aiohttp 3.13.4

on Python PyPI

Features

• Added max_headers parameter to limit the number of headers that should be read from a response -- by :user:Dreamsorcerer.

  Related issues and pull requests on GitHub:
  #11955.

• Added a dns_cache_max_size parameter to TCPConnector to limit the size of the cache -- by :user:Dreamsorcerer.

  Related issues and pull requests on GitHub:
  #12106.

Bug fixes

• Fixed server hanging indefinitely when chunked transfer encoding chunk-size
  does not match actual data length. The server now raises
  TransferEncodingError instead of waiting forever for data that will
  never arrive -- by :user:Fridayai700.

  Related issues and pull requests on GitHub:
  #10596.

• Fixed access log timestamps ignoring daylight saving time (DST) changes. The
  previous implementation used :py:data:time.timezone which is a constant and
  does not reflect DST transitions -- by :user:nightcityblade.

  Related issues and pull requests on GitHub:
  #11283.

• Fixed RuntimeError: An event loop is running error when using aiohttp.GunicornWebWorker
  or aiohttp.GunicornUVLoopWebWorker on Python >=3.14.
  -- by :user:Tasssadar.

  Related issues and pull requests on GitHub:
  #11701.

• Fixed :exc:ValueError when creating a TLS connection with ClientTimeout(total=0) by converting 0 to None before passing to ssl_handshake_timeout in :py:meth:asyncio.loop.start_tls -- by :user:veeceey.

  Related issues and pull requests on GitHub:
  #11859.

• Restored :py:meth:~aiohttp.BodyPartReader.decode as a synchronous method
  for backward compatibility. The method was inadvertently changed to async
  in 3.13.3 as part of the decompression bomb security fix. A new
  :py:meth:~aiohttp.BodyPartReader.decode_iter method is now available
  for non-blocking decompression of large payloads using an async generator.
  Internal aiohttp code uses the async variant to maintain security protections.

  Changed multipart processing chunk sizes from 64 KiB to 256KiB, to better
  match aiohttp internals
  -- by :user:bdraco and :user:Dreamsorcerer.

  Related issues and pull requests on GitHub:
  #11898.

• Fixed false-positive :py:class:DeprecationWarning for passing enable_cleanup_closed=True to :py:class:~aiohttp.TCPConnector specifically on Python 3.12.7.
  -- by :user:Robsdedude.

  Related issues and pull requests on GitHub:
  #11972.

• Fixed _sendfile_fallback over-reading beyond requested count -- by :user:bysiber.

  Related issues and pull requests on GitHub:
  #12096.

• Fixed digest auth dropping challenge fields with empty string values -- by :user:bysiber.

  Related issues and pull requests on GitHub:
  #12097.

• ClientConnectorCertificateError.os_error no longer raises :exc:AttributeError
  -- by :user:themylogin.

  Related issues and pull requests on GitHub:
  #12136.

• Adjusted pure-Python request header value validation to align with RFC 9110 control-character handling, while preserving lax response parser behavior, and added regression tests for Host/header control-character cases.
  -- by :user:rodrigobnogueira.

  Related issues and pull requests on GitHub:
  #12231.

• Rejected duplicate singleton headers (Host, Content-Type,
  Content-Length, etc.) in the C extension HTTP parser to match
  the pure Python parser behaviour, preventing potential host-based
  access control bypasses via parser differentials
  -- by :user:rodrigobnogueira.

  Related issues and pull requests on GitHub:
  #12240.

• Aligned the pure-Python HTTP request parser with the C parser by splitting
  comma-separated and repeated Connection header values for keep-alive,
  close, and upgrade handling -- by :user:rodrigobnogueira.

  Related issues and pull requests on GitHub:
  #12249.

Improved documentation

• Documented :exc:asyncio.TimeoutError for WebSocketResponse.receive()
  and related methods -- by :user:veeceey.

  Related issues and pull requests on GitHub:
  #12042.

Packaging updates and notes for downstreams

• Upgraded llhttp to 3.9.1 -- by :user:Dreamsorcerer.

  Related issues and pull requests on GitHub:
  #12069.

Contributor-facing changes

• The benchmark CI job now runs only in the upstream repository -- by :user:Cycloctane.

  It used to always fail in forks, which this change fixed.

  Related issues and pull requests on GitHub:
  #11737.

• Fixed flaky performance tests by using appropriate fixed thresholds that account for CI variability -- by :user:rodrigobnogueira.

  Related issues and pull requests on GitHub:
  #11992.

Miscellaneous internal changes

• Fixed test_invalid_idna to work with idna 3.11 by using an invalid character (\u0080) that is rejected by yarl during URL construction -- by :user:rodrigobnogueira.

  Related issues and pull requests on GitHub:
  #12027.

• Fixed race condition in test_data_file on Python 3.14 free-threaded builds -- by :user:rodrigobnogueira.

  Related issues and pull requests on GitHub:
  #12170.