https://github.com/tonybaloney/CSnakes/issues/504

buffer_test.py

from collections.abc import Buffer

def test(length: int = 10000000, fill: int = 42) -> Buffer:
    return bytearray([42] * length)

BufferDemo.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFramework>net9.0</TargetFramework>
    <OutputType>Exe</OutputType>
  </PropertyGroup>

  <ItemGroup>
    <None Remove="*.py" />
  </ItemGroup>

  <ItemGroup>
    <AdditionalFiles Include="*.py">
      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
    </AdditionalFiles>
  </ItemGroup>

  <ItemGroup>
    <PackageReference Include="CSnakes.Runtime" Version="1.0.35" />
  </ItemGroup>

</Project>

Program.cs

using System;
using CSnakes.Runtime;
using CSnakes.Runtime.Locators;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

var builder = Host.CreateApplicationBuilder();
_ = builder.Services
           .WithPython()
           .FromRedistributable(RedistributablePythonVersion.Python3_12);
builder.Logging.SetMinimumLevel(LogLevel.Debug);
var app = builder.Build();
using var env = app.Services.GetRequiredService<IPythonEnvironment>();
using var test = env.BufferTest();

Span<byte> GetBufferSpan(byte fill)
{
    using var buffer = test.Test(fill: fill);
    return buffer.AsSpan<byte>();
}

const byte fill = 42;
var span = GetBufferSpan(fill);
if (span.IndexOfAnyExcept(fill) is var i and >= 0)
    throw new($"Buffer contains unexpected value at index {i} (expected {fill}, but was {span[i]}).");