Content type automatically added by Mt.multipart

[lyrm]

This issue is about the two following functions of the Mt module :

val multipart : rng:'g rng -> ?header:Header.t -> ?boundary:string -> part list -> multipart
val make : Header.t -> 'x body -> 'x -> t

There are two ways of building the "same" email with predefined header header.

More intuitive choice

let mail = 
   Mt.multipart ~rng:Mt.rng parts 
   |> Mt.make header Mt.multi

Second choice

let mail = 
   Mt.multipart ~header ~rng:Mt.rng parts 
   |> Mt.make Header.empty Mt.multi

The issue is the following: the multipart function checks the input header for the content type and adds it if necessary. So the first solution does not work properly : the final headers can have multiple content-type headers (the one in the predefined header and the added one).

But the first solution is clearly suggested by the API as header is an optional argument for multipart but not for make.

I think an easy solution will be to remove the header argument of the make function.

[dinosaure]

Hmmhmm, I can see your point but spontaneously, when we want to make an email with only one part (so Mt.simple), we expect to pass the global header to our email via make instead of to use the header from the given part. I think, your solution (to delete header from make) can be good if we have a good documentation 👍.

[paurkedal]

Would the following not be a simpler interface?

val make_simple : header: Header.t -> part -> t
val make_multi : ?header: Header.t -> multipart -> t

Would something be lost by dropping/deprecating the _ body abstraction?