Repository: theupdateframework/python-tuf
Pull request #2804 (2025-03-03 21:47:15)

build(deps): bump ruff from 0.9.7 to 0.9.9 in the test-and-lint-dependencies group
Bumps the test-and-lint-dependencies group with 1 update: [ruff](https://github.com/astral-sh/ruff).

Updates `ruff` from 0.9.7 to 0.9.9
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a href="https://github.com/astral-sh/ruff/releases">ruff's releases</a>.</em></p>
<blockquote>
<h2>0.9.9</h2>
<h2>Release Notes</h2>
<h3>Preview features</h3>
<ul>
<li>Fix caching of unsupported-syntax errors (<a href="https://redirect.github.com/astral-sh/ruff/pull/16425">#16425</a>)</li>
</ul>
<h3>Bug fixes</h3>
<ul>
<li>Only show unsupported-syntax errors in editors when preview mode is enabled (<a href="https://redirect.github.com/astral-sh/ruff/pull/16429">#16429</a>)</li>
</ul>
<h2>Contributors</h2>
<ul>
<li><a href="https://github.com/InSyncWithFoo"><code>@​InSyncWithFoo</code></a></li>
<li><a href="https://github.com/MichaReiser"><code>@​MichaReiser</code></a></li>
<li><a href="https://github.com/dhruvmanila"><code>@​dhruvmanila</code></a></li>
<li><a href="https://github.com/ntBre"><code>@​ntBre</code></a></li>
</ul>
<h2>Install ruff 0.9.9</h2>
<h3>Install prebuilt binaries via shell script</h3>
<pre lang="sh"><code>curl --proto '=https' --tlsv1.2 -LsSf https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-installer.sh | sh
</code></pre>
<h3>Install prebuilt binaries via powershell script</h3>
<pre lang="sh"><code>powershell -ExecutionPolicy ByPass -c &quot;irm https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-installer.ps1 | iex&quot;
</code></pre>
<h2>Download ruff 0.9.9</h2>
<table>
<thead>
<tr>
<th>File</th>
<th>Platform</th>
<th>Checksum</th>
</tr>
</thead>
<tbody>
<tr>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-aarch64-apple-darwin.tar.gz">ruff-aarch64-apple-darwin.tar.gz</a></td>
<td>Apple Silicon macOS</td>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-aarch64-apple-darwin.tar.gz.sha256">checksum</a></td>
</tr>
<tr>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-x86_64-apple-darwin.tar.gz">ruff-x86_64-apple-darwin.tar.gz</a></td>
<td>Intel macOS</td>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-x86_64-apple-darwin.tar.gz.sha256">checksum</a></td>
</tr>
<tr>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-aarch64-pc-windows-msvc.zip">ruff-aarch64-pc-windows-msvc.zip</a></td>
<td>ARM64 Windows</td>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-aarch64-pc-windows-msvc.zip.sha256">checksum</a></td>
</tr>
<tr>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-i686-pc-windows-msvc.zip">ruff-i686-pc-windows-msvc.zip</a></td>
<td>x86 Windows</td>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-i686-pc-windows-msvc.zip.sha256">checksum</a></td>
</tr>
<tr>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-x86_64-pc-windows-msvc.zip">ruff-x86_64-pc-windows-msvc.zip</a></td>
<td>x64 Windows</td>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-x86_64-pc-windows-msvc.zip.sha256">checksum</a></td>
</tr>
<tr>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-aarch64-unknown-linux-gnu.tar.gz">ruff-aarch64-unknown-linux-gnu.tar.gz</a></td>
<td>ARM64 Linux</td>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-aarch64-unknown-linux-gnu.tar.gz.sha256">checksum</a></td>
</tr>
<tr>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-i686-unknown-linux-gnu.tar.gz">ruff-i686-unknown-linux-gnu.tar.gz</a></td>
<td>x86 Linux</td>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-i686-unknown-linux-gnu.tar.gz.sha256">checksum</a></td>
</tr>
<tr>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-powerpc64-unknown-linux-gnu.tar.gz">ruff-powerpc64-unknown-linux-gnu.tar.gz</a></td>
<td>PPC64 Linux</td>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-powerpc64-unknown-linux-gnu.tar.gz.sha256">checksum</a></td>
</tr>
<tr>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-powerpc64le-unknown-linux-gnu.tar.gz">ruff-powerpc64le-unknown-linux-gnu.tar.gz</a></td>
<td>PPC64LE Linux</td>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-powerpc64le-unknown-linux-gnu.tar.gz.sha256">checksum</a></td>
</tr>
<tr>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-s390x-unknown-linux-gnu.tar.gz">ruff-s390x-unknown-linux-gnu.tar.gz</a></td>
<td>S390x Linux</td>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-s390x-unknown-linux-gnu.tar.gz.sha256">checksum</a></td>
</tr>
<tr>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-x86_64-unknown-linux-gnu.tar.gz">ruff-x86_64-unknown-linux-gnu.tar.gz</a></td>
<td>x64 Linux</td>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-x86_64-unknown-linux-gnu.tar.gz.sha256">checksum</a></td>
</tr>
<tr>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-armv7-unknown-linux-gnueabihf.tar.gz">ruff-armv7-unknown-linux-gnueabihf.tar.gz</a></td>
<td>ARMv7 Linux</td>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-armv7-unknown-linux-gnueabihf.tar.gz.sha256">checksum</a></td>
</tr>
<tr>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-aarch64-unknown-linux-musl.tar.gz">ruff-aarch64-unknown-linux-musl.tar.gz</a></td>
<td>ARM64 MUSL Linux</td>
<td><a href="https://github.com/astral-sh/ruff/releases/download/0.9.9/ruff-aarch64-unknown-linux-musl.tar.gz.sha256">checksum</a></td>
</tr>
</tbody>
</table>
<!-- raw HTML omitted -->
</blockquote>
<p>... (truncated)</p>
</details>
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a href="https://github.com/astral-sh/ruff/blob/main/CHANGELOG.md">ruff's changelog</a>.</em></p>
<blockquote>
<h2>0.9.9</h2>
<h3>Preview features</h3>
<ul>
<li>Fix caching of unsupported-syntax errors (<a href="https://redirect.github.com/astral-sh/ruff/pull/16425">#16425</a>)</li>
</ul>
<h3>Bug fixes</h3>
<ul>
<li>Only show unsupported-syntax errors in editors when preview mode is enabled (<a href="https://redirect.github.com/astral-sh/ruff/pull/16429">#16429</a>)</li>
</ul>
<h2>0.9.8</h2>
<h3>Preview features</h3>
<ul>
<li>Start detecting version-related syntax errors in the parser (<a href="https://redirect.github.com/astral-sh/ruff/pull/16090">#16090</a>)</li>
</ul>
<h3>Rule changes</h3>
<ul>
<li>[<code>pylint</code>] Mark fix unsafe (<code>PLW1507</code>) (<a href="https://redirect.github.com/astral-sh/ruff/pull/16343">#16343</a>)</li>
<li>[<code>pylint</code>] Catch <code>case np.nan</code>/<code>case math.nan</code> in <code>match</code> statements (<code>PLW0177</code>) (<a href="https://redirect.github.com/astral-sh/ruff/pull/16378">#16378</a>)</li>
<li>[<code>ruff</code>] Add more Pydantic models variants to the list of default copy semantics (<code>RUF012</code>) (<a href="https://redirect.github.com/astral-sh/ruff/pull/16291">#16291</a>)</li>
</ul>
<h3>Server</h3>
<ul>
<li>Avoid indexing the project if <code>configurationPreference</code> is <code>editorOnly</code> (<a href="https://redirect.github.com/astral-sh/ruff/pull/16381">#16381</a>)</li>
<li>Avoid unnecessary info at non-trace server log level (<a href="https://redirect.github.com/astral-sh/ruff/pull/16389">#16389</a>)</li>
<li>Expand <code>ruff.configuration</code> to allow inline config (<a href="https://redirect.github.com/astral-sh/ruff/pull/16296">#16296</a>)</li>
<li>Notify users for invalid client settings (<a href="https://redirect.github.com/astral-sh/ruff/pull/16361">#16361</a>)</li>
</ul>
<h3>Configuration</h3>
<ul>
<li>Add <code>per-file-target-version</code> option (<a href="https://redirect.github.com/astral-sh/ruff/pull/16257">#16257</a>)</li>
</ul>
<h3>Bug fixes</h3>
<ul>
<li>[<code>refurb</code>] Do not consider docstring(s) (<code>FURB156</code>) (<a href="https://redirect.github.com/astral-sh/ruff/pull/16391">#16391</a>)</li>
<li>[<code>flake8-self</code>] Ignore attribute accesses on instance-like variables (<code>SLF001</code>) (<a href="https://redirect.github.com/astral-sh/ruff/pull/16149">#16149</a>)</li>
<li>[<code>pylint</code>] Fix false positives, add missing methods, and support positional-only parameters (<code>PLE0302</code>) (<a href="https://redirect.github.com/astral-sh/ruff/pull/16263">#16263</a>)</li>
<li>[<code>flake8-pyi</code>] Mark <code>PYI030</code> fix unsafe when comments are deleted (<a href="https://redirect.github.com/astral-sh/ruff/pull/16322">#16322</a>)</li>
</ul>
<h3>Documentation</h3>
<ul>
<li>Fix example for <code>S611</code> (<a href="https://redirect.github.com/astral-sh/ruff/pull/16316">#16316</a>)</li>
<li>Normalize inconsistent markdown headings in docstrings (<a href="https://redirect.github.com/astral-sh/ruff/pull/16364">#16364</a>)</li>
<li>Document MSRV policy (<a href="https://redirect.github.com/astral-sh/ruff/pull/16384">#16384</a>)</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/astral-sh/ruff/commit/091d0af2ab026a08b82d4aa7d3ab6b1ca4db778c"><code>091d0af</code></a> Bump version to Ruff 0.9.9 (<a href="https://redirect.github.com/astral-sh/ruff/issues/16434">#16434</a>)</li>
<li><a href="https://github.com/astral-sh/ruff/commit/3d72138740ed8c3ec9f733ace10fd40af0ff77eb"><code>3d72138</code></a> Check <code>LinterSettings::preview</code> for version-related syntax errors (<a href="https://redirect.github.com/astral-sh/ruff/issues/16429">#16429</a>)</li>
<li><a href="https://github.com/astral-sh/ruff/commit/4a237560244ecc1c2b4217724bcbaf605c844468"><code>4a23756</code></a> Avoid caching files with unsupported syntax errors (<a href="https://redirect.github.com/astral-sh/ruff/issues/16425">#16425</a>)</li>
<li><a href="https://github.com/astral-sh/ruff/commit/af62f7932bfee8a35b411c8351fbb81068caf7a6"><code>af62f79</code></a> Prioritize &quot;bug&quot; label for changelog sections (<a href="https://redirect.github.com/astral-sh/ruff/issues/16433">#16433</a>)</li>
<li><a href="https://github.com/astral-sh/ruff/commit/0ced8d053c2ff6ff86f3329f24c7c0854fa8466b"><code>0ced8d0</code></a> [<code>flake8-copyright</code>] Add links to applicable options (<code>CPY001</code>) (<a href="https://redirect.github.com/astral-sh/ruff/issues/16421">#16421</a>)</li>
<li><a href="https://github.com/astral-sh/ruff/commit/a8e171f82c14d7a6d617b204eca39978eb2ad2df"><code>a8e171f</code></a> Fix string-length limit in documentation for PYI054 (<a href="https://redirect.github.com/astral-sh/ruff/issues/16432">#16432</a>)</li>
<li><a href="https://github.com/astral-sh/ruff/commit/cf83584abb130574059064ad5f0dd806c22e45d5"><code>cf83584</code></a> Show version-related syntax errors in the playground (<a href="https://redirect.github.com/astral-sh/ruff/issues/16419">#16419</a>)</li>
<li><a href="https://github.com/astral-sh/ruff/commit/764aa0e6a1b16284c1c939332c19d742dae8aee1"><code>764aa0e</code></a> Allow passing <code>ParseOptions</code> to inline tests (<a href="https://redirect.github.com/astral-sh/ruff/issues/16357">#16357</a>)</li>
<li><a href="https://github.com/astral-sh/ruff/commit/568cf88c6c5b5551a675ae2b13deedec0fe226cb"><code>568cf88</code></a> Bump version to 0.9.8 (<a href="https://redirect.github.com/astral-sh/ruff/issues/16414">#16414</a>)</li>
<li><a href="https://github.com/astral-sh/ruff/commit/040071bbc5b21306f2759693ca6ee2c3fc5420bf"><code>040071b</code></a> [red-knot] Ignore surrounding whitespace when looking for `&lt;!-- snapshot-diag...</li>
<li>Additional commits viewable in <a href="https://github.com/astral-sh/ruff/compare/0.9.7...0.9.9">compare view</a></li>
</ul>
</details>
<br />


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Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting `@dependabot rebase`.

[//]: # (dependabot-automerge-start)
[//]: # (dependabot-automerge-end)

---

<details>
<summary>Dependabot commands and options</summary>
<br />

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</details>


Patch:
diff --git a/.github/workflows/cd.yml b/.github/workflows/cd.yml
index da36a6c7..623fae02 100644
--- a/.github/workflows/cd.yml
+++ b/.github/workflows/cd.yml
@@ -54,7 +54,7 @@ jobs:
       release_id: ${{ steps.gh-release.outputs.result }}
     steps:
       - name: Fetch build artifacts
-        uses: actions/download-artifact@fa0a91b85d4f404e444e00e005971372dc801d16 # v4.1.8
+        uses: actions/download-artifact@cc203385981b70ca67e1cc392babf9cc229d5806 # v4.1.9
         with:
           name: build-artifacts
 
@@ -96,7 +96,7 @@ jobs:
       id-token: write # to authenticate as Trusted Publisher to pypi.org
     steps:
       - name: Fetch build artifacts
-        uses: actions/download-artifact@fa0a91b85d4f404e444e00e005971372dc801d16 # v4.1.8
+        uses: actions/download-artifact@cc203385981b70ca67e1cc392babf9cc229d5806 # v4.1.9
         with:
           name: build-artifacts
 
diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index a1203eb9..d3ccf453 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -1,5 +1,21 @@
 # Changelog
 
+## Unreleased
+
+### Changed
+
+This release is API compatible but contains a major internal change in the HTTP handling.
+
+* ngclient: urllib3 is used as the HTTP library by default instead of requests (#2762,
+  #2773, #2789)
+  * This removes dependencies on `requests`, `idna`, `charset-normalizer` and `certifi`
+  * The deprecated RequestsFetcher implementation is available but requires selecting
+    the fetcher at Updater initialization and explicitly depending on requests
+* ngclient: TLS certificate source was changed. Certificates now come from operating
+  system certificate store instead of `certifi` (#2762)
+* Test infrastucture has improved and should now be more usable externally, e.g. in
+  distro test suites (#2749)
+
 ## v5.1.0
 
 ### Changed
diff --git a/requirements/lint.txt b/requirements/lint.txt
index 80e2c0c6..68247aa3 100644
--- a/requirements/lint.txt
+++ b/requirements/lint.txt
@@ -6,7 +6,7 @@
 # Lint tools
 # (We are not so interested in the specific versions of the tools: the versions
 # are pinned to prevent unexpected linting failures when tools update)
-ruff==0.9.7
+ruff==0.9.9
 mypy==1.15.0
 zizmor==1.3.1
 
diff --git a/tuf/ngclient/_internal/proxy.py b/tuf/ngclient/_internal/proxy.py
new file mode 100644
index 00000000..b42ea2f4
--- /dev/null
+++ b/tuf/ngclient/_internal/proxy.py
@@ -0,0 +1,101 @@
+# Copyright New York University and the TUF contributors
+# SPDX-License-Identifier: MIT OR Apache-2.0
+
+"""Proxy environment variable handling with Urllib3"""
+
+from __future__ import annotations
+
+from typing import Any
+from urllib.request import getproxies
+
+from urllib3 import BaseHTTPResponse, PoolManager, ProxyManager
+from urllib3.util.url import parse_url
+
+
+# TODO: ProxyEnvironment could implement the whole PoolManager.RequestMethods
+# Mixin: We only need request() so nothing else is currently implemented
+class ProxyEnvironment:
+    """A PoolManager manager for automatic proxy handling based on env variables
+
+    Keeps track of PoolManagers for different proxy urls based on proxy
+    environment variables. Use `get_pool_manager()` or `request()` to access
+    the right manager for a scheme/host.
+
+    Supports '*_proxy' variables, with special handling for 'no_proxy' and
+    'all_proxy'.
+    """
+
+    def __init__(
+        self,
+        **kw_args: Any,  # noqa: ANN401
+    ) -> None:
+        self._pool_managers: dict[str | None, PoolManager] = {}
+        self._kw_args = kw_args
+
+        self._proxies = getproxies()
+        self._all_proxy = self._proxies.pop("all", None)
+        no_proxy = self._proxies.pop("no", None)
+        if no_proxy is None:
+            self._no_proxy_hosts = []
+        else:
+            # split by comma, remove leading periods
+            self._no_proxy_hosts = [
+                h.lstrip(".") for h in no_proxy.replace(" ", "").split(",") if h
+            ]
+
+    def _get_proxy(self, scheme: str | None, host: str | None) -> str | None:
+        """Get a proxy url for scheme and host based on proxy env variables"""
+
+        if host is None:
+            # urllib3 only handles http/https but we can do something reasonable
+            # even for schemes that don't require host (like file)
+            return None
+
+        # does host match any of the "no_proxy" hosts?
+        for no_proxy_host in self._no_proxy_hosts:
+            # wildcard match, exact hostname match, or parent domain match
+            if no_proxy_host in ("*", host) or host.endswith(
+                f".{no_proxy_host}"
+            ):
+                return None
+
+        if scheme in self._proxies:
+            return self._proxies[scheme]
+        if self._all_proxy is not None:
+            return self._all_proxy
+
+        return None
+
+    def get_pool_manager(
+        self, scheme: str | None, host: str | None
+    ) -> PoolManager:
+        """Get a poolmanager for scheme and host.
+
+        Returns a ProxyManager if that is correct based on current proxy env
+        variables, otherwise returns a PoolManager
+        """
+
+        proxy = self._get_proxy(scheme, host)
+        if proxy not in self._pool_managers:
+            if proxy is None:
+                self._pool_managers[proxy] = PoolManager(**self._kw_args)
+            else:
+                self._pool_managers[proxy] = ProxyManager(
+                    proxy,
+                    **self._kw_args,
+                )
+
+        return self._pool_managers[proxy]
+
+    def request(
+        self,
+        method: str,
+        url: str,
+        **request_kw: Any,  # noqa: ANN401
+    ) -> BaseHTTPResponse:
+        """Make a request using a PoolManager chosen based on url and
+        proxy environment variables.
+        """
+        u = parse_url(url)
+        manager = self.get_pool_manager(u.scheme, u.host)
+        return manager.request(method, url, **request_kw)
diff --git a/tuf/ngclient/updater.py b/tuf/ngclient/updater.py
index 5af7cfe4..a40c1fca 100644
--- a/tuf/ngclient/updater.py
+++ b/tuf/ngclient/updater.py
@@ -36,6 +36,19 @@
 A simple example of using the Updater to implement a Python TUF client that
 downloads target files is available in `examples/client
 <https://github.com/theupdateframework/python-tuf/tree/develop/examples/client>`_.
+
+Notes on how Updater uses HTTP by default:
+  * urllib3 is the HTTP library
+  * Typically all requests are retried by urllib3 three times (in cases where
+    this seems useful)
+  * Operating system certificate store is used for TLS, in other words
+    ``certifi`` is not used as the certificate source
+  * Proxy use can be configured with ``https_proxy`` and other similar
+    environment variables
+
+All of the HTTP decisions can be changed with ``fetcher`` argument:
+Custom ``FetcherInterface`` implementations are possible. The alternative
+``RequestsFetcher`` implementation is also provided (although deprecated).
 """
 
 from __future__ import annotations
diff --git a/tuf/ngclient/urllib3_fetcher.py b/tuf/ngclient/urllib3_fetcher.py
index 5d4bb1cf..88d447bd 100644
--- a/tuf/ngclient/urllib3_fetcher.py
+++ b/tuf/ngclient/urllib3_fetcher.py
@@ -15,6 +15,7 @@
 
 import tuf
 from tuf.api import exceptions
+from tuf.ngclient._internal.proxy import ProxyEnvironment
 from tuf.ngclient.fetcher import FetcherInterface
 
 if TYPE_CHECKING:
@@ -49,7 +50,7 @@ def __init__(
         if app_user_agent is not None:
             ua = f"{app_user_agent} {ua}"
 
-        self._poolManager = urllib3.PoolManager(headers={"User-Agent": ua})
+        self._proxy_env = ProxyEnvironment(headers={"User-Agent": ua})
 
     def _fetch(self, url: str) -> Iterator[bytes]:
         """Fetch the contents of HTTP/HTTPS url from a remote server.
@@ -72,7 +73,7 @@ def _fetch(self, url: str) -> Iterator[bytes]:
         #  - connect timeout (max delay before first byte is received)
         #  - read (gap) timeout (max delay between bytes received)
         try:
-            response = self._poolManager.request(
+            response = self._proxy_env.request(
                 "GET",
                 url,
                 preload_content=False,


Test patch:
diff --git a/tests/test_proxy_environment.py b/tests/test_proxy_environment.py
new file mode 100644
index 00000000..ade7b350
--- /dev/null
+++ b/tests/test_proxy_environment.py
@@ -0,0 +1,217 @@
+# Copyright 2025, the TUF contributors
+# SPDX-License-Identifier: MIT OR Apache-2.0
+
+"""Test ngclient ProxyEnvironment"""
+
+from __future__ import annotations
+
+import sys
+import unittest
+from unittest.mock import Mock, patch
+
+from urllib3 import PoolManager, ProxyManager
+
+from tests import utils
+from tuf.ngclient._internal.proxy import ProxyEnvironment
+
+
+class TestProxyEnvironment(unittest.TestCase):
+    """Test ngclient ProxyEnvironment implementation
+
+    These tests use the ProxyEnvironment.get_pool_manager() endpoint and then
+    look at the ProxyEnvironment._poolmanagers dict keys to decide if the result
+    is correct.
+
+    The test environment is changed via mocking getproxies(): this is a urllib
+    method that returns a dict with the proxy environment variable contents.
+
+    Testing ProxyEnvironment.request() would possibly be better but far more
+    difficult: the current test implementation does not require actually setting up
+    all of the different proxies.
+    """
+
+    def assert_pool_managers(
+        self, env: ProxyEnvironment, expected: list[str | None]
+    ) -> None:
+        # Pool managers have the expected proxy urls
+        self.assertEqual(list(env._pool_managers.keys()), expected)
+
+        # Pool manager types are as expected
+        for proxy_url, pool_manager in env._pool_managers.items():
+            self.assertIsInstance(pool_manager, PoolManager)
+            if proxy_url is not None:
+                self.assertIsInstance(pool_manager, ProxyManager)
+
+    @patch("tuf.ngclient._internal.proxy.getproxies")
+    def test_no_variables(self, mock_getproxies: Mock) -> None:
+        mock_getproxies.return_value = {}
+
+        env = ProxyEnvironment()
+        env.get_pool_manager("http", "example.com")
+        env.get_pool_manager("https", "example.com")
+        env.get_pool_manager("https", "example.com")
+        env.get_pool_manager("https", "subdomain.example.com")
+        env.get_pool_manager("https", "differentsite.com")
+
+        # There is a single pool manager (no proxies)
+        self.assert_pool_managers(env, [None])
+
+    @patch("tuf.ngclient._internal.proxy.getproxies")
+    def test_proxy_set(self, mock_getproxies: Mock) -> None:
+        mock_getproxies.return_value = {
+            "https": "http://localhost:8888",
+        }
+
+        env = ProxyEnvironment()
+        env.get_pool_manager("http", "example.com")
+        env.get_pool_manager("https", "example.com")
+        env.get_pool_manager("https", "example.com")
+        env.get_pool_manager("https", "differentsite.com")
+
+        # There are two pool managers: A plain poolmanager and https proxymanager
+        self.assert_pool_managers(env, [None, "http://localhost:8888"])
+
+    @patch("tuf.ngclient._internal.proxy.getproxies")
+    def test_proxies_set(self, mock_getproxies: Mock) -> None:
+        mock_getproxies.return_value = {
+            "http": "http://localhost:8888",
+            "https": "http://localhost:9999",
+        }
+
+        env = ProxyEnvironment()
+        env.get_pool_manager("http", "example.com")
+        env.get_pool_manager("https", "example.com")
+        env.get_pool_manager("https", "example.com")
+        env.get_pool_manager("https", "subdomain.example.com")
+        env.get_pool_manager("https", "differentsite.com")
+
+        # There are two pool managers: A http proxymanager and https proxymanager
+        self.assert_pool_managers(
+            env, ["http://localhost:8888", "http://localhost:9999"]
+        )
+
+    @patch("tuf.ngclient._internal.proxy.getproxies")
+    def test_no_proxy_set(self, mock_getproxies: Mock) -> None:
+        mock_getproxies.return_value = {
+            "http": "http://localhost:8888",
+            "https": "http://localhost:9999",
+            "no": "somesite.com, example.com, another.site.com",
+        }
+
+        env = ProxyEnvironment()
+        env.get_pool_manager("http", "example.com")
+        env.get_pool_manager("https", "example.com")
+        env.get_pool_manager("https", "example.com")
+
+        # There is a single pool manager (no proxies)
+        self.assert_pool_managers(env, [None])
+
+        env.get_pool_manager("http", "differentsite.com")
+        env.get_pool_manager("https", "differentsite.com")
+
+        # There are three pool managers: plain poolmanager for no_proxy domains,
+        # http proxymanager and https proxymanager
+        self.assert_pool_managers(
+            env, [None, "http://localhost:8888", "http://localhost:9999"]
+        )
+
+    @patch("tuf.ngclient._internal.proxy.getproxies")
+    def test_no_proxy_subdomain_match(self, mock_getproxies: Mock) -> None:
+        mock_getproxies.return_value = {
+            "https": "http://localhost:9999",
+            "no": "somesite.com, example.com, another.site.com",
+        }
+
+        env = ProxyEnvironment()
+
+        # this should match example.com in no_proxy
+        env.get_pool_manager("https", "subdomain.example.com")
+
+        # There is a single pool manager (no proxies)
+        self.assert_pool_managers(env, [None])
+
+        # this should not match example.com in no_proxy
+        env.get_pool_manager("https", "xexample.com")
+
+        # There are two pool managers: plain poolmanager for no_proxy domains,
+        # and a https proxymanager
+        self.assert_pool_managers(env, [None, "http://localhost:9999"])
+
+    @patch("tuf.ngclient._internal.proxy.getproxies")
+    def test_no_proxy_wildcard(self, mock_getproxies: Mock) -> None:
+        mock_getproxies.return_value = {
+            "https": "http://localhost:8888",
+            "no": "*",
+        }
+
+        env = ProxyEnvironment()
+        env.get_pool_manager("https", "example.com")
+        env.get_pool_manager("https", "differentsite.com")
+        env.get_pool_manager("https", "subdomain.example.com")
+
+        # There is a single pool manager, no proxies
+        self.assert_pool_managers(env, [None])
+
+    @patch("tuf.ngclient._internal.proxy.getproxies")
+    def test_no_proxy_leading_dot(self, mock_getproxies: Mock) -> None:
+        mock_getproxies.return_value = {
+            "https": "http://localhost:8888",
+            "no": ".example.com",
+        }
+
+        env = ProxyEnvironment()
+        env.get_pool_manager("https", "example.com")
+        env.get_pool_manager("https", "subdomain.example.com")
+
+        # There is a single pool manager, no proxies
+        self.assert_pool_managers(env, [None])
+
+    @patch("tuf.ngclient._internal.proxy.getproxies")
+    def test_all_proxy_set(self, mock_getproxies: Mock) -> None:
+        mock_getproxies.return_value = {
+            "all": "http://localhost:8888",
+        }
+
+        env = ProxyEnvironment()
+        env.get_pool_manager("http", "example.com")
+        env.get_pool_manager("https", "example.com")
+        env.get_pool_manager("https", "example.com")
+        env.get_pool_manager("https", "subdomain.example.com")
+        env.get_pool_manager("https", "differentsite.com")
+
+        # There is a single proxy manager
+        self.assert_pool_managers(env, ["http://localhost:8888"])
+
+        # This urllib3 currently only handles http and https but let's test anyway
+        env.get_pool_manager("file", None)
+
+        # proxy manager and a plain pool manager
+        self.assert_pool_managers(env, ["http://localhost:8888", None])
+
+    @patch("tuf.ngclient._internal.proxy.getproxies")
+    def test_all_proxy_and_no_proxy_set(self, mock_getproxies: Mock) -> None:
+        mock_getproxies.return_value = {
+            "all": "http://localhost:8888",
+            "no": "somesite.com, example.com, another.site.com",
+        }
+
+        env = ProxyEnvironment()
+        env.get_pool_manager("http", "example.com")
+        env.get_pool_manager("https", "example.com")
+        env.get_pool_manager("https", "example.com")
+        env.get_pool_manager("https", "subdomain.example.com")
+
+        # There is a single pool manager (no proxies)
+        self.assert_pool_managers(env, [None])
+
+        env.get_pool_manager("http", "differentsite.com")
+        env.get_pool_manager("https", "differentsite.com")
+
+        # There are two pool managers: plain poolmanager for no_proxy domains and
+        # one proxymanager
+        self.assert_pool_managers(env, [None, "http://localhost:8888"])
+
+
+if __name__ == "__main__":
+    utils.configure_test_logging(sys.argv)
+    unittest.main()
diff --git a/tests/test_updater_ng.py b/tests/test_updater_ng.py
index b37003bb..50ef5ee3 100644
--- a/tests/test_updater_ng.py
+++ b/tests/test_updater_ng.py
@@ -331,8 +331,10 @@ def test_non_existing_target_file(self) -> None:
     def test_user_agent(self) -> None:
         # test default
         self.updater.refresh()
-        session = self.updater._fetcher._poolManager
-        ua = session.headers["User-Agent"]
+        poolmgr = self.updater._fetcher._proxy_env.get_pool_manager(
+            "http", "localhost"
+        )
+        ua = poolmgr.headers["User-Agent"]
         self.assertEqual(ua[:11], "python-tuf/")
 
         # test custom UA
@@ -344,8 +346,10 @@ def test_user_agent(self) -> None:
             config=UpdaterConfig(app_user_agent="MyApp/1.2.3"),
         )
         updater.refresh()
-        session = updater._fetcher._poolManager
-        ua = session.headers["User-Agent"]
+        poolmgr = updater._fetcher._proxy_env.get_pool_manager(
+            "http", "localhost"
+        )
+        ua = poolmgr.headers["User-Agent"]
 
         self.assertEqual(ua[:23], "MyApp/1.2.3 python-tuf/")