MDEV-28910 remove the 5.5.5- version hack

no longer needed, MySQL replication was fixed meanwhile.

client code still can recognize and strip the prefix though.

include/mysql_com.h

@@ -41,27 +41,6 @@
 #define MYSQL50_TABLE_NAME_PREFIX_LENGTH  (sizeof(MYSQL50_TABLE_NAME_PREFIX)-1)
 #define SAFE_NAME_LEN (NAME_LEN + MYSQL50_TABLE_NAME_PREFIX_LENGTH)
 
-/*
-  MDEV-4088
-
-  MySQL (and MariaDB 5.x before the fix) was using the first character of the
-  server version string (as sent in the first handshake protocol packet) to
-  decide on the replication event formats. And for 10.x the first character
-  is "1", which the slave thought comes from some ancient 1.x version
-  (ignoring the fact that the first ever MySQL version was 3.x).
-
-  To support replication to these old clients, we fake the version in the
-  first handshake protocol packet to start from "5.5.5-" (for example,
-  it might be "5.5.5-10.0.1-MariaDB-debug-log".
-
-  On the client side we remove this fake version prefix to restore the
-  correct server version. The version "5.5.5" did not support
-  pluggable authentication, so any version starting from "5.5.5-" and
-  claiming to support pluggable auth, must be using this fake prefix.
-*/
-/* this version must be the one that *does not* support pluggable auth */
-#define RPL_VERSION_HACK "5.5.5-"
-
 #define SERVER_VERSION_LENGTH 60
 #define SQLSTATE_LENGTH 5
 #define LIST_PROCESS_HOST_LEN 64

sql-common/client.c

@@ -3070,9 +3070,10 @@ CLI_MYSQL_REAL_CONNECT(MYSQL *mysql,const char *host, const char *user,
   mysql->port=port;
 
   /*
-    remove the rpl hack from the version string,
-    see RPL_VERSION_HACK comment
+    remove the rpl hack from the version string, in case we're connecting
+    to a pre-11.0 server
   */
+#define RPL_VERSION_HACK "5.5.5-"
   if ((mysql->server_capabilities & CLIENT_PLUGIN_AUTH) &&
       strncmp(mysql->server_version, RPL_VERSION_HACK,
               sizeof(RPL_VERSION_HACK) - 1) == 0)

sql/mysqld.cc

@@ -594,7 +594,6 @@ extern "C" {
 char server_version[SERVER_VERSION_LENGTH];
 }
 char *server_version_ptr;
-bool using_custom_server_version= false;
 char *mysqld_unix_port, *opt_mysql_tmpdir;
 ulong thread_handling;
 
@@ -8051,7 +8050,6 @@ mysqld_get_one_option(const struct my_option *opt, const char *argument,
       strmake(server_version, argument, sizeof(server_version) - 1);
       set_sys_var_value_origin(&server_version_ptr,
                 *filename ? sys_var::CONFIG : sys_var::COMMAND_LINE, filename);
-      using_custom_server_version= true;
     }
 #ifndef EMBEDDED_LIBRARY
     else

sql/mysqld.h

@@ -740,7 +740,6 @@ extern const char *mysql_real_data_home_ptr;
 extern ulong thread_handling;
 extern "C" MYSQL_PLUGIN_IMPORT char server_version[SERVER_VERSION_LENGTH];
 extern char *server_version_ptr;
-extern bool using_custom_server_version;
 extern MYSQL_PLUGIN_IMPORT char mysql_real_data_home[];
 extern char mysql_unpacked_real_data_home[];
 extern MYSQL_PLUGIN_IMPORT struct system_variables global_system_variables;

sql/sql_acl.cc

@@ -13307,12 +13307,7 @@ static bool send_server_handshake_packet(MPVIO_EXT *mpvio,
     data_len= SCRAMBLE_LENGTH;
   }
 
-  /* When server version is specified in config file, don't include
-     the replication hack prefix. */
-  if (using_custom_server_version)
-    end= strnmov(end, server_version, SERVER_VERSION_LENGTH) + 1;
-  else
-    end= strxnmov(end, SERVER_VERSION_LENGTH, RPL_VERSION_HACK, server_version, NullS) + 1;
+  end= strnmov(end, server_version, SERVER_VERSION_LENGTH) + 1;
 
   int4store((uchar*) end, mpvio->auth_info.thd->thread_id);
   end+= 4;