MINOR: checks: mysql-check: Add support for v4.1+ authentication

MySQL will in stop supporting pre-4.1 authentication packets in the future
and is already giving us a hard time regarding non-silencable warnings
which are logged on each health check. Warnings look like the following:

"[Warning] Client failed to provide its character set. 'latin1' will be used
as client character set."

This patch adds basic support for post-4.1 authentication by sending the proper
authentication packet with the character set, along with the QUIT command.

doc/configuration.txt

@@ -4458,13 +4458,14 @@ no option logasap
              logging.
 
 
-option mysql-check [ user <username> ]
+option mysql-check [ user <username> [ post-41 ] ]
   Use MySQL health checks for server testing
   May be used in sections :   defaults | frontend | listen | backend
                                  yes   |    no    |   yes  |   yes
   Arguments :
     <username> This is the username which will be used when connecting to MySQL
                server.
+    post-41    Send post v4.1 client compatible checks
 
   If you specify a username, the check consists of sending two MySQL packet,
   one Client Authentication packet, and one QUIT packet, to correctly close

src/cfgparse.c

@@ -3869,7 +3869,7 @@ stats_error_parsing:
 			curproxy->options2 &= ~PR_O2_CHK_ANY;
 			curproxy->options2 |= PR_O2_MYSQL_CHK;
 
-			/* This is an exemple of an MySQL >=4.0 client Authentication packet kindly provided by Cyril Bonte.
+			/* This is an example of a MySQL >=4.0 client Authentication packet kindly provided by Cyril Bonte.
 			 * const char mysql40_client_auth_pkt[] = {
 			 * 	"\x0e\x00\x00"	// packet length
 			 * 	"\x01"		// packet number
@@ -3883,6 +3883,23 @@ stats_error_parsing:
 			 * };
 			 */
 
+			/* This is an example of a MySQL >=4.1  client Authentication packet provided by Nenad Merdanovic.
+			 * const char mysql41_client_auth_pkt[] = {
+			 * 	"\x0e\x00\x00\"		// packet length
+			 * 	"\x01"			// packet number
+			 * 	"\x00\x00\x00\x00"	// client capabilities
+			 * 	"\x00\x00\x00\x01"	// max packet
+			 *	"\x21"			// character set (UTF-8)
+			 *	char[23]		// All zeroes
+			 * 	"haproxy\x00"		// username (null terminated string)
+			 * 	"\x00"			// filler (always 0x00)
+			 * 	"\x01\x00\x00"		// packet length
+			 * 	"\x00"			// packet number
+			 * 	"\x01"			// COM_QUIT command
+			 * };
+			 */
+
+
 			if (*(args[2])) {
 				int cur_arg = 2;
 
@@ -3900,6 +3917,35 @@ stats_error_parsing:
 						}
 						mysqluser = args[cur_arg + 1];
 						userlen   = strlen(mysqluser);
+
+						if (*(args[cur_arg+2])) {
+							if (!strcmp(args[cur_arg+2], "post-41")) {
+		                                                packetlen = userlen + 7 + 27;
+								reqlen    = packetlen + 9;
+
+								free(curproxy->check_req);
+								curproxy->check_req = (char *)calloc(1, reqlen);
+								curproxy->check_len = reqlen;
+
+								snprintf(curproxy->check_req, 4, "%c%c%c",
+									((unsigned char) packetlen & 0xff),
+									((unsigned char) (packetlen >> 8) & 0xff),
+									((unsigned char) (packetlen >> 16) & 0xff));
+
+								curproxy->check_req[3] = 1;
+								curproxy->check_req[5] = 130;
+								curproxy->check_req[11] = 1;
+								curproxy->check_req[12] = 33;
+								memcpy(&curproxy->check_req[36], mysqluser, userlen);
+								curproxy->check_req[36 + userlen + 1 + 1]     = 1;
+								curproxy->check_req[36 + userlen + 1 + 1 + 4] = 1;
+								cur_arg += 3;
+							} else {
+								Alert("parsing [%s:%d] : keyword '%s' only supports option 'post-41'.\n", file, linenum, args[cur_arg+2]);
+								err_code |= ERR_ALERT | ERR_FATAL;
+								goto out;
+							}
+						} else {
 							packetlen = userlen + 7;
 							reqlen    = packetlen + 9;
 
@@ -3919,6 +3965,7 @@ stats_error_parsing:
 							curproxy->check_req[9 + userlen + 1 + 1]     = 1;
 							curproxy->check_req[9 + userlen + 1 + 1 + 4] = 1;
 							cur_arg += 2;
+						}
 					} else {
 						/* unknown suboption - catchall */
 						Alert("parsing [%s:%d] : '%s %s' only supports optional values: 'user'.\n",