HpackHuffmanEncoder Class — netty Architecture

Source Code

codec-http2/src/main/java/io/netty/handler/codec/http2/HpackHuffmanEncoder.java lines 40–194

final class HpackHuffmanEncoder {

    private final int[] codes;
    private final byte[] lengths;
    private final EncodedLengthProcessor encodedLengthProcessor = new EncodedLengthProcessor();
    private final EncodeProcessor encodeProcessor = new EncodeProcessor();

    HpackHuffmanEncoder() {
        this(HpackUtil.HUFFMAN_CODES, HpackUtil.HUFFMAN_CODE_LENGTHS);
    }

    /**
     * Creates a new Huffman encoder with the specified Huffman coding.
     *
     * @param codes the Huffman codes indexed by symbol
     * @param lengths the length of each Huffman code
     */
    private HpackHuffmanEncoder(int[] codes, byte[] lengths) {
        this.codes = codes;
        this.lengths = lengths;
    }

    /**
     * Compresses the input string literal using the Huffman coding.
     *
     * @param out the output stream for the compressed data
     * @param data the string literal to be Huffman encoded
     */
    public void encode(ByteBuf out, CharSequence data) {
        ObjectUtil.checkNotNull(out, "out");
        if (data instanceof AsciiString) {
            AsciiString string = (AsciiString) data;
            try {
                encodeProcessor.out = out;
                string.forEachByte(encodeProcessor);
            } catch (Exception e) {
                PlatformDependent.throwException(e);
            } finally {
                encodeProcessor.end();
            }
        } else {
            encodeSlowPath(out, data);
        }
    }

    private void encodeSlowPath(ByteBuf out, CharSequence data) {
        long current = 0;
        int n = 0;

        for (int i = 0; i < data.length(); i++) {
            int b = AsciiString.c2b(data.charAt(i)) & 0xFF;
            int code = codes[b];
            int nbits = lengths[b];

            current <<= nbits;
            current |= code;
            n += nbits;

            while (n >= 8) {
                n -= 8;
                out.writeByte((int) (current >> n));
            }
        }

        if (n > 0) {
            current <<= 8 - n;
            current |= 0xFF >>> n; // this should be EOS symbol
            out.writeByte((int) current);
        }
    }

    /**
     * Returns the number of bytes required to Huffman encode the input string literal.
     *
     * @param data the string literal to be Huffman encoded
     * @return the number of bytes required to Huffman encode {@code data}
     */
    int getEncodedLength(CharSequence data) {
        if (data instanceof AsciiString) {
            AsciiString string = (AsciiString) data;
            try {