Log the bad packet in a prettier way. Also, don't show the authlib debug data in the log file.

fml/src/main/java/cpw/mods/fml/common/network/ByteBufUtils.java

@@ -179,4 +179,74 @@ public class ByteBufUtils {
             throw Throwables.propagate(e);
         }
     }
+
+    public static String getContentDump(ByteBuf buffer)
+    {
+        int currentLength = buffer.readableBytes();
+        StringBuffer returnString = new StringBuffer((currentLength * 3) + // The
+                                                                           // hex
+                (currentLength) + // The ascii
+                (currentLength / 4) + // The tabs/\n's
+                30); // The text
+
+        // returnString.append("Buffer contents:\n");
+        int i, j; // Loop variables
+        for (i = 0; i < currentLength; i++)
+        {
+            if ((i != 0) && (i % 16 == 0))
+            {
+                // If it's a multiple of 16 and i isn't null, show the ascii
+                returnString.append('\t');
+                for (j = i - 16; j < i; j++)
+                {
+                    if (buffer.getByte(j) < 0x20 || buffer.getByte(j) > 0x7F)
+                        returnString.append('.');
+                    else
+                        returnString.append((char) buffer.getByte(j));
+                }
+                // Add a linefeed after the string
+                returnString.append("\n");
+            }
+
+            returnString.append(Integer.toString((buffer.getByte(i) & 0xF0) >> 4, 16) + Integer.toString((buffer.getByte(i) & 0x0F) >> 0, 16));
+            returnString.append(' ');
+        }
+
+        // Add padding spaces if it's not a multiple of 16
+        if (i != 0 && i % 16 != 0)
+        {
+            for (j = 0; j < ((16 - (i % 16)) * 3); j++)
+            {
+                returnString.append(' ');
+            }
+        }
+        // Add the tab for alignment
+        returnString.append('\t');
+
+        // Add final chararacters at right, after padding
+
+        // If it was at the end of a line, print out the full line
+        if (i > 0 && (i % 16) == 0)
+        {
+            j = i - 16;
+        } else
+        {
+            j = (i - (i % 16));
+        }
+
+        for (; i >= 0 && j < i; j++)
+        {
+            if (buffer.getByte(j) < 0x20 || buffer.getByte(j) > 0x7F)
+                returnString.append('.');
+            else
+                returnString.append((char) buffer.getByte(j));
+        }
+
+        // Finally, tidy it all up with a newline
+        returnString.append('\n');
+        returnString.append("Length: " + currentLength);
+
+        return returnString.toString();
+
+    }
 }

fml/src/main/java/cpw/mods/fml/common/network/internal/FMLRuntimeCodec.java

@@ -1,9 +1,10 @@
 package cpw.mods.fml.common.network.internal;
 
+import com.google.common.base.Splitter;
 import io.netty.buffer.ByteBuf;
 import io.netty.channel.ChannelHandlerContext;
-import com.google.common.primitives.Bytes;
 import cpw.mods.fml.common.FMLLog;
+import cpw.mods.fml.common.network.ByteBufUtils;
 import cpw.mods.fml.common.network.FMLIndexedMessageToMessageCodec;
 import cpw.mods.fml.common.network.FMLNetworkException;
 
@@ -33,9 +34,10 @@ public class FMLRuntimeCodec extends FMLIndexedMessageToMessageCodec<FMLMessage>
         if (msg.payload().getByte(0) == 0 && msg.payload().readableBytes() > 2)
         {
             FMLLog.severe("The connection appears to have sent an invalid FML packet of type 0, this is likely because it think's it's talking to 1.6.4 FML");
-            byte[] badData = new byte[msg.payload().readableBytes()];
-            msg.payload().getBytes(0, badData);
-            FMLLog.info("Bad data : %s",Bytes.asList(badData));
+            FMLLog.info("Bad data :");
+            for (String l : Splitter.on('\n').split(ByteBufUtils.getContentDump(msg.payload()))) {
+                FMLLog.info("\t%s",l);
+            }
             throw new FMLNetworkException("Invalid FML packet");
         }
     }

fml/src/main/resources/log4j2.xml

@@ -27,6 +27,11 @@
         </RollingRandomAccessFile>
     </Appenders>
     <Loggers>
+        <Logger level="info" name="com.mojang" additivity="false">
+            <AppenderRef ref="SysOut" level="INFO"/>
+            <AppenderRef ref="File" />
+            <AppenderRef ref="ServerGuiConsole" level="INFO"/>
+        </Logger>
         <Logger level="info" name="net.minecraft" additivity="false">
             <filters>
                 <MarkerFilter marker="NETWORK_PACKETS" onMatch="DENY" onMismatch="NEUTRAL" />