Netty Source Learning-delimiterbasedframedecoder

Look at the API of Delimiterbasedframedecoder, there are examples:

The Channelbuffer received are as follows:

+--------------+ | abc\ndef\r\n | +--------------+

After Delimiterbasedframedecoder (Delimiters.linedelimiter ()), get:

+-----+-----+ | ABC | DEF | +-----+-----+

Instead of

+----------+ | Abc\ndef |

Why?

First, be clear, if not specified, delimiterbasedframedecoder default will remove the delimiter

Next look at Delimiters.linedelimiter (), which returns two sets of delimiter, corresponding to windows and Linux line breaks

public static channelbuffer[] Linedelimiter () {        return new channelbuffer[] {                Channelbuffers.wrappedbuffer (new byte[] {' \ r ', ' \ n '},                Channelbuffers.wrappedbuffer (new byte[] {' \ n '}),        };    

Examine the two sets of separators

Programme I

with "\ r \ n" as the separator, the return

Framea = "Abc\ndef"

Programme II

return with "\ n"

Frameb_0 = "ABC"

frameb_1 = "Def\r"

Since the length of the frameb_0 is shorter than the Framea, in this case, Scenario II is used

But there is a question, why not compare all, but only compare frameb_0?

To know, length (FRAMEA) = Length (frameb_0) + length (frameb_1), both equal

At first, I thought, like split, scenario two would return "abcdef\r" one time.

Not actually.

It is encountered with a delimiter and returns a result

This can be demonstrated by the following code:

public class ClientHandler extends Simplechannelupstreamhandler {    @Override public    void channelconnected ( Channelhandlercontext CTX, channelstateevent e)            throws Exception {        String msg = "abc\ndef\r\n";        Channelbuffer buff = Channelbuffers.buffer (Msg.length ());        Buff.writebytes (Msg.getbytes ());        E.getchannel (). write (buff);    }}

Server:

Bootstrap.setpipelinefactory (New Channelpipelinefactory () {public            channelpipeline Getpipeline () throws Exception {                Channelpipeline pipeline = Channels.pipeline ();//Set here: Do not remove delimiters, easy to observe                pipeline.addlast ("Handler1", New Delimiterbasedframedecoder (8192, False, Delimiters.linedelimiter ()));                Pipeline.addlast ("Handler2", New Serverstringhandler ());// print decode result                return pipeline;            }        );

Serverstringhandler:

public class Serverstringhandler extends simplechannelupstreamhandler{    @Override public    void messagereceived (Channelhandlercontext ctx, messageevent e)            Throws Exception {        Channelbuffer buff = (channelbuffer) e.getmessage ();        String msg = (string) buff.tostring (Helper.charset_utf8);                String s = "abc\n"; The Msg_escape will output "abc\n" instead of "abc" plus a newline        String msg_escape = Stringescapeutils.escapejava (msg);          System.out.println ("msg =" + Msg_escape);}    }

Results Serverstringhandler will be output two times:

msg = Abc\nmsg = def\r\n

View the source code, will be more clear:

public class Delimiterbasedframedecoder extends Framedecoder {private final channelbuffer[] delimiters; Private final int maxframelength;/* Returns the result, whether the usual call to remove the delimiter is to remove the delimiter, such as New Delimiterbasedframedecoder (8192, Delimiters.linedelimiter ()) is equivalent to the new Delimiterbasedframedecoder (8192,/*stripdelimiter=*/true, Delimiters.linedelimiter ()) */private Final Boolean stripdelimiter; @Override protected Object decode (Cha Nnelhandlercontext CTX, channel channel, Channelbuffer buffer) throws Exception {//Try all delimiters and choose        The delimiter which yields the shortest frame.        int minframelength = Integer.max_value; Channelbuffer Mindelim = null;/* iteration for each delimiter, try to decode, and then choose the shortest that returns "delimiter frame" in indexof this method */for (            Channelbuffer delim:delimiters) {int framelength = indexOf (buffer, delim);                if (framelength >= 0 && framelength < minframelength) {minframelength = Framelength; MiNdelim = Delim;            }} if (Mindelim! = null) {int mindelimlength = mindelim.capacity ();            Channelbuffer frame;                if (stripdelimiter) {frame = Buffer.readbytes (minframelength);            Buffer.skipbytes (mindelimlength);            } else {frame = Buffer.readbytes (minframelength + mindelimlength);        } return frame; }}/* the frame (haystack) to find the first delimiter (needle), this position is recorded as I return (I-haystack.readerindex), that is, the length of the first sub frame after separation can be seen, it is " Find one and return a "*/private static int indexOf (Channelbuffer haystack, channelbuffer needle) {//Traversal haystack for each byte for (int i = Haystack.readerindex (); I < Haystack.writerindex ();            i + +) {int haystackindex = i; int Needleindex;/*haystack Whether delimiter appears, note delimiter is a channelbuffer (byte[]) For example haystack= "Abc\r\ndef", needle= "\ r\n "Then when haystackindex=3, found" \ r ", at this time needleindex=0 continue to execute the loop, haystackindex++,needleindex++, found" \ n "So far, the entire needle matchThe program then executes to the IF (Needleindex = = Needle.capacity ()) and returns the result */for (Needleindex = 0; Needleindex < needle.capacity ();                    Needleindex + +) {if (Haystack.getbyte (haystackindex)! = Needle.getbyte (Needleindex)) {                Break                    } else {haystackindex + +;                        if (Haystackindex = = Haystack.writerindex () && Needleindex! = needle.capacity ()-1) {                    return-1;  }}} if (Needleindex = = Needle.capacity ()) {//Found the needle from                The haystack!            return I-haystack.readerindex ();    }} return-1; }}

Netty Source Learning-delimiterbasedframedecoder