Example of dynamically generating a zip file download from ASP.NET Core (on the full framework), with minimal threading and memory usage.

Specifically, with this code:

• No file is ever completely in memory at any time. As files are read, they are immediately compressed and sent to the browser.
• No threads are ever blocked waiting on reads or writes. The fully-asynchronous code permits threads to return to the thread pool unless they are actually executing code.

This example uses its own FileCallbackResult to stream output on demand, and uses DotNetZip to create the zip stream. Due to the DotNetZip dependency, this ASP.NET Core project can only run on the full .NET Framework.