The Annoyance Filter.pdf - Fourmilab

§152 ANNOYANCE-FILTER MAIL FOLDER 131
152. If we’re in the body of text encoded in a multiple-byte character set, pass the text through the
interpreter to convert it into a form we can better recognise.
〈 Decode multiple byte character set 152 〉 ≡
if ((mbi ≠ Λ) ∧ (¬inHeader ) ∧ (¬inPartHeader )) {
s = mbi ⃗ decodeLine (s);
}
This code is used in section 130.
153. If we’ve just reached the end of a MIME part header, determine if the body which follows
requires decoding. If so, activate the appropriate decoder and place it in the pipeline between the raw
mail folder and our parsing code.
〈 Activate MIME decoder if required 153 〉 ≡
if (multiPart ) {
assert(mdp ≡ Λ);
#ifdef TYPE_LOG /∗ If TYPE_LOG is defined, we create a file containing all of the part properties
we’ve seen. You can obtain a list of things you may need to worry about by processing one of
the fields n of this file with a command like cut −fn /tmp/typelog.txt | sort | uniq. ∗/
typeLog ≪ mimeContentType ≪ "\t" ≪ mimeContentTypeCharset ≪ "\t" ≪
mimeContentTransferEncoding ≪ endl ;
#endif
〈 Check for change of sentinel within message 154 〉;
〈 Check for application file types for which we have a decoder 155 〉;
〈 Detect binary parts worth parsing for embedded ASCII strings 156 〉;
〈 Test for Content-Types we always ignore 157 〉
〈 Process Content-Types we are interested in parsing 158 〉;
}
This code is cited in section 256.
This code is used in section 141.
154. The sentinel which delimits parts of a multi-part message may be changed in the middle of the
message by a Content−Type of multipart/alternative specifying a new boundary=. Detect this and
change the part boundary on the fly. These parts usually seem devoid of content, but just in case fake
a content type of text/plain so anything which may be there gets looked at.
〈 Check for change of sentinel within message 154 〉 ≡
if (mimeContentType ≡ "multipart/alternative") {
if (mimeContentTypeBoundary ≠ "") {
partBoundaryStack .push (partBoundary );
partBoundary = mimeContentTypeBoundary ;
}
else {
if (Annotate (’d’)) {
ostringstream os ;
}
}
}
os ≪ "Boundary␣missing␣from␣Content−Type␣of␣multipart/alternative.";
reportParserDiagnostic(os );
This code is used in section 153.