read_mail (rdm) enhancement for brief header display mode

[Trn]

rdm would be greatly enhanced with an equivalent of Emacs rmail-header-format brief-formatting-mode.

Modern internet header bloat makes handling intersystem Mail in rdm less than friendly.

As rdm already support the "-lghe" control argument (long header), I propose that only a subset of important headers, ala rmail brief-formatting-mode be the default, and the full header can be displayed only if specifically requested.

Other alternative implementations are possible and the proposal likely merits further discussion.

[Eric Swenson]

What exists

• read_mail -brief_header (-bfhe) makes brief headers the default for the whole read_mail session. The print request takes -bfhe, -header (the normal default) and -long_header. Brief mode shows the date, the authors, the subject if any, a recipient count when it matters, and forwarding comments (read_mail.info, print.info).
• So a user can have brief headers now, with an abbrev, e.g. .ab rdm read_mail -brief_header, or in their start_up. The ticket's request to make brief the *system* default would change behavior for every user; I don't recommend it.

What is actually missing

The trouble with Internet mail is the default (-header) mode. In
mlsys_format_ (bound_mail_system_, around line 2017, "Finally, process
the user-defined fields") every user-defined field is printed. Fields the
mail system does not know (X-*, DKIM-Signature, MIME-Version,
Content-Type, List-*, ARC-*, ...) are all user-defined fields, so
they all appear. Received is trace and is already left out. Brief mode
drops all user-defined fields; there is nothing in between.

Possible enhancement (Emacs rmail-ignored-headers style)

• A per-user list of field names to leave out (or keep) in the default mode, kept in the user's value segment, e.g. `value_set -pn mail_system read_mail.ignored_fields "X-* DKIM-Signature ...", read by read_mail` at startup and settable with a new control argument / print -ignore FIELDS.
• Implementation: mlsys_format_ would skip a user-defined field whose name matches the list (star-name matching with match_star_name_). The list has to get there through the format options, so format_message_options (in mlsys_format_options.incl.pl1) needs a new version with a pointer to the list. The callers that build that structure (read_mail's print, print_mail, send_mail's print, Emacs rmail via the mail system) would keep working on the old version.
• A system-wide default list (installed in a site value segment) could give reasonable behavior without changing -bfhe semantics.

This changes bound_mail_system_ and the read_mail/print_mail requests
and docs. A decision on the approach is needed first.