MySQL客户端显示binary字符代码改造

一、客户端显示字符背景介绍

MySQL最新版本有一个新功能，在使用客户端的时候，最后加上--skip-binary-as-hex选项可以直接显示二进制值对应的字符串，不加该选项就可以按照原来的设置格式显示。先来看一下以下的varbaniry的显示例子。

#建表：
create table varb(id int,bb varbinary(1000));
insert into varb values(1,'abcd');
#登录：
mysql -h 127.0.0.1 -P3307 -uroot  --skip-binary-as-hex
mysql> select * from varb;
+------+------+
| id   | bb   |
+------+------+
|    1 | abcd |
+------+------+
1 row in set (0.00 sec)

如果不加--skip-binary-as-hex选项的显示如下：

mysql -h 127.0.0.1 -P3307 -uroot
mysql> select * from varb;
+------+------------+
| id   | bb         |
+------+------------+
|    1 | 0x61626364 |
+------+------------+
1 row in set (0.01 sec)

这个功能对于用惯了旧版本的同学们有的会觉得不方便，今天这里动手改造一下都显示成字符格式而不用通过--skip-binary-as-hex选项设置。

二、代码跟踪

沿用上面的表查询一下哪段代码决定字符的显示格式，代码解析如下：

输入该命令后找到相关字符显示的代码：

mysql> select * from varb;

class Item_field的成员函数如下：

const CHARSET_INFO *charset_for_protocol(void) override {
    return field->charset_for_protocol(); 
    #表字段的字符显示取决于field的字符设置。
  }

继续找到class Field的成员函数如下：

const CHARSET_INFO *charset_for_protocol() const {
    return binary() ? &my_charset_bin : charset(); 
    #field的字符设置取决于是否binary类型。
  }

输入以上命令GDB跟踪一下代码堆栈：

Thread 47 "mysqld" hit Breakpoint 3, Item_field::charset_for_protocol (this=0x7fff340bc1f0)
    at /home/greatdb/sql/item.h:4373
4373   const CHARSET_INFO *charset_for_protocol(void) override {
(gdb) bt
#0  Item_field::charset_for_protocol (this=0x7fff340bc1f0)
    at /home/greatdb/sql/item.h:4373#1  0x0000555558e60ca8 in THD::send_result_metadata (this=0x7fff34000c00, list=..., flags=5)
    at /home/greatdb/sql/sql_class.cc:2831
#2  0x0000555558d9fe59 in Query_result_send::send_result_set_metadata (this=0x7fff3429cfa0, 
    thd=0x7fff34000c00, list=..., flags=5)
    at /home/greatdb/sql/query_result.cc:74
#3  0x0000555559093d1b in Query_expression::ExecuteIteratorQuery (this=0x7fff3429ae08, 
    thd=0x7fff34000c00) at /home/greatdb/sql/sql_union.cc:1169
#4  0x0000555559094452 in Query_expression::execute (this=0x7fff3429ae08, thd=0x7fff34000c00)
    at /home/greatdb/sql/sql_union.cc:1305
#5  0x0000555558fd4b18 in Sql_cmd_dml::execute_inner (this=0x7fff3429cf68, thd=0x7fff34000c00)
    at /home/greatdb/sql/sql_select.cc:810
#6  0x0000555558fd3f24 in Sql_cmd_dml::execute (this=0x7fff3429cf68, thd=0x7fff34000c00)
    at /home/greatdb/sql/sql_select.cc:578
#7  0x0000555558f4ac03 in mysql_execute_command (thd=0x7fff34000c00, first_level=true)
    at /home/greatdb/sql/sql_parse.cc:4784
#8  0x0000555558f4cd80 in dispatch_sql_command (thd=0x7fff34000c00, parser_state=0x7fffe82ab990, 
    update_userstat=false) at /home/greatdb/sql/sql_parse.cc:5384
#9  0x0000555558f42257 in dispatch_command (thd=0x7fff34000c00, com_data=0x7fffe82acb70, 
    command=COM_QUERY) at /home/greatdb/sql/sql_parse.cc:1992
#10 0x0000555558f405c7 in do_command (thd=0x7fff34000c00)
    at /home/greatdb/sql/sql_parse.cc:1440
#11 0x0000555559163f7e in handle_connection (arg=0x55556091c920)
    at /home/greatdb/sql/conn_handler/connection_handler_per_thread.cc:307
#12 0x000055555ad85edf in pfs_spawn_thread (arg=0x5555607808c0)
    at /home/greatdb/storage/perfschema/pfs
                        来源：https://www.51cto.com/article/715282.html