Discussion: Resolving DLL Import Errors for libtorrent on Windows

[a-sajjad72]

Background

There are multiple open issues in the repository regarding DLL import errors on Windows when using the Python bindings. These errors primarily arise due to missing OpenSSL DLLs (libcrypto-1_1-x64.dll and libssl-1_1-x64.dll) or incorrect side-by-side configuration.

Current Issues

Below are the related issues:

• ImportError: DLL load failed while importing libtorrent: #7920
• ImportError: DLL load failed while importing libtorrent #7338
• Python 3.10 - ImportError: DLL load failed while importing libtorrent: The specified module could not be found. #6689

Proposal

This discussion aims to resolve these errors systematically by evaluating possible approaches:

1. Bundling OpenSSL DLLs in the libtorrent Wheel

• Include libcrypto-1_1-x64.dll and libssl-1_1-x64.dll in the Windows wheel package.
• Users can install the wheel without needing to manage DLLs manually.
• Pros: Simple for users.
• Cons: Larger wheel size, requires regular updates for security.

2. Requiring a Separate Wheel for OpenSSL

• Create a new wheel package (libtorrent-openssl or libtorrent-windows-dll) that installs the required DLLs alongside libtorrent.
• Notably, in Issue #7338, a user mentioned creating a custom wheel package (libtorrent-windows-dll) to address this problem. This package contained the missing DLLs and placed them next to the .pyd file in site-packages/libtorrent. A similar approach could be formalized to ensure seamless installation.
• Automatically install this dependency when installing libtorrent.
• Pros: Keeps libtorrent lightweight, DLLs are managed separately.
• Cons: Adds complexity and requires coordination between the two packages.

3. Static Linking of OpenSSL Libraries

• Build the libtorrent wheel with statically linked OpenSSL libraries.
• Pros: No runtime DLL dependency.
• Cons: Larger binary size, harder to update OpenSSL for security.

4. Dynamic Download of DLLs

• Modify the libtorrent wheel to download the required DLLs at runtime if missing.
• Pros: Keeps the wheel lightweight, always fetches the latest DLLs.
• Cons: Requires internet access and adds runtime complexity.

5. Improved Documentation

• Update installation instructions to clearly explain how to install and configure OpenSSL manually on Windows.
• Pros: Simple for maintainers.
• Cons: Leaves the burden on users.

Workarounds

Until a permanent solution is implemented, users can resolve the DLL import errors with the following workarounds:

Option 1: Place DLLs in System32 (default PATH location)

• Download the required DLLs (libcrypto-1_1-x64.dll and libssl-1_1-x64.dll) from a trusted source, such as the official OpenSSL binaries.
• Copy these DLLs to C:\\Windows\\System32, which is included in the PATH by default.

Option 2: Place DLLs next to the .pyd

• Locate the libtorrent.cpXXX-win_amd64.pyd file in your site-packages/libtorrent directory (e.g., C:\\Python310\\Lib\\site-packages\\libtorrent).
• Download the required DLLs and place them in the same directory as the .pyd file.

These workarounds should resolve the import errors until a more seamless solution is provided.

Call to Action

We invite feedback from the community and the maintainers, especially @arvidn @AllSeeingEyeTolledEweSew and @baseplate-admin, on which approach to pursue. Let us collaboratively decide the best way to resolve these recurring DLL import errors.