Posting articles discard original headers

[mildred]

When handling a POST request with the NNTP server library, the headers are parsed and the original headers are discarded.

In particular, the header order is discarded as the parsed headers are stored in a map that doesn't keep the order.

It would be great to have access to unparsed posted message. Once the message is stored in a buffer, we can then parse at will the headers afterwards. I can prepare a pull request for that.

[dustin]

The problem seems to be next/textproto's MIMEHeader type. Not sure why it was a map, but it's not surprising nobody can figure out how to handle headers.