From f733258ed9e5e71b7b97511f5654efd6799cac46 Mon Sep 17 00:00:00 2001
From: vivodi <103735539+vivodi@users.noreply.github.com>
Date: Mon, 2 Dec 2024 22:32:24 +0800
Subject: [PATCH] Support absolute url to override base url (#10074)
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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: 🇺🇦 Sviatoslav Sydorenko (Святослав Сидоренко) <wk.cvs.github@sydorenko.org.ua>
---
 CHANGES/10074.feature.rst    |  2 ++
 CONTRIBUTORS.txt             |  1 +
 aiohttp/client.py            |  6 ++----
 docs/client_reference.rst    |  4 ++++
 tests/test_client_session.py | 18 ++++++++++++++++++
 5 files changed, 27 insertions(+), 4 deletions(-)
 create mode 100644 CHANGES/10074.feature.rst

diff --git a/CHANGES/10074.feature.rst b/CHANGES/10074.feature.rst
new file mode 100644
index 00000000000..d956c38af57
--- /dev/null
+++ b/CHANGES/10074.feature.rst
@@ -0,0 +1,2 @@
+Added support for overriding the base URL with an absolute one in client sessions
+-- by :user:`vivodi`.
diff --git a/CONTRIBUTORS.txt b/CONTRIBUTORS.txt
index 5d5f922e6fb..66c706cde4f 100644
--- a/CONTRIBUTORS.txt
+++ b/CONTRIBUTORS.txt
@@ -54,6 +54,7 @@ Arseny Timoniq
 Artem Yushkovskiy
 Arthur Darcet
 Austin Scola
+Bai Haoran
 Ben Bader
 Ben Greiner
 Ben Kallus
diff --git a/aiohttp/client.py b/aiohttp/client.py
index 16c8c749ea0..bc6c0aaaa5d 100644
--- a/aiohttp/client.py
+++ b/aiohttp/client.py
@@ -414,11 +414,9 @@ def request(
 
     def _build_url(self, str_or_url: StrOrURL) -> URL:
         url = URL(str_or_url)
-        if self._base_url is None:
-            return url
-        else:
-            assert not url.absolute
+        if self._base_url and not url.absolute:
             return self._base_url.join(url)
+        return url
 
     async def _request(
         self,
diff --git a/docs/client_reference.rst b/docs/client_reference.rst
index 937e5e8afbb..9a76bfbd14b 100644
--- a/docs/client_reference.rst
+++ b/docs/client_reference.rst
@@ -79,6 +79,10 @@ The client session supports the context manager protocol for self closing.
 
       .. versionadded:: 3.8
 
+      .. versionchanged:: 3.12
+
+         Added support for overriding the base URL with an absolute one in client sessions.
+
    :param aiohttp.BaseConnector connector: BaseConnector
       sub-class instance to support connection pooling.
 
diff --git a/tests/test_client_session.py b/tests/test_client_session.py
index 8ea0ed6c345..1c40505e9e2 100644
--- a/tests/test_client_session.py
+++ b/tests/test_client_session.py
@@ -1140,6 +1140,24 @@ async def test_requote_redirect_url_default_disable() -> None:
             URL("http://example.com/test1/test2?q=foo#bar"),
             id="base_url=URL('http://example.com/test1/') url='test2?q=foo#bar'",
         ),
+        pytest.param(
+            URL("http://example.com/test1/"),
+            "http://foo.com/bar",
+            URL("http://foo.com/bar"),
+            id="base_url=URL('http://example.com/test1/') url='http://foo.com/bar'",
+        ),
+        pytest.param(
+            URL("http://example.com"),
+            "http://foo.com/bar",
+            URL("http://foo.com/bar"),
+            id="base_url=URL('http://example.com') url='http://foo.com/bar'",
+        ),
+        pytest.param(
+            URL("http://example.com/test1/"),
+            "http://foo.com",
+            URL("http://foo.com"),
+            id="base_url=URL('http://example.com/test1/') url='http://foo.com'",
+        ),
     ],
 )
 async def test_build_url_returns_expected_url(