Fix missing hostname when publishing via API

This fixes a bug that occurred only when publishing via API and
authenticating via token (rather than cookie).

Previously, the instance's hostname wouldn't be added to the Collection
that got passed around after retrieving the owned post, meaning an
incomplete URL was returned in the API response, and federation failed due
to the missing host.

database.go

@@ -73,7 +73,7 @@ type writestore interface {
 	GetAnonymousPosts(u *User) (*[]PublicPost, error)
 	GetUserPosts(u *User) (*[]PublicPost, error)
 
-	CreateOwnedPost(post *SubmittedPost, accessToken, collAlias string) (*PublicPost, error)
+	CreateOwnedPost(post *SubmittedPost, accessToken, collAlias, hostName string) (*PublicPost, error)
 	CreatePost(userID, collID int64, post *SubmittedPost) (*Post, error)
 	UpdateOwnedPost(post *AuthenticatedPost, userID int64) error
 	GetEditablePost(id, editToken string) (*PublicPost, error)
@@ -541,7 +541,7 @@ func (db *datastore) GetTemporaryOneTimeAccessToken(userID int64, validSecs int,
 	return u.String(), nil
 }
 
-func (db *datastore) CreateOwnedPost(post *SubmittedPost, accessToken, collAlias string) (*PublicPost, error) {
+func (db *datastore) CreateOwnedPost(post *SubmittedPost, accessToken, collAlias, hostName string) (*PublicPost, error) {
 	var userID, collID int64 = -1, -1
 	var coll *Collection
 	var err error
@@ -555,6 +555,7 @@ func (db *datastore) CreateOwnedPost(post *SubmittedPost, accessToken, collAlias
 			if err != nil {
 				return nil, err
 			}
+			coll.hostName = hostName
 			if coll.OwnerID != userID {
 				return nil, ErrForbiddenCollection
 			}

posts.go

@@ -556,7 +556,7 @@ func newPost(app *App, w http.ResponseWriter, r *http.Request) error {
 	var coll *Collection
 	var err error
 	if accessToken != "" {
-		newPost, err = app.db.CreateOwnedPost(p, accessToken, collAlias)
+		newPost, err = app.db.CreateOwnedPost(p, accessToken, collAlias, app.cfg.App.Host)
 	} else {
 		//return ErrNotLoggedIn
 		// TODO: verify user is logged in