IFormFile/StreamPart in shared model library

[frogcrush]

Has anyone come up with a good method for sharing models that take IFormFile/StreamPart?

[glennawatson]

The trick is to keep the shared model framework-agnostic and only adapt to the Refit/ASP.NET types at the edges.

Things to know:

• Refit multipart parameters accept plain Stream, FileInfo, byte[] and string directly. You do not have to use StreamPart in your shared types. StreamPart/ByteArrayPart/FileInfoPart only add control over file name and content type.
• IFormFile is an ASP.NET Core abstraction (Microsoft.AspNetCore.Http). Refit does not consume it directly, so do not put IFormFile in a model shared with non-ASP.NET clients.

Recommended layout:

• In the shared library, model the upload with primitives: a Stream (or byte[]) plus optional FileName/ContentType strings. No Refit and no ASP.NET reference needed.
• On the Refit client interface, take those primitives, or take Refit StreamPart only in the client project (not the shared model) when you need to set file name / content type:

// shared model project (no Refit, no ASP.NET)
public sealed record UploadRequest(Stream Content, string FileName, string ContentType);

// client project (references Refit)
public interface IFilesApi
{
    [Multipart]
    [Post("/files")]
    Task Upload([AliasAs("file")] StreamPart file);
}

// adapter, client side
var part = new StreamPart(req.Content, req.FileName, req.ContentType);
await api.Upload(part);

• On the server side, map IFormFile to the shared primitives at the controller boundary (formFile.OpenReadStream(), formFile.FileName, formFile.ContentType). Keep IFormFile out of the shared contract.

Bottom line: share Stream/byte[] + metadata strings, and convert to StreamPart (client) or from IFormFile (server) only in the projects that actually reference those frameworks.