SocialPub/PrivaPub/Federation/Outbox/DeliveryService.cs

using MongoDB.Entities;

using PrivaPub.Models.Federation;
using PrivaPub.StaticServices;

using System.Net;
using System.Net.Http.Headers;
using System.Text;
using System.Text.Json.Nodes;
using PrivaPub.Federation.Actors;
using PrivaPub.Federation.Signing;
using PrivaPub.Infrastructure.Http;
using PrivaPub.Infrastructure.Jobs;
using PrivaPub.Infrastructure.Statistics;
using PrivaPub.Federation.Objects;
using PrivaPub.Models.Statistics;
using PrivaPub.Models.Jobs;

using System.Diagnostics;
using System.Text.Json;

namespace PrivaPub.Federation.Outbox
{
	public interface IDeliveryService
	{
		// again: a delivery made once more on purpose, which an earlier one of the same activity does not stop; deliveries
		// with the same again are made once
		Task Enqueue(LocalActor signer, IEnumerable<string> inboxes, JsonObject activity, CancellationToken token, string again = default);
		Task EnqueueToFollowers(LocalActor signer, JsonObject activity, CancellationToken token, IEnumerable<string> extraInboxes = default);
		Task<IReadOnlyList<string>> FollowerInboxes(LocalActor actor, CancellationToken token);
	}

	public sealed record DeliveryPayload(string SignerId, LocalActorKind SignerKind, string Inbox, string Body);

	public class DeliveryService : IDeliveryService
	{
		readonly DbEntities _dbEntities;
		readonly IJobQueue _queue;

		public DeliveryService(DbEntities dbEntities, IJobQueue queue)
		{
			_dbEntities = dbEntities;
			_queue = queue;
		}

		public async Task Enqueue(LocalActor signer, IEnumerable<string> inboxes, JsonObject activity, CancellationToken token, string again = default)
		{
			var body = activity.ToJsonString();
			var activityId = activity["id"] is JsonValue id && id.TryGetValue<string>(out var text) ? text : default;
			var targets = inboxes
				.Where(i => !string.IsNullOrEmpty(i) && !i.StartsWith(signer.BaseAddress + "/", StringComparison.OrdinalIgnoreCase))
				.Distinct(StringComparer.Ordinal)
				.ToList();
			// what goes to a relay carries the signer's proof (FEP-8b32): the relay passes it on as it came, signed with its own
			// key, and Mastodon takes it on the proof's strength. Nothing else does: a server that knew the persona before it
			// had its key (Mitra) refuses a proof by a key it does not hold, and does not read the actor again
			var relayed = new HashSet<string>(StringComparer.Ordinal);
			if (!string.IsNullOrEmpty(signer.SigningKey) && activity["actor"] is JsonValue actor && actor.TryGetValue<string>(out var actorUri) && actorUri == signer.Uri)
				relayed = (await DB.Default.Find<RelaySubscription, string>().Match(s => targets.Contains(s.InboxURL)).Project(s => s.InboxURL).ExecuteAsync(token))
					.ToHashSet(StringComparer.Ordinal);
			var provenBody = default(string);
			if (relayed.Count > 0)
			{
				var proven = activity.DeepClone().AsObject();
				proven.Remove("proof");
				proven["proof"] = IntegrityProofs.Create(proven, signer.AssertionKeyId, signer.SigningKey, DateTime.UtcNow);
				provenBody = proven.ToJsonString();
			}
			var jobs = targets
				.Select(inbox => Uri.TryCreate(inbox, UriKind.Absolute, out var uri) ? (inbox, uri) : default)
				.Where(target => target.uri != default)
				.Select(target => new Job
				{
					Kind = JobKind.Deliver,
					Host = target.uri.Host.ToLowerInvariant(),
					DedupeKey = activityId == default ? default : again == default ? $"{activityId}|{target.inbox}" : $"{activityId}|{target.inbox}|{again}",
					Payload = JsonSerializer.Serialize(new DeliveryPayload(signer.Id, signer.Kind, target.inbox, relayed.Contains(target.inbox) ? provenBody : body))
				})
				.ToList();
			if (jobs.Count > 0)
				await _queue.EnqueueMany(jobs, token);
		}

		public async Task EnqueueToFollowers(LocalActor signer, JsonObject activity, CancellationToken token, IEnumerable<string> extraInboxes = default)
		{
			var inboxes = (await FollowerInboxes(signer, token)).Concat(extraInboxes ?? Enumerable.Empty<string>());
			await Enqueue(signer, inboxes, activity, token);
		}

		public async Task<IReadOnlyList<string>> FollowerInboxes(LocalActor actor, CancellationToken token)
		{
			var followers = await _dbEntities.Followers
				.Match(f => f.LocalActorId == actor.Id && f.LocalActorKind == actor.Kind && f.IsAccepted)
				.ExecuteAsync(token);
			return followers.Select(f => string.IsNullOrEmpty(f.SharedInboxURL) ? f.InboxURL : f.SharedInboxURL)
				.Distinct(StringComparer.Ordinal)
				.ToList();
		}
	}

	public class DeliveryJobHandler : IJobHandler
	{
		readonly ILocalActorService _actors;
		readonly IFederationHttp _http;
		readonly IHostCircuitBreaker _breaker;
		readonly ILogger<DeliveryJobHandler> _logger;
		readonly IInteractionLedger _ledger;

		readonly int _concurrency;

		public DeliveryJobHandler(ILocalActorService actors, IFederationHttp http, IHostCircuitBreaker breaker, ILogger<DeliveryJobHandler> logger,
			IInteractionLedger ledger = default, Microsoft.Extensions.Options.IOptions<Infrastructure.Http.FederationOptions> federation = default)
		{
			_concurrency = Math.Max(1, federation?.Value.DeliveryConcurrency ?? 8);
			_actors = actors;
			_http = http;
			_breaker = breaker;
			_logger = logger;
			_ledger = ledger;
		}

		sealed class Attempt
		{
			public DeliveryPayload Payload;
			public LocalActor Signer;
			public int? Status;
			public string Reason;
			public int? LatencyMs;
		}

		public JobKind Kind => JobKind.Deliver;
		public int Concurrency => _concurrency;
		public int MaxAttempts => 16;
		public int PerHostLimit => 2;

		public async Task<JobOutcome> Handle(Job job, CancellationToken token)
		{
			var attempt = new Attempt();
			JobOutcome outcome = default;
			try
			{
				outcome = await Deliver(job, attempt, token);
				return outcome;
			}
			finally
			{
				Record(job, attempt, outcome);
			}
		}

		void Record(Job job, Attempt attempt, JobOutcome outcome)
		{
			if (_ledger == default)
				return;
			var shape = attempt.Payload == default ? default : ActivityShape.Of(attempt.Payload.Body);
			_ledger.Record(new InteractionEvent
			{
				Channel = Interactions.Out,
				Host = job.Host,
				Activity = shape?.Type,
				Object = shape?.ObjectType,
				Outcome = outcome?.Result switch
				{
					JobResult.Done => Interactions.Ok,
					JobResult.Defer => Interactions.Deferred,
					JobResult.Retry when job.Attempts >= MaxAttempts => Interactions.Dead,
					JobResult.Retry => Interactions.Retry,
					JobResult.Dead => Interactions.Dead,
					_ => Interactions.Failed
				},
				Reason = attempt.Reason,
				Status = attempt.Status,
				LatencyMs = attempt.LatencyMs,
				WaitMs = (int)Math.Min(int.MaxValue, Math.Max(0, (DateTime.UtcNow - job.CreatedAt).TotalMilliseconds)),
				Bytes = attempt.Payload?.Body == default ? default : Encoding.UTF8.GetByteCount(attempt.Payload.Body),
				Attempt = job.Attempts,
				Audience = shape?.Audience,
				LocalKind = attempt.Signer switch
				{
					null => default,
					{ IsCircle: true } => default,
					{ Kind: LocalActorKind.Person } => "person",
					{ Kind: LocalActorKind.Group } => "group",
					{ Kind: LocalActorKind.Reporter } => "reporter",
					_ => "application"
				},
				Signature = "cavage:rsa-sha256"
			});
		}

		// FEP-8fcf: what a delivery to the persona's followers tells the receiving server of its followers there; nothing for
		// a while after a restore, whose losses are not the other server's to mend
		static async Task<(string, string)[]> Synchronization(LocalActor signer, string body, Uri inbox, CancellationToken token)
		{
			if (!FollowersSynchronization.Synchronizes(signer) || await Infrastructure.Backup.RestoreRecord.InFollowersGrace(token) || JsonNode.Parse(body) is not JsonObject activity || !FollowersSynchronization.ForFollowers(activity, signer))
				return [];
			var there = await FollowersSynchronization.On(signer, FollowersSynchronization.Origin(inbox.AbsoluteUri), token);
			return [(FollowersSynchronization.Header, FollowersSynchronization.HeaderValue(signer, FollowersSynchronization.Digest(there)))];
		}

		async Task<JobOutcome> Deliver(Job job, Attempt attempt, CancellationToken token)
		{
			var payload = JsonSerializer.Deserialize<DeliveryPayload>(job.Payload);
			attempt.Payload = payload;
			if (payload == default || !Uri.TryCreate(payload.Inbox, UriKind.Absolute, out var inbox) || !_http.IsAllowed(inbox))
			{
				attempt.Reason = "not-deliverable";
				return JobOutcome.Dead("not a deliverable inbox");
			}

			var unavailableUntil = await _breaker.UnavailableUntil(job.Host, token);
			if (unavailableUntil.HasValue)
			{
				attempt.Reason = "host-unavailable";
				return JobOutcome.Defer(unavailableUntil.Value, "the host is unavailable");
			}

			var signer = await _actors.FindById(payload.SignerKind, payload.SignerId, token);
			attempt.Signer = signer;
			if (signer == default)
			{
				attempt.Reason = "signer-gone";
				return JobOutcome.Dead("the signing actor no longer exists");
			}

			var body = Encoding.UTF8.GetBytes(payload.Body);
			using var request = new HttpRequestMessage(HttpMethod.Post, inbox) { Content = new ByteArrayContent(body) };
			request.Content.Headers.ContentType = MediaTypeHeaderValue.Parse(RemoteActorService.ActivityJson);
			HttpSignatures.Sign(request, signer, body, await Synchronization(signer, payload.Body, inbox, token));

			var started = Stopwatch.GetTimestamp();
			try
			{
				using var response = await _http.Send(request, token);
				attempt.LatencyMs = (int)Stopwatch.GetElapsedTime(started).TotalMilliseconds;
				var status = (int)response.StatusCode;
				attempt.Status = status;
				attempt.Reason = response.IsSuccessStatusCode ? default : status.ToString(System.Globalization.CultureInfo.InvariantCulture);
				if (response.IsSuccessStatusCode)
				{
					await _breaker.Succeeded(job.Host, token);
					return JobOutcome.Done;
				}
				if (response.StatusCode == HttpStatusCode.TooManyRequests
					|| response.StatusCode == HttpStatusCode.ServiceUnavailable && response.Headers.RetryAfter != default)
				{
					var retryAfter = response.Headers.RetryAfter?.Delta ?? (response.Headers.RetryAfter?.Date - DateTimeOffset.UtcNow);
					return retryAfter > TimeSpan.Zero
						? JobOutcome.Defer(DateTime.UtcNow + Min(retryAfter.Value, TimeSpan.FromHours(6)), $"{status}")
						: JobOutcome.Retry($"{status}");
				}
				// Mastodon answers 422 when two first contacts from one actor race to create its account (RecordInvalid on the
				// unique uri) and 409 while another worker holds its lock: a Follow refused that way was lost for good, and the
				// persona waited on "requested" forever (found by the town). Both get a few tries before they count as refusals.
				if (status is 409 or 422 && job.Attempts < TransientRefusalAttempts)
					return JobOutcome.Retry($"{status} {response.ReasonPhrase}");
				if (status is >= 400 and < 500 && status != 408)
				{
					await _breaker.Succeeded(job.Host, token);
					_logger.LogInformation("Delivery to {Inbox} refused with {Status}", payload.Inbox, status);
					return JobOutcome.Dead($"{status} {response.ReasonPhrase}");
				}
				// a gateway's 502, 503 or 504 says the server behind it is down, which counts against the host; any other 5xx
				// says the server is up and failed on this activity (Smithereen's 500 on a document its JSON-LD reader
				// refused), retried on its own while the host's other deliveries go on
				if (status is 502 or 503 or 504)
					await _breaker.Failed(job.Host, $"{status}", token);
				return JobOutcome.Retry($"{status} {response.ReasonPhrase}");
			}
			catch (BlockedDestinationException ex)
			{
				attempt.Reason = "private-address";
				return JobOutcome.Dead(ex.Message);
			}
			catch (Exception ex) when (ex is HttpRequestException or TaskCanceledException && !token.IsCancellationRequested)
			{
				attempt.LatencyMs = (int)Stopwatch.GetElapsedTime(started).TotalMilliseconds;
				attempt.Reason = ex is TaskCanceledException ? "timeout" : "network";
				await _breaker.Failed(job.Host, ex.GetType().Name, token);
				return JobOutcome.Retry(ex.Message);
			}
		}

		const int TransientRefusalAttempts = 3;

		static TimeSpan Min(TimeSpan a, TimeSpan b) => a < b ? a : b;
	}
}