FileShare/Avalonia-API/Extensions/FileStreamEndpointExtensions.cs

using Avalonia_EFCore.Database;
using Microsoft.EntityFrameworkCore;

namespace Avalonia_API.Extensions
{
    public static class FileStreamEndpointExtensions
    {
        public static IEndpointRouteBuilder MapFileStreamEndpoints(this IEndpointRouteBuilder app)
        {
            app.MapMethods("/api/files/{id:int}/stream", ["GET", "HEAD"], async (int id, AppDataContext db, HttpContext httpContext) =>
            {
                // Browsers cancel in-flight range requests aggressively while seeking.
                // Keep this small metadata lookup independent from RequestAborted so
                // EF does not throw TaskCanceledException before the file is opened.
                var file = await db.ManagedFileRecords
                    .AsNoTracking()
                    .Include(item => item.LibraryRoot)
                    .FirstOrDefaultAsync(item =>
                        item.Id == id
                        && item.Exists
                        && item.LibraryRoot != null
                        && item.LibraryRoot.IsAvailable);

                if (file is null || !System.IO.File.Exists(file.AbsolutePath))
                {
                    return Results.NotFound();
                }

                var stream = System.IO.File.Open(file.AbsolutePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
                httpContext.Response.Headers.ContentDisposition = $"inline; filename=\"{Uri.EscapeDataString(file.FileName)}\"";
                httpContext.Response.Headers.AcceptRanges = "bytes";
                httpContext.Response.Headers.CacheControl = "public, max-age=3600";

                return Results.File(
                    stream,
                    contentType: file.ContentType,
                    fileDownloadName: null,
                    lastModified: file.LastWriteTimeUtc,
                    enableRangeProcessing: true);
            })
            .WithName("StreamManagedFile")
            .WithTags("FileLibrary");

            return app;
        }
    }
}