WL#13905: libmysql support for DNS SRV

RB#24157

Author: gkodinov

client/mysql.cc

@@ -179,6 +179,7 @@ static int connect_flag = CLIENT_INTERACTIVE;
 static bool opt_binary_mode = false;
 static bool opt_connect_expired_password = false;
 static char *current_host;
+static char *dns_srv_host;
 static char *current_db;
 static char *current_user = nullptr;
 static char *opt_password = nullptr;
@@ -1479,6 +1480,7 @@ void mysql_end(int sig) {
   my_free(opt_mysql_unix_port);
   my_free(current_db);
   my_free(current_host);
+  my_free(dns_srv_host);
   my_free(current_user);
   my_free(full_username);
   my_free(part_username);
@@ -1567,8 +1569,15 @@ static void kill_query(const char *reason) {
   }
 #endif
 
-  if (!mysql_real_connect(kill_mysql, current_host, current_user, opt_password,
-                          "", opt_mysql_port, opt_mysql_unix_port, 0)) {
+  MYSQL *ret;
+  if (dns_srv_host)
+    ret = mysql_real_connect_dns_srv(kill_mysql, dns_srv_host, current_user,
+                                     opt_password, "", 0);
+  else
+    ret =
+        mysql_real_connect(kill_mysql, current_host, current_user, opt_password,
+                           "", opt_mysql_port, opt_mysql_unix_port, 0);
+  if (!ret) {
 #ifdef HAVE_SETNS
     if (opt_network_namespace) (void)restore_original_network_namespace();
 #endif
@@ -1732,6 +1741,9 @@ static struct my_option my_long_options[] = {
      nullptr, GET_BOOL, NO_ARG, 0, 0, 0, nullptr, 0, nullptr},
     {"host", 'h', "Connect to host.", &current_host, &current_host, nullptr,
      GET_STR_ALLOC, REQUIRED_ARG, 0, 0, 0, nullptr, 0, nullptr},
+    {"dns_srv_host", -1, "Connect to a DNS SRV resource", &dns_srv_host,
+     &dns_srv_host, nullptr, GET_STR_ALLOC, REQUIRED_ARG, 0, 0, 0, nullptr, 0,
+     nullptr},
     {"html", 'H', "Produce HTML output.", &opt_html, &opt_html, nullptr,
      GET_BOOL, NO_ARG, 0, 0, 0, nullptr, 0, nullptr},
     {"xml", 'X', "Produce XML output.", &opt_xml, &opt_xml, nullptr, GET_BOOL,
@@ -4115,6 +4127,8 @@ static int com_connect(String *buffer, char *line) {
       if (tmp) {
         my_free(current_host);
         current_host = my_strdup(PSI_NOT_INSTRUMENTED, tmp, MYF(MY_WME));
+        my_free(dns_srv_host);
+        dns_srv_host = nullptr;
       }
     } else {
       /* Quick re-connect */
@@ -4458,10 +4472,16 @@ static int sql_real_connect(char *host, char *database, char *user,
     return ignore_errors ? -1 : 1;  // Abort
   }
 #endif
-
-  if (!mysql_real_connect(&mysql, host, user, password, database,
-                          opt_mysql_port, opt_mysql_unix_port,
-                          connect_flag | CLIENT_MULTI_STATEMENTS)) {
+  MYSQL *ret;
+  if (dns_srv_host)
+    ret = mysql_real_connect_dns_srv(&mysql, dns_srv_host, user, password,
+                                     database,
+                                     connect_flag | CLIENT_MULTI_STATEMENTS);
+  else
+    ret = mysql_real_connect(&mysql, host, user, password, database,
+                             opt_mysql_port, opt_mysql_unix_port,
+                             connect_flag | CLIENT_MULTI_STATEMENTS);
+  if (!ret) {
 #ifdef HAVE_SETNS
     if (opt_network_namespace) (void)restore_original_network_namespace();
 #endif

config.h.cmake

@@ -339,4 +339,9 @@
 
 #define SO_EXT "@CMAKE_SHARED_MODULE_SUFFIX@"
 
+
+/* From libmysql/CMakeLists.txt */
+#cmakedefine HAVE_UNIX_DNS_SRV @HAVE_UNIX_DNS_SRV@
+#cmakedefine HAVE_WIN32_DNS_SRV @HAVE_WIN32_DNS_SRV@
+
 #endif

include/errmsg.h

@@ -128,7 +128,8 @@ extern const char *client_errors[]; /* Error messages */
 #define CR_KERBEROS_USER_NOT_FOUND 2067
 #define CR_LOAD_DATA_LOCAL_INFILE_REJECTED 2068
 #define CR_LOAD_DATA_LOCAL_INFILE_REALPATH_FAIL 2069
-#define CR_ERROR_LAST /*Copy last error nr:*/ 2069
+#define CR_DNS_SRV_LOOKUP_FAILED 2070
+#define CR_ERROR_LAST /*Copy last error nr:*/ 2070
 /* Add error numbers before CR_ERROR_LAST and change it accordingly. */
 
 /* Visual Studio requires '__inline' for C code */

include/mysql.h

@@ -786,6 +786,12 @@ void STDCALL mysql_reset_server_public_key(void);
 
 #define HAVE_MYSQL_REAL_CONNECT
 
+MYSQL *STDCALL mysql_real_connect_dns_srv(MYSQL *mysql,
+                                          const char *dns_srv_name,
+                                          const char *user, const char *passwd,
+                                          const char *db,
+                                          unsigned long client_flag);
+
 #ifdef __cplusplus
 }
 #endif

include/mysql.h.pp

@@ -359,7 +359,7 @@
 void finish_client_errs(void);
 extern const char *client_errors[];
 static inline const char *ER_CLIENT(int client_errno) {
-  if (client_errno >= 2000 && client_errno <= 2069)
+  if (client_errno >= 2000 && client_errno <= 2070)
     return client_errors[client_errno - 2000];
   return client_errors[2000];
 }
@@ -805,3 +805,8 @@
 int mysql_stmt_next_result(MYSQL_STMT *stmt);
 void mysql_close(MYSQL *sock);
 void mysql_reset_server_public_key(void);
+MYSQL * mysql_real_connect_dns_srv(MYSQL *mysql,
+                                          const char *dns_srv_name,
+                                          const char *user, const char *passwd,
+                                          const char *db,
+                                          unsigned long client_flag);

libmysql/CMakeLists.txt

@@ -139,7 +139,7 @@ SET(CLIENT_API_FUNCTIONS
   mysql_thread_safe
   mysql_use_result
   mysql_warning_count
-
+  mysql_real_connect_dns_srv
   CACHE INTERNAL "Functions exported by client API"
 )
 
@@ -177,6 +177,7 @@ SET(CLIENT_API_NONBLOCKING_FUNCTIONS
 SET(CLIENT_SOURCES
   libmysql.cc
   errmsg.cc
+  dns_srv.cc
   ../sql-common/client.cc
   ../sql-common/client_plugin.cc
   ../sql-common/client_authentication.cc
@@ -232,6 +233,31 @@ ENDIF()
 
 LIST(APPEND LIBS_TO_LINK ${SSL_LIBRARIES})
 
+UNSET(HAVE_WIN32_DNS_SRV)
+UNSET(HAVE_UNIX_DNS_SRV)
+SET(HAVE_DNS_SRV 0)
+IF(WIN32)
+  LIST(APPEND LIBS_TO_LINK dnsapi)
+  SET(HAVE_WIN32_DNS_SRV 1 PARENT_SCOPE)
+  SET(HAVE_DNS_SRV 1)
+  MESSAGE(STATUS "Found Win32 DNS SRV APIs")
+ELSEIF(FREEBSD)
+  SET(HAVE_DNS_SRV 1)
+  SET(HAVE_UNIX_DNS_SRV 1 PARENT_SCOPE)
+  MESSAGE(STATUS "BSD built in DNS SRV APIs")
+ELSE()
+  FIND_LIBRARY(RESOLV_LIBRARY NAMES resolv)
+  IF (RESOLV_LIBRARY)
+    LIST(APPEND LIBS_TO_LINK ${RESOLV_LIBRARY})
+    SET(HAVE_UNIX_DNS_SRV 1 PARENT_SCOPE)
+    SET(HAVE_DNS_SRV 1)
+    MESSAGE(STATUS "Found Unix DNS SRV APIs")
+  ENDIF()
+ENDIF()
+
+IF(HAVE_DNS_SRV EQUAL 0)
+  MESSAGE(FATAL_ERROR "Can't find neither Win32 nor Unix DNS SRV APIs")
+ENDIF()
 #
 # On Windows platform client library includes the client-side 
 # Windows Native Authentication plugin.

libmysql/dns_srv.cc

@@ -0,0 +1,184 @@
+/* Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License, version 2.0,
+   as published by the Free Software Foundation.
+
+   This program is also distributed with certain software (including
+   but not limited to OpenSSL) that is licensed under separate terms,
+   as designated in a particular file or component or in included license
+   documentation.  The authors of MySQL hereby grant you an additional
+   permission to link the program and your derivative works with the
+   separately licensed software that they have included with MySQL.
+
+   Without limiting anything contained in the foregoing, this file,
+   which is part of C Driver for MySQL (Connector/C), is also subject to the
+   Universal FOSS Exception, version 1.0, a copy of which can be found at
+   http://oss.oracle.com/licenses/universal-foss-exception.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License, version 2.0, for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
+
+#include <my_config.h>
+#include <sql_common.h>
+#include "dns_srv_data.h"
+
+#ifdef HAVE_UNIX_DNS_SRV
+
+#ifdef __FreeBSD__
+#include <netinet/in.h>
+#endif
+#include <netdb.h>
+#include <resolv.h>
+
+// POSIX version
+
+static bool get_dns_srv(Dns_srv_data &data, const char *dnsname, int &error) {
+  struct __res_state state {};
+  res_ninit(&state);
+  unsigned char query_buffer[NS_PACKETSZ];
+  bool ret = true;
+
+  data.clear();
+
+  int res = res_nsearch(&state, dnsname, ns_c_in, ns_t_srv, query_buffer,
+                        sizeof(query_buffer));
+
+  if (res >= 0) {
+    ns_msg msg;
+    ns_initparse(query_buffer, res, &msg);
+
+    for (int x = 0; x < ns_msg_count(msg, ns_s_an); x++) {
+      // Get next DNS SRV record and its data
+
+      ns_rr rr;
+      ns_parserr(&msg, ns_s_an, x, &rr);
+      const unsigned char *srv_data = ns_rr_rdata(rr);
+
+      // Read port, priority and weight.
+      // Note: Each NS_GET16 call moves srv_data to next value
+
+      uint16_t port, prio, weight;
+
+      NS_GET16(prio, srv_data);
+      NS_GET16(weight, srv_data);
+      NS_GET16(port, srv_data);
+
+      // Read host name
+
+      char name_buffer[NS_MAXDNAME];
+
+      dn_expand(ns_msg_base(msg), ns_msg_end(msg), srv_data, name_buffer,
+                sizeof(name_buffer));
+      data.add(name_buffer, port, prio, weight);
+    }
+    ret = false;
+  } else {
+    ret = true;
+    error = h_errno;
+  }
+
+  res_nclose(&state);
+  return ret;
+}
+
+#elif defined(HAVE_WIN32_DNS_SRV)
+#include <windns.h>
+#include <winsock2.h>
+
+// Windows version
+
+static bool get_dns_srv(Dns_srv_data &data, const char *dnsname, int &error) {
+  DNS_STATUS status;                 // Return value of  DnsQuery_A() function.
+  PDNS_RECORD pDnsRecord = nullptr;  // Pointer to DNS_RECORD structure.
+
+  data.clear();
+  status = DnsQuery(dnsname, DNS_TYPE_SRV, DNS_QUERY_STANDARD, nullptr,
+                    &pDnsRecord, nullptr);
+
+  if (status == ERROR_SUCCESS) {
+    // Iterate over linked list of DNS records
+
+    PDNS_RECORD pRecord = pDnsRecord;
+    while (pRecord) {
+      if (pRecord->wType == DNS_TYPE_SRV) {
+        data.add(pRecord->Data.Srv.pNameTarget, pRecord->Data.Srv.wPort,
+                 pRecord->Data.Srv.wPriority, pRecord->Data.Srv.wWeight);
+      }
+      pRecord = pRecord->pNext;
+    }
+
+    DnsRecordListFree(pDnsRecord, DnsFreeRecordListDeep);
+  } else
+    error = status;
+  return status != ERROR_SUCCESS;
+}
+#else
+
+#error "No DNS SRV Support detected for your OS. Consider adjusting Cmake."
+
+#if 0
+// dummy function returning an error in case it's not supported by the OS
+
+static bool get_dns_srv(Dns_srv_data &data, const char *dnsname, int &error) {
+  error = -1;  // set a special error code for not supported
+  return true;
+}
+#endif
+#endif
+
+/**
+  Connect to a server using a DNS SRV name
+
+  See rfc2782 for what a DNS SRV is and how is one read
+
+  @param mysql a MySQL handle to use
+  @param dns_srv_name  the name of the DNS SRV resource to query. ANSI
+  @param user  the user name to pass to @ref mysql_real_connect
+  @param passwd the password to pass to @ref mysql_real_connect
+  @param db the database to pass to @ref mysql_real_connect
+  @param client_flag the client flag to pass to @ref mysql_real_connect
+
+  @retval NULL an error has occurred
+  @retval non-NULL the connected MySQL handle to use
+
+  If the OS doesn't support it the function returns OS error -1.
+
+  SRV FORMAT:
+  _service._proto.name. TTL class SRV priority weight port target.
+
+  Example:
+  _sip._tcp.example.com. 86400 IN SRV 0 5 5060 sipserver.example.com.
+
+  @sa mysql_real_connect
+*/
+MYSQL *STDCALL mysql_real_connect_dns_srv(MYSQL *mysql,
+                                          const char *dns_srv_name,
+                                          const char *user, const char *passwd,
+                                          const char *db,
+                                          unsigned long client_flag) {
+  Dns_srv_data data;
+  int err = 0;
+
+  if (get_dns_srv(data, dns_srv_name, err)) {
+    set_mysql_extended_error(mysql, CR_DNS_SRV_LOOKUP_FAILED, unknown_sqlstate,
+                             ER_CLIENT(CR_DNS_SRV_LOOKUP_FAILED), err);
+    return nullptr;
+  }
+
+  std::string host;
+  uint port;
+  while (!data.pop_next(host, port)) {
+    MYSQL *ret =
+        mysql_real_connect(mysql, host.c_str(), user, passwd, db, port, NULL,
+                           client_flag | CLIENT_REMEMBER_OPTIONS);
+    if (ret) return ret;
+  }
+  return nullptr;
+}