Netty源码分析-HttpObjectDecoder

 

/*
 * 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 io.netty.handler.codec.http;

import static io.netty.util.internal.ObjectUtil.checkPositive;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelPipeline;
import io.netty.handler.codec.ByteToMessageDecoder;
import io.netty.handler.codec.DecoderResult;
import io.netty.handler.codec.PrematureChannelClosureException;
import io.netty.handler.codec.TooLongFrameException;
import io.netty.util.ByteProcessor;
import io.netty.util.internal.AppendableCharSequence;

import java.util.List;

/**
 * Decodes {@link ByteBuf}s into {@link HttpMessage}s and
 * {@link HttpContent}s.
 *
 * 
Parameters that prevents excessive memory consumption
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
 * 
Name
Meaning
{@code maxInitialLineLength}
The maximum length of the initial line
 *     (e.g. {@code "GET / HTTP/1.0"} or {@code "HTTP/1.0 200 OK"})
 *     If the length of the initial line exceeds this value, a
 *     {@link TooLongFrameException} will be raised.
{@code maxHeaderSize}
The maximum length of all headers.  If the sum of the length of each
 *     header exceeds this value, a {@link TooLongFrameException} will be raised.
{@code maxChunkSize}
The maximum length of the content or each chunk.  If the content length
 *     (or the length of each chunk) exceeds this value, the content or chunk
 *     will be split into multiple {@link HttpContent}s whose length is
 *     {@code maxChunkSize} at maximum.
 *
 * 
Chunked Content
 *
 * If the content of an HTTP message is greater than {@code maxChunkSize} or
 * the transfer encoding of the HTTP message is 'chunked', this decoder
 * generates one {@link HttpMessage} instance and its following
 * {@link HttpContent}s per single HTTP message to avoid excessive memory
 * consumption. For example, the following HTTP message:
 * 
 * GET / HTTP/1.1
 * Transfer-Encoding: chunked
 *
 * 1a
 * abcdefghijklmnopqrstuvwxyz
 * 10
 * 1234567890abcdef
 * 0
 * Content-MD5: ...
 * [blank line]
 * 
 * triggers {@link HttpRequestDecoder} to generate 3 objects:
 * 

 * 
An {@link HttpRequest},
 * 
The first {@link HttpContent} whose content is {@code 'abcdefghijklmnopqrstuvwxyz'},
 * 
The second {@link LastHttpContent} whose content is {@code '1234567890abcdef'}, which marks
 * the end of the content.
 * 
 *
 * If you prefer not to handle {@link HttpContent}s by yourself for your
 * convenience, insert {@link HttpObjectAggregator} after this decoder in the
 * {@link ChannelPipeline}.  However, please note that your server might not
 * be as memory efficient as without the aggregator.
 *
 * 
Extensibility
 *
 * Please note that this decoder is designed to be extended to implement
 * a protocol derived from HTTP, such as
 * RTSP and
 * ICAP.
 * To implement the decoder of such a derived protocol, extend this class and
 * implement all abstract methods properly.
 */
public abstract class HttpObjectDecoder extends ByteToMessageDecoder {
    private static final String EMPTY_VALUE = "";

    //最大读取一个数据块的大小 默认8192
    private final int maxChunkSize;
    //是否支持Http块方式协议
    private final boolean chunkedSupported;
    protected final boolean validateHeaders;

    //Http头解析器，按行解析，通过回车换行符(\r\n)解析出一行字符串
    private final HeaderParser headerParser;
    private final LineParser lineParser;

    //实体类封装Http消息，只包含了版本，METHOD，Http头等信息，没有Body数据.
    private HttpMessage message;

    //每块大小
    private long chunkSize;
    private long contentLength = Long.MIN_VALUE;
    private volatile boolean resetRequested;

    // These will be updated by splitHeader(...)
    private CharSequence name;
    private CharSequence value;

    private LastHttpContent trailer;

    /**
     * The internal state of {@link HttpObjectDecoder}.
     * Internal use only.
     */
    //当前解码器状态
    private enum State {
        SKIP_CONTROL_CHARS,
        READ_INITIAL, //读取第一行(POST http://127.0.0.17:8080/ HTTP/1.1)
        READ_HEADER, //读取Http头信息
        READ_VARIABLE_LENGTH_CONTENT, //Http内容长度可变
        READ_FIXED_LENGTH_CONTENT, //Http内容长度固定
        READ_CHUNK_SIZE, //以块的方式读取
        READ_CHUNKED_CONTENT,
        READ_CHUNK_DELIMITER,
        READ_CHUNK_FOOTER,
        BAD_MESSAGE, //错误请求状态
        UPGRADED
    }

    private State currentState = State.SKIP_CONTROL_CHARS;

    /**
     * Creates a new instance with the default
     * {@code maxInitialLineLength (4096}}, {@code maxHeaderSize (8192)}, and
     * {@code maxChunkSize (8192)}.
     */
    protected HttpObjectDecoder() {
        this(4096, 8192, 8192, true);
    }

    /**
     * Creates a new instance with the specified parameters.
     */
    protected HttpObjectDecoder(
            int maxInitialLineLength, int maxHeaderSize, int maxChunkSize, boolean chunkedSupported) {
        this(maxInitialLineLength, maxHeaderSize, maxChunkSize, chunkedSupported, true);
    }

    /**
     * Creates a new instance with the specified parameters.
     */
    protected HttpObjectDecoder(
            int maxInitialLineLength, int maxHeaderSize, int maxChunkSize,
            boolean chunkedSupported, boolean validateHeaders) {
        this(maxInitialLineLength, maxHeaderSize, maxChunkSize, chunkedSupported, validateHeaders, 128);
    }

    protected HttpObjectDecoder(
            int maxInitialLineLength, int maxHeaderSize, int maxChunkSize,
            boolean chunkedSupported, boolean validateHeaders, int initialBufferSize) {
        checkPositive(maxInitialLineLength, "maxInitialLineLength");
        checkPositive(maxHeaderSize, "maxHeaderSize");
        checkPositive(maxChunkSize, "maxChunkSize");

        AppendableCharSequence seq = new AppendableCharSequence(initialBufferSize);
        lineParser = new LineParser(seq, maxInitialLineLength);
        headerParser = new HeaderParser(seq, maxHeaderSize);
        this.maxChunkSize = maxChunkSize;
        this.chunkedSupported = chunkedSupported;
        this.validateHeaders = validateHeaders;
    }

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf buffer, List