C.2.5.1 Message Header Entries

These entries specify which message header lines should be included in an SMS message and how they should be abbreviated or otherwise converted. Only if a header line is successfully mapped to a string of non-zero length by one of these entries will it be included in the SMS message being generated. Each entry has the format

H|pattern replacement-text

If a message header line matches the pattern then it will be replaced with the replacement text replacement-text using the mapping file’s pattern matching and string substitution facilities. The final result of mapping the header line will then be included in the SMS message provided that the metacharacter $Y was specified in the replacement text. If a header line does not match any pattern string, if it maps to a string of length zero, or if the $Y metacharacter is not specified in the replacement text, then the header line will be omitted from the SMS message. The two entries

H|From:* F:$0$Y 
H|Subject:* S:$0$Y

cause the From: and Subject: header lines to be included in SMS messages with From: and Subject: abbreviated as F: and S:. The entries:

H|Date:* H|D:$0$R$Y 
H|D:*,*%19%%*:*:* H|D:$0$ $5:$6$R$Y

cause the Date: header line to be accepted and mapped such that, for instance, the header line

Date: Wed, 16 Dec 1992 16:13:27 -0700 (PDT)

will be converted to

D: Wed 16:13

Very complicated, iterative mappings may be built. Sites wishing to set up custom filters will first need to understand how the mapping file works. The H| in the right-hand-side of the entry may be omitted, if desired. The H| is allowed in that side so as to cut down on the number of table entries required by sets of iterative mappings.