DllNotFoundException on Linux with .NET 8 even when libleptonica-1.82.0.so exists

[Tojan-Naiem]

When running on Linux (Ubuntu) with .NET8 and the Tesseract NuGet
(wrapper from charlesw/tesseract), I get:

System.DllNotFoundException: Failed to find library "libleptonica-1.82.0.so" for platform x64.

Even when:

• libleptonica-1.82.0.so is placed in runtimes/linux-x64/native/
• NativeLibrary.Load is called manually before TesseractEngine

This seems to be caused by InteropDotNet loader not finding the .so
in expected runtime paths, nor following symlinks or preloaded libs.

Worked around by using external tesseract CLI instead.

[SlavomirDev]

I also caught this error when I was running the backend in docker containers. However, my container was Debian. But maybe it will help on Ubuntu too.

I found a way to solve this problem when I learned the source code of the library in detail.
The fact is that LibraryLoader searches for paths:

• /app/bin/Debug/net8.0/x64/libleptonica-1.82.0.so
• /app/x64/libleptonica-1.82.0.so

And when he tries to upload it, he doesn't find these files.

For Docker, it helped me:

RUN apt-get update && apt-get install -y --no-install-recommends \
    tesseract-ocr \
    tesseract-ocr-rus \
    tesseract-ocr-eng \
    libleptonica-dev \
    && rm -rf /var/lib/apt/lists/*

RUN ln -sf /usr/lib/x86_64-linux-gnu/liblept.so /app/x64/libleptonica-1.82.0.so \
    && ln -sf /usr/lib/x86_64-linux-gnu/libtesseract.so.5 /app/x64/libtesseract50.so \
    && ln -sf /lib/x86_64-linux-gnu/libdl.so.2 /lib/x86_64-linux-gnu/libdl.so

Here I have prescribed symlinks.

There is also a way after receiving libleptonica-1.82.0.so and libtesseract.so 5 Add them to the project in the x64 folder so that they are copied during assembly.