HttpContentEncoder Class — netty Architecture

Source Code

codec-http/src/main/java/io/netty/handler/codec/http/HttpContentEncoder.java lines 57–383

public abstract class HttpContentEncoder extends MessageToMessageCodec<HttpRequest, HttpObject> {

    private enum State {
        PASS_THROUGH,
        AWAIT_HEADERS,
        AWAIT_CONTENT
    }

    private static final CharSequence ZERO_LENGTH_HEAD = "HEAD";
    private static final CharSequence ZERO_LENGTH_CONNECT = "CONNECT";

    private final Queue<CharSequence> acceptEncodingQueue = new ArrayDeque<CharSequence>();
    private EmbeddedChannel encoder;
    private State state = State.AWAIT_HEADERS;

    public HttpContentEncoder() {
        super(HttpRequest.class, HttpObject.class);
    }

    @Override
    public boolean acceptOutboundMessage(Object msg) throws Exception {
        return msg instanceof HttpContent || msg instanceof HttpResponse;
    }

    @Override
    protected void decode(ChannelHandlerContext ctx, HttpRequest msg, List<Object> out) throws Exception {
        CharSequence acceptEncoding;
        List<String> acceptEncodingHeaders = msg.headers().getAll(ACCEPT_ENCODING);
        switch (acceptEncodingHeaders.size()) {
        case 0:
            acceptEncoding = HttpContentDecoder.IDENTITY;
            break;
        case 1:
            acceptEncoding = acceptEncodingHeaders.get(0);
            break;
        default:
            // Multiple message-header fields https://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2
            acceptEncoding = StringUtil.join(",", acceptEncodingHeaders);
            break;
        }

        HttpMethod method = msg.method();
        if (HttpMethod.HEAD.equals(method)) {
            acceptEncoding = ZERO_LENGTH_HEAD;
        } else if (HttpMethod.CONNECT.equals(method)) {
            acceptEncoding = ZERO_LENGTH_CONNECT;
        }

        acceptEncodingQueue.add(acceptEncoding);
        out.add(ReferenceCountUtil.retain(msg));
    }

    @Override
    protected void encode(ChannelHandlerContext ctx, HttpObject msg, List<Object> out) throws Exception {
        final boolean isFull = msg instanceof HttpResponse && msg instanceof LastHttpContent;
        switch (state) {
            case AWAIT_HEADERS: {
                ensureHeaders(msg);
                assert encoder == null;

                final HttpResponse res = (HttpResponse) msg;
                final int code = res.status().code();
                final HttpStatusClass codeClass = res.status().codeClass();
                final CharSequence acceptEncoding;
                if (codeClass == HttpStatusClass.INFORMATIONAL) {
                    // We need to not poll the encoding when response with 1xx codes as another response will follow
                    // for the issued request.
                    // See https://github.com/netty/netty/issues/12904 and https://github.com/netty/netty/issues/4079
                    acceptEncoding = null;
                } else {
                    // Get the list of encodings accepted by the peer.
                    acceptEncoding = acceptEncodingQueue.poll();
                    if (acceptEncoding == null) {
                        throw new IllegalStateException("cannot send more responses than requests");
                    }
                }

                /*
                 * per rfc2616 4.3 Message Body
                 * All 1xx (informational), 204 (no content), and 304 (not modified) responses MUST NOT include a
                 * message-body. All other responses do include a message-body, although it MAY be of zero length.