Consider using System.Text.Encoding for encodings?

[haf]

This would mean that you don't have to parse the encoding every request, from string, but instead could pass the actual value you're going to use around.

[relentless]

I don't know about this, seems that it would put more of a burden on the caller. If it makes the user's job easier, I don't mind a bit of extra parsing on our part.

[haf]

It depends on how you program your code; in all my app code, I already have UTF8 encoding there and ready to use, because I interface with web APIs or write them.

However, how about a withBodyEncodingString (enc : string) ...?

Also, if you are forced to pass a valid encoding, you can rely much more on your compiler and that takes the burden from the programmer.