AlpnSelector Class — netty Architecture

Source Code

handler/src/main/java/io/netty/handler/ssl/JdkAlpnSslEngine.java lines 37–78

    final class AlpnSelector implements BiFunction<SSLEngine, List<String>, String> {
        private final ProtocolSelector selector;
        private boolean called;

        AlpnSelector(ProtocolSelector selector) {
            this.selector = selector;
        }

        @Override
        public String apply(SSLEngine sslEngine, List<String> strings) {
            assert !called;
            called = true;

            try {
                String selected = selector.select(strings);
                return selected == null ? StringUtil.EMPTY_STRING : selected;
            } catch (Exception cause) {
                // Returning null means we want to fail the handshake.
                //
                // See https://download.java.net/java/jdk9/docs/api/javax/net/ssl/
                // SSLEngine.html#setHandshakeApplicationProtocolSelector-java.util.function.BiFunction-
                return null;
            }
        }

        void checkUnsupported() {
            if (called) {
                // ALPN message was received by peer and so apply(...) was called.
                // See:
                // https://hg.openjdk.java.net/jdk9/dev/jdk/file/65464a307408/src/
                // java.base/share/classes/sun/security/ssl/ServerHandshaker.java#l933
                return;
            }
            String protocol = getApplicationProtocol();
            assert protocol != null;

            if (protocol.isEmpty()) {
                // ALPN is not supported
                selector.unsupported();
            }
        }
    }