/*
* Copyright 2012 The Netty Project
*
* The Netty Project 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 com.facebook.presto.jdbc.internal.netty.handler.codec.frame;
import com.facebook.presto.jdbc.internal.netty.buffer.ChannelBuffer;
import com.facebook.presto.jdbc.internal.netty.channel.Channel;
import com.facebook.presto.jdbc.internal.netty.channel.ChannelHandlerContext;
import com.facebook.presto.jdbc.internal.netty.channel.Channels;
/**
* A decoder that splits the received {@link ChannelBuffer}s by one or more
* delimiters. It is particularly useful for decoding the frames which ends
* with a delimiter such as {@link Delimiters#nulDelimiter() NUL} or
* {@linkplain Delimiters#lineDelimiter() newline characters}.
*
* <h3>Predefined delimiters</h3>
* <p>
* {@link Delimiters} defines frequently used delimiters for convenience' sake.
*
* <h3>Specifying more than one delimiter</h3>
* <p>
* {@link DelimiterBasedFrameDecoder} allows you to specify more than one
* delimiter. If more than one delimiter is found in the buffer, it chooses
* the delimiter which produces the shortest frame. For example, if you have
* the following data in the buffer:
* <pre>
* +--------------+
* | ABC\nDEF\r\n |
* +--------------+
* </pre>
* a {@link DelimiterBasedFrameDecoder}{@code (}{@link Delimiters#lineDelimiter() Delimiters.lineDelimiter()}{@code )}
* will choose {@code '\n'} as the first delimiter and produce two frames:
* <pre>
* +-----+-----+
* | ABC | DEF |
* +-----+-----+
* </pre>
* rather than incorrectly choosing {@code '\r\n'} as the first delimiter:
* <pre>
* +----------+
* | ABC\nDEF |
* +----------+
* </pre>
*
*
* @apiviz.uses com.facebook.presto.jdbc.internal.netty.handler.codec.frame.Delimiters - - useful
*/
public class DelimiterBasedFrameDecoder extends FrameDecoder {
private final ChannelBuffer[] delimiters;
private final int maxFrameLength;
private final boolean stripDelimiter;
private final boolean failFast;
private boolean discardingTooLongFrame;
private int tooLongFrameLength;
/** Set only when decoding with "\n" and "\r\n" as the delimiter. */
private final LineBasedFrameDecoder lineBasedDecoder;
/**
* Creates a new instance.
*
* @param maxFrameLength the maximum length of the decoded frame.
* A {@link TooLongFrameException} is thrown if
* the length of the frame exceeds this value.
* @param delimiter the delimiter
*/
public DelimiterBasedFrameDecoder(int maxFrameLength, ChannelBuffer delimiter) {
this(maxFrameLength, true, delimiter);
}
/**
* Creates a new instance.
*
* @param maxFrameLength the maximum length of the decoded frame.
* A {@link TooLongFrameException} is thrown if
* the length of the frame exceeds this value.
* @param stripDelimiter whether the decoded frame should strip out the
* delimiter or not
* @param delimiter the delimiter
*/
public DelimiterBasedFrameDecoder(
int maxFrameLength, boolean stripDelimiter, ChannelBuffer delimiter) {
this(maxFrameLength, stripDelimiter, false, delimiter);
}
/**
* Creates a new instance.
*
* @param maxFrameLength the maximum length of the decoded frame.
* A {@link TooLongFrameException} is thrown if
* the length of the frame exceeds this value.
* @param stripDelimiter whether the decoded frame should strip out the
* delimiter or not
* @param failFast If <tt>true</tt>, a {@link TooLongFrameException} is
* thrown as soon as the decoder notices the length of the
* frame will exceed <tt>maxFrameLength</tt> regardless of
* whether the entire frame has been read.
* If <tt>false</tt>, a {@link TooLongFrameException} is
* thrown after the entire frame that exceeds
* <tt>maxFrameLength</tt> has been read.
* @param delimiter the delimiter
*/
public DelimiterBasedFrameDecoder(
int maxFrameLength, boolean stripDelimiter, boolean failFast,
ChannelBuffer delimiter) {
this(maxFrameLength, stripDelimiter, failFast, new ChannelBuffer[] {
delimiter.slice(
delimiter.readerIndex(), delimiter.readableBytes()) });
}
/**
* Creates a new instance.
*
* @param maxFrameLength the maximum length of the decoded frame.
* A {@link TooLongFrameException} is thrown if
* the length of the frame exceeds this value.
* @param delimiters the delimiters
*/
public DelimiterBasedFrameDecoder(int maxFrameLength, ChannelBuffer... delimiters) {
this(maxFrameLength, true, delimiters);
}
/**
* Creates a new instance.
*
* @param maxFrameLength the maximum length of the decoded frame.
* A {@link TooLongFrameException} is thrown if
* the length of the frame exceeds this value.
* @param stripDelimiter whether the decoded frame should strip out the
* delimiter or not
* @param delimiters the delimiters
*/
public DelimiterBasedFrameDecoder(
int maxFrameLength, boolean stripDelimiter, ChannelBuffer... delimiters) {
this(maxFrameLength, stripDelimiter, false, delimiters);
}
/**
* Creates a new instance.
*
* @param maxFrameLength the maximum length of the decoded frame.
* A {@link TooLongFrameException} is thrown if
* the length of the frame exceeds this value.
* @param stripDelimiter whether the decoded frame should strip out the
* delimiter or not
* @param failFast If <tt>true</tt>, a {@link TooLongFrameException} is
* thrown as soon as the decoder notices the length of the
* frame will exceed <tt>maxFrameLength</tt> regardless of
* whether the entire frame has been read.
* If <tt>false</tt>, a {@link TooLongFrameException} is
* thrown after the entire frame that exceeds
* <tt>maxFrameLength</tt> has been read.
* @param delimiters the delimiters
*/
public DelimiterBasedFrameDecoder(
int maxFrameLength, boolean stripDelimiter, boolean failFast, ChannelBuffer... delimiters) {
validateMaxFrameLength(maxFrameLength);
if (delimiters == null) {
throw new NullPointerException("delimiters");
}
if (delimiters.length == 0) {
throw new IllegalArgumentException("empty delimiters");
}
if (isLineBased(delimiters) && !isSubclass()) {
lineBasedDecoder = new LineBasedFrameDecoder(maxFrameLength, stripDelimiter, failFast);
this.delimiters = null;
} else {
this.delimiters = new ChannelBuffer[delimiters.length];
for (int i = 0; i < delimiters.length; i ++) {
ChannelBuffer d = delimiters[i];
validateDelimiter(d);
this.delimiters[i] = d.slice(d.readerIndex(), d.readableBytes());
}
lineBasedDecoder = null;
}
this.maxFrameLength = maxFrameLength;
this.stripDelimiter = stripDelimiter;
this.failFast = failFast;
}
/** Returns true if the delimiters are "\n" and "\r\n". */
private static boolean isLineBased(final ChannelBuffer[] delimiters) {
if (delimiters.length != 2) {
return false;
}
ChannelBuffer a = delimiters[0];
ChannelBuffer b = delimiters[1];
if (a.capacity() < b.capacity()) {
a = delimiters[1];
b = delimiters[0];
}
return a.capacity() == 2 && b.capacity() == 1
&& a.getByte(0) == '\r' && a.getByte(1) == '\n'
&& b.getByte(0) == '\n';
}
/**
* Return {@code true} if the current instance is a subclass of DelimiterBasedFrameDecoder
*/
private boolean isSubclass() {
return getClass() != DelimiterBasedFrameDecoder.class;
}
@Override
protected Object decode(
ChannelHandlerContext ctx, Channel channel, ChannelBuffer buffer) throws Exception {
if (lineBasedDecoder != null) {
return lineBasedDecoder.decode(ctx, channel, buffer);
}
// Try all delimiters and choose the delimiter which yields the shortest frame.
int minFrameLength = Integer.MAX_VALUE;
ChannelBuffer minDelim = null;
for (ChannelBuffer delim: delimiters) {
int frameLength = indexOf(buffer, delim);
if (frameLength >= 0 && frameLength < minFrameLength) {
minFrameLength = frameLength;
minDelim = delim;
}
}
if (minDelim != null) {
int minDelimLength = minDelim.capacity();
ChannelBuffer frame;
if (discardingTooLongFrame) {
// We've just finished discarding a very large frame.
// Go back to the initial state.
discardingTooLongFrame = false;
buffer.skipBytes(minFrameLength + minDelimLength);
int tooLongFrameLength = this.tooLongFrameLength;
this.tooLongFrameLength = 0;
if (!failFast) {
fail(ctx, tooLongFrameLength);
}
return null;
}
if (minFrameLength > maxFrameLength) {
// Discard read frame.
buffer.skipBytes(minFrameLength + minDelimLength);
fail(ctx, minFrameLength);
return null;
}
if (stripDelimiter) {
frame = extractFrame(buffer, buffer.readerIndex(), minFrameLength);
} else {
frame = extractFrame(buffer, buffer.readerIndex(), minFrameLength + minDelimLength);
}
buffer.skipBytes(minFrameLength + minDelimLength);
return frame;
} else {
if (!discardingTooLongFrame) {
if (buffer.readableBytes() > maxFrameLength) {
// Discard the content of the buffer until a delimiter is found.
tooLongFrameLength = buffer.readableBytes();
buffer.skipBytes(buffer.readableBytes());
discardingTooLongFrame = true;
if (failFast) {
fail(ctx, tooLongFrameLength);
}
}
} else {
// Still discarding the buffer since a delimiter is not found.
tooLongFrameLength += buffer.readableBytes();
buffer.skipBytes(buffer.readableBytes());
}
return null;
}
}
private void fail(ChannelHandlerContext ctx, long frameLength) {
if (frameLength > 0) {
Channels.fireExceptionCaught(
ctx.getChannel(),
new TooLongFrameException(
"frame length exceeds " + maxFrameLength +
": " + frameLength + " - discarded"));
} else {
Channels.fireExceptionCaught(
ctx.getChannel(),
new TooLongFrameException(
"frame length exceeds " + maxFrameLength +
" - discarding"));
}
}
/**
* Returns the number of bytes between the readerIndex of the haystack and
* the first needle found in the haystack. -1 is returned if no needle is
* found in the haystack.
*/
private static int indexOf(ChannelBuffer haystack, ChannelBuffer needle) {
for (int i = haystack.readerIndex(); i < haystack.writerIndex(); i ++) {
int haystackIndex = i;
int needleIndex;
for (needleIndex = 0; needleIndex < needle.capacity(); needleIndex ++) {
if (haystack.getByte(haystackIndex) != needle.getByte(needleIndex)) {
break;
} else {
haystackIndex ++;
if (haystackIndex == haystack.writerIndex() &&
needleIndex != needle.capacity() - 1) {
return -1;
}
}
}
if (needleIndex == needle.capacity()) {
// Found the needle from the haystack!
return i - haystack.readerIndex();
}
}
return -1;
}
private static void validateDelimiter(ChannelBuffer delimiter) {
if (delimiter == null) {
throw new NullPointerException("delimiter");
}
if (!delimiter.readable()) {
throw new IllegalArgumentException("empty delimiter");
}
}
private static void validateMaxFrameLength(int maxFrameLength) {
if (maxFrameLength <= 0) {
throw new IllegalArgumentException(
"maxFrameLength must be a positive integer: " +
maxFrameLength);
}
}
}