The Annoyance Filter.pdf - Fourmilab

§63 ANNOYANCE-FILTER QUOTED-PRINTABLE MIME DECODER 59
63. Some systems pad text lines with white space (ASCII blank or horizontal tab characters). This
may result in a line encoded with a “soft line break” at the end appearing, when decoded, with white
space between the supposedly-trailing equal sign and the end of line sequence. If white space follows
an equal sign escape, we ignore it up to the beginning of an end of line sequence. Non-white space
appearing before we sense the end of line is an error; these erroneous characters are ignored.
〈 Ignore white space after soft line break 63 〉 ≡
while (〈 Character is white space 62 〉) {
ch1 = getNextChar ( );
if (ch1 ≡ ’\n’) {
continue;
}
if (¬〈 Character is white space 62 〉) {
nDecodeErrors ++;
}
}
ostringstream os ;
os ≪ "Invalid␣character␣’" ≪ static cast〈char〉(ch1 ) ≪
"’␣after␣soft␣line␣break␣in␣Quoted−Printable␣MIME␣part.";
mf ⃗ reportParserDiagnostic(os .str ( ));
ch1 = ’␣’; /∗ Fake a space and soldier on ∗/
This code is used in section 60.
64. The hex to nybble method converts a hexadecimal digit in the sequence “0123456789ABCDEF” or
the equivalent with lower case letters to its binary value. If an invalid hexadecimal digit is supplied, −1
is returned.
〈 Class implementations 11 〉 +≡
int quotedPrintableMIMEdecoder ::hex to nybble (const int ch )
{
if ((ch ≥ ’0’) ∧ (ch ≤ (’0’ + 9))) {
return ch − ’0’;
}
else if ((ch ≥ ’A’) ∧ (ch ≤ (’A’ + 5))) {
return 10 + (ch − ’A’);
}
else if ((ch ≥ ’a’) ∧ (ch ≤ (’a’ + 5))) {
return 10 + (ch − ’a’);
}
return −1;
}