jellyfin-multilang/tests/Jellyfin.Plugin.Multilang.Tests/ItemsProxyRequestCoalescerTests.cs

using Jellyfin.Plugin.Multilang.Services;

namespace Jellyfin.Plugin.Multilang.Tests;

public sealed class ItemsProxyRequestCoalescerTests
{
    [Fact]
    public async Task MatchingRequestsShareOneInFlightFetch()
    {
        var coalescer = new ItemsProxyRequestCoalescer();
        var response = new TaskCompletionSource<ItemsProxyUpstreamResponse>(TaskCreationOptions.RunContinuationsAsynchronously);
        var fetches = 0;

        Task<ItemsProxyUpstreamResponse> Fetch(CancellationToken _)
        {
            fetches++;
            return response.Task;
        }

        var first = coalescer.GetOrFetchAsync("user|/Items", Fetch, CancellationToken.None);
        var second = coalescer.GetOrFetchAsync("user|/Items", Fetch, CancellationToken.None);

        Assert.Equal(1, fetches);
        response.SetResult(new ItemsProxyUpstreamResponse(200, "{}", "application/json"));

        var firstResult = await first;
        var secondResult = await second;
        Assert.False(firstResult.JoinedExistingRequest);
        Assert.True(secondResult.JoinedExistingRequest);
        Assert.Equal("{}", firstResult.Response.Body);
        Assert.Equal(firstResult.Response, secondResult.Response);
    }

    [Fact]
    public async Task CancellingOneWaiterDoesNotCancelTheSharedFetch()
    {
        var coalescer = new ItemsProxyRequestCoalescer();
        var response = new TaskCompletionSource<ItemsProxyUpstreamResponse>(TaskCreationOptions.RunContinuationsAsynchronously);
        using var cancellation = new CancellationTokenSource();

        var cancelledWaiter = coalescer.GetOrFetchAsync("user|/Items", _ => response.Task, cancellation.Token);
        var activeWaiter = coalescer.GetOrFetchAsync("user|/Items", _ => response.Task, CancellationToken.None);
        cancellation.Cancel();

        await Assert.ThrowsAnyAsync<OperationCanceledException>(() => cancelledWaiter);
        response.SetResult(new ItemsProxyUpstreamResponse(200, "{}", "application/json"));

        var result = await activeWaiter;
        Assert.True(result.JoinedExistingRequest);
        Assert.Equal(200, result.Response.StatusCode);
    }
}