The Annoyance Filter.pdf - Fourmilab

§157 ANNOYANCE-FILTER MAIL FOLDER 133
157. Test for Content-Types we are never interested in parsing, regardless of their encoding. This
includes images, video, and most application specific files which UNIX strings would make no sense
of. These parts are dispatched to the sink decoder for disposal. Note that some of these items may
be compressed files and/or archives (zip, gzip, tar, etc.) which might be comprehensible if we could
enlist the appropriate utilities, but we’ll defer that refinement for now.
〈 Test for Content-Types we always ignore 157 〉 ≡
if (Annotate (’d’)) {
ostringstream os ;
reportParserDiagnostic("");
os ≪ "mimeContentType:␣{" ≪ mimeContentType ≪ "}";
reportParserDiagnostic(os );
os .str ("");
os ≪ "mimeContentTypeCharset:␣{" ≪ mimeContentTypeCharset ≪ "}";
reportParserDiagnostic(os );
os .str ("");
os ≪ "mimeContentTransferEncoding:␣{" ≪ mimeContentTransferEncoding ≪ "}";
reportParserDiagnostic(os );
}
if ((asp ≡ Λ) ∧ (mimeContentType .substr (0, 6) ≡ "image/") ∨ (mimeContentType .substr (0,
6) ≡ "video/")) {
smd .set(is , this, partBoundary , tlist );
mdp = &smd ;
if (Annotate (’d’)) {
ostringstream os ;
}
os ≪ "Activating␣MIME␣sink␣decoder␣with␣sentinel:␣\"" ≪ partBoundary ≪
"\"␣due␣to␣Content−Type␣=␣" ≪ mimeContentType ;
reportParserDiagnostic(os );
}
if (dlist ) {
dlist ⃗ push back (Xfile + "−Decoder:␣Sink");
}
This code is used in section 153.
158. Next, check for content types we’re always interested parsing. This includes most forms labeled
as text and embedded mail messages. If the content is of interest but is encoded, make sure we have
the requisite decoder and, if so, plumb it into the pipeline.
〈 Process Content-Types we are interested in parsing 158 〉 ≡
else
if (byteStream ∨ (asp ≠ Λ) ∨ (mimeContentType ≡ "plain/txt") ∨ (mimeContentType .substr (0,
5) ≡ "text/") ∨ (mimeContentType ≡ "message/rfc822")) {
〈 Test for multiple byte character sets and activate decoder if available 159 〉;
〈 Verify Content-Transfer-Encoding and activate decoder if necessary 160 〉;
〈 Cancel byte stream interpretation for non-binary encoded parts 161 〉;
〈 Test for message/rfc822 embedded as part 162 〉;
}
This code is used in section 153.