LineBasedFrameDecoder Class — netty Architecture

Source Code

codec-base/src/main/java/io/netty/handler/codec/LineBasedFrameDecoder.java lines 42–187

public class LineBasedFrameDecoder extends ByteToMessageDecoder {

    /** Maximum length of a frame we're willing to decode.  */
    private final int maxLength;
    /** Whether or not to throw an exception as soon as we exceed maxLength. */
    private final boolean failFast;
    private final boolean stripDelimiter;

    /** True if we're discarding input because we're already over maxLength.  */
    private boolean discarding;
    private int discardedBytes;

    /** Last scan position. */
    private int offset;

    /**
     * Creates a new decoder.
     * @param maxLength  the maximum length of the decoded frame.
     *                   A {@link TooLongFrameException} is thrown if
     *                   the length of the frame exceeds this value.
     */
    public LineBasedFrameDecoder(final int maxLength) {
        this(maxLength, true, false);
    }

    /**
     * Creates a new decoder.
     * @param maxLength  the maximum length of the decoded frame.
     *                   A {@link TooLongFrameException} is thrown if
     *                   the length of the frame exceeds this value.
     * @param stripDelimiter  whether the decoded frame should strip out the
     *                        delimiter or not
     * @param failFast  If <tt>true</tt>, a {@link TooLongFrameException} is
     *                  thrown as soon as the decoder notices the length of the
     *                  frame will exceed <tt>maxFrameLength</tt> regardless of
     *                  whether the entire frame has been read.
     *                  If <tt>false</tt>, a {@link TooLongFrameException} is
     *                  thrown after the entire frame that exceeds
     *                  <tt>maxFrameLength</tt> has been read.
     */
    public LineBasedFrameDecoder(final int maxLength, final boolean stripDelimiter, final boolean failFast) {
        this.maxLength = maxLength;
        this.failFast = failFast;
        this.stripDelimiter = stripDelimiter;
    }

    @Override
    protected final void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        Object decoded = decode(ctx, in);
        if (decoded != null) {
            out.add(decoded);
        }
    }

    /**
     * Create a frame out of the {@link ByteBuf} and return it.
     *
     * @param   ctx             the {@link ChannelHandlerContext} which this {@link ByteToMessageDecoder} belongs to
     * @param   buffer          the {@link ByteBuf} from which to read data
     * @return  frame           the {@link ByteBuf} which represent the frame or {@code null} if no frame could
     *                          be created.
     */
    protected Object decode(ChannelHandlerContext ctx, ByteBuf buffer) throws Exception {
        final int eol = findEndOfLine(buffer);
        if (!discarding) {
            if (eol >= 0) {
                final ByteBuf frame;
                final int length = eol - buffer.readerIndex();
                final int delimLength = buffer.getByte(eol) == '\r'? 2 : 1;

                if (length > maxLength) {
                    buffer.readerIndex(eol + delimLength);
                    fail(ctx, length);
                    return null;
                }

                if (stripDelimiter) {
                    frame = buffer.readRetainedSlice(length);
                    buffer.skipBytes(delimLength);
                } else {
                    frame = buffer.readRetainedSlice(length + delimLength);