feat: NO_PROXY environment variable can be used to override `HTTP(S…

…)_PROXY` values

When determining if a proxy should be used, the SDK would:

1. Check the `config.http_config.http_proxy` value. If that is set, use
   that value without further consideration.
2. If the target URI is `https`, use the value from the `HTTPS_PROXY`
   environment variable.
3. If the target is `http`, use `HTTP_PROXY` instead.

The SDK will now support another environment variable -- `NO_PROXY`.
This variable can be set to a comma-separated list of hosts to exclude
from proxy support, or the special case '*' meaning to ignore all hosts.

The `NO_PROXY` variable will only take affect if the SDK isn't
explicitly configured to use a proxy as specified in #1 above.

ldclient/impl/http.py

@@ -2,6 +2,9 @@
 import certifi
 from os import environ
 import urllib3
+from urllib.parse import urlparse
+from typing import Tuple
+
 
 def _application_header_value(application: dict) -> str:
     parts = []
@@ -34,9 +37,11 @@ def _base_headers(config):
 
     return headers
 
+
 def _http_factory(config):
     return HTTPFactory(_base_headers(config), config.http)
 
+
 class HTTPFactory:
     def __init__(self, base_headers, http_config, override_read_timeout=None):
         self.__base_headers = base_headers
@@ -73,26 +78,77 @@ def create_pool_manager(self, num_pools, target_base_uri):
                 num_pools=num_pools,
                 cert_reqs=cert_reqs,
                 ca_certs=ca_certs
-                )
+            )
         else:
             # Get proxy authentication, if provided
             url = urllib3.util.parse_url(proxy_url)
             proxy_headers = None
-            if url.auth != None:
+            if url.auth is not None:
                 proxy_headers = urllib3.util.make_headers(proxy_basic_auth=url.auth)
             # Create a proxied connection
             return urllib3.ProxyManager(
                 proxy_url,
                 num_pools=num_pools,
                 cert_reqs=cert_reqs,
-                ca_certs = ca_certs,
+                ca_certs=ca_certs,
                 proxy_headers=proxy_headers
             )
 
+
 def _get_proxy_url(target_base_uri):
+    """
+    Determine the proxy URL to use for a given target URI, based on the
+    environment variables http_proxy, https_proxy, and no_proxy.
+
+    If the target URI is an https URL, the proxy will be determined from the HTTPS_PROXY variable.
+    If the target URI is not https, the proxy will be determined from the HTTP_PROXY variable.
+
+    In either of the above instances, if the NO_PROXY variable contains either
+    the target domain or '*', no proxy will be used.
+    """
     if target_base_uri is None:
         return None
-    is_https = target_base_uri.startswith('https:')
-    if is_https:
-        return environ.get('https_proxy')
-    return environ.get('http_proxy')
+
+    target_host, target_port, is_https = _get_target_host_and_port(target_base_uri)
+
+    proxy_url = environ.get('https_proxy') if is_https else environ.get('http_proxy')
+    no_proxy = environ.get('no_proxy', '').strip()
+
+    if proxy_url is None or no_proxy == '*':
+        return None
+    elif no_proxy == '':
+        return proxy_url
+
+    for no_proxy_entry in no_proxy.split(','):
+        parts = no_proxy_entry.strip().split(':')
+        if len(parts) == 1:
+            if target_host.endswith(no_proxy_entry):
+                return None
+            continue
+
+        if target_host.endswith(parts[0]) and target_port == int(parts[1]):
+            return None
+
+    return proxy_url
+
+
+def _get_target_host_and_port(uri: str) -> Tuple[str, int, bool]:
+    """
+    Given a URL, return the effective hostname, port, and whether it is considered a secure scheme.
+
+    If a scheme is not supplied, the port is assumed to be 80 and the connection unsecure.
+    If a scheme and port is provided, the port will be parsed from the URI.
+    If only a scheme is provided, the port will be 443 if the scheme is 'https', otherwise 80.
+    """
+    if '//' not in uri:
+        parts = uri.split(':')
+        return (parts[0], int(parts[1]) if len(parts) > 1 else 80, False)
+
+    parsed = urlparse(uri)
+    is_https = parsed.scheme == 'https'
+
+    port = parsed.port
+    if port is None:
+        port = 443 if is_https else 80
+
+    return parsed.hostname or "", port, is_https

ldclient/testing/impl/test_http.py

@@ -0,0 +1,46 @@
+import pytest
+
+from typing import Optional
+from ldclient.impl.http import _get_proxy_url
+
+
+@pytest.mark.parametrize(
+    'target_uri, no_proxy, expected',
+    [
+        ('https://secure.example.com', '', 'https://secure.proxy:1234'),
+        ('http://insecure.example.com', '', 'http://insecure.proxy:6789'),
+
+        ('https://secure.example.com', 'secure.example.com', None),
+        ('https://secure.example.com', 'secure.example.com:443', None),
+        ('https://secure.example.com', 'secure.example.com:80', 'https://secure.proxy:1234'),
+        ('https://secure.example.com', 'wrong.example.com', 'https://secure.proxy:1234'),
+
+        ('https://secure.example.com', 'example.com', None),
+        ('https://secure.example.com', 'example.com:443', None),
+        ('https://secure.example.com', 'example.com:80', 'https://secure.proxy:1234'),
+
+        ('http://insecure.example.com', 'insecure.example.com', None),
+        ('http://insecure.example.com', 'insecure.example.com:443', 'http://insecure.proxy:6789'),
+        ('http://insecure.example.com', 'insecure.example.com:80', None),
+        ('http://insecure.example.com', 'wrong.example.com', 'http://insecure.proxy:6789'),
+
+        ('http://insecure.example.com', 'example.com', None),
+        ('http://insecure.example.com', 'example.com:443', 'http://insecure.proxy:6789'),
+        ('http://insecure.example.com', 'example.com:80', None),
+
+        ('secure.example.com', 'secure.example.com', None),
+        ('secure.example.com', 'secure.example.com:443', 'http://insecure.proxy:6789'),
+        ('secure.example.com', 'secure.example.com:80', None),
+        ('secure.example.com', 'wrong.example.com', 'http://insecure.proxy:6789'),
+        ('secure.example.com:8080', 'secure.example.com', None),
+        ('secure.example.com:8080', 'secure.example.com:80', 'http://insecure.proxy:6789'),
+    ]
+)
+def test_honors_no_proxy(target_uri: str, no_proxy: str, expected: Optional[str], monkeypatch):
+    monkeypatch.setenv('https_proxy', 'https://secure.proxy:1234')
+    monkeypatch.setenv('http_proxy', 'http://insecure.proxy:6789')
+    monkeypatch.setenv('no_proxy', no_proxy)
+
+    proxy_url = _get_proxy_url(target_uri)
+
+    assert proxy_url == expected

ldclient/testing/proxy_test_util.py

@@ -1,5 +1,6 @@
 from ldclient.config import Config, HTTPConfig
-from ldclient.testing.http_util import start_server, BasicResponse, JsonResponse
+from ldclient.testing.http_util import start_server
+
 
 # Runs tests of all of our supported proxy server configurations: secure or insecure, configured
 # by Config.http_proxy or by an environment variable, with or without authentication. The action
@@ -16,7 +17,8 @@ def do_proxy_tests(action, action_method, monkeypatch):
         (False, True, False),
         (True, False, False),
         (True, False, True),
-        (True, True, False)]:
+        (True, True, False)
+    ]:
         test_desc = "%s, %s, %s" % (
             "using env vars" if use_env_vars else "using Config",
             "secure" if secure else "insecure",
@@ -27,23 +29,23 @@ def do_proxy_tests(action, action_method, monkeypatch):
             if use_env_vars:
                 monkeypatch.setenv('https_proxy' if secure else 'http_proxy', proxy_uri)
             config = Config(
-                sdk_key = 'sdk_key',
-                base_uri = target_uri,
-                events_uri = target_uri,
-                stream_uri = target_uri,
-                http = HTTPConfig(http_proxy=proxy_uri),
-                diagnostic_opt_out = True)
+                sdk_key='sdk_key',
+                base_uri=target_uri,
+                events_uri=target_uri,
+                stream_uri=target_uri,
+                http=HTTPConfig(http_proxy=proxy_uri),
+                diagnostic_opt_out=True)
             try:
                 action(server, config, secure)
-            except:
+            except Exception:
                 print("test action failed (%s)" % test_desc)
                 raise
             # For an insecure proxy request, our stub server behaves enough like the real thing to satisfy the
             # HTTP client, so we should be able to see the request go through. Note that the URI path will
             # actually be an absolute URI for a proxy request.
             try:
                 req = server.require_request()
-            except:
+            except Exception:
                 print("server did not receive a request (%s)" % test_desc)
                 raise
             expected_method = 'CONNECT' if secure else action_method