[feature] Federate interaction policies + Accepts; enforce policies (#3138)

* [feature] Federate interaction policies + Accepts; enforce policies

* use Acceptable type

* fix index

* remove appendIRIStrs

* add GetAccept federatingdb function

* lock on object IRI

internal/processing/fedi/accept.go

@@ -0,0 +1,84 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package fedi
+
+import (
+	"context"
+	"errors"
+
+	"github.com/superseriousbusiness/gotosocial/internal/ap"
+	"github.com/superseriousbusiness/gotosocial/internal/db"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+)
+
+// AcceptGet handles the getting of a fedi/activitypub
+// representation of a local interaction approval.
+//
+// It performs appropriate authentication before
+// returning a JSON serializable interface.
+func (p *Processor) AcceptGet(
+	ctx context.Context,
+	requestedUser string,
+	approvalID string,
+) (interface{}, gtserror.WithCode) {
+	// Authenticate incoming request, getting related accounts.
+	auth, errWithCode := p.authenticate(ctx, requestedUser)
+	if errWithCode != nil {
+		return nil, errWithCode
+	}
+
+	if auth.handshakingURI != nil {
+		// We're currently handshaking, which means
+		// we don't know this account yet. This should
+		// be a very rare race condition.
+		err := gtserror.Newf("network race handshaking %s", auth.handshakingURI)
+		return nil, gtserror.NewErrorInternalError(err)
+	}
+
+	receivingAcct := auth.receivingAcct
+
+	approval, err := p.state.DB.GetInteractionApprovalByID(ctx, approvalID)
+	if err != nil && !errors.Is(err, db.ErrNoEntries) {
+		err := gtserror.Newf("db error getting approval %s: %w", approvalID, err)
+		return nil, gtserror.NewErrorInternalError(err)
+	}
+
+	if approval.AccountID != receivingAcct.ID {
+		const text = "approval does not belong to receiving account"
+		return nil, gtserror.NewErrorNotFound(errors.New(text))
+	}
+
+	if approval == nil {
+		err := gtserror.Newf("approval %s not found", approvalID)
+		return nil, gtserror.NewErrorNotFound(err)
+	}
+
+	accept, err := p.converter.InteractionApprovalToASAccept(ctx, approval)
+	if err != nil {
+		err := gtserror.Newf("error converting approval: %w", err)
+		return nil, gtserror.NewErrorInternalError(err)
+	}
+
+	data, err := ap.Serialize(accept)
+	if err != nil {
+		err := gtserror.Newf("error serializing accept: %w", err)
+		return nil, gtserror.NewErrorInternalError(err)
+	}
+
+	return data, nil
+}