| msg338061 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) *  |
Date: 2019-03-16 08:06 |
| There is a flaw in PyUnicode_DecodeCodePageStateful() (exposed as _codecs.code_page_decode() at Python level). Since MultiByteToWideChar() takes the size of the input as C int, it can not be used for decoding more than 2 GiB. Large input is split on chunks of size 2 GiB which are decoded separately. The problem is if it split in the middle of a multibyte character. In this case decoding chunks will always fail or replace incomplete parts of the multibyte character at both ends with what the error handler returns. It is hard to reproduce this bug, because you need to decode more than 2 GiB, and you will need at least 14 GiB of RAM for this (maybe more). |
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| msg338626 - (view) |
Author: Terry J. Reedy (terry.reedy) * |
Date: 2019-03-22 23:30 |
| I have 24G if all working and would be willing to try to run a test case. |
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| msg348921 - (view) |
Author: Steve Dower (steve.dower) * |
Date: 2019-08-02 21:34 |
| If we reduce our chunk size below INT_MAX, then we avoid the issue entirely. Our logic for hitting the middle of a multibyte character is fine (perhaps fixed since this issue was opened?), there's just a weird edge case at 2 GiB in the API call. As a bonus, smaller chunks seems to have a performance benefit too. It seems like INT_MAX/4 is the sweet spot - it took about a quarter of the time for my 2GiB test case as INT_MAX (and we're measuring in tens of seconds here, so I'm pretty comfortable with the direction of the result). INT_MAX/2 and INT_MAX/8 were both slower than INT_MAX/4. |
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| msg350131 - (view) |
Author: Steve Dower (steve.dower) * |
Date: 2019-08-21 23:22 |
| New changeset 7ebdda0dbee7df6f0c945a7e1e623e47676e112d by Steve Dower in branch 'master': bpo-36311: Fixes decoding multibyte characters around chunk boundaries and improves decoding performance (GH-15083) https://github.com/python/cpython/commit/7ebdda0dbee7df6f0c945a7e1e623e47676e112d |
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| msg350133 - (view) |
Author: Steve Dower (steve.dower) * |
Date: 2019-08-21 23:29 |
| I'll get the 3.7 and 3.8 backports merged - looks like they're trivial. Going to need some help with the 2.7 backport, but I'm happy to approve a PR. |
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| msg350136 - (view) |
Author: miss-islington (miss-islington) |
Date: 2019-08-21 23:53 |
| New changeset f93c15aedc2ea2cb8b56fc9dbb0d412918992e86 by Miss Islington (bot) in branch '3.8': bpo-36311: Fixes decoding multibyte characters around chunk boundaries and improves decoding performance (GH-15083) https://github.com/python/cpython/commit/f93c15aedc2ea2cb8b56fc9dbb0d412918992e86 |
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| msg350137 - (view) |
Author: miss-islington (miss-islington) |
Date: 2019-08-21 23:56 |
| New changeset 735a960ac98cf414caf910565220ab2761fa542a by Miss Islington (bot) in branch '3.7': bpo-36311: Fixes decoding multibyte characters around chunk boundaries and improves decoding performance (GH-15083) https://github.com/python/cpython/commit/735a960ac98cf414caf910565220ab2761fa542a |
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| msg351391 - (view) |
Author: Steve Dower (steve.dower) * |
Date: 2019-09-09 09:53 |
| Declaring this out-of-scope for 2.7, unless someone wants to insist (and provide a PR). |
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