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Java implementation of the Sendmail Milter protocol.
There is a newer version: 0.8
/*
 * Licensed 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 org.nightcode.milter.net;

import java.util.UUID;

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.util.Attribute;
import io.netty.util.AttributeKey;
import org.nightcode.milter.MilterContext;
import org.nightcode.milter.MilterHandler;
import org.nightcode.milter.codec.MilterPacket;
import org.nightcode.milter.command.CommandEngine;
import org.nightcode.milter.util.Log;

import static java.lang.String.format;

public class MilterChannelHandler extends SimpleChannelInboundHandler {

  private static final class MilterPacketSenderImpl implements MilterPacketSender {
    private final ChannelHandlerContext ctx;

    private MilterPacketSenderImpl(ChannelHandlerContext ctx) {
      this.ctx = ctx;
    }

    @Override public void close() {
      ctx.channel().attr(AttributeKey.valueOf("milterContext")).set(null);
      if (ctx.channel().isActive()) {
        ctx.close();
      }
    }

    @Override public void send(MilterPacket packet) {
      ctx.writeAndFlush(packet);
    }
  }

  private final MilterHandler milterHandler;
  private final CommandEngine commandManager;

  private final AttributeKey milterContextAttrKey = AttributeKey.valueOf("milterContext");

  public MilterChannelHandler(MilterHandler milterHandler) {
    this.milterHandler = milterHandler;
    this.commandManager = CommandEngine.instance();
  }

  @Override protected void channelRead0(ChannelHandlerContext ctx, MilterPacket milterPacket) {
    MilterContext milterContext = getOrCreateMilterContext(ctx);
    commandManager.submit(milterContext, milterPacket);
  }

  @Override public void channelInactive(ChannelHandlerContext ctx) throws Exception {
    MilterContext milterContext = getMilterContext(ctx);
    if (milterContext != null) {
      milterHandler.closeSession(milterContext);
    }
    super.channelInactive(ctx);
  }

  @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
    MilterContext milterContext = getMilterContext(ctx);
    UUID          contextId     = (milterContext != null) ? milterContext.id() : null;
    Log.warn().log(getClass(), format("[%s] channel exception: %s", contextId, cause.getMessage()), cause);

    if (milterContext != null) {
      milterHandler.abortSession(milterContext, null);
    }
    ctx.close();
  }

  private MilterContext getMilterContext(ChannelHandlerContext ctx) {
    return ctx.channel().attr(milterContextAttrKey).get();
  }

  private MilterContext getOrCreateMilterContext(ChannelHandlerContext ctx) {
    Attribute attr          = ctx.channel().attr(milterContextAttrKey);
    MilterContext            milterContext = attr.get();
    if (milterContext == null) {
      milterContext = milterHandler.createContext(new MilterPacketSenderImpl(ctx));
      attr.set(milterContext);
    }
    return milterContext;
  }
}