HpackDecoder Class — netty Architecture

Source Code

codec-http2/src/main/java/io/netty/handler/codec/http2/HpackDecoder.java lines 54–571

final class HpackDecoder {
    private static final Http2Exception DECODE_ULE_128_DECOMPRESSION_EXCEPTION =
            Http2Exception.newStatic(COMPRESSION_ERROR, "HPACK - decompression failure",
                    Http2Exception.ShutdownHint.HARD_SHUTDOWN, HpackDecoder.class,
            "decodeULE128(..)");
    private static final Http2Exception DECODE_ULE_128_TO_LONG_DECOMPRESSION_EXCEPTION =
            Http2Exception.newStatic(COMPRESSION_ERROR, "HPACK - long overflow",
                    Http2Exception.ShutdownHint.HARD_SHUTDOWN, HpackDecoder.class, "decodeULE128(..)");
    private static final Http2Exception DECODE_ULE_128_TO_INT_DECOMPRESSION_EXCEPTION =
            Http2Exception.newStatic(COMPRESSION_ERROR, "HPACK - int overflow",
                    Http2Exception.ShutdownHint.HARD_SHUTDOWN, HpackDecoder.class, "decodeULE128ToInt(..)");
    private static final Http2Exception DECODE_ILLEGAL_INDEX_VALUE =
            Http2Exception.newStatic(COMPRESSION_ERROR, "HPACK - illegal index value",
                    Http2Exception.ShutdownHint.HARD_SHUTDOWN, HpackDecoder.class, "decode(..)");
    private static final Http2Exception INDEX_HEADER_ILLEGAL_INDEX_VALUE =
            Http2Exception.newStatic(COMPRESSION_ERROR, "HPACK - illegal index value",
                    Http2Exception.ShutdownHint.HARD_SHUTDOWN, HpackDecoder.class, "indexHeader(..)");
    private static final Http2Exception READ_NAME_ILLEGAL_INDEX_VALUE =
            Http2Exception.newStatic(COMPRESSION_ERROR, "HPACK - illegal index value",
                    Http2Exception.ShutdownHint.HARD_SHUTDOWN, HpackDecoder.class, "readName(..)");
    private static final Http2Exception INVALID_MAX_DYNAMIC_TABLE_SIZE =
            Http2Exception.newStatic(COMPRESSION_ERROR, "HPACK - invalid max dynamic table size",
                    Http2Exception.ShutdownHint.HARD_SHUTDOWN, HpackDecoder.class,
            "setDynamicTableSize(..)");
    private static final Http2Exception MAX_DYNAMIC_TABLE_SIZE_CHANGE_REQUIRED =
            Http2Exception.newStatic(COMPRESSION_ERROR, "HPACK - max dynamic table size change required",
                    Http2Exception.ShutdownHint.HARD_SHUTDOWN, HpackDecoder.class, "decode(..)");
    private static final byte READ_HEADER_REPRESENTATION = 0;
    private static final byte READ_INDEXED_HEADER = 1;
    private static final byte READ_INDEXED_HEADER_NAME = 2;
    private static final byte READ_LITERAL_HEADER_NAME_LENGTH_PREFIX = 3;
    private static final byte READ_LITERAL_HEADER_NAME_LENGTH = 4;
    private static final byte READ_LITERAL_HEADER_NAME = 5;
    private static final byte READ_LITERAL_HEADER_VALUE_LENGTH_PREFIX = 6;
    private static final byte READ_LITERAL_HEADER_VALUE_LENGTH = 7;
    private static final byte READ_LITERAL_HEADER_VALUE = 8;

    private final HpackHuffmanDecoder huffmanDecoder = new HpackHuffmanDecoder();
    private final HpackDynamicTable hpackDynamicTable;
    private long maxHeaderListSize;
    private long maxDynamicTableSize;
    private long encoderMaxDynamicTableSize;
    private boolean maxDynamicTableSizeChangeRequired;

    /**
     * Create a new instance.
     * @param maxHeaderListSize This is the only setting that can be configured before notifying the peer.
     *  This is because <a href="https://tools.ietf.org/html/rfc7540#section-6.5.1">SETTINGS_MAX_HEADER_LIST_SIZE</a>
     *  allows a lower than advertised limit from being enforced, and the default limit is unlimited
     *  (which is dangerous).
     */
    HpackDecoder(long maxHeaderListSize) {
        this(maxHeaderListSize, DEFAULT_HEADER_TABLE_SIZE);
    }

    /**
     * Exposed Used for testing only! Default values used in the initial settings frame are overridden intentionally
     * for testing but violate the RFC if used outside the scope of testing.
     */
    HpackDecoder(long maxHeaderListSize, int maxHeaderTableSize) {
        this.maxHeaderListSize = checkPositive(maxHeaderListSize, "maxHeaderListSize");

        maxDynamicTableSize = encoderMaxDynamicTableSize = maxHeaderTableSize;
        maxDynamicTableSizeChangeRequired = false;
        hpackDynamicTable = new HpackDynamicTable(maxHeaderTableSize);
    }

    /**
     * Decode the header block into header fields.
     * <p>
     * This method assumes the entire header block is contained in {@code in}.
     */
    void decode(int streamId, ByteBuf in, Http2Headers headers, boolean validateHeaders) throws Http2Exception {
        Http2HeadersSink sink = new Http2HeadersSink(
                streamId, headers, maxHeaderListSize, validateHeaders);
        // Check for dynamic table size updates, which must occur at the beginning:
        // https://www.rfc-editor.org/rfc/rfc7541.html#section-4.2
        decodeDynamicTableSizeUpdates(in);
        decode(in, sink);

        // Now that we've read all of our headers we can perform the validation steps. We must