private int writePlaintextDataDirect(ByteBuffer src, int pos, int len) throws IOException {
        return ssl.writeDirectByteBuffer(directByteBufferAddress(src, pos), len);
    }
Write plaintext data to the OpenSSL internal BIO

Calling this function with src.remaining == 0 is undefined.
common/src/main/java/org/conscrypt/ConscryptEngine.java