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POAssembling a Netty Message in the Handler
 

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    <p>I am in the process of prototyping Netty for my project. I am trying to implement a simple Text/String oriented protocol on top of Netty. In my pipeline I am using the following:</p> <pre><code>public class TextProtocolPipelineFactory implements ChannelPipelineFactory { @Override public ChannelPipeline getPipeline() throws Exception { // Create a default pipeline implementation. ChannelPipeline pipeline = pipeline(); // Add the text line codec combination first, pipeline.addLast("framer", new DelimiterBasedFrameDecoder(2000000, Delimiters.lineDelimiter())); pipeline.addLast("decoder", new StringDecoder()); pipeline.addLast("encoder", new StringEncoder()); // and then business logic. pipeline.addLast("handler", new TextProtocolHandler()); return pipeline; } } </code></pre> <p>I have a DelimiterBasedFrameDecoder, a String Decoder, and a String Encoder in the pipeline.</p> <p>As a result of this setup my incoming message is split into multiple Strings. This results in multiple invocations of the "messageReceived" method of my handler. This is fine. However , this requires me to accumulate these messages in memory and re-construct the message when the last string packet of the message is received.</p> <p>My question is, what is the most memory efficient way to "accumulate the strings" and then "re-construct them into the final message". I have 3 options so far. They are:</p> <ul> <li><p>Use a StringBuilder to accumulate and toString to construct. (This gives the worst memory performance. In fact for large payloads with lots of concurrent users this gives non-acceptable performance)</p></li> <li><p>Accumulate into a ByteArray via a ByteArrayOutputStream and then construct using the byte-array (this gives a much better performance than option 1, but it still hogs quite a bit of memory)</p></li> <li><p>Accumulate into a Dymamic Channel Buffer and use toString(charset) to construct. I have not profiled this setup yet but I am curious how this compares to the above two options. Has anyone solved this issue using the Dynamic Channel Buffer?</p></li> </ul> <p>I am new to Netty and its possible I may be doing something wrong architecturally. Your input will be greatly appreciated.</p> <p>Thanks in advance Sohil</p> <p><strong>Adding my implementation of a custom FrameDecoder for Norman to review</strong></p> <pre><code>public final class TextProtocolFrameDecoder extends FrameDecoder { public static ChannelBuffer messageDelimiter() { return ChannelBuffers.wrappedBuffer(new byte[] {'E','O','F'}); } @Override protected Object decode(ChannelHandlerContext ctx, Channel channel,ChannelBuffer buffer) throws Exception { int eofIndex = find(buffer, messageDelimiter()); if(eofIndex != -1) { ChannelBuffer frame = buffer.readBytes(buffer.readableBytes()); return frame; } return null; } private static int find(ChannelBuffer haystack, ChannelBuffer needle) { for (int i = haystack.readerIndex(); i &lt; haystack.writerIndex(); i ++) { int haystackIndex = i; int needleIndex; for (needleIndex = 0; needleIndex &lt; needle.capacity(); needleIndex ++) { if (haystack.getByte(haystackIndex) != needle.getByte(needleIndex)) { break; } else { haystackIndex ++; if (haystackIndex == haystack.writerIndex() &amp;&amp; needleIndex != needle.capacity() - 1) { return -1; } } } if (needleIndex == needle.capacity()) { // Found the needle from the haystack! return i - haystack.readerIndex(); } } return -1; } } </code></pre>
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