Java tutorial
/* * Copyright 2014 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.jamierf.jsonrpc.util; import java.util.List; import io.netty.buffer.ByteBuf; import io.netty.buffer.ByteBufUtil; import io.netty.channel.ChannelHandler; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.ChannelPipeline; import io.netty.handler.codec.ByteToMessageDecoder; import io.netty.handler.codec.CorruptedFrameException; import io.netty.handler.codec.TooLongFrameException; /** * Splits a byte stream of JSON objects and arrays into individual objects/arrays and passes them up the * {@link ChannelPipeline}. * * This class does not do any real parsing or validation. A sequence of bytes is considered a JSON object/array * if it contains a matching number of opening and closing braces/brackets. It's up to a subsequent * {@link ChannelHandler} to parse the JSON text into a more usable form i.e. a POJO. */ public class JsonObjectDecoder extends ByteToMessageDecoder { private static final int ST_CORRUPTED = -1; private static final int ST_INIT = 0; private static final int ST_DECODING_NORMAL = 1; private static final int ST_DECODING_ARRAY_STREAM = 2; private int openBraces; private int idx; private int state; private boolean insideString; private final int maxObjectLength; private final boolean streamArrayElements; public JsonObjectDecoder() { // 1 MB this(1024 * 1024); } public JsonObjectDecoder(int maxObjectLength) { this(maxObjectLength, false); } public JsonObjectDecoder(boolean streamArrayElements) { this(1024 * 1024, streamArrayElements); } /** * @param maxObjectLength maximum number of bytes a JSON object/array may use (including braces and all). * Objects exceeding this length are dropped and an {@link TooLongFrameException} * is thrown. * @param streamArrayElements if set to true and the "top level" JSON object is an array, each of its entries * is passed through the pipeline individually and immediately after it was fully * received, allowing for arrays with "infinitely" many elements. * */ public JsonObjectDecoder(int maxObjectLength, boolean streamArrayElements) { if (maxObjectLength < 1) { throw new IllegalArgumentException("maxObjectLength must be a positive int"); } this.maxObjectLength = maxObjectLength; this.streamArrayElements = streamArrayElements; } @Override protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception { if (state == ST_CORRUPTED) { in.skipBytes(in.readableBytes()); return; } // index of next byte to process. int idx = this.idx; int wrtIdx = in.writerIndex(); if (wrtIdx > maxObjectLength) { // buffer size exceeded maxObjectLength; discarding the complete buffer. in.skipBytes(in.readableBytes()); reset(); throw new TooLongFrameException( "object length exceeds " + maxObjectLength + ": " + wrtIdx + " bytes discarded"); } for (/* use current idx */; idx < wrtIdx; idx++) { byte c = in.getByte(idx); if (state == ST_DECODING_NORMAL) { decodeByte(c, in, idx); // All opening braces/brackets have been closed. That's enough to conclude // that the JSON object/array is complete. if (openBraces == 0) { ByteBuf json = extractObject(ctx, in, in.readerIndex(), idx + 1 - in.readerIndex()); if (json != null) { out.add(json); } // The JSON object/array was extracted => discard the bytes from // the input buffer. in.readerIndex(idx + 1); // Reset the object state to get ready for the next JSON object/text // coming along the byte stream. reset(); } } else if (state == ST_DECODING_ARRAY_STREAM) { decodeByte(c, in, idx); if (!insideString && (openBraces == 1 && c == ',' || openBraces == 0 && c == ']')) { // skip leading spaces. No range check is needed and the loop will terminate // because the byte at position idx is not a whitespace. for (int i = in.readerIndex(); Character.isWhitespace(in.getByte(i)); i++) { in.skipBytes(1); } // skip trailing spaces. int idxNoSpaces = idx - 1; while (idxNoSpaces >= in.readerIndex() && Character.isWhitespace(in.getByte(idxNoSpaces))) { idxNoSpaces--; } ByteBuf json = extractObject(ctx, in, in.readerIndex(), idxNoSpaces + 1 - in.readerIndex()); if (json != null) { out.add(json); } in.readerIndex(idx + 1); if (c == ']') { reset(); } } // JSON object/array detected. Accumulate bytes until all braces/brackets are closed. } else if (c == '{' || c == '[') { initDecoding(c); if (state == ST_DECODING_ARRAY_STREAM) { // Discard the array bracket in.skipBytes(1); } // Discard leading spaces in front of a JSON object/array. } else if (Character.isWhitespace(c)) { in.skipBytes(1); } else { state = ST_CORRUPTED; throw new CorruptedFrameException( "invalid JSON received at byte position " + idx + ": " + ByteBufUtil.hexDump(in)); } } if (in.readableBytes() == 0) { this.idx = 0; } else { this.idx = idx; } } /** * Override this method if you want to filter the json objects/arrays that get passed through the pipeline. */ @SuppressWarnings("UnusedParameters") protected ByteBuf extractObject(ChannelHandlerContext ctx, ByteBuf buffer, int index, int length) { return buffer.slice(index, length).retain(); } private void decodeByte(byte c, ByteBuf in, int idx) { if ((c == '{' || c == '[') && !insideString) { openBraces++; } else if ((c == '}' || c == ']') && !insideString) { openBraces--; } else if (c == '"') { // start of a new JSON string. It's necessary to detect strings as they may // also contain braces/brackets and that could lead to incorrect results. if (!insideString) { insideString = true; // If the double quote wasn't escaped then this is the end of a string. } else if (in.getByte(idx - 1) != '\\') { insideString = false; } } } private void initDecoding(byte openingBrace) { openBraces = 1; if (openingBrace == '[' && streamArrayElements) { state = ST_DECODING_ARRAY_STREAM; } else { state = ST_DECODING_NORMAL; } } private void reset() { insideString = false; state = ST_INIT; openBraces = 0; } }