MDEV-4088 Replication 10.0 -> 5.5 fails

update 5.1 to replicate from 10.0 and
to show the server version (as of 10.0) correctly

sql-common/client.c:
  mdev:4088
sql/slave.cc:
  use the version number, not just the first character of the version string
  (we want 10 > 4 not "10" < "4").

include/mysql_com.h

@@ -27,6 +27,31 @@
 #define NAME_LEN                (NAME_CHAR_LEN*SYSTEM_CHARSET_MBMAXLEN)
 #define USERNAME_LENGTH         (USERNAME_CHAR_LENGTH*SYSTEM_CHARSET_MBMAXLEN)
 
+/*
+  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.
+*/
+#ifdef EMBEDDED_LIBRARY
+#define RPL_VERSION_HACK ""
+#else
+/* this version must be the one that *does not* support pluggable auth */
+#define RPL_VERSION_HACK "5.5.5-"
+#endif
+
 #define SERVER_VERSION_LENGTH 60
 #define SQLSTATE_LENGTH 5
 
@@ -145,6 +170,8 @@ enum enum_server_command
 #define CLIENT_MULTI_STATEMENTS (1UL << 16) /* Enable/disable multi-stmt support */
 #define CLIENT_MULTI_RESULTS    (1UL << 17) /* Enable/disable multi-results */
 
+#define CLIENT_PLUGIN_AUTH  (1UL << 19) /* Client supports plugin authentication */
+
 #define CLIENT_SSL_VERIFY_SERVER_CERT (1UL << 30)
 #define CLIENT_REMEMBER_OPTIONS (1UL << 31)
 

sql-common/client.c

@@ -2264,6 +2264,12 @@ CLI_MYSQL_REAL_CONNECT(MYSQL *mysql,const char *host, const char *user,
   strmov(mysql->server_version,(char*) net->read_pos+1);
   mysql->port=port;
 
+  /* remove the rpl hack from the version string, see RPL_VERSION_HACK comment */
+  if (mysql->server_capabilities & CLIENT_PLUGIN_AUTH &&
+      strncmp(mysql->server_version, RPL_VERSION_HACK,
+              sizeof(RPL_VERSION_HACK) - 1) == 0)
+    mysql->server_version+= sizeof(RPL_VERSION_HACK) - 1;
+
   /*
     Part 2: format and send client info to the server for access check
   */

sql/slave.cc

@@ -872,6 +872,7 @@ static int get_master_version_and_clock(MYSQL* mysql, Master_info* mi)
   int err_code= 0;
   MYSQL_RES *master_res= 0;
   MYSQL_ROW master_row;
+  uint version= mysql_get_server_version(mysql) / 10000;
   DBUG_ENTER("get_master_version_and_clock");
 
   /*
@@ -892,20 +893,20 @@ static int get_master_version_and_clock(MYSQL* mysql, Master_info* mi)
     /*
       Note the following switch will bug when we have MySQL branch 30 ;)
     */
-    switch (*mysql->server_version)
+    switch (version)
     {
-    case '0':
-    case '1':
-    case '2':
+    case 0:
+    case 1:
+    case 2:
       errmsg = "Master reported unrecognized MySQL version";
       err_code= ER_SLAVE_FATAL_ERROR;
       sprintf(err_buff, ER(err_code), errmsg);
       break;
-    case '3':
+    case 3:
       mi->rli.relay_log.description_event_for_queue= new
         Format_description_log_event(1, mysql->server_version);
       break;
-    case '4':
+    case 4:
       mi->rli.relay_log.description_event_for_queue= new
         Format_description_log_event(3, mysql->server_version);
       break;
@@ -1069,10 +1070,10 @@ maybe it is a *VERY OLD MASTER*.");
   */
 
   /* redundant with rest of code but safer against later additions */
-  if (*mysql->server_version == '3')
+  if (version == 3)
     goto err;
 
-  if (*mysql->server_version == '4')
+  if (version == 4)
   {
     master_res= NULL;
     if (!mysql_real_query(mysql,
@@ -1133,7 +1134,7 @@ inconsistency if replicated data deals with collation.");
     This check is only necessary for 4.x masters (and < 5.0.4 masters but
     those were alpha).
   */
-  if (*mysql->server_version == '4')
+  if (version == 4)
   {
     master_res= NULL;
     if (!mysql_real_query(mysql, STRING_WITH_LEN("SELECT @@GLOBAL.TIME_ZONE")) &&