Change Send_field::type from enum_field_types to Type_handler*

protocol.cc has various tests for MYSQL_TYPE_XXX, for example:

bool Protocol_text::store(const char *from, size_t length,

                          CHARSET_INFO *fromcs, CHARSET_INFO *tocs)

{

#ifndef DBUG_OFF

  DBUG_ASSERT(field_types == 0 ||

	      field_types[field_pos] == MYSQL_TYPE_DECIMAL ||

              field_types[field_pos] == MYSQL_TYPE_BIT ||

              field_types[field_pos] == MYSQL_TYPE_NEWDECIMAL ||

	      (field_types[field_pos] >= MYSQL_TYPE_ENUM &&

	       field_types[field_pos] <= MYSQL_TYPE_GEOMETRY));

  field_pos++;

#endif

  return store_string_aux(from, length, fromcs, tocs);

}

This is not friendly to new/pluggable data types.

To fix this problem, we'll do the following changes:

• change Send_field::type from enum_field_type to const Type_handler *
• add a new enum:

  enum protocol_send_type_t

  {

  PROTOCOL_SEND_STRING,

  PROTOCOL_SEND_FLOAT,

  PROTOCOL_SEND_DOUBLE,

  PROTOCOL_SEND_TINY,

  PROTOCOL_SEND_SHORT,

  PROTOCOL_SEND_LONG,

  PROTOCOL_SEND_LONGLONG,

  PROTOCOL_SEND_DATETIME,

  PROTOCOL_SEND_DATE,

  PROTOCOL_SEND_TIME

  };

• add a new virtual method in Type_handler:

  virtual protocol_send_type_t protocol_send_type() const= 0;

So the ::store() method implementations will simplify to something like:

bool Protocol_text::store(const char *from, size_t length,

                          CHARSET_INFO *fromcs, CHARSET_INFO *tocs)

{

#ifndef DBUG_OFF

  DBUG_ASSERT(valid_handler(field_pos, PROTOCOL_SEND_STRING));

  field_pos++;

#endif

  return store_string_aux(from, length, fromcs, tocs);

}

New data types will just need to implement a proper virtual implementation of Type_handler_xxx::protocol_send_type().