douyin/tests/dy.net.Tests/MediaDownloadTests.cs

using System.Net;
using System.Net.Http.Headers;
using dy.net.model.dto;
using dy.net.service;
using dy.net.Tests.TestInfrastructure;

namespace dy.net.Tests;

public class MediaDownloadTests
{
    [Fact]
    public async Task RedirectToCdn_DoesNotForwardDouyinCookie()
    {
        using var temporary = new TemporaryDirectory();
        var handler = new RecordingMediaHandler(request =>
        {
            if (request.RequestUri.Host == "www.douyin.com")
            {
                var redirect = new HttpResponseMessage(HttpStatusCode.Redirect);
                redirect.Headers.Location = new Uri("https://v3.douyinvod.com/media/video.mp4");
                return redirect;
            }
            var success = new HttpResponseMessage(HttpStatusCode.OK)
            {
                Content = new ByteArrayContent(new byte[] { 1, 2, 3, 4 })
            };
            success.Content.Headers.ContentType = new MediaTypeHeaderValue("video/mp4");
            return success;
        });
        using var factory = new StubHttpClientFactory(handler);
        var service = new DouyinHttpClientService(factory, null);

        var result = await service.DownloadAsync(
            "https://www.douyin.com/aweme/v1/play?id=signed-secret",
            Path.Combine(temporary.Path, "video.mp4"),
            "sessionid=secret-cookie");

        Assert.True(result.Success);
        Assert.Equal(2, handler.Requests.Count);
        Assert.Equal("sessionid=secret-cookie", handler.Requests[0].Cookie);
        Assert.Null(handler.Requests[1].Cookie);
        Assert.Equal("v3.douyinvod.com", result.SourceHost);
    }

    [Fact]
    public async Task DuplicateCandidates_AreTriedOnceAndAllForbiddenIsStructured()
    {
        using var temporary = new TemporaryDirectory();
        var handler = new RecordingMediaHandler(_ => new HttpResponseMessage(HttpStatusCode.Forbidden));
        using var factory = new StubHttpClientFactory(handler);
        var service = new DouyinHttpClientService(factory, null);
        var first = "https://www.douyin.com/media/one?signature=secret-one";
        var second = "https://www.douyin.com/media/two?signature=secret-two";

        var result = await service.DownloadAsync(first, Path.Combine(temporary.Path, "video.mp4"), "sessionid=secret",
            new List<string> { first, second, second }, maxRetryCount: 12);

        Assert.False(result.Success);
        Assert.Equal(MediaDownloadFailureKind.SourceForbidden, result.FailureKind);
        Assert.Equal(403, result.HttpStatusCode);
        Assert.Equal(2, result.AttemptedUrlCount);
        Assert.Equal(2, handler.Requests.Count);
    }

    [Fact]
    public async Task MixedCandidateErrors_AreNotCountedAsAllForbidden()
    {
        using var temporary = new TemporaryDirectory();
        var handler = new RecordingMediaHandler(request => new HttpResponseMessage(
            request.RequestUri.AbsolutePath.EndsWith("one", StringComparison.Ordinal)
                ? HttpStatusCode.NotFound
                : HttpStatusCode.Forbidden));
        using var factory = new StubHttpClientFactory(handler);
        var service = new DouyinHttpClientService(factory, null);

        var result = await service.DownloadAsync("https://www.douyin.com/media/one",
            Path.Combine(temporary.Path, "video.mp4"), "sessionid=secret",
            new List<string> { "https://www.douyin.com/media/two" }, maxRetryCount: 12);

        Assert.False(result.Success);
        Assert.Equal(MediaDownloadFailureKind.SourceUnavailable, result.FailureKind);
        Assert.Equal(2, result.AttemptedUrlCount);
    }

    [Fact]
    public async Task Unauthorized_StopsWithoutTryingMoreCandidates()
    {
        using var temporary = new TemporaryDirectory();
        var handler = new RecordingMediaHandler(_ => new HttpResponseMessage(HttpStatusCode.Unauthorized));
        using var factory = new StubHttpClientFactory(handler);
        var service = new DouyinHttpClientService(factory, null);

        var result = await service.DownloadAsync("https://www.douyin.com/media/one",
            Path.Combine(temporary.Path, "video.mp4"), "sessionid=secret",
            new List<string> { "https://www.douyin.com/media/two" });

        Assert.Equal(MediaDownloadFailureKind.SourceUnauthorized, result.FailureKind);
        Assert.Single(handler.Requests);
    }

    [Theory]
    [InlineData(HttpStatusCode.NotFound)]
    [InlineData(HttpStatusCode.Gone)]
    public async Task MissingOrGoneSource_IsAnItemLevelFailure(HttpStatusCode status)
    {
        using var temporary = new TemporaryDirectory();
        var handler = new RecordingMediaHandler(_ => new HttpResponseMessage(status));
        using var factory = new StubHttpClientFactory(handler);
        var service = new DouyinHttpClientService(factory, null);

        var result = await service.DownloadAsync("https://www.douyin.com/media/one",
            Path.Combine(temporary.Path, "video.mp4"), "sessionid=secret");

        Assert.Equal(MediaDownloadFailureKind.SourceNotFound, result.FailureKind);
        Assert.Equal((int)status, result.HttpStatusCode);
    }

    [Fact]
    public async Task RateLimit_HonorsRetryAfterOnceThenReturnsStructuredCooldown()
    {
        using var temporary = new TemporaryDirectory();
        var handler = new RecordingMediaHandler(_ =>
        {
            var response = new HttpResponseMessage((HttpStatusCode)429);
            response.Headers.RetryAfter = new RetryConditionHeaderValue(DateTimeOffset.UtcNow);
            return response;
        });
        using var factory = new StubHttpClientFactory(handler);
        var service = new DouyinHttpClientService(factory, null);

        var result = await service.DownloadAsync("https://www.douyin.com/media/one",
            Path.Combine(temporary.Path, "video.mp4"), "sessionid=secret");

        Assert.Equal(MediaDownloadFailureKind.SourceRateLimited, result.FailureKind);
        Assert.Equal(2, handler.Requests.Count);
        Assert.NotNull(result.RetryAfter);
    }

    [Fact]
    public async Task MediaConnectTimeout_RetriesTwiceWithBackoffThenSucceeds()
    {
        using var temporary = new TemporaryDirectory();
        var requestCount = 0;
        var delays = new List<TimeSpan>();
        var handler = new RecordingMediaHandler(_ =>
        {
            requestCount++;
            if (requestCount <= 2) throw new HttpRequestException("connect timeout");
            var response = new HttpResponseMessage(HttpStatusCode.OK)
            {
                Content = new ByteArrayContent(new byte[] { 1, 2, 3 })
            };
            response.Content.Headers.ContentType = new MediaTypeHeaderValue("video/mp4");
            return response;
        });
        using var factory = new StubHttpClientFactory(handler);
        var service = new DouyinHttpClientService(factory, null, (delay, _) =>
        {
            delays.Add(delay);
            return Task.CompletedTask;
        });

        var result = await service.DownloadAsync("https://www.douyin.com/media/retry",
            Path.Combine(temporary.Path, "video.mp4"), "sessionid=secret");

        Assert.True(result.Success);
        Assert.Equal(3, requestCount);
        Assert.Equal(2, delays.Count);
        Assert.True(delays[1] > delays[0]);
    }

    [Fact]
    public async Task FollowPostConnectTimeout_RetriesBeforeFailingTheAuthorScan()
    {
        var requestCount = 0;
        var handler = new RecordingMediaHandler(_ =>
        {
            requestCount++;
            if (requestCount <= 2) throw new TaskCanceledException("connect timeout");
            return new HttpResponseMessage(HttpStatusCode.OK)
            {
                Content = new StringContent("{}")
            };
        });
        using var factory = new StubHttpClientFactory(handler, "https://www.douyin.com");
        var service = new DouyinHttpClientService(factory, null, (_, _) => Task.CompletedTask);

        var result = await service.SyncUpderPostVideos("20", "0", "sec-user", "sessionid=secret");

        Assert.NotNull(result);
        Assert.Equal(3, requestCount);
    }

    private sealed record RecordedMediaRequest(string Host, string Cookie);

    private sealed class RecordingMediaHandler : HttpMessageHandler
    {
        private readonly Func<HttpRequestMessage, HttpResponseMessage> _response;

        public RecordingMediaHandler(Func<HttpRequestMessage, HttpResponseMessage> response) => _response = response;

        public List<RecordedMediaRequest> Requests { get; } = new();

        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            Requests.Add(new RecordedMediaRequest(
                request.RequestUri.Host,
                request.Headers.TryGetValues("Cookie", out var values) ? values.Single() : null));
            return Task.FromResult(_response(request));
        }
    }
}