Why Streaming an Upload Requires an End-to-End Architecture, Not Just a Stream API

Accepting a stream in an upload handler does not guarantee the entire file is never held in memory — it depends on how bytes travel through every layer of the pipeline. A common pattern involving browser files routed through an interactive UI circuit, converted to byte arrays, encoded as Base64, and wrapped in JSON can cause multiple full-file copies to overlap in memory simultaneously. Base64 encoding alone inflates binary data by roughly one third before accounting for the surrounding JSON and transport overhead, making this approach a risk for large or concurrent uploads. A more robust architecture routes the browser's multipart HTTP upload directly to a dedicated endpoint, which passes a stream and declared length straight to storage without intermediate conversions. Even then, frameworks like ASP.NET Core may buffer smaller files in memory and larger ones on disk, so claims of zero-copy or constant-memory usage are rarely fully accurate.