Dereference remote replies (#132)

* decided where to put reply dereferencing

* fiddling with dereferencing threads

* further adventures

* tidy up some stuff

* move dereferencing functionality

* a bunch of refactoring

* go fmt

* more refactoring

* bleep bloop

* docs and linting

* start implementing replies collection on gts side

* fiddling around

* allow dereferencing our replies

* lint, fmt

internal/federation/dereferencing/collectionpage.go

@@ -0,0 +1,70 @@
+/*
+   GoToSocial
+   Copyright (C) 2021 GoToSocial Authors admin@gotosocial.org
+
+   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 dereferencing
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/url"
+
+	"github.com/go-fed/activity/streams"
+	"github.com/go-fed/activity/streams/vocab"
+	"github.com/superseriousbusiness/gotosocial/internal/ap"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+)
+
+// DereferenceCollectionPage returns the activitystreams CollectionPage at the specified IRI, or an error if something goes wrong.
+func (d *deref) DereferenceCollectionPage(username string, pageIRI *url.URL) (ap.CollectionPageable, error) {
+	if blocked, err := d.blockedDomain(pageIRI.Host); blocked || err != nil {
+		return nil, fmt.Errorf("DereferenceCollectionPage: domain %s is blocked", pageIRI.Host)
+	}
+
+	transport, err := d.transportController.NewTransportForUsername(username)
+	if err != nil {
+		return nil, fmt.Errorf("DereferenceCollectionPage: error creating transport: %s", err)
+	}
+
+	b, err := transport.Dereference(context.Background(), pageIRI)
+	if err != nil {
+		return nil, fmt.Errorf("DereferenceCollectionPage: error deferencing %s: %s", pageIRI.String(), err)
+	}
+
+	m := make(map[string]interface{})
+	if err := json.Unmarshal(b, &m); err != nil {
+		return nil, fmt.Errorf("DereferenceCollectionPage: error unmarshalling bytes into json: %s", err)
+	}
+
+	t, err := streams.ToType(context.Background(), m)
+	if err != nil {
+		return nil, fmt.Errorf("DereferenceCollectionPage: error resolving json into ap vocab type: %s", err)
+	}
+
+	if t.GetTypeName() != gtsmodel.ActivityStreamsCollectionPage {
+		return nil, fmt.Errorf("DereferenceCollectionPage: type name %s not supported", t.GetTypeName())
+	}
+
+	p, ok := t.(vocab.ActivityStreamsCollectionPage)
+	if !ok {
+		return nil, errors.New("DereferenceCollectionPage: error resolving type as activitystreams collection page")
+	}
+
+	return p, nil
+}