Java tutorial
/**************************************************************** * Licensed to the Apache Software Foundation (ASF) under one * * or more contributor license agreements. See the NOTICE file * * distributed with this work for additional information * * regarding copyright ownership. The ASF licenses this file * * to you under the Apache License, Version 2.0 (the * * "License"); you may not use this file except in compliance * * with the License. You may obtain a copy of the License at * * * * http://www.apache.org/licenses/LICENSE-2.0 * * * * Unless required by applicable law or agreed to in writing, * * software distributed under the License is distributed on an * * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY * * KIND, either express or implied. See the License for the * * specific language governing permissions and limitations * * under the License. * ****************************************************************/ package org.apache.james.mime4j.codec; import java.io.IOException; import java.io.InputStream; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; /** * Performs Quoted-Printable decoding on an underlying stream. */ public class QuotedPrintableInputStream extends InputStream { private static Log log = LogFactory.getLog(QuotedPrintableInputStream.class); private InputStream stream; ByteQueue byteq = new ByteQueue(); ByteQueue pushbackq = new ByteQueue(); private byte state = 0; private boolean closed = false; public QuotedPrintableInputStream(InputStream stream) { this.stream = stream; } /** * Terminates Quoted-Printable coded content. This method does NOT close * the underlying input stream. * * @throws IOException on I/O errors. */ @Override public void close() throws IOException { this.closed = true; } @Override public int read() throws IOException { if (closed) { throw new IOException("QuotedPrintableInputStream has been closed"); } fillBuffer(); if (byteq.count() == 0) return -1; else { byte val = byteq.dequeue(); if (val >= 0) return val; else return val & 0xFF; } } /** * Pulls bytes out of the underlying stream and places them in the * pushback queue. This is necessary (vs. reading from the * underlying stream directly) to detect and filter out "transport * padding" whitespace, i.e., all whitespace that appears immediately * before a CRLF. * * @throws IOException Underlying stream threw IOException. */ private void populatePushbackQueue() throws IOException { //Debug.verify(pushbackq.count() == 0, "PopulatePushbackQueue called when pushback queue was not empty!"); if (pushbackq.count() != 0) return; while (true) { int i = stream.read(); switch (i) { case -1: // stream is done pushbackq.clear(); // discard any whitespace preceding EOF return; case ' ': case '\t': pushbackq.enqueue((byte) i); break; case '\r': case '\n': pushbackq.clear(); // discard any whitespace preceding EOL pushbackq.enqueue((byte) i); return; default: pushbackq.enqueue((byte) i); return; } } } /** * Causes the pushback queue to get populated if it is empty, then * consumes and decodes bytes out of it until one or more bytes are * in the byte queue. This decoding step performs the actual QP * decoding. * * @throws IOException Underlying stream threw IOException. */ private void fillBuffer() throws IOException { byte msdChar = 0; // first digit of escaped num while (byteq.count() == 0) { if (pushbackq.count() == 0) { populatePushbackQueue(); if (pushbackq.count() == 0) return; } byte b = pushbackq.dequeue(); switch (state) { case 0: // start state, no bytes pending if (b != '=') { byteq.enqueue(b); break; // state remains 0 } else { state = 1; break; } case 1: // encountered "=" so far if (b == '\r') { state = 2; break; } else if ((b >= '0' && b <= '9') || (b >= 'A' && b <= 'F') || (b >= 'a' && b <= 'f')) { state = 3; msdChar = b; // save until next digit encountered break; } else if (b == '=') { /* * Special case when == is encountered. * Emit one = and stay in this state. */ if (log.isWarnEnabled()) { log.warn("Malformed MIME; got =="); } byteq.enqueue((byte) '='); break; } else { if (log.isWarnEnabled()) { log.warn("Malformed MIME; expected \\r or " + "[0-9A-Z], got " + b); } state = 0; byteq.enqueue((byte) '='); byteq.enqueue(b); break; } case 2: // encountered "=\r" so far if (b == '\n') { state = 0; break; } else { if (log.isWarnEnabled()) { log.warn("Malformed MIME; expected " + (int) '\n' + ", got " + b); } state = 0; byteq.enqueue((byte) '='); byteq.enqueue((byte) '\r'); byteq.enqueue(b); break; } case 3: // encountered =<digit> so far; expecting another <digit> to complete the octet if ((b >= '0' && b <= '9') || (b >= 'A' && b <= 'F') || (b >= 'a' && b <= 'f')) { byte msd = asciiCharToNumericValue(msdChar); byte low = asciiCharToNumericValue(b); state = 0; byteq.enqueue((byte) ((msd << 4) | low)); break; } else { if (log.isWarnEnabled()) { log.warn("Malformed MIME; expected " + "[0-9A-Z], got " + b); } state = 0; byteq.enqueue((byte) '='); byteq.enqueue(msdChar); byteq.enqueue(b); break; } default: // should never happen log.error("Illegal state: " + state); state = 0; byteq.enqueue(b); break; } } } /** * Converts '0' => 0, 'A' => 10, etc. * @param c ASCII character value. * @return Numeric value of hexadecimal character. */ private byte asciiCharToNumericValue(byte c) { if (c >= '0' && c <= '9') { return (byte) (c - '0'); } else if (c >= 'A' && c <= 'Z') { return (byte) (0xA + (c - 'A')); } else if (c >= 'a' && c <= 'z') { return (byte) (0xA + (c - 'a')); } else { /* * This should never happen since all calls to this method * are preceded by a check that c is in [0-9A-Za-z] */ throw new IllegalArgumentException((char) c + " is not a hexadecimal digit"); } } }