fix: handle opaque attachment references

server/store/file_test.go

@@ -0,0 +1,30 @@
+package store
+
+import (
+	"testing"
+
+	"github.com/tinode/chat/server/store/types"
+)
+
+func TestFileLinkUserIDAllowsOpaqueTopicReferences(t *testing.T) {
+	tests := []struct {
+		name    string
+		topic   string
+		isUser  bool
+		wantUID types.Uid
+	}{
+		{name: "cultivate reference", topic: "cvpbzxw1aio4ni8x0"},
+		{name: "short opaque reference", topic: "x"},
+		{name: "empty reference", topic: ""},
+		{name: "user reference", topic: types.Uid(42).UserId(), isUser: true, wantUID: types.Uid(42)},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			gotUID, gotIsUser := fileLinkUserID(test.topic)
+			if gotIsUser != test.isUser || gotUID != test.wantUID {
+				t.Fatalf("fileLinkUserID(%q) = (%v, %v), want (%v, %v)", test.topic, gotUID, gotIsUser, test.wantUID, test.isUser)
+			}
+		})
+	}
+}