HttpObjectEncoder Class — netty Architecture

Source Code

codec-http/src/main/java/io/netty/handler/codec/http/HttpObjectEncoder.java lines 55–618

public abstract class HttpObjectEncoder<H extends HttpMessage> extends MessageToMessageEncoder<Object> {

    // this is a constant to decide when it is appropriate to copy the data content into the header buffer
    private static final int COPY_CONTENT_THRESHOLD = 128;
    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 = LeakPresenceDetector.staticInitializer(() -> unreleasableBuffer(
            directBuffer(2).writeByte(CR).writeByte(LF)).asReadOnly());
    private static final ByteBuf ZERO_CRLF_CRLF_BUF = LeakPresenceDetector.staticInitializer(() -> unreleasableBuffer(
            directBuffer(ZERO_CRLF_CRLF.length).writeBytes(ZERO_CRLF_CRLF)).asReadOnly());
    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;

    private final List<Object> out = new ArrayList<Object>();

    private static boolean checkContentState(int state) {
        return state == ST_CONTENT_CHUNK || state == ST_CONTENT_NON_CHUNK || state == ST_CONTENT_ALWAYS_EMPTY;
    }

    public HttpObjectEncoder() {
        super(Object.class);
    }

    @Override
    public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
        try {
            if (acceptOutboundMessage(msg)) {
                encode(ctx, msg, out);
                if (out.isEmpty()) {
                    throw new EncoderException(
                            StringUtil.simpleClassName(this) + " must produce at least one message.");
                }
            } else {
                ctx.write(msg, promise);
            }
        } catch (EncoderException e) {
            throw e;
        } catch (Throwable t) {
            throw new EncoderException(t);
        } finally {
            writeOutList(ctx, out, promise);
        }
    }

    private static void writeOutList(ChannelHandlerContext ctx, List<Object> out, ChannelPromise promise) {
        final int size = out.size();
        try {
            if (size == 1) {
                ctx.write(out.get(0), promise);
            } else if (size > 1) {
                // Check if we can use a voidPromise for our extra writes to reduce GC-Pressure
                // See https://github.com/netty/netty/issues/2525
                if (promise == ctx.voidPromise()) {
                    writeVoidPromise(ctx, out);
                } else {
                    writePromiseCombiner(ctx, out, promise);
                }
            }