python · gpshead · Apr 21, 2025 · Jul 23, 2024 · Jul 23, 2024 · Aug 1, 2024
@@ -272,7 +272,10 @@ a file or file-like object.
   *fileobj* must be a file-like object opened for reading in binary mode.
   It accepts file objects from  builtin :func:`open`, :class:`~io.BytesIO`
   instances, SocketIO objects from :meth:`socket.socket.makefile`, and
-   similar. The function may bypass Python's I/O and use the file descriptor
+   similar. *fileobj* must be opened in blocking mode, otherwise a
+   :exc:`BlockingIOError` may be raised.
+
+   The function may bypass Python's I/O and use the file descriptor
   from :meth:`~io.IOBase.fileno` directly. *fileobj* must be assumed to be
   in an unknown state after this function returns or raises. It is up to
   the caller to close *fileobj*.
@@ -301,6 +304,10 @@ a file or file-like object.

   .. versionadded:: 3.11

+   .. versionchanged:: next
+      Now raises a :exc:`BlockingIOError` if the file is opened in blocking
+      mode. Previously, spurious null bytes were added to the digest.
+

 Key derivation
 --------------

@@ -231,6 +231,8 @@ def file_digest(fileobj, digest, /, *, _bufsize=2**18):
    view = memoryview(buf)
    while True:
        size = fileobj.readinto(buf)
+        if size is None:
+            raise BlockingIOError("I/O operation would block.")
        if size == 0:
            break  # EOF
        digestobj.update(view[:size])

@@ -1199,6 +1199,15 @@ def test_file_digest(self):
        with self.assertRaises(ValueError):
            hashlib.file_digest(None, "sha256")

+        class NonBlocking:
+            def readinto(self, buf):
+                return None
+            def readable(self):
+                return True
+
+        with self.assertRaises(BlockingIOError):
+            hashlib.file_digest(NonBlocking(), hashlib.sha256)
+

 if __name__ == "__main__":
    unittest.main()
diff --git a/Misc/NEWS.d/next/Library/2024-07-23-17-08-41.gh-issue-122179.0jZm9h.rst b/Misc/NEWS.d/next/Library/2024-07-23-17-08-41.gh-issue-122179.0jZm9h.rst
@@ -0,0 +1,3 @@
+:func:`hashlib.file_digest` now raises :exc:`BlockingIOError` when no data
+is available during non-blocking I/O. Before, it added spurious null bytes
+to the digest.