MDEV-15935 Add redirection support

mysql-test/main/mysqld--help.result

@@ -976,6 +976,15 @@ The following specify which files/extra groups are read (specified before remain
  --read-rnd-buffer-size=# 
  When reading rows in sorted order after a sort, the rows
  are read through this buffer to avoid a disk seeks
+ --redirect-enabled  Return redirection information to client.
+ --redirect-server-host[=name] 
+ The server host that client can choose to redirect to.
+ --redirect-server-port[=name] 
+ The server host port that client can choose to redirect
+ to.
+ --redirect-server-ttl[=name] 
+ The life time of the validity of redirected information
+ with unit second.
  --relay-log=name    The location and name to use for relay logs.
  --relay-log-index=name 
  The location and name to use for the file that keeps a
@@ -1725,6 +1734,10 @@ read-binlog-speed-limit 0
 read-buffer-size 131072
 read-only FALSE
 read-rnd-buffer-size 262144
+redirect-enabled FALSE
+redirect-server-host 
+redirect-server-port 
+redirect-server-ttl 0
 relay-log (No default value)
 relay-log-index (No default value)
 relay-log-info-file relay-log.info

sql/mysqld.cc

@@ -381,6 +381,10 @@ my_bool locked_in_memory;
 bool opt_using_transactions;
 bool volatile abort_loop;
 uint volatile global_disable_checkpoint;
+my_bool redirect_enabled;
+const char *redirect_server_host;
+const char *redirect_server_port;
+const char *redirect_server_ttl;
 #if defined(_WIN32) && !defined(EMBEDDED_LIBRARY)
 ulong slow_start_timeout;
 #endif
@@ -7845,6 +7849,10 @@ static int mysql_init_variables(void)
   opt_endinfo= using_udf_functions= 0;
   opt_using_transactions= 0;
   abort_loop= select_thread_in_use= signal_thread_in_use= 0;
+  redirect_enabled= 0;
+  redirect_server_host= NullS;
+  redirect_server_port= NullS;
+  redirect_server_ttl= NullS;
   grant_option= 0;
   aborted_threads= aborted_connects= aborted_connects_preauth= 0;
   subquery_cache_miss= subquery_cache_hit= 0;

sql/mysqld.h

@@ -119,6 +119,10 @@ extern bool opt_ignore_builtin_innodb;
 extern my_bool opt_character_set_client_handshake;
 extern my_bool debug_assert_on_not_freed_memory;
 extern bool volatile abort_loop;
+extern my_bool redirect_enabled;
+extern const char *redirect_server_host;
+extern const char *redirect_server_port;
+extern const char *redirect_server_ttl;
 extern Atomic_counter<uint> connection_count;
 extern my_bool opt_safe_user_create;
 extern my_bool opt_safe_show_db, opt_local_infile, opt_myisam_use_mmap;

sql/sql_acl.cc

@@ -58,6 +58,7 @@
 #include "sql_plugin_compat.h"
 
 #define MAX_SCRAMBLE_LENGTH 1024
+#define MAX_REDIRECTION_LEN  512
 
 bool mysql_user_table_is_in_short_password_format= false;
 bool using_global_priv_table= true;
@@ -14312,6 +14313,22 @@ bool acl_authenticate(THD *thd, uint com_change_user_pkt_len)
 
   if (res == CR_OK_HANDSHAKE_COMPLETE)
     thd->get_stmt_da()->disable_status();
+  else if (redirect_enabled)
+  {
+    char msg[MAX_REDIRECTION_LEN];
+    size_t len = 0;
+
+    msg[0] = '\0';
+    len = snprintf(msg + 1, MAX_REDIRECTION_LEN - 1, "Location: mysql://[%s]:%s/user=%s&ttl=%s", 
+      redirect_server_host, redirect_server_port, sctx->user, redirect_server_ttl);
+
+    if (len >= MAX_REDIRECTION_LEN - 1){
+      sql_print_error("redirection info is too large to return to client (len= %u)",len);
+      my_ok(thd);
+    }
+    else
+      my_ok(thd, 0, 0, msg);
+  }
   else
     my_ok(thd);
 

sql/sys_vars.cc

@@ -6683,3 +6683,28 @@ static Sys_var_ulonglong Sys_max_rowid_filter_size(
        SESSION_VAR(max_rowid_filter_size), CMD_LINE(REQUIRED_ARG),
        VALID_RANGE(1024, (ulonglong)~(intptr)0), DEFAULT(128*1024),
        BLOCK_SIZE(1));
+
+static Sys_var_mybool Sys_redirect_enabled(
+       "redirect_enabled",
+       "Return redirection information to client.",
+       GLOBAL_VAR(redirect_enabled), CMD_LINE(OPT_ARG),
+       DEFAULT(FALSE), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
+       ON_UPDATE(0));
+
+static Sys_var_charptr Sys_redirect_server_host(
+       "redirect_server_host",
+       "The server host that client can choose to redirect to.",
+       READ_ONLY GLOBAL_VAR(redirect_server_host), CMD_LINE(OPT_ARG),
+       DEFAULT(""));
+
+static Sys_var_charptr Sys_redirect_server_port(
+       "redirect_server_port",
+       "The server host port that client can choose to redirect to.",
+       READ_ONLY GLOBAL_VAR(redirect_server_port), CMD_LINE(OPT_ARG),
+       DEFAULT(""));
+
+static Sys_var_charptr Sys_redirect_server_ttl(
+       "redirect_server_ttl",
+       "The life time of the validity of redirected information with unit second.",
+       READ_ONLY GLOBAL_VAR(redirect_server_ttl), CMD_LINE(OPT_ARG),
+       DEFAULT("0"));