I am working on an image file upload method in Web API 2 and have noticed that the extension method IsMimeMultipartContent can take a string subtype parameter, as documented here:
https://learn.microsoft.com/en-us/previous-versions/aspnet/hh835657(v%3Dvs.118)
However, the only specification for this parameter is "The MIME multipart subtype to match." and no examples of format are present in the documentation.
I presume that, as a string value, it must take a value such as "image/png". Is there a way for it to check against all images, such as using a wildcard value "image/*" or value separated by semicolons on commas? What is the required format of this parameter?
If it can't check for multiple MIME types, is there a better way to check?
The string subtype parameter is a multipart MIME subtype. It is appended to the mime type multipart/ and compared to the incoming MIME type of the data, as such:
content.Headers.ContentType.MediaType.Equals("multipart/" + subtype, StringComparison.OrdinalIgnoreCase)
This has been taken from the source code, publicly visible here.
It will not work with image/png because it looks for multipart/<subtype> MIME types.
Typical valid subtypes are form-data and byteranges. More can be read about MIME types and subtypes here.