SocialPub/PrivaPub/Federation/Inbox/InboxReceiver.cs

using PrivaPub.Federation.Actors;
using PrivaPub.Federation.Moderation;
using PrivaPub.Federation.Objects;
using PrivaPub.Federation.Signing;
using PrivaPub.Infrastructure.Jobs;
using PrivaPub.Models.Federation;
using PrivaPub.Models.Jobs;

using System.Text.Json;
using System.Text.Json.Nodes;

using static PrivaPub.Federation.Objects.ActivityJson;

namespace PrivaPub.Federation.Inbox
{
	public sealed record InboxResult(int StatusCode, string Error = default, int? RetryAfterSeconds = default);

	public sealed record InboxPayload(string ActorURI, string Activity, string Inbox = default, string KeyId = default, string Algorithm = default,
		string[] SignedHeaders = default, DateTime? ReceivedAt = default);

	public interface IInboxReceiver
	{
		Task<InboxResult> Receive(HttpRequest request, LocalActor recipient, CancellationToken token);
	}

	public class InboxReceiver : IInboxReceiver
	{
		const int KeyRetrySeconds = 300;

		const int MaxBodyBytes = 1024 * 1024;

		readonly ILocalActorService _localActors;
		readonly IRemoteActorService _remoteActors;
		readonly IJobQueue _queue;
		readonly IDomainBlocks _domainBlocks;
		readonly ILogger<InboxReceiver> _logger;

		public InboxReceiver(ILocalActorService localActors, IRemoteActorService remoteActors, IJobQueue queue, IDomainBlocks domainBlocks,
			ILogger<InboxReceiver> logger)
		{
			_localActors = localActors;
			_remoteActors = remoteActors;
			_queue = queue;
			_domainBlocks = domainBlocks;
			_logger = logger;
		}

		public async Task<InboxResult> Receive(HttpRequest request, LocalActor recipient, CancellationToken token)
		{
			if (request.ContentLength > MaxBodyBytes)
				return new(StatusCodes.Status413PayloadTooLarge);

			using var buffer = new MemoryStream();
			await request.Body.CopyToAsync(buffer, token);
			if (buffer.Length > MaxBodyBytes)
				return new(StatusCodes.Status413PayloadTooLarge);
			var body = buffer.ToArray();

			JsonNode activity;
			try
			{
				activity = JsonNode.Parse(body);
			}
			catch (JsonException)
			{
				return new(StatusCodes.Status400BadRequest, "the body is not JSON");
			}
			if (activity is not JsonObject)
				return new(StatusCodes.Status400BadRequest, "the body is not an activity");

			var type = Value(activity, "type");
			var actorUri = Id(activity["actor"]);
			if (string.IsNullOrEmpty(type) || string.IsNullOrEmpty(actorUri))
				return new(StatusCodes.Status400BadRequest, "type and actor are required");

			var parameters = HttpSignatures.Parse(request.Headers["Signature"].ToString());
			if (parameters == default)
				return new(StatusCodes.Status401Unauthorized, "missing or unreadable Signature header");
			if (_domainBlocks.IsSuspended(HostOf(parameters.KeyId)) || _domainBlocks.IsSuspended(HostOf(actorUri)))
				return new(StatusCodes.Status202Accepted);

			var requestProblem = HttpSignatures.CheckRequest(request, parameters, body);
			if (requestProblem != default)
				return new(StatusCodes.Status401Unauthorized, requestProblem);

			var signingString = HttpSignatures.SigningString(request, parameters);
			var keyOwner = await _remoteActors.GetActorByKeyId(parameters.KeyId, refresh: false, token);
			if (keyOwner == default && type == "Delete" && Id(activity["object"]) == actorUri)
				return new(StatusCodes.Status202Accepted);
			if (keyOwner == default || !HttpSignatures.Verify(keyOwner.PublicKey, signingString, parameters.Signature))
			{
				keyOwner = await _remoteActors.GetActorByKeyId(parameters.KeyId, refresh: true, token);
				if (keyOwner == default && _remoteActors.KeyTemporarilyUnavailable(parameters.KeyId))
					return new(StatusCodes.Status503ServiceUnavailable, "the signing key could not be fetched; try again later", KeyRetrySeconds);
				if (keyOwner == default || !HttpSignatures.Verify(keyOwner.PublicKey, signingString, parameters.Signature))
					return new(StatusCodes.Status401Unauthorized, "the signature does not verify");
			}

			if (!string.Equals(keyOwner.ActorURI, actorUri, StringComparison.Ordinal))
				return new(StatusCodes.Status401Unauthorized, "the activity's actor is not the key's owner");

			var shapeProblem = await ShapeProblem(type, activity, actorUri, token);
			if (shapeProblem != default)
				return shapeProblem;

			var activityId = Id(activity);
			var payload = new InboxPayload(actorUri, activity.ToJsonString(), recipient == default ? "shared" : "personal", parameters.KeyId,
				parameters.Algorithm, parameters.Headers, DateTime.UtcNow);
			await _queue.Enqueue(JobKind.ProcessInbox, JsonSerializer.Serialize(payload),
				new Uri(actorUri).Host.ToLowerInvariant(), activityId == default ? default : "inbox|" + activityId, token);
			_logger.LogInformation("Inbox {Recipient}: {Type} from {Actor} queued", recipient?.Handle ?? "shared", type, actorUri);
			return new(StatusCodes.Status202Accepted);
		}

		static string HostOf(string uri) => Uri.TryCreate(uri, UriKind.Absolute, out var parsed) ? parsed.Host : default;

		async Task<InboxResult> ShapeProblem(string type, JsonNode activity, string actorUri, CancellationToken token)
		{
			var activityId = Id(activity);
			if (activityId != default && !Origin.Same(activityId, actorUri))
				return new(StatusCodes.Status400BadRequest, "the activity's id is not on its actor's origin");

			var inner = activity["object"];
			switch (type)
			{
				case "Follow":
					var target = await _localActors.FindByUri(Id(inner), token);
					if (target is not { IsFederated: true } || target.Kind == LocalActorKind.Application)
						return new(StatusCodes.Status404NotFound, "no such local actor");
					break;
				case "Undo" when inner is JsonObject && Id(inner["actor"]) != actorUri:
					return new(StatusCodes.Status400BadRequest, "an actor can only undo its own activities");
				case "Create" or "Update" when inner is JsonObject && Origin.Same(Id(inner), actorUri)
					&& inner["attributedTo"] != default && Id(inner["attributedTo"]) != actorUri
					&& Value(inner, "type") is not ("Person" or "Service" or "Application" or "Group" or "Organization"):
					return new(StatusCodes.Status400BadRequest, "the object is not attributed to the actor");
			}
			return default;
		}
	}
}