mhn.me

早期freebsd实现

if someone's sent you a message in several parts,
you might put them all in their own folder and do:
.sp
.in +.5i
mhn all -store
.in -.5i
.sp
This will store exactly one message,
containing the sum of the parts.
Note that if \fImhn\fR can not locate each part,
it will not store anything.

Finally,
if the `\-auto' switch is given and the content contains information
indicating the filename the content should be stored as
(and if the filename doesn't begin with a '/'),
then the filename from the content will be used instead.

.Uh "External Access"
For contents of type message/external-body,
.ne 12
\fImhn\fR supports these access-types:
.sp
.nf
.in +.5i
afs
anon-ftp
ftp
local-file
mail-server
.in -.5i
.fi
.sp
For the \*(lqanon-ftp\*(rq and \*(lqftp\*(rq access types,
if your system supports a SOCKETs interface to TCP/IP,
then \fImhn\fR will use a built-in FTP client.
Otherwise,
\fImhn\fR will look for the \fBmhn-access-ftp\fR profile entry,
.ne 6
e.g.,
.sp
.in +.5i
mhn-access-ftp: myftp.sh
.in -.5i
.sp
to determine the pathname of a program to perform the FTP retrieval.
.ne 14
This program is invoked with these arguments:
.sp
.nf
.in +.5i
domain name of FTP-site
username
password
remote directory
remote filename
local filename
\*(lqascii\*(rq or \*(lqbinary\*(rq
.in -.5i
.fi
.sp
The program should terminate with a zero-valued exit-status if the
retrieval is successful.

.Uh "The Content Cache"
When \fImhn\fR encounters an external content containing a
\*(lqContent-ID:\*(rq field,
and if the content allows caching,
then depending on the caching behavior of \fImhn\fR,
the content might be read from or written to a cache.

The caching behavior of \fImhn\fR is controlled with
the `\-rcache' and `\-wcache' switches,
which define the policy for reading from,
and writing to,
the cache, respectively.
One of four policies may be specified:
\*(lqpublic\*(rq,
indicating that \fImhn\fR should make use of a
publically-accessible content cache;
\*(lqprivate\*(rq,
indicating that \fImhn\fR should make use of the user's
private content cache;
\*(lqnever\*(rq,
indicating that \fImhn\fR should never make use of caching;
and,
\*(lqask\*(rq,
indicating that \fImhn\fR should ask the user.

There are two directories where contents may be cached:
the profile entry \fBmhn-cache\fR names a directory containing
world-readable contents,
and,
the profile entry \fBmhn-private-cache\fR names a directory containing
private contents.
The former should be an absolute (rooted) directory name.
.ne 6
For example,
.sp
.in +.5i
mhn-cache: /tmp
.in -.5i
.sp
might be used if you didn't care that the cache got wiped after each reboot
of the system.
The latter is interpreted relative to the user's MH directory,
if not rooted,
.ne 6
e.g.,
.sp
.in +.5i
mhn-private-cache: .cache
.in -.5i
.sp
(which is the default value).

.Uh "Caching the Contents"
When you encounter a content of type message/external-body with access type
\*(lqmail-server\*(rq,
\fImhn\fR will ask you if may send a message to a mail-server
requesting the content,
.ne 14
e.g.,
.sp
.nf
.in +.5i
% show 1
Retrieve content by asking mail-server@...

SEND file

? yes
mhn: request sent
.in -.5i
.fi
.sp
Regardless of your decision,
\fImhn\fR can't perform any other processing on the content.

However,
if \fImhn\fR is allowed to request the content,
then when it arrives,
there should be a top-level \*(lqContent-ID:\*(rq field which
corresponds to the value in the original message/external-body content.
You should now use the `-cache' switch to tell \fImhn\fR to enter the
arriving content into the content cache,
.ne 8
e.g.,
.sp
.nf
.in +.5i
% mhn -cache 2
caching message 2 as file ...
.in -.5i
.fi
.sp
You can then re-process the original message/external-body content,
and \*(lqthe right thing should happen\*(rq,
.ne 8
e.g.,
.sp
.nf
.in +.5i
% show 1
\0...
.in -.5i
.fi

.Uh "Composing the Contents"
The \fImhn\fR program can also be used as a simple editor to aid in
composing multi-media messages.
When invoked by a \fIwhatnow\fR program,
\fImhn\fR will expect the body of the draft to be formatted as an
\*(lq\fImhn\fR composition file.\*(rq

.ne 59
The syntax of this is straight-forward:
.sp
.nf
.in +.5i
   body         ::=     1*(content | EOL)

   content      ::=     directive | plaintext

   directive    ::=     "#" type "/" subtype
                            0*(";" attribute "=" value)
                            [ "(" comment ")" ]
                            [ "<" id ">" ]
                            [ "[" description "]" ]
                            [ filename ]
                            EOL

                      | "#@" type "/" subtype
                            0*(";" attribute "=" value)
                            [ "(" comment ")" ]
                            [ "<" id ">" ]
                            [ "[" description "]" ]
                            external-parameters
                            EOL

                      | "#forw"
                            [ "<" id ">" ]
                            [ "[" description "]" ]
                            [ "+"folder ] [ 0*msg ]
                            EOL

                      | "#begin"
                              [ "<" id ">" ]
                              [ "[" description "]" ]
                              [   "alternative"
                                | "parallel"
                                | something-else    ]
                              EOL
                            1*body
                        "#end" EOL

   plaintext    ::=     [ "Content-Description:"
                              description EOL EOL ]
                            1*line
                        [ "#" EOL ]

                      | "#<" type "/" subtype
                            0*(";" attribute "=" value)
                            [ "(" comment ")" ]
                            [ "[" description "]" ]
                            EOL
                            1*line
                        [ "#" EOL ]

   line         ::=     "##" text EOL
                        -- interpreted as "#"text EOL
                      | text EOL
.in -.5i
.fi
.sp
Basically,
the body contains one or more contents.
A content consists of either a directive,
indicated with a \*(lq#\*(rq as the first character of a line;
or,
plaintext (one or more lines of text).
The continuation character, \*(lq\\\*(lq, may be used to enter a single
.ne 11
directive on more than one line,
e.g.,
.sp
.nf
.in +.5i
#@application/octet-stream; \\
    type=tar; \\
    x-conversions=compress
.in -.5i
.fi
.sp
There are four kinds of directives:
\*(lqtype\*(rq directives,
which name the type and subtype of the content;
\*(lqexternal-type\*(rq directives,
which also name the type and subtype of the content;
the \*(lqforw\*(rq directive,
which is used to forward a digest of messages;
and,
the \*(lqbegin\*(rq directive,
which is used to create a multipart content.

For the type directives,
the user may optionally specify the name of a file containing the
contents in \*(lqnative\*(rq (decoded) format.
(If the filename starts with the \*(lq|\*(rq character,
then this gives a command whose output is captured accordingly.)
If a filename is not given,
\fImhn\fR will look for information in the user's profile to determine
how the different contents should be composed.
This is accomplished by consulting a composition string,
and executing it under \fB/bin/sh\fR,
with the standard output set to the content.
.ne 13
The composition string may contain these escapes:
.sp
.nf
.in +.5i
.ta \w'%P  'u
%a	additional arguments
%f	filename containing content
%F	%f, and stdout is not re-directed
%s	subtype
.re
.in -.5i
.fi
.sp
First,
\fImhn\fR will look for an entry of the form:
.sp
.in +.5i
mhn-compose-<type>/<subtype>
.in -.5i
.sp
to determine the command to use to compose the content.
If this isn't found,
\fImhn\fR will look for an entry of the form:
.sp
.in +.5i
mhn-compose-<type>
.in -.5i
.sp
to determine the composition command.
If this isn't found,
\fImhn\fR will complain.

An example entry might be:
.sp
.in +.5i
mhn-compose-audio/basic: record | raw2audio -F
.in -.5i
.sp
Because commands like these will vary,
depending on the display environment used for login,
composition strings for different contents should probably be put in
the file specified by the \fB$MHN\fR environment variable,
instead of directly in your user profile.

The external-type directives are used to provide a reference to a content,
rather than enclosing the contents itself.
Hence,
instead of providing a filename as with the type directives,
external-parameters are supplied.
These look like regular parameters,
.ne 15
so they must be separated accordingly,
e.g.,
.sp
.nf
.in +.5i
#@application/octet-stream; \\
    type=tar; \\
    x-conversions=compress [] \\
    access-type=anon-ftp; \\
    name="mh-mime.tar.Z"; \\
    directory="mrose/mh-mime"; \\
    site="ftp.ics.uci.edu"
.in -.5i
.fi
.sp
By specifying \*(lq[]\*(rq,
an empty description string is given,
and the start of the external-parameters is identified.
.ne 19
These parameters are of the form:
.sp
.nf
.in +.5i
.ta \w'access-type=  'u
access-type=	usually \fIanon-ftp\fR or \fImail-server\fR
name=	filename
permission=	read-only or read-write
site=	hostname
directory=	directoryname (optional)
mode=	usually \fIascii\fR or \fIimage\fR (optional)
size=	number of octets
server=	mailbox
subject=	subject to send
body=	command to send for retrieval
.re
.in -.5i
.fi
.sp

For the forw directive,
the user may optionally specify the name of the folder and which
messages are to be forwarded.
if a folder is not given,
it defaults to the current folder.
Similarly,
if a message is not given,
it defaults to the current message.
Hence,
the forw directive is similar to the \fIforw\fR\0(1) command,
except that the former uses the MIME rules for encapsulation
rather than those specified in RFC 934.
Usage of the `\-rfc934mode' switch indicates whether \fImhn\fR should
attempt to utilize the encapsulation rules in such a way as to appear
that RFC 934 is being used.
If given,
then RFC 934-compliant user-agents should be able to burst the message on
reception\0--\0providing that the messages being encapsulated do not
contain encapsulated messages themselves.
The drawback of this approach is that the encapsulations are generated
by placing an extra newline at the end of the body of each message.

For the begin directive,
the user must specify at least one content between
the begin and end pairs.