely done, yup.