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`Base64Decoder` raises `DecodeError` on line-wrapped (MIME-style) base64

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@prudhvi1709 已经在做这个了。

开始于 2026年10月18日。

  • #341 来自 @prudhvi1709 —— 未关闭

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难度
2/5
预计耗时
1-3 小时
新手友好度
25/100
Issue 类型
缺陷
描述清晰度
描述清楚
活跃度
停滞
技术栈
python
领域
api

调研方向

Start by reading Base64Decoder.write() and reproduce the failure with the provided CRLF example, then try split writes and base64.encodebytes data in small chunks. A regression test should show that MIME-wrapped input decodes to the expected bytes regardless of line breaks or chunk boundaries; pull request #341 already submits a fix.

由索引模型根据 Issue 内容生成。

描述

Base64Decoder.write() slices the input to a multiple of 4 bytes before decoding, but it counts line breaks and spaces as base64 characters. Standard base64 as used in MIME (RFC 2045) is wrapped with CRLF or LF, so any quartet that straddles a line break is miscounted and decoding fails. The result also depends on how the stream is chunked.

Reproduction
from io import BytesIO
from python_multipart.decoders import Base64Decoder

out = BytesIO()
d = Base64Decoder(out)
d.write(b"Zm9v\r\nYmFy")   # DecodeError
d.finalize()

Expected: b"foobar", which is what base64.b64decode(b"Zm9v\r\nYmFy") returns.

Split writes fail the same way:

d.write(b"Zm9v\r")
d.write(b"\nYmFy")         # DecodeError

base64.encodebytes(bytes(range(200))) (76-character lines) written in chunks of 10, 7 or 1 bytes also raises DecodeError.

Cause

write() computes decode_len = (len(data) // 4) * 4 on data that still contains \r, \n, space and tab. b64decode() then discards those bytes (it is not called with validate=True), leaving a slice that is not a multiple of 4, and raises "Incorrect padding".

Version: python-multipart 0.0.32, main at 51ff1a4, Python 3.13.

Fix

A fix with a regression test is submitted in #341.

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