Java tutorial
/* * 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 io.netty.buffer.ByteBuf; import io.netty.buffer.ByteBufUtil; import io.netty.buffer.Unpooled; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.FileRegion; import io.netty.handler.codec.MessageToMessageEncoder; import io.netty.util.CharsetUtil; import io.netty.util.internal.StringUtil; import java.util.Iterator; import java.util.List; import java.util.Map.Entry; import static io.netty.buffer.Unpooled.directBuffer; import static io.netty.buffer.Unpooled.unreleasableBuffer; import static io.netty.handler.codec.http.HttpConstants.CR; import static io.netty.handler.codec.http.HttpConstants.LF; /** * Encodes an {@link HttpMessage} or an {@link HttpContent} into * a {@link ByteBuf}. * * <h3>Extensibility</h3> * * Please note that this encoder is designed to be extended to implement * a protocol derived from HTTP, such as * <a href="http://en.wikipedia.org/wiki/Real_Time_Streaming_Protocol">RTSP</a> and * <a href="http://en.wikipedia.org/wiki/Internet_Content_Adaptation_Protocol">ICAP</a>. * To implement the encoder of such a derived protocol, extend this class and * implement all abstract methods properly. */ public abstract class HttpObjectEncoder<H extends HttpMessage> extends MessageToMessageEncoder<Object> { static final int CRLF_SHORT = (CR << 8) | LF; private static final int ZERO_CRLF_MEDIUM = ('0' << 16) | CRLF_SHORT; private static final byte[] ZERO_CRLF_CRLF = { '0', CR, LF, CR, LF }; private static final ByteBuf CRLF_BUF = unreleasableBuffer(directBuffer(2).writeByte(CR).writeByte(LF)); private static final ByteBuf ZERO_CRLF_CRLF_BUF = unreleasableBuffer( directBuffer(ZERO_CRLF_CRLF.length).writeBytes(ZERO_CRLF_CRLF)); private static final float HEADERS_WEIGHT_NEW = 1 / 5f; private static final float HEADERS_WEIGHT_HISTORICAL = 1 - HEADERS_WEIGHT_NEW; private static final float TRAILERS_WEIGHT_NEW = HEADERS_WEIGHT_NEW; private static final float TRAILERS_WEIGHT_HISTORICAL = HEADERS_WEIGHT_HISTORICAL; private static final int ST_INIT = 0; private static final int ST_CONTENT_NON_CHUNK = 1; private static final int ST_CONTENT_CHUNK = 2; private static final int ST_CONTENT_ALWAYS_EMPTY = 3; @SuppressWarnings("RedundantFieldInitialization") private int state = ST_INIT; /** * Used to calculate an exponential moving average of the encoded size of the initial line and the headers for * a guess for future buffer allocations. */ private float headersEncodedSizeAccumulator = 256; /** * Used to calculate an exponential moving average of the encoded size of the trailers for * a guess for future buffer allocations. */ private float trailersEncodedSizeAccumulator = 256; @Override protected void encode(ChannelHandlerContext ctx, Object msg, List<Object> out) throws Exception { ByteBuf buf = null; if (msg instanceof HttpMessage) { if (state != ST_INIT) { throw new IllegalStateException( "unexpected message type: " + StringUtil.simpleClassName(msg) + ", state: " + state); } @SuppressWarnings({ "unchecked", "CastConflictsWithInstanceof" }) H m = (H) msg; buf = ctx.alloc().buffer((int) headersEncodedSizeAccumulator); // Encode the message. encodeInitialLine(buf, m); state = isContentAlwaysEmpty(m) ? ST_CONTENT_ALWAYS_EMPTY : HttpUtil.isTransferEncodingChunked(m) ? ST_CONTENT_CHUNK : ST_CONTENT_NON_CHUNK; sanitizeHeadersBeforeEncode(m, state == ST_CONTENT_ALWAYS_EMPTY); encodeHeaders(m.headers(), buf); ByteBufUtil.writeShortBE(buf, CRLF_SHORT); headersEncodedSizeAccumulator = HEADERS_WEIGHT_NEW * padSizeForAccumulation(buf.readableBytes()) + HEADERS_WEIGHT_HISTORICAL * headersEncodedSizeAccumulator; } // Bypass the encoder in case of an empty buffer, so that the following idiom works: // // ch.write(Unpooled.EMPTY_BUFFER).addListener(ChannelFutureListener.CLOSE); // // See https://github.com/netty/netty/issues/2983 for more information. if (msg instanceof ByteBuf) { final ByteBuf potentialEmptyBuf = (ByteBuf) msg; if (!potentialEmptyBuf.isReadable()) { out.add(potentialEmptyBuf.retain()); return; } } if (msg instanceof HttpContent || msg instanceof ByteBuf || msg instanceof FileRegion) { switch (state) { case ST_INIT: throw new IllegalStateException("unexpected message type: " + StringUtil.simpleClassName(msg)); case ST_CONTENT_NON_CHUNK: final long contentLength = contentLength(msg); if (contentLength > 0) { if (buf != null && buf.writableBytes() >= contentLength && msg instanceof HttpContent) { // merge into other buffer for performance reasons buf.writeBytes(((HttpContent) msg).content()); out.add(buf); } else { if (buf != null) { out.add(buf); } out.add(encodeAndRetain(msg)); } if (msg instanceof LastHttpContent) { state = ST_INIT; } break; } // fall-through! case ST_CONTENT_ALWAYS_EMPTY: if (buf != null) { // We allocated a buffer so add it now. out.add(buf); } else { // Need to produce some output otherwise an // IllegalStateException will be thrown as we did not write anything // Its ok to just write an EMPTY_BUFFER as if there are reference count issues these will be // propagated as the caller of the encode(...) method will release the original // buffer. // Writing an empty buffer will not actually write anything on the wire, so if there is a user // error with msg it will not be visible externally out.add(Unpooled.EMPTY_BUFFER); } break; case ST_CONTENT_CHUNK: if (buf != null) { // We allocated a buffer so add it now. out.add(buf); } encodeChunkedContent(ctx, msg, contentLength(msg), out); break; default: throw new Error(); } if (msg instanceof LastHttpContent) { state = ST_INIT; } } else if (buf != null) { out.add(buf); } } /** * Encode the {@link HttpHeaders} into a {@link ByteBuf}. */ protected void encodeHeaders(HttpHeaders headers, ByteBuf buf) { Iterator<Entry<CharSequence, CharSequence>> iter = headers.iteratorCharSequence(); while (iter.hasNext()) { Entry<CharSequence, CharSequence> header = iter.next(); HttpHeadersEncoder.encoderHeader(header.getKey(), header.getValue(), buf); } } private void encodeChunkedContent(ChannelHandlerContext ctx, Object msg, long contentLength, List<Object> out) { if (contentLength > 0) { String lengthHex = Long.toHexString(contentLength); ByteBuf buf = ctx.alloc().buffer(lengthHex.length() + 2); buf.writeCharSequence(lengthHex, CharsetUtil.US_ASCII); ByteBufUtil.writeShortBE(buf, CRLF_SHORT); out.add(buf); out.add(encodeAndRetain(msg)); out.add(CRLF_BUF.duplicate()); } if (msg instanceof LastHttpContent) { HttpHeaders headers = ((LastHttpContent) msg).trailingHeaders(); if (headers.isEmpty()) { out.add(ZERO_CRLF_CRLF_BUF.duplicate()); } else { ByteBuf buf = ctx.alloc().buffer((int) trailersEncodedSizeAccumulator); ByteBufUtil.writeMediumBE(buf, ZERO_CRLF_MEDIUM); encodeHeaders(headers, buf); ByteBufUtil.writeShortBE(buf, CRLF_SHORT); trailersEncodedSizeAccumulator = TRAILERS_WEIGHT_NEW * padSizeForAccumulation(buf.readableBytes()) + TRAILERS_WEIGHT_HISTORICAL * trailersEncodedSizeAccumulator; out.add(buf); } } else if (contentLength == 0) { // Need to produce some output otherwise an // IllegalStateException will be thrown out.add(encodeAndRetain(msg)); } } /** * Allows to sanitize headers of the message before encoding these. */ protected void sanitizeHeadersBeforeEncode(@SuppressWarnings("unused") H msg, boolean isAlwaysEmpty) { // noop } /** * Determine whether a message has a content or not. Some message may have headers indicating * a content without having an actual content, e.g the response to an HEAD or CONNECT request. * * @param msg the message to test * @return {@code true} to signal the message has no content */ protected boolean isContentAlwaysEmpty(@SuppressWarnings("unused") H msg) { return false; } @Override public boolean acceptOutboundMessage(Object msg) throws Exception { return msg instanceof HttpObject || msg instanceof ByteBuf || msg instanceof FileRegion; } private static Object encodeAndRetain(Object msg) { if (msg instanceof ByteBuf) { return ((ByteBuf) msg).retain(); } if (msg instanceof HttpContent) { return ((HttpContent) msg).content().retain(); } if (msg instanceof FileRegion) { return ((FileRegion) msg).retain(); } throw new IllegalStateException("unexpected message type: " + StringUtil.simpleClassName(msg)); } private static long contentLength(Object msg) { if (msg instanceof HttpContent) { return ((HttpContent) msg).content().readableBytes(); } if (msg instanceof ByteBuf) { return ((ByteBuf) msg).readableBytes(); } if (msg instanceof FileRegion) { return ((FileRegion) msg).count(); } throw new IllegalStateException("unexpected message type: " + StringUtil.simpleClassName(msg)); } /** * Add some additional overhead to the buffer. The rational is that it is better to slightly over allocate and waste * some memory, rather than under allocate and require a resize/copy. * @param readableBytes The readable bytes in the buffer. * @return The {@code readableBytes} with some additional padding. */ private static int padSizeForAccumulation(int readableBytes) { return (readableBytes << 2) / 3; } @Deprecated protected static void encodeAscii(String s, ByteBuf buf) { buf.writeCharSequence(s, CharsetUtil.US_ASCII); } protected abstract void encodeInitialLine(ByteBuf buf, H message) throws Exception; }