HttpServerKeepAliveHandler Class — netty Architecture

Source Code

codec-http/src/main/java/io/netty/handler/codec/http/HttpServerKeepAliveHandler.java lines 47–128

public class HttpServerKeepAliveHandler extends ChannelDuplexHandler {
    private static final String MULTIPART_PREFIX = "multipart";

    private boolean persistentConnection = true;
    // Track pending responses to support client pipelining: https://tools.ietf.org/html/rfc7230#section-6.3.2
    private int pendingResponses;

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        // read message and track if it was keepAlive
        if (msg instanceof HttpRequest) {
            final HttpRequest request = (HttpRequest) msg;
            if (persistentConnection) {
                pendingResponses += 1;
                persistentConnection = isKeepAlive(request);
            }
        }
        super.channelRead(ctx, msg);
    }

    @Override
    public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
        // modify message on way out to add headers if needed
        if (msg instanceof HttpResponse) {
            final HttpResponse response = (HttpResponse) msg;
            trackResponse(response);
            // Assume the response writer knows if they can persist or not and sets isKeepAlive on the response
            if (!isKeepAlive(response) || !isSelfDefinedMessageLength(response)) {
                // No longer keep alive as the client can't tell when the message is done unless we close connection
                pendingResponses = 0;
                persistentConnection = false;
            }
            // Server might think it can keep connection alive, but we should fix response header if we know better
            if (!shouldKeepAlive()) {
                setKeepAlive(response, false);
            }
        }
        if (msg instanceof LastHttpContent && !shouldKeepAlive()) {
            promise = promise.unvoid().addListener(ChannelFutureListener.CLOSE);
        }
        super.write(ctx, msg, promise);
    }

    private void trackResponse(HttpResponse response) {
        if (!isInformational(response)) {
            pendingResponses -= 1;
        }
    }

    private boolean shouldKeepAlive() {
        return pendingResponses != 0 || persistentConnection;
    }

    /**
     * Keep-alive only works if the client can detect when the message has ended without relying on the connection being
     * closed.
     * <p>
     * <ul>
     *     <li>See <a href="https://tools.ietf.org/html/rfc7230#section-6.3"/></li>
     *     <li>See <a href="https://tools.ietf.org/html/rfc7230#section-3.3.2"/></li>
     *     <li>See <a href="https://tools.ietf.org/html/rfc7230#section-3.3.3"/></li>
     * </ul>
     *
     * @param response The HttpResponse to check
     *
     * @return true if the response has a self defined message length.
     */
    private static boolean isSelfDefinedMessageLength(HttpResponse response) {
        return isContentLengthSet(response) || isTransferEncodingChunked(response) || isMultipart(response) ||
               isInformational(response) || response.status().code() == HttpResponseStatus.NO_CONTENT.code();
    }

    private static boolean isInformational(HttpResponse response) {
        return response.status().codeClass() == HttpStatusClass.INFORMATIONAL;
    }

    private static boolean isMultipart(HttpResponse response) {
        String contentType = response.headers().get(HttpHeaderNames.CONTENT_TYPE);
        return contentType != null &&
               contentType.regionMatches(true, 0, MULTIPART_PREFIX, 0, MULTIPART_PREFIX.length());
    }