code: public int getSchemaId(final DirectBuffer buffer, final int bufferOffset)
      {
          return Types.getInt(buffer, bufferOffset + schemaIdOffset, schemaIdType, schemaIdByteOrder);
      }
docs: Get the schema id number from the message header.
  
  @param buffer       from which to read the value.
  @param bufferOffset in the buffer at which the message header begins.
  @return the value of the schema id number.