name : cset_narrowing.h /* Copyright (c) 2023, MariaDB Corporation. This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; version 2 of the License. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA */ #ifndef CSET_NARROWING_H_INCLUDED #define CSET_NARROWING_H_INCLUDED /* A singleton class to provide "utf8mb3_from_mb4.charset()". This is a variant of utf8mb3_general_ci that one can use when they have data in MB4 and want to make index lookup keys in MB3. */ extern class Charset_utf8narrow { struct my_charset_handler_st cset_handler; struct charset_info_st cset; public: Charset_utf8narrow() : cset_handler(*my_charset_utf8mb3_general_ci.cset), cset(my_charset_utf8mb3_general_ci) /* Copy the CHARSET_INFO structure */ { /* Insert our function wc_mb */ cset_handler.wc_mb= my_wc_mb_utf8mb4_bmp_only; cset.cset=&cset_handler; /* Charsets are compared by their name, so assign a different name */ LEX_CSTRING tmp= {STRING_WITH_LEN("utf8_mb4_to_mb3")}; cset.cs_name= tmp; } CHARSET_INFO *charset() { return &cset; } } utf8mb3_from_mb4; /* A class to temporary change a field that uses utf8mb3_general_ci to enable correct lookup key construction from string value in utf8mb4_general_ci Intended usage: // can do this in advance: bool do_narrowing= Utf8_narrow::should_do_narrowing(field, value_cset); ... // This sets the field to do narrowing if necessary: Utf8_narrow narrow(field, do_narrowing); // write to 'field' here // item->save_in_field(field) or something else // Stop doing narrowing narrow.stop(); */ class Utf8_narrow { Field *field; DTCollation save_collation; public: static bool should_do_narrowing(const THD *thd, CHARSET_INFO *field_cset, CHARSET_INFO *value_cset); static bool should_do_narrowing(const Field *field, CHARSET_INFO *value_cset) { CHARSET_INFO *field_cset= field->charset(); THD *thd= field->table->in_use; return should_do_narrowing(thd, field_cset, value_cset); } Utf8_narrow(Field *field_arg, bool is_applicable) { field= NULL; if (is_applicable) { DTCollation mb3_from_mb4= utf8mb3_from_mb4.charset(); field= field_arg; save_collation= field->dtcollation(); field->change_charset(mb3_from_mb4); } } void stop() { if (field) field->change_charset(save_collation); #ifndef NDEBUG field= NULL; #endif } ~Utf8_narrow() { DBUG_ASSERT(!field); } }; /* @brief Check if two fields can participate in a multiple equality using charset narrowing. @detail Normally, check_simple_equality() checks this by calling: left_field->eq_def(right_field) This function does the same but takes into account we might use charset narrowing: - collations are not the same but rather an utf8mb{3,4}_general_ci pair - for field lengths, should compare # characters, not #bytes. */ inline bool fields_equal_using_narrowing(const THD *thd, const Field *left, const Field *right) { return dynamic_cast<const Field_longstr*>(left) && dynamic_cast<const Field_longstr*>(right) && left->real_type() == right->real_type() && (Utf8_narrow::should_do_narrowing(left, right->charset()) || Utf8_narrow::should_do_narrowing(right, left->charset())) && left->char_length() == right->char_length(); }; #endif /* CSET_NARROWING_H_INCLUDED */