Handle massive values in Retry-After when calculating time to sleep for (#3743)

meeb · web-flow · commit 13f0bfd55e44 · 2025-12-29T19:41:41.000+02:00
diff --git a/changelog/3743.bugfix.rst b/changelog/3743.bugfix.rst
@@ -0,0 +1 @@
+Started treating ``Retry-After`` times greater than 6 hours as 6 hours by default.
diff --git a/src/urllib3/util/retry.py b/src/urllib3/util/retry.py
@@ -178,6 +178,11 @@ class Retry:
         Sequence of headers to remove from the request when a response
         indicating a redirect is returned before firing off the redirected
         request.
+
+    :param int retry_after_max: Number of seconds to allow as the maximum for
+        Retry-After headers. Defaults to :attr:`Retry.DEFAULT_RETRY_AFTER_MAX`.
+        Any Retry-After headers larger than this value will be limited to this
+        value.
     """
 
     #: Default methods to be used for ``allowed_methods``
@@ -196,6 +201,10 @@ class Retry:
     #: Default maximum backoff time.
     DEFAULT_BACKOFF_MAX = 120
 
+    # This is undocumented in the RFC. Setting to 6 hours matches other popular libraries.
+    #: Default maximum allowed value for Retry-After headers in seconds
+    DEFAULT_RETRY_AFTER_MAX: typing.Final[int] = 21600
+
     # Backward compatibility; assigned outside of the class.
     DEFAULT: typing.ClassVar[Retry]
 
@@ -219,6 +228,7 @@ def __init__(
             str
         ] = DEFAULT_REMOVE_HEADERS_ON_REDIRECT,
         backoff_jitter: float = 0.0,
+        retry_after_max: int = DEFAULT_RETRY_AFTER_MAX,
     ) -> None:
         self.total = total
         self.connect = connect
@@ -235,6 +245,7 @@ def __init__(
         self.allowed_methods = allowed_methods
         self.backoff_factor = backoff_factor
         self.backoff_max = backoff_max
+        self.retry_after_max = retry_after_max
         self.raise_on_redirect = raise_on_redirect
         self.raise_on_status = raise_on_status
         self.history = history or ()
@@ -256,6 +267,7 @@ def new(self, **kw: typing.Any) -> Self:
             status_forcelist=self.status_forcelist,
             backoff_factor=self.backoff_factor,
             backoff_max=self.backoff_max,
+            retry_after_max=self.retry_after_max,
             raise_on_redirect=self.raise_on_redirect,
             raise_on_status=self.raise_on_status,
             history=self.history,
@@ -320,6 +332,10 @@ def parse_retry_after(self, retry_after: str) -> float:
 
         seconds = max(seconds, 0)
 
+        # Check the seconds do not exceed the specified maximum
+        if seconds > self.retry_after_max:
+            seconds = self.retry_after_max
+
         return seconds
 
     def get_retry_after(self, response: BaseHTTPResponse) -> float | None:
diff --git a/test/test_retry.py b/test/test_retry.py
@@ -181,6 +181,18 @@ def test_configurable_backoff_max(self) -> None:
         retry = retry.increment(method="GET")
         assert retry.get_backoff_time() == max_backoff
 
+    def test_configurable_retry_after_max(self) -> None:
+        """Configurable retry after is computed correctly"""
+        max_retry_after = Retry.DEFAULT_RETRY_AFTER_MAX
+
+        retry = Retry()
+        assert retry.parse_retry_after(str(max_retry_after)) == max_retry_after
+        assert retry.parse_retry_after(str(max_retry_after + 1)) == max_retry_after
+
+        retry = Retry(retry_after_max=1)
+        assert retry.parse_retry_after(str(1)) == 1
+        assert retry.parse_retry_after(str(2)) == 1
+
     def test_backoff_jitter(self) -> None:
         """Backoff with jitter is computed correctly"""
         max_backoff = 1

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	+Started treating ``Retry-After`` times greater than 6 hours as 6 hours by default.