1 files changed, 67 insertions, 0 deletions
diff --git a/internal/api/activitypub/users/followers.go b/internal/api/activitypub/users/followers.go
new file mode 100644
index 000000000..69b9f52fd
--- /dev/null
+++ b/internal/api/activitypub/users/followers.go
@@ -0,0 +1,67 @@
+/*
+   GoToSocial
+   Copyright (C) 2021-2022 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 users
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+	"strings"
+
+	"github.com/gin-gonic/gin"
+	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+)
+
+// FollowersGETHandler returns a collection of URIs for followers of the target user, formatted so that other AP servers can understand it.
+func (m *Module) FollowersGETHandler(c *gin.Context) {
+	// usernames on our instance are always lowercase
+	requestedUsername := strings.ToLower(c.Param(UsernameKey))
+	if requestedUsername == "" {
+		err := errors.New("no username specified in request")
+		apiutil.ErrorHandler(c, gtserror.NewErrorBadRequest(err, err.Error()), m.processor.InstanceGet)
+		return
+	}
+
+	format, err := apiutil.NegotiateAccept(c, apiutil.HTMLOrActivityPubHeaders...)
+	if err != nil {
+		apiutil.ErrorHandler(c, gtserror.NewErrorNotAcceptable(err, err.Error()), m.processor.InstanceGet)
+		return
+	}
+
+	if format == string(apiutil.TextHTML) {
+		// redirect to the user's profile
+		c.Redirect(http.StatusSeeOther, "/@"+requestedUsername)
+		return
+	}
+
+	resp, errWithCode := m.processor.GetFediFollowers(apiutil.TransferSignatureContext(c), requestedUsername, c.Request.URL)
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGet)
+		return
+	}
+
+	b, err := json.Marshal(resp)
+	if err != nil {
+		apiutil.ErrorHandler(c, gtserror.NewErrorInternalError(err), m.processor.InstanceGet)
+		return
+	}
+
+	c.Data(http.StatusOK, format, b)
+}