NuGet/NuGetGallery — comment on commit d71e5e99ac5d53078d7f3436a17e6b365975c438
File: Website/App_Start/Routes.cs line 101
By Haacked:

Well, depends on how you define "idempotent". You can call it multiple times without changing the data. The first time it uploads the package. The remaining times, you get an error back. :)