[poofeg]

Same goal as #102, but without the _OleStreamReader workaround: this version relies on the lazy OleStream from olefile (decalage2/olefile#177), so OOXMLFile.decrypt() reads EncryptedPackage directly via openstream().

Closes #101

Problem

OOXMLFile.decrypt() materialized the entire decrypted OOXML package in memory and copied it several times: the agile/standard decrypt methods accumulated output in a BytesIO and returned a second copy, and the result was copied again into a BytesIO just to run zipfile.is_zipfile. Peak RSS was ~4–5× the input size.

Changes

• msoffcrypto/method/ecma376_agile.py: extracted the 4096-byte segment loop into a streaming generator decrypt_stream(...); decrypt(...) remains as a thin b"".join(...) wrapper (public API unchanged).
• msoffcrypto/method/ecma376_standard.py: added decrypt_stream(...) feeding AES-ECB incrementally in chunks and yielding exactly totalSize plaintext bytes; decrypt(...) unchanged.
• msoffcrypto/format/ooxml.py: OOXMLFile.decrypt() streams decrypted bytes to outfile chunk-by-chunk; the post-decryption check now validates only the end-of-central-directory record in the last 65,557 bytes (_is_zipfile_tail) instead of zipfile.is_zipfile(io.BytesIO(obuf)), so no full-payload copy is made. Same InvalidKeyError on failure.
• tests/test_ooxml_streaming.py: streaming output is byte-identical to the buffered decrypt(), works with a non-seekable output, and a wrong password still raises InvalidKeyError.

Compatibility note

This version intentionally omits the _OleStreamReader workaround from #102 and expects the lazy OleStream from decalage2/olefile#177 (currently unreleased). Once that lands, the minimum olefile version in pyproject.toml should be bumped accordingly. Until then, users on released olefile (0.47) will still get the eagerly buffered stream — use #102 for a fix that works with any olefile version.

Public API is unchanged: OOXMLFile.decrypt(outfile), OfficeFile.decrypt(outfile) and the method-level decrypt() keep their signatures.

Tests

pytest → 29 passed.

Memory

Measured with /usr/bin/time -l on a 1.79 GB agile-encrypted .ppsx:

• before: ~4.95 GiB peak RSS
• after: ~0.88 GiB peak RSS

The remaining ~0.88 GiB comes from olefile.OleFileIO.__init__ parsing the OLE structure (loadfat building the FAT with array + array), which is fixed separately in decalage2/olefile#176.