The Annoyance Filter.pdf - Fourmilab

§160 ANNOYANCE-FILTER MAIL FOLDER 135
160. If the contents appear to be in a character set we understand, we still aren’t home free—the part
may be encoded in a manner for which we lack a decoder. Analyse the Content−Transfer−Encoding
specification and select the appropriate decoder. If we lack a decoder, we must regretfully consign the
part to the sink decoder.
If we end up accreting any additional decoders, this should probably be re-written to look up the
decoder in a map〈string, MIMEdecoder ∗〉 and use common code for every decoder.
〈 Verify Content-Transfer-Encoding and activate decoder if necessary 160 〉 ≡
if (¬gibberish ) {
if ((mimeContentTransferEncoding .length ( ) ≡ 0) ∨ (mimeContentTransferEncoding .substr (0,
4) ≡ "7bit") ∨ (mimeContentTransferEncoding .substr (0,
4) ≡ "8bit") ∨ (mimeContentTransferEncoding ≡ "ascii")) {
imd .set(is , this, partBoundary , tlist ); /∗ Identity ∗/
mdp = &imd ;
}
else if (mimeContentTransferEncoding ≡ "base64") {
bmd .set(is , this, partBoundary , tlist ); /∗ Base64 ∗/
mdp = &bmd ;
}
else if (mimeContentTransferEncoding ≡ "quoted−printable") {
qmd .set(is , this, partBoundary , tlist ); /∗ Quoted−Printable ∗/
mdp = &qmd ;
}
else {
gibberish = true ;
smd .set(is , this, partBoundary , tlist ); /∗ Sink ∗/
mdp = &smd ;
}
assert(mdp ≠ Λ);
if (Annotate (’d’)) {
ostringstream os ;
}
os ≪ (gibberish ? "Rejecting" : "Accepting") ≪
"␣part␣in␣Content−Transfer−Encoding:␣" ≪ mimeContentTransferEncoding ≪
"␣␣(" ≪ mimeContentTypeCharset ≪ "␣" ≪ mimeContentType ≪ ")";
reportParserDiagnostic(os );
}
if (dlist ) {
dlist ⃗ push back (Xfile + "−Decoder:␣" + mdp ⃗ name ( ));
}
if (Annotate (’d’)) {
ostringstream os ;
}
os ≪ "Activating␣MIME␣" ≪ mdp ⃗ name ( ) ≪ "␣decoder␣with␣sentinel:␣" ≪ partBoundary ;
reportParserDiagnostic(os );
This code is cited in section 256.
This code is used in section 158.