pem.unarmor very poor performance

[James-E-A]

The attached test file (a Classic McEliece keypair, which includes a 1MiB public key, encoded per RFC5958+RFC7468) takes around 7 seconds to unarmor with asn1crypto. (Tested on asn1crypto version 1.5.1 .)

Path.read_bytes() takes only an instant, as (crucially) does OneAsymmetricKey.load()*; it's only the asn1crypto.pem.unarmor() step that takes an eternity.

I haven't done any Fancy Intra-Function Profiling yet, but the looped += byte construction here looks extremely painful.

Three solutions come immediately to mind:

• Leave the code 99% as-is, just use base64_data = bytearray as a band-aid since it's got an optimized mutating __iadd__
• Factor the body line loop out, and use b''.join() on a generator
• Refactor the code to actually stream the body into base64.decode(), probably by duck typing

Of these, the second seems like an immediately reasonable choice, at least while "objects that don't even fit into RAM" still isn't on the table.

Would you be interested in a pull request, or is this something you are going to fix yourself?

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*My own derivative of asn1crypto.keys.PrivateKeyInfo that's been updated to 'v2'; it's not directly relevant to this bug report, except I wanted to emphasize that according to time.perf_counter() the DER decoding is not the weak link.

3e-07 Moving key into RAM with Path.read_bytes()...
0.057328 Done.
0.0896701 Unarmoring key with pem.unarmor()...
7.0062617 Done.
7.0573913 Loading key with OneAsymmetricKey.load()...
7.0779615 Done.