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Bug when temporary download path is exactly 255 characters long (Windows) #5486

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opened 2026-02-21 17:52:52 -05:00 by deekerman · 5 comments

deekerman commented

2026-02-21 17:52:52 -05:00

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Originally created by @bluikko on GitHub (Apr 30, 2017).

Please provide the following information

qBittorrent version and Operating System:

qBittorrent 3.3.12 x64, Windows 7 x64 fully updated

What is the problem:

If the download temporary path on NTFS is exactly 255 characters long (including the ".qb!" temporary file additional extension), qBittorrent fails to complete the download when the file reaches 100%. Instead an IO error is displayed and the torrent stalls.

What is the expected behavior:

After downloaded file reaches 100%, the temporary "unfinished" file with ".qb!" extension should be completed. Instead, qBittorrent gives an IO error with "The system cannot find the file specified".

Steps to reproduce:

Download a torrent that includes a file that when put to the "unfinished" folder has a pathname of exactly 255 characters, including the ".qb!" unfinished file extension. Wait until file reaches 100% and the file will get an IO error.

Extra info(if any):

Seems to be an edge case that was missed - issue #18 probably handles cases where the path length is longer than the maximum length and not the case where the path reaches exactly the maximum path length.

Originally created by @bluikko on GitHub (Apr 30, 2017). **Please provide the following information** ### qBittorrent version and Operating System: qBittorrent 3.3.12 x64, Windows 7 x64 fully updated ### What is the problem: If the download temporary path on NTFS is *exactly* 255 characters long (including the ".qb!" temporary file additional extension), qBittorrent fails to complete the download when the file reaches 100%. Instead an IO error is displayed and the torrent stalls. ### What is the expected behavior: After downloaded file reaches 100%, the temporary "unfinished" file with ".qb!" extension should be completed. Instead, qBittorrent gives an IO error with "The system cannot find the file specified". ### Steps to reproduce: Download a torrent that includes a file that when put to the "unfinished" folder has a pathname of exactly 255 characters, including the ".qb!" unfinished file extension. Wait until file reaches 100% and the file will get an IO error. ### Extra info(if any): Seems to be an edge case that was missed - issue #18 probably handles cases where the path length is *longer* than the maximum length and not the case where the path reaches exactly the maximum path length.

deekerman

2026-02-21 17:52:52 -05:00

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OS: Windows
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deekerman commented

2026-02-21 17:52:59 -05:00

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@arvidn commented on GitHub (Apr 30, 2017):

the 255 character restriction applies to each individual path element, right? libtorrent uses UNC paths which are supposed to extend the limit of the full path to 32k characters, but you're right that there may still be logic to make sure each individual name in the path does not exceed 255.

@arvidn commented on GitHub (Apr 30, 2017): the 255 character restriction applies to each individual path element, right? libtorrent uses UNC paths which are supposed to extend the limit of the full path to 32k characters, but you're right that there may still be logic to make sure each individual name in the path does not exceed 255.

deekerman commented

2026-02-21 17:52:59 -05:00

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@arvidn commented on GitHub (Apr 30, 2017):

actually, the current logic (when loading .torrent files) is to truncate directory names with long names to avoid this problem. The current limit is 240 characters (+ file extension).

https://github.com/arvidn/libtorrent/blob/RC_1_1/src/torrent_info.cpp#L340

Can you tell whether this logic triggers?

@arvidn commented on GitHub (Apr 30, 2017): actually, the current logic (when loading .torrent files) is to truncate directory names with long names to avoid this problem. The current limit is 240 characters (+ file extension). https://github.com/arvidn/libtorrent/blob/RC_1_1/src/torrent_info.cpp#L340 Can you tell whether this logic triggers?

deekerman commented

2026-02-21 17:52:59 -05:00

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@bluikko commented on GitHub (Apr 30, 2017):

The issue I am having is for path that is exactly 255 characters long total, including drive, path to unfinished downloads, torrent directory and filename, plus the ".qb!" extension of unfinished download file. Example:
d:\torrent\unfinished\torrent_with_long_path\torrent_with_long_file....ext.qb!
The whole above path is 255 characters long.

@bluikko commented on GitHub (Apr 30, 2017): The issue I am having is for path that is exactly 255 characters long total, including drive, path to unfinished downloads, torrent directory and filename, plus the ".qb!" extension of unfinished download file. Example: d:\torrent\unfinished\torrent_with_long_path\torrent_with_long_file....ext.qb! The whole above path is 255 characters long.

deekerman commented

2026-02-21 17:52:59 -05:00

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@arvidn commented on GitHub (Apr 30, 2017):

I see, so perhaps libtorrent makes sure that it won't produce longer filenames, but once qBT appends its extension it exceeds the limit. Perhaps libtorrent should leave some margin

@arvidn commented on GitHub (Apr 30, 2017): I see, so perhaps libtorrent makes sure that it won't produce longer filenames, but once qBT appends its extension it exceeds the limit. Perhaps libtorrent should leave some margin

deekerman commented

2026-02-21 17:52:59 -05:00

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@FranciscoPombal commented on GitHub (Mar 22, 2020):

Should be fixed by https://github.com/qbittorrent/qBittorrent/pull/12154, which will land in 4.2.2. Open a new issue report if you experience the same problem with that version.

@FranciscoPombal commented on GitHub (Mar 22, 2020): Should be fixed by https://github.com/qbittorrent/qBittorrent/pull/12154, which will land in 4.2.2. Open a new issue report if you experience the same problem with that version.