The MIME-compliant content type, called multipart/form-data, makes writing HTML that uploads files almost trivial. On the server side though, ASP does not have a way to access data in the multipart/form-data format. The most flexible way to access the uploaded file is through a C++ ISAPI Extension DLL. This article describes a reusable ISAPI extension DLL that allows you to upload images and files without writing C++ code. It is coupled with a few COM components that make it readily reusable for ASP development. With .NET, this whole process is much easier, and this article shows preliminary code that uploads files using ASP.NET features.
MSDN Magazine October 2001
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