René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Email MIME `base64` parser stops at the end of the first padding","articleBody":"# Bug report\n\n### Bug description:\n\nHi Cpython Developers,\n\nI was testing and comparing different email parsers, and found a parsing discrepancy that seems to be a problem.\n```\nMIME-Version: 1.0\nContent-Type: application/zip\nContent-Disposition: attachment; filename=archive.zip\nContent-Transfer-Encoding: base64\n\nUEsDBBQAAAAIAA==\nemVkIGZpbGUgY29udGVudA==\n```\nWith the [python's email get_payload method](https://github.com/python/cpython/blob/5d64571b43bc75b2971af6aa046dfba64fb43ef8/Lib/email/message.py#L243), the return content would stopped at the first \"==\" as it seems to be the default behavior of `base64.b64decode`.\nMeanwhile, peer implementations (e.g. **apache.commons.mal (java)**, **MimeKit (c#)**, **PhpMimeMailParser (php)**) will return the whole content.\n\nBelow is an running example in python.\n```python\nimport base64\nimport email\n\n\"\"\"\n  Parsing the mime format\n\"\"\"\nrequest = \"\"\"MIME-Version: 1.0\nContent-Type: application/zip\nContent-Disposition: attachment; filename=archive.zip\nContent-Transfer-Encoding: base64\n\nUEsDBBQAAAAIAA==\nemVkIGZpbGUgY29udGVudA==\n\"\"\"\nmsg = email.message_from_string(request)\nprint(\"Part content:\", repr(msg.get_payload(decode=True)))\nprint()\n\n\"\"\"\n  Examples of base64\n\"\"\"\ncontents = [\n        \"UEsDBBQAAAAIAA==\\nemVkIGZpbGUgY29udGVudA==\",\n        \"UEsDBBQAAAAIAA==emVkIGZpbGUgY29udGVudA==\",\n        \"UEsDBBQAAAAIAA=emVkIGZpbGUgY29udGVudA==\",\n        \"UEsDBBQAAAAIAAemVkIGZpbGUgY29udGVudA==\",\n        \"UEsDBBQAAAAIAA==\",\n        \"emVkIGZpbGUgY29udGVudA==\"\n        ]\nfor content in contents:\n    decoded_bytes = base64.b64decode(content)\n    print(repr(content), \" -\u003e\")\n    print(\"  \", decoded_bytes)\n```\n\nOutput:\n```\nPart content: b'PK\\x03\\x04\\x14\\x00\\x00\\x00\\x08\\x00'\n\n'UEsDBBQAAAAIAA==\\nemVkIGZpbGUgY29udGVudA=='  -\u003e\n   b'PK\\x03\\x04\\x14\\x00\\x00\\x00\\x08\\x00'\n'UEsDBBQAAAAIAA==emVkIGZpbGUgY29udGVudA=='  -\u003e\n   b'PK\\x03\\x04\\x14\\x00\\x00\\x00\\x08\\x00'\n'UEsDBBQAAAAIAA=emVkIGZpbGUgY29udGVudA=='  -\u003e\n   b'PK\\x03\\x04\\x14\\x00\\x00\\x00\\x08\\x00\\x07\\xa6VB\\x06f\\x96\\xc6R\\x066\\xf6\\xe7FV\\xe7@'\n'UEsDBBQAAAAIAAemVkIGZpbGUgY29udGVudA=='  -\u003e\n   b'PK\\x03\\x04\\x14\\x00\\x00\\x00\\x08\\x00\\x07\\xa6VB\\x06f\\x96\\xc6R\\x066\\xf6\\xe7FV\\xe7@'\n'UEsDBBQAAAAIAA=='  -\u003e\n   b'PK\\x03\\x04\\x14\\x00\\x00\\x00\\x08\\x00'\n'emVkIGZpbGUgY29udGVudA=='  -\u003e\n   b'zed file content'\n```\n\n\nThank you,\nWei-Cheng\n\n\n### CPython versions tested on:\n\n3.15\n\n### Operating systems tested on:\n\nLinux","author":{"url":"https://github.com/spencerwuwu","@type":"Person","name":"spencerwuwu"},"datePublished":"2025-08-12T18:59:36.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":6},"url":"https://github.com/137687/cpython/issues/137687"}