s-o-1036 June 1994

10.2. Header Synthesis

News  articles prepared by gateways MUST be legal news arti-
cles.  In particular, they MUST include all of the mandatory
headers  (see  section  5)  and  MUST  fully  conform to the
restrictions on said headers.  This often  requires  that  a
gateway function not only as a relayer, but also partly as a
posting agent, aiding in the synthesis of a conforming arti-
cle from non-conforming input.

     NOTE:  The full-conformance requirement needs par-
     ticularly careful attention when gatewaying  mail-
     ing  lists to news, because a number of constructs
     that are legal in MAIL headers are NOT permissible
     in  news  headers.   (Note  also that not all mail
     traffic fully conforms to even the MAIL specifica-
     tion.)   The  rest of this section will be phrased
     in terms of mail-to-news gatewaying, but  most  of
     it is more generally applicable.

The mandatory headers generally present few problems.

If no date information is available, the gateway should sup-
ply a Date header with the gateway's current date.  If  only
partial  information  is available (e.g. date but not time),
this should be fleshed out to a full Date header  by  adding
default values, not by mixing in parts of the gateway's cur-
rent date.  (Defaults should be chosen so  that  fleshed-out
dates  will  not  be in the future!)  It may be necessary to
map timezone information to the restricted  forms  permitted
in the news Date header.  See section 5.1.

     NOTE:  The  prohibition  of mixing dates is on the
     theory that it is better to admit  ignorance  than
     to lie.

If  the author's address as supplied in the original message
is not suitable for inclusion in a From header, the  gateway
MUST  transform it so it is, e.g. by use of the "% hack" and
the domain address of the gateway.  The desire  to  preserve
information  is  NOT  an excuse for violating the rules.  If
the transformation is drastic enough that there is reason to
suspect  loss of information, it may be desirable to include
the original form in an X- header,  but  the  From  header's
contents MUST be as specified in section 5.2.

If  the  message  contains a Message-ID header, the contents
should be dealt with as discussed in section 10.3.  If there
is no message ID present, it will be necessary to synthesize

INTERNET DRAFT to be        NEWS                   sec. 10.2


one, following the news rules (see section 5.3).

Every effort should be made to produce a meaningful  Subject
header;  see section 5.4.  Many news readers select articles
to read based on Subject headers,  and  inserting  a  place-
holder  like  "<no  subject available>" is considered highly
objectionable.  Even synthesizing a Subject header by  pick-
ing  out  the  first  half-dozen nouns and adjectives in the
article body is better than using a  placeholder,  since  it
offers SOME indication of what the article might contain.

The contents of the Newsgroups header (section 5.5) are usu-
ally predetermined by gateway configuration, but  a  gateway
to  a network that has its own concept of newsgroups or dis-
cussions might have to make transformations.  Such transfor-
mations  should be reversible; otherwise confusion is likely
on both sides.

It will rarely be possible for gateways to  provide  a  Path
header  that is both an accurate history of the relayers the
article has passed  through  AS  NEWS  and  a  usable  reply
address.   The  history function MUST be given priority; see
the discussion in section 5.6.  It will usually be necessary
for  a  gateway to supply an empty path list, abandoning the
reply function.

It is desirable for gatewayed articles  to  convey  as  much
useful information as possible, e.g. by use of optional news
headers (see section 6) when  the  relevant  information  is
available.  Synthesis of optional headers can generally fol-
low similar rules.

Software synthesizing References  headers  should  note  the
discussion  in  section  6.5  concerning the incompatibility
between MAIL and news.  Also of interest is the  possibility
of  incorporating  information  from In-Reply-To headers and
from attribution lines in the body; an incomplete  or  some-
what  conjectural References header is much better than none
at all, and reading agents already have to cope with  incom-
plete or slightly erroneous References lists.