Removed support to handle ARPAnet (RFC733) addresses containing ` at '.

[mmh] / docs / README.attachments

Jon Steinhart's (jon@fourwinds.com) Attachment Handling Mods
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

A bunch of changes have been made to improve the nmh user interface for
handling MIME attachments.

Why Did I Do This?
~~~~~~~~~~~~~~~~~~

Although nmh contains the necessary functionality for MIME message handing,
the interface to this functionality is pretty obtuse.  There's no way that
I'm ever going to convince my partner to write mhbuild composition files!
And even though I know how to write them, I often screw up when sending a
message that contains a shell script because I forget that I have to double
any # at the start of a line, which shell scripts have galore.

These changes simplify the task of managing attachments on draft files.
They allow attachments to be added, listed, and deleted.  MIME messages are
automatically created when drafts with attachments are sent.

The Simple Setup
~~~~~~~~~~~~~~~~

The gory details are all given below.  Here's how to set things up simply.  This
only works if you're using the "standard" interface, i.e., whatnow.  Life is more
complicated if you run mh-e.

Add the following to your .mh_profile:

        send: -attach X-MH-Attachment
        whatnow: -attach X-MH-Attachment

You may already have send and whatnow lines in your .mh_profile; if you do, just add
the new stuff to the end of the line.  For example, mine looks like:

        send: -alias aliases -attach X-MH-Attachment
        whatnow: -attach X-MH-Attachment

That's it.  Next time you want to send an attachment, say "attach filename" at the
whatnow prompt and you're done.  You can check your attachments by saying "alist".

Did I Do This Correctly?
~~~~~~~~~~~~~~~~~~~~~~~~

Hard to say.  Despite lots of time looking at the nmh code, I can't say that
I get the philosophy behind its structure.

I am aware of two deviations from what I saw in the nmh code.

 1.  I commented my changes.

 2.  It's been years since I've used a VT-100, so I don't try to make code
     fit into 80 columns anymore.  Seems silly to me.

What Did I Do?
~~~~~~~~~~~~~~

I made changes to the following files:

        h/
                prototypes.h
        man/
                anno.man
                send.man
                whatnow.man
        uip/
                Makefile.in
                anno.c
                annosbr.c
                send.c
                sendsbr.c
                viamail.c       (needed change for new sendsbr argument)
                whatnowsbr.c

Attachments are associated with messages using header fields.  For example, a
draft that looks like this

        To: jon
        Subject: test of attachments
        X-MH-Attachment: /export/home/jon/foo
        X-MH-Attachment: /export/home/jon/bar
        X-MH-Attachment: /export/home/jon/test/foo
        --------

has the files "foo", "bar", and foo as attachments.

Although I use the header field name "X-MH-Attachment" to indicate
attachments, the implementation allows any header field name.

The advantage of using header fields is that the list of attachments
travels with the draft so it remains valid across editing sessions.

Note that the header fields for attachments are removed from the message
before it is sent.

Since I was adding header fields to messages, it seemed sensible to use the
existing anno program to do this for me.  This required several changes to
generalize anno:

 o  I added a -draft option that permits annotations (header fields) to
    be added to the draft instead of a message sequence.

 o  I added a -delete option that allows annotations to be deleted.

 o  I added a -list option that allows annotations to be listed.

 o  I added a -number option that modifies the behavior of -delete and -list.

 o  I added a -append option so that annotations are appended to the headers
    instead of the default prepend.  Without this, attachments come out in
    reverse order.

Using the modified anno, the example above could be created (assuming that the
draft exists) by

        prompt% anno -draft -comp X-MH-Attachment -text /export/home/jon/foo -nodate -append
        prompt% anno -draft -comp X-MH-Attachment -text /export/home/jon/bar -nodate -append
        prompt% anno -draft -comp X-MH-Attachment -text /export/home/jon/test/foo -nodate -append

One can quite easily make an "attach" command using shell scripts, aliases or functions.
For example, here's a bash function that does the job:

        function attach() { for i in $*; do anno -append -nodate -draft -comp X-MH-Attachment -text "$i"; done; }

The following examples show the different ways in which attachments can be
listed.

        prompt% anno -list -draft -comp X-MH-Attachment
        foo
        bar
        foo

        prompt% anno -list -draft -comp X-MH-Attachment -text /
        /export/home/jon/foo
        /export/home/jon/bar
        /export/home/jon/test/foo

        prompt% anno -list -draft -comp X-MH-Attachment -number
        1       foo
        2       bar
        3       foo

        prompt% anno -list -draft -comp X-MH-Attachment -text / -number
        1       /export/home/jon/foo
        2       /export/home/jon/bar
        3       /export/home/jon/test/foo

        prompt%

Why all these listing options?

I feel that the listing as produced by the first example is what most people
would want most of the time.

The listing as produced by the second example seemed necessary for situations
where there were several attachments with the same file name in different
directories.

I included the numbering option so that attachments could be deleted by number
which might be easier in situations where there were several attachments with
the same file name in different directories, as in the above example.

Attachments are deleted using the -delete option.

        prompt% anno -delete -draft -comp X-MH-Attachment -text foo

deletes the first attachment since the foo matches the basename of the attachment
name.

        prompt% anno -delete -draft -comp X-MH-Attachment -text /export/home/jon/test/foo

deletes the third attachment since the text is a full path name and matches.

        prompt% anno -delete -draft -comp X-MH-Attachment -number 2

deletes the second attachment.

The attachment annotations are converted to a MIME message by send.  I'm not
completely sure that this is the right place to do it, as opposed to doing
it in post, but both would work.  It seemed to me to make more sense to do
it in send so that all of the various post options would apply to the MIME
message instead of the original draft file.

I added an -attach option to send that specifies the header field name used
for attachments.  Send performs the following additional steps if this option
is set:

 o  It scans the header of the draft for attachments.  Normal behavior applies
    if none exist.

 o  A temporary mhbuild composition file is created if there are attachments.

 o  All non-attachment headers are copied from the draft file to the
    composition file.

 o  The body of the draft is copied to a temporary body file if it contains at
    least one non-whitespace character.  A mhbuild directive for this file is
    appended to the composition file.  Note that this eliminates the problem
    of lines beginning with the # character in the message body.

 o  A mhbuild directive is appended to the composition file for each attachment
    header.

 o  mhbuild is run on the composition file, converting it to a MIME message.

 o  The converted composition file is substituted for the original draft file
    and run through the rest of send.

 o  The original draft file is renamed instead of the converted composition
    file.  This preserves the original message instead of the composition file
    which is really what a user would want.

 o  The ,file.orig file created by mhbuild is removed as it's a nuisance.

The mhbuild directives appended to the composition file are constructed as
follows:

 o  The content-type a file with a dot-suffix is obtained from the list of
    mhshow-suffix- entries in the profile.

 o  A file with no dot-suffix or no entry in the profile is assigned a
    content-type of application/octet-stream if it contains any non-ASCII
    characters.

 o  A file with no dot-suffix or no entry in the profile is assigned a
    content-type of text/plain if it contains only ASCII characters.

 o  The directive is of the form:

        #content-type; name="basename"; x-unix-mode=mode [ description ] filename

    The content type is derived as discussed above.  The basename is the
    last component of the pathname given in the body of the attachment header
    field.  The mode is file permissions.  The description is obtained by
    running the file command on the attachment file.  The filename is the
    field body from the attachment header field.

I added an -attach option to whatnow that specifies the header field name for
attachments.

I added to the commands available at the whatnow prompt to provide an interface
to the attachment mechanism.

I'm not completely happy with some of these additions because they duplicate
shell functionality.  I'm not sure that there's a good way around it other than
to not use whatnow.

The first three additions (the ones I'm not happy with) are cd, ls, and pwd.
These do the same thing as their system counterparts.  As a matter of fact,
these are implemented by running the commands in a subshell.  I did this because
I wanted proper interpretation of shell-specific things like ~ and wildcard
expansion.

The next command is attach.  This takes a list of files and adds them to the draft
as attachments using the same code as the modified anno.  The list of files is
run through ls using the user's shell, so wildcard expansion and all that works.

The alist command lists the attachments on the current draft using listing function
that I added to anno.  It takes two optional options, -l for a long listing meaning
full path names, and -n for a numbered listing.

The detach command removes attachments from the current draft, again using the
modified anno.  The arguments are interpreted as numbers if the -n option is used,
otherwise they're interpreted as file names.  File names are shoveled through ls
using the user's shell in the directory containing the file for wildcard expansion
and such.  File names are matched against the last pathname component unless they
begin with a / in which case they're matched against the entire name.

What's Left To Do?
~~~~~~~~~~~~~~~~~~

Nothing on this stuff.  When I get time I'd like to improve the interface
for reading messages with attachments.  It's my opinion that, because of the
command line nature of nmh, it makes the most sense to treat attachments as
separate messages.  In other words one should be able to read the next
attachment using next, and the previous one using prev.  One should be able
to show and scan attachments.  This would probably involve a major change
in the message numbering scheme to allow something like 123.4 to indicate
attachment 4 on message 123.

        Jon Steinhart