A faviocon handler for Netty HTTP apps. Handles the cache headers and caches the icon bytes.

FaviconHandler

package com.outbrain.ob1k.server.netty;

import static io.netty.handler.codec.http.HttpHeaders.Names.CONNECTION;
import static io.netty.handler.codec.http.HttpHeaders.Names.CONTENT_TYPE;
import static io.netty.handler.codec.http.HttpHeaders.Names.DATE;
import static io.netty.handler.codec.http.HttpHeaders.Names.IF_MODIFIED_SINCE;
import static io.netty.handler.codec.http.HttpHeaders.isKeepAlive;
import static io.netty.handler.codec.http.HttpResponseStatus.BAD_REQUEST;
import static io.netty.handler.codec.http.HttpResponseStatus.NOT_MODIFIED;
import static io.netty.handler.codec.http.HttpVersion.HTTP_1_1;

import java.io.IOException;
import java.io.InputStream;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.Locale;
import java.util.TimeZone;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.io.ByteStreams;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.codec.http.DefaultFullHttpResponse;
import io.netty.handler.codec.http.DefaultHttpResponse;
import io.netty.handler.codec.http.FullHttpRequest;
import io.netty.handler.codec.http.FullHttpResponse;
import io.netty.handler.codec.http.HttpHeaders;
import io.netty.handler.codec.http.HttpMethod;
import io.netty.handler.codec.http.HttpResponseStatus;
import io.netty.handler.codec.http.HttpVersion;
import io.netty.util.CharsetUtil;

/**
 * A handler that serves a cached favicon file from a specified (resource) path.
 *
 * @author Eran Harel
 */
@ChannelHandler.Sharable
public class FaviconHandler extends SimpleChannelInboundHandler<FullHttpRequest> {

  private static final Logger log = LoggerFactory.getLogger(FaviconHandler.class);
  public static final String HTTP_DATE_FORMAT = "EEE, dd MMM yyyy HH:mm:ss zzz";
  public static final String HTTP_DATE_GMT_TIMEZONE = "GMT";

  private final byte[] iconBytes;
  private long startupTime = System.currentTimeMillis();

  public FaviconHandler(final String iconFilePath) {
    iconBytes = loadIconBytes(iconFilePath);
  }

  private byte[] loadIconBytes(final String iconFilePath) {
    InputStream inputStream = this.getClass().getClassLoader().getResourceAsStream(iconFilePath);
    if (null == inputStream) {
      log.error("Failed to find icon file {}", iconFilePath);
      return null;
    }

    try {
      return ByteStreams.toByteArray(inputStream);
    } catch (IOException e) {
      log.error("Failed to load icon file {}", iconFilePath);
      return null;
    }
  }

  // handle only /favicon.ico http requests
  public boolean acceptInboundMessage(Object msg) throws Exception {
    if (null == iconBytes || !(msg instanceof FullHttpRequest)) {
      return false;
    }

    FullHttpRequest request = (FullHttpRequest) msg;
    String uri = request.getUri();

    return HttpMethod.GET.equals(request.getMethod()) && "/favicon.ico".endsWith(uri);
  }

  @Override
  protected void channelRead0(final ChannelHandlerContext ctx, final FullHttpRequest request) throws Exception {
    if (!request.getDecoderResult().isSuccess()) {
      sendError(ctx, BAD_REQUEST);
      return;
    }

    // Cache Validation
    String ifModifiedSince = request.headers().get(IF_MODIFIED_SINCE);
    if (ifModifiedSince != null && !ifModifiedSince.isEmpty()) {
      SimpleDateFormat dateFormatter = new SimpleDateFormat(HTTP_DATE_FORMAT, Locale.US);
      // Only compare up to the second because the datetime format we send to the client
      // does not have milliseconds
      long lastDownloadTime = dateFormatter.parse(ifModifiedSince).getTime();
      if (startupTime < lastDownloadTime) {
        sendNotModified(ctx);
        return;
      }
    }

    final DefaultHttpResponse response = new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.OK, Unpooled.copiedBuffer(iconBytes));
    response.headers().set(HttpHeaders.Names.CONTENT_LENGTH, iconBytes.length);
    response.headers().set(HttpHeaders.Names.CONTENT_TYPE, "image/x-icon");
    if (isKeepAlive(request)) {
      response.headers().set(CONNECTION, HttpHeaders.Values.KEEP_ALIVE);
    }

    ChannelFuture lastContentFuture = ctx.writeAndFlush(response);

    // Decide whether to close the connection or not.
    if (!isKeepAlive(request)) {
      // Close the connection when the whole content is written out.
      lastContentFuture.addListener(ChannelFutureListener.CLOSE);
    }
  }

  private static void sendError(ChannelHandlerContext ctx, HttpResponseStatus status) {
    final ByteBuf content = Unpooled.copiedBuffer("Failure: " + status.toString() + "\r\n", CharsetUtil.UTF_8);
    FullHttpResponse response = new DefaultFullHttpResponse(HTTP_1_1, status, content);
    response.headers().set(CONTENT_TYPE, "text/plain; charset=UTF-8");

    // Close the connection as soon as the error message is sent.
    ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
  }

  /**
   * When file timestamp is the same as what the browser is sending up, send a "304 Not Modified"
   *
   * @param ctx Context
   */
  private static void sendNotModified(ChannelHandlerContext ctx) {
    FullHttpResponse response = new DefaultFullHttpResponse(HTTP_1_1, NOT_MODIFIED);
    setDateHeader(response);

    // Close the connection as soon as the error message is sent.
    ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
  }

  /**
   * Sets the Date header for the HTTP response
   *
   * @param response HTTP response
   */
  private static void setDateHeader(FullHttpResponse response) {
    SimpleDateFormat dateFormatter = new SimpleDateFormat(HTTP_DATE_FORMAT, Locale.US);
    dateFormatter.setTimeZone(TimeZone.getTimeZone(HTTP_DATE_GMT_TIMEZONE));

    Calendar time = new GregorianCalendar();
    response.headers().set(DATE, dateFormatter.format(time.getTime()));
  }
}