What problem does it solve? Building file upload endpoints in ASP.NET Core minimal APIs involves several non-obvious pitfalls: IFormFile binding rules, two separate size limits (Kestrel and FormOptions), automatic anti-forgery validation in .NET 8+, and security risks from trusting user-supplied filenames or content types. This Skill provides correct, production-oriented patterns for each of these concerns. ## Core Features & Use Cases - IFormFile Binding Patterns: Correctly bind single files, multiple files (IFormFileCollection), and mixed form fields using [FromForm] in minimal API endpoints. - Size Limit Configuration: Configure both Kestrel MaxRequestBodySize and FormOptions.MultipartBodyLengthLimit, plus per-endpoint overrides with RequestSizeLimit and DisableRequestSizeLimit. - Security Validation: Validate uploads via magic bytes instead of trusting Content-Type or file extensions, and prevent path traversal by generating safe filenames. - Large File Streaming: Use MultipartReader to stream large uploads directly to disk without buffering entire files in memory. - Use Case: You are building a .NET 8 API that accepts image uploads from a mobile client. Use this Skill to implement the endpoint with proper size limits, anti-forgery opt-out for JWT-authenticated APIs, and content-based file type verification. ## Quick Start Ask the AI to create a minimal API file upload endpoint in .NET 8 that accepts images with size limits and content validation.
