private int read0()

in core/src/main/java/org/apache/james/mime4j/codec/QuotedPrintableInputStream.java [177:294]
100 lines of code
35 McCabe index (conditional complexity)

    private int read0(final byte[] buffer, final int off, final int len) throws IOException {
        boolean eof = false;
        int to = off + len;
        int index = off;

        // check if a previous invocation left decoded content
        if (decodedBuf.length() > 0) {
            int chunk = Math.min(decodedBuf.length(), to - index);
            System.arraycopy(decodedBuf.buffer(), 0, buffer, index, chunk);
            decodedBuf.remove(0, chunk);
            index += chunk;
        }

        while (index < to) {

            if (limit - pos < 3) {
                int bytesRead = fillBuffer();
                eof = bytesRead == -1;
            }

            // end of stream?
            if (limit - pos == 0 && eof) {
                return index == off ? -1 : index - off;
            }

            while (pos < limit && index < to) {
                int b = encoded[pos++] & 0xFF;

                if (lastWasCR && b != LF) {
                    if (monitor.warn("Found CR without LF", "Leaving it as is")) {
                        throw new IOException("Found CR without LF");
                    }
                    index = transfer(CR, buffer, index, to, false);
                } else if (!lastWasCR && b == LF) {
                    if (monitor.warn("Found LF without CR", "Translating to CRLF")) {
                        throw new IOException("Found LF without CR");
                    }
                }

                if (b == CR) {
                    lastWasCR = true;
                    continue;
                } else {
                    lastWasCR = false;
                }

                if (b == LF) {
                    // at end of line
                    if (blanks.length() == 0) {
                        index = transfer(CR, buffer, index, to, false);
                        index = transfer(LF, buffer, index, to, false);
                    } else {
                        if (blanks.byteAt(0) != EQ) {
                            // hard line break
                            index = transfer(CR, buffer, index, to, false);
                            index = transfer(LF, buffer, index, to, false);
                        }
                    }
                    blanks.clear();
                } else if (b == EQ) {
                    if (limit - pos < 2 && !eof) {
                        // not enough buffered data
                        pos--;
                        break;
                    }

                    // found special char '='
                    int b2 = getnext();
                    if (b2 == EQ) {
                        index = transfer(b2, buffer, index, to, true);
                        // deal with '==\r\n' brokenness
                        int bb1 = peek(0);
                        int bb2 = peek(1);
                        if (bb1 == LF || (bb1 == CR && bb2 == LF)) {
                            monitor.warn("Unexpected ==EOL encountered", "== 0x"+bb1+" 0x"+bb2);
                            blanks.append(b2);
                        } else {
                            monitor.warn("Unexpected == encountered", "==");
                        }
                    } else if (Character.isWhitespace((char) b2)) {
                        // soft line break
                        int b3 = peek(0);
                        if (!(b2 == CR && b3 == LF)) {
                            if (monitor.warn("Found non-standard soft line break", "Translating to soft line break")) {
                                throw new IOException("Non-standard soft line break");
                            }
                        }
                        if (b3 == LF) {
                            lastWasCR = b2 == CR;
                        }
                        index = transfer(-1, buffer, index, to, true);
                        if (b2 != LF) {
                            blanks.append(b);
                            blanks.append(b2);
                        }
                    } else {
                        int b3 = getnext();
                        int upper = convert(b2);
                        int lower = convert(b3);
                        if (upper < 0 || lower < 0) {
                            monitor.warn("Malformed encoded value encountered", "leaving "+((char) EQ)+((char) b2)+((char) b3)+" as is");
                            // TODO see MIME4J-160
                            index = transfer(EQ, buffer, index, to, true);
                            index = transfer(b2, buffer, index, to, false);
                            index = transfer(b3, buffer, index, to, false);
                        } else {
                            index = transfer((upper << 4) | lower, buffer, index, to, true);
                        }
                    }
                } else if (Character.isWhitespace(b)) {
                    blanks.append(b);
                } else {
                    index = transfer(b & 0xFF, buffer, index, to, true);
                }
            }
        }
        return to - off;
    }