Sent user activities to distant federated server (#8792)

This PR is part of #4767. It contains

* a refactoring of validation error messages
* adds the ability to send user-activities to distant federated servers

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/8792
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Michael Jerger <michael.jerger@meissa-gmbh.de>
Co-committed-by: Michael Jerger <michael.jerger@meissa-gmbh.de>

services/federation/user_activity.go

@@ -0,0 +1,83 @@
+// Copyright 2024 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package federation
+
+import (
+	"context"
+
+	activities_model "forgejo.org/models/activities"
+	"forgejo.org/models/forgefed"
+	"forgejo.org/models/user"
+	"forgejo.org/modules/setting"
+	"forgejo.org/modules/structs"
+	"forgejo.org/services/convert"
+
+	ap "github.com/go-ap/activitypub"
+	"github.com/go-ap/jsonld"
+)
+
+func SendUserActivity(ctx context.Context, doer *user.User, activity *activities_model.Action) error {
+	followers, err := user.GetFollowersForUser(ctx, doer)
+	if err != nil {
+		return err
+	}
+
+	userActivity, err := convert.ActionToForgeUserActivity(ctx, activity)
+	if err != nil {
+		return err
+	}
+
+	payload, err := jsonld.WithContext(
+		jsonld.IRI(ap.ActivityBaseURI),
+	).Marshal(userActivity)
+	if err != nil {
+		return err
+	}
+
+	for _, follower := range followers {
+		_, federatedUserFollower, err := user.GetFederatedUserByUserID(ctx, follower.FollowingUserID)
+		if err != nil {
+			return err
+		}
+
+		federationHost, err := forgefed.GetFederationHost(ctx, federatedUserFollower.FederationHostID)
+		if err != nil {
+			return err
+		}
+
+		hostURL := federationHost.AsURL()
+		if err := deliveryQueue.Push(deliveryQueueItem{
+			InboxURL: hostURL.JoinPath(federatedUserFollower.InboxPath).String(),
+			Doer:     doer,
+			Payload:  payload,
+		}); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func NotifyActivityPubFollowers(ctx context.Context, actions []activities_model.Action) error {
+	if !setting.Federation.Enabled {
+		return nil
+	}
+	for _, act := range actions {
+		if act.Repo != nil {
+			if act.Repo.IsPrivate {
+				continue
+			}
+			if act.Repo.Owner.KeepActivityPrivate || act.Repo.Owner.Visibility != structs.VisibleTypePublic {
+				continue
+			}
+		}
+		if act.ActUser.KeepActivityPrivate || act.ActUser.Visibility != structs.VisibleTypePublic {
+			continue
+		}
+		if err := SendUserActivity(ctx, act.ActUser, &act); err != nil {
+			return err
+		}
+	}
+	return nil
+}