[feature] Federate pinned posts (aka `featuredCollection`) in and out (#1560)

* start fiddling

* the ol' fiddle + update

* start working on fetching statuses

* poopy doopy doo where r u uwu

* further adventures in featuring statuses

* finishing up

* fmt

* simply status unpin loop

* move empty featured check back to caller function

* remove unnecessary log.WithContext calls

* remove unnecessary IsIRI() checks

* add explanatory comment about status URIs

* change log level to error

* better test names

4 files changed, 131 insertions, 3 deletions

diff --git a/internal/typeutils/astointernal.go b/internal/typeutils/astointernal.go
index 11633ad4e..4e1b59613 100644
--- a/internal/typeutils/astointernal.go
+++ b/internal/typeutils/astointernal.go
@@ -181,9 +181,14 @@ func (c *converter) ASRepresentationToAccount(ctx context.Context, accountable a
 		acct.FollowersURI = accountable.GetActivityStreamsFollowers().GetIRI().String()
 	}
 
-	// FeaturedURI
-	if accountable.GetTootFeatured() != nil && accountable.GetTootFeatured().GetIRI() != nil {
-		acct.FeaturedCollectionURI = accountable.GetTootFeatured().GetIRI().String()
+	// FeaturedURI aka pinned collection:
+	// Only trust featured URI if it has at least two domains,
+	// from the right, in common with the domain of the account
+	if featured := accountable.GetTootFeatured(); featured != nil && featured.IsIRI() {
+		if featuredURI := featured.GetIRI(); // nocollapse
+		featuredURI != nil && dns.CompareDomainName(acct.Domain, featuredURI.Host) >= 2 {
+			acct.FeaturedCollectionURI = featuredURI.String()
+		}
 	}
 
 	// TODO: FeaturedTagsURI
diff --git a/internal/typeutils/converter.go b/internal/typeutils/converter.go
index c63bd8d8c..ec0c1bb8c 100644
--- a/internal/typeutils/converter.go
+++ b/internal/typeutils/converter.go
@@ -178,6 +178,9 @@ type TypeConverter interface {
 	//
 	// Appropriate 'next' and 'prev' fields will be created based on the highest and lowest IDs present in the statuses slice.
 	StatusesToASOutboxPage(ctx context.Context, outboxID string, maxID string, minID string, statuses []*gtsmodel.Status) (vocab.ActivityStreamsOrderedCollectionPage, error)
+	// StatusesToASFeaturedCollection converts a slice of statuses into an ordered collection
+	// of URIs, suitable for serializing and serving via the activitypub API.
+	StatusesToASFeaturedCollection(ctx context.Context, featuredCollectionID string, statuses []*gtsmodel.Status) (vocab.ActivityStreamsOrderedCollection, error)
 	// ReportToASFlag converts a gts model report into an activitystreams FLAG, suitable for federation.
 	ReportToASFlag(ctx context.Context, r *gtsmodel.Report) (vocab.ActivityStreamsFlag, error)
 
diff --git a/internal/typeutils/internaltoas.go b/internal/typeutils/internaltoas.go
index 06b49c18f..bbcf6c84b 100644
--- a/internal/typeutils/internaltoas.go
+++ b/internal/typeutils/internaltoas.go
@@ -1296,6 +1296,34 @@ func (c *converter) OutboxToASCollection(ctx context.Context, outboxID string) (
 	return collection, nil
 }
 
+func (c *converter) StatusesToASFeaturedCollection(ctx context.Context, featuredCollectionID string, statuses []*gtsmodel.Status) (vocab.ActivityStreamsOrderedCollection, error) {
+	collection := streams.NewActivityStreamsOrderedCollection()
+
+	collectionIDProp := streams.NewJSONLDIdProperty()
+	featuredCollectionIDURI, err := url.Parse(featuredCollectionID)
+	if err != nil {
+		return nil, fmt.Errorf("error parsing url %s", featuredCollectionID)
+	}
+	collectionIDProp.SetIRI(featuredCollectionIDURI)
+	collection.SetJSONLDId(collectionIDProp)
+
+	itemsProp := streams.NewActivityStreamsOrderedItemsProperty()
+	for _, s := range statuses {
+		uri, err := url.Parse(s.URI)
+		if err != nil {
+			return nil, fmt.Errorf("error parsing url %s", s.URI)
+		}
+		itemsProp.AppendIRI(uri)
+	}
+	collection.SetActivityStreamsOrderedItems(itemsProp)
+
+	totalItemsProp := streams.NewActivityStreamsTotalItemsProperty()
+	totalItemsProp.Set(len(statuses))
+	collection.SetActivityStreamsTotalItems(totalItemsProp)
+
+	return collection, nil
+}
+
 func (c *converter) ReportToASFlag(ctx context.Context, r *gtsmodel.Report) (vocab.ActivityStreamsFlag, error) {
 	flag := streams.NewActivityStreamsFlag()
 
diff --git a/internal/typeutils/internaltoas_test.go b/internal/typeutils/internaltoas_test.go
index 2ea393db3..887d78884 100644
--- a/internal/typeutils/internaltoas_test.go
+++ b/internal/typeutils/internaltoas_test.go
@@ -21,11 +21,13 @@ package typeutils_test
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/suite"
 	"github.com/superseriousbusiness/activity/streams"
+	"github.com/superseriousbusiness/gotosocial/internal/db"
 	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
 	"github.com/superseriousbusiness/gotosocial/testrig"
 )
@@ -544,6 +546,96 @@ func (suite *InternalToASTestSuite) TestReportToAS() {
 }`, string(bytes))
 }
 
+func (suite *InternalToASTestSuite) TestPinnedStatusesToASSomeItems() {
+	ctx := context.Background()
+
+	testAccount := suite.testAccounts["admin_account"]
+	statuses, err := suite.db.GetAccountPinnedStatuses(ctx, testAccount.ID)
+	if err != nil {
+		suite.FailNow(err.Error())
+	}
+
+	collection, err := suite.typeconverter.StatusesToASFeaturedCollection(ctx, testAccount.FeaturedCollectionURI, statuses)
+	if err != nil {
+		suite.FailNow(err.Error())
+	}
+
+	ser, err := streams.Serialize(collection)
+	suite.NoError(err)
+
+	bytes, err := json.MarshalIndent(ser, "", "  ")
+	suite.NoError(err)
+
+	suite.Equal(`{
+  "@context": "https://www.w3.org/ns/activitystreams",
+  "id": "http://localhost:8080/users/admin/collections/featured",
+  "orderedItems": [
+    "http://localhost:8080/users/admin/statuses/01F8MHAAY43M6RJ473VQFCVH37",
+    "http://localhost:8080/users/admin/statuses/01F8MH75CBF9JFX4ZAD54N0W0R"
+  ],
+  "totalItems": 2,
+  "type": "OrderedCollection"
+}`, string(bytes))
+}
+
+func (suite *InternalToASTestSuite) TestPinnedStatusesToASNoItems() {
+	ctx := context.Background()
+
+	testAccount := suite.testAccounts["local_account_1"]
+	statuses, err := suite.db.GetAccountPinnedStatuses(ctx, testAccount.ID)
+	if err != nil && !errors.Is(err, db.ErrNoEntries) {
+		suite.FailNow(err.Error())
+	}
+
+	collection, err := suite.typeconverter.StatusesToASFeaturedCollection(ctx, testAccount.FeaturedCollectionURI, statuses)
+	if err != nil {
+		suite.FailNow(err.Error())
+	}
+
+	ser, err := streams.Serialize(collection)
+	suite.NoError(err)
+
+	bytes, err := json.MarshalIndent(ser, "", "  ")
+	suite.NoError(err)
+
+	suite.Equal(`{
+  "@context": "https://www.w3.org/ns/activitystreams",
+  "id": "http://localhost:8080/users/the_mighty_zork/collections/featured",
+  "orderedItems": [],
+  "totalItems": 0,
+  "type": "OrderedCollection"
+}`, string(bytes))
+}
+
+func (suite *InternalToASTestSuite) TestPinnedStatusesToASOneItem() {
+	ctx := context.Background()
+
+	testAccount := suite.testAccounts["local_account_2"]
+	statuses, err := suite.db.GetAccountPinnedStatuses(ctx, testAccount.ID)
+	if err != nil {
+		suite.FailNow(err.Error())
+	}
+
+	collection, err := suite.typeconverter.StatusesToASFeaturedCollection(ctx, testAccount.FeaturedCollectionURI, statuses)
+	if err != nil {
+		suite.FailNow(err.Error())
+	}
+
+	ser, err := streams.Serialize(collection)
+	suite.NoError(err)
+
+	bytes, err := json.MarshalIndent(ser, "", "  ")
+	suite.NoError(err)
+
+	suite.Equal(`{
+  "@context": "https://www.w3.org/ns/activitystreams",
+  "id": "http://localhost:8080/users/1happyturtle/collections/featured",
+  "orderedItems": "http://localhost:8080/users/1happyturtle/statuses/01G20ZM733MGN8J344T4ZDDFY1",
+  "totalItems": 1,
+  "type": "OrderedCollection"
+}`, string(bytes))
+}
+
 func TestInternalToASTestSuite(t *testing.T) {
 	suite.Run(t, new(InternalToASTestSuite))
 }