1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one 3 * or more contributor license agreements. See the NOTICE file 4 * distributed with this work for additional information 5 * regarding copyright ownership. The ASF licenses this file 6 * to you under the Apache License, Version 2.0 (the 7 * "License"); you may not use this file except in compliance 8 * with the License. You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, 13 * software distributed under the License is distributed on an 14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 15 * KIND, either express or implied. See the License for the 16 * specific language governing permissions and limitations 17 * under the License. 18 * 19 */ 20 package org.apache.mina.filter.codec; 21 22 import org.apache.mina.core.buffer.IoBuffer; 23 import org.apache.mina.core.service.TransportMetadata; 24 import org.apache.mina.core.session.AttributeKey; 25 import org.apache.mina.core.session.IoSession; 26 27 /** 28 * A {@link ProtocolDecoder} that cumulates the content of received 29 * buffers to a <em>cumulative buffer</em> to help users implement decoders. 30 * <p> 31 * If the received {@link IoBuffer} is only a part of a message. 32 * decoders should cumulate received buffers to make a message complete or 33 * to postpone decoding until more buffers arrive. 34 * <p> 35 * Here is an example decoder that decodes CRLF terminated lines into 36 * <code>Command</code> objects: 37 * <pre> 38 * public class CrLfTerminatedCommandLineDecoder 39 * extends CumulativeProtocolDecoder { 40 * 41 * private Command parseCommand(IoBuffer in) { 42 * // Convert the bytes in the specified buffer to a 43 * // Command object. 44 * ... 45 * } 46 * 47 * protected boolean doDecode( 48 * IoSession session, IoBuffer in, ProtocolDecoderOutput out) 49 * throws Exception { 50 * 51 * // Remember the initial position. 52 * int start = in.position(); 53 * 54 * // Now find the first CRLF in the buffer. 55 * byte previous = 0; 56 * while (in.hasRemaining()) { 57 * byte current = in.get(); 58 * 59 * if (previous == '\r' && current == '\n') { 60 * // Remember the current position and limit. 61 * int position = in.position(); 62 * int limit = in.limit(); 63 * try { 64 * in.position(start); 65 * in.limit(position); 66 * // The bytes between in.position() and in.limit() 67 * // now contain a full CRLF terminated line. 68 * out.write(parseCommand(in.slice())); 69 * } finally { 70 * // Set the position to point right after the 71 * // detected line and set the limit to the old 72 * // one. 73 * in.position(position); 74 * in.limit(limit); 75 * } 76 * // Decoded one line; CumulativeProtocolDecoder will 77 * // call me again until I return false. So just 78 * // return true until there are no more lines in the 79 * // buffer. 80 * return true; 81 * } 82 * 83 * previous = current; 84 * } 85 * 86 * // Could not find CRLF in the buffer. Reset the initial 87 * // position to the one we recorded above. 88 * in.position(start); 89 * 90 * return false; 91 * } 92 * } 93 * </pre> 94 * <p> 95 * Please note that this decoder simply forward the call to 96 * {@link #doDecode(IoSession, IoBuffer, ProtocolDecoderOutput)} if the 97 * underlying transport doesn't have a packet fragmentation. Whether the 98 * transport has fragmentation or not is determined by querying 99 * {@link TransportMetadata}. 100 * 101 * @author The Apache MINA Project (dev@mina.apache.org) 102 */ 103 public abstract class CumulativeProtocolDecoder extends ProtocolDecoderAdapter { 104 105 private final AttributeKey BUFFER = new AttributeKey(getClass(), "buffer"); 106 107 /** 108 * Creates a new instance. 109 */ 110 protected CumulativeProtocolDecoder() { 111 // Do nothing 112 } 113 114 /** 115 * Cumulates content of <tt>in</tt> into internal buffer and forwards 116 * decoding request to {@link #doDecode(IoSession, IoBuffer, ProtocolDecoderOutput)}. 117 * <tt>doDecode()</tt> is invoked repeatedly until it returns <tt>false</tt> 118 * and the cumulative buffer is compacted after decoding ends. 119 * 120 * @throws IllegalStateException if your <tt>doDecode()</tt> returned 121 * <tt>true</tt> not consuming the cumulative buffer. 122 */ 123 public void decode(IoSession session, IoBuffer in, 124 ProtocolDecoderOutput out) throws Exception { 125 if (!session.getTransportMetadata().hasFragmentation()) { 126 while (in.hasRemaining()) { 127 if (!doDecode(session, in, out)) { 128 break; 129 } 130 } 131 132 return; 133 } 134 135 boolean usingSessionBuffer = true; 136 IoBuffer buf = (IoBuffer) session.getAttribute(BUFFER); 137 // If we have a session buffer, append data to that; otherwise 138 // use the buffer read from the network directly. 139 if (buf != null) { 140 boolean appended = false; 141 // Make sure that the buffer is auto-expanded. 142 if (buf.isAutoExpand()) { 143 try { 144 buf.put(in); 145 appended = true; 146 } catch (IllegalStateException e) { 147 // A user called derivation method (e.g. slice()), 148 // which disables auto-expansion of the parent buffer. 149 } catch (IndexOutOfBoundsException e) { 150 // A user disabled auto-expansion. 151 } 152 } 153 154 if (appended) { 155 buf.flip(); 156 } else { 157 // Reallocate the buffer if append operation failed due to 158 // derivation or disabled auto-expansion. 159 buf.flip(); 160 IoBuffer newBuf = IoBuffer.allocate( 161 buf.remaining() + in.remaining()).setAutoExpand(true); 162 newBuf.order(buf.order()); 163 newBuf.put(buf); 164 newBuf.put(in); 165 newBuf.flip(); 166 buf = newBuf; 167 168 // Update the session attribute. 169 session.setAttribute(BUFFER, buf); 170 } 171 } else { 172 buf = in; 173 usingSessionBuffer = false; 174 } 175 176 for (;;) { 177 int oldPos = buf.position(); 178 boolean decoded = doDecode(session, buf, out); 179 if (decoded) { 180 if (buf.position() == oldPos) { 181 throw new IllegalStateException( 182 "doDecode() can't return true when buffer is not consumed."); 183 } 184 185 if (!buf.hasRemaining()) { 186 break; 187 } 188 } else { 189 break; 190 } 191 } 192 193 // if there is any data left that cannot be decoded, we store 194 // it in a buffer in the session and next time this decoder is 195 // invoked the session buffer gets appended to 196 if (buf.hasRemaining()) { 197 if (usingSessionBuffer && buf.isAutoExpand()) { 198 buf.compact(); 199 } else { 200 storeRemainingInSession(buf, session); 201 } 202 } else { 203 if (usingSessionBuffer) { 204 removeSessionBuffer(session); 205 } 206 } 207 } 208 209 /** 210 * Implement this method to consume the specified cumulative buffer and 211 * decode its content into message(s). 212 * 213 * @param in the cumulative buffer 214 * @return <tt>true</tt> if and only if there's more to decode in the buffer 215 * and you want to have <tt>doDecode</tt> method invoked again. 216 * Return <tt>false</tt> if remaining data is not enough to decode, 217 * then this method will be invoked again when more data is cumulated. 218 * @throws Exception if cannot decode <tt>in</tt>. 219 */ 220 protected abstract boolean doDecode(IoSession session, IoBuffer in, 221 ProtocolDecoderOutput out) throws Exception; 222 223 /** 224 * Releases the cumulative buffer used by the specified <tt>session</tt>. 225 * Please don't forget to call <tt>super.dispose( session )</tt> when 226 * you override this method. 227 */ 228 @Override 229 public void dispose(IoSession session) throws Exception { 230 removeSessionBuffer(session); 231 } 232 233 private void removeSessionBuffer(IoSession session) { 234 session.removeAttribute(BUFFER); 235 } 236 237 private void storeRemainingInSession(IoBuffer buf, IoSession session) { 238 final IoBuffer remainingBuf = IoBuffer.allocate(buf.capacity()).setAutoExpand(true); 239 240 remainingBuf.order(buf.order()); 241 remainingBuf.put(buf); 242 243 session.setAttribute(BUFFER, remainingBuf); 244 } 245 }