AbstractSniHandler Class — netty Architecture

Source Code

handler/src/main/java/io/netty/handler/ssl/AbstractSniHandler.java lines 36–221

public abstract class AbstractSniHandler<T> extends SslClientHelloHandler<T> {

    private static String extractSniHostname(ByteBuf in) {
        // See https://tools.ietf.org/html/rfc5246#section-7.4.1.2
        //
        // Decode the ssl client hello packet.
        //
        // struct {
        //    ProtocolVersion client_version;
        //    Random random;
        //    SessionID session_id;
        //    CipherSuite cipher_suites<2..2^16-2>;
        //    CompressionMethod compression_methods<1..2^8-1>;
        //    select (extensions_present) {
        //        case false:
        //            struct {};
        //        case true:
        //            Extension extensions<0..2^16-1>;
        //    };
        // } ClientHello;
        //

        // We have to skip bytes until SessionID (which sum to 34 bytes in this case).
        int offset = in.readerIndex();
        int endOffset = in.writerIndex();
        offset += 34;

        if (endOffset - offset >= 6) {
            final int sessionIdLength = in.getUnsignedByte(offset);
            offset += sessionIdLength + 1;

            final int cipherSuitesLength = in.getUnsignedShort(offset);
            offset += cipherSuitesLength + 2;

            final int compressionMethodLength = in.getUnsignedByte(offset);
            offset += compressionMethodLength + 1;

            final int extensionsLength = in.getUnsignedShort(offset);
            offset += 2;
            final int extensionsLimit = offset + extensionsLength;

            // Extensions should never exceed the record boundary.
            if (extensionsLimit <= endOffset) {
                while (extensionsLimit - offset >= 4) {
                    final int extensionType = in.getUnsignedShort(offset);
                    offset += 2;

                    final int extensionLength = in.getUnsignedShort(offset);
                    offset += 2;

                    if (extensionsLimit - offset < extensionLength) {
                        break;
                    }

                    // SNI
                    // See https://tools.ietf.org/html/rfc6066#page-6
                    if (extensionType == 0) {
                        offset += 2;
                        if (extensionsLimit - offset < 3) {
                            break;
                        }

                        final int serverNameType = in.getUnsignedByte(offset);
                        offset++;

                        if (serverNameType == 0) {
                            final int serverNameLength = in.getUnsignedShort(offset);
                            offset += 2;

                            if (extensionsLimit - offset < serverNameLength) {
                                break;
                            }

                            final String hostname = in.toString(offset, serverNameLength, CharsetUtil.US_ASCII);
                            return hostname.toLowerCase(Locale.US);
                        } else {
                            // invalid enum value
                            break;
                        }
                    }