libmaxminddb(3)



libmaxminddb(3)                                                libmaxminddb(3)

NAME
       libmaxminddb - a library for working with MaxMind DB files

SYNOPSIS

           #include <maxminddb.h>

           int MMDB_open(
               const char *const filename,
               uint32_t flags,
               MMDB_s *const mmdb);
           void MMDB_close(MMDB_s *const mmdb);

           MMDB_lookup_result_s MMDB_lookup_string(
               MMDB_s *const mmdb,
               const char *const ipstr,
               int *const gai_error,
               int *const mmdb_error);
           MMDB_lookup_result_s MMDB_lookup_sockaddr(
               MMDB_s *const mmdb,
               const struct sockaddr *const
               sockaddr,
               int *const mmdb_error);

           int MMDB_get_value(
               MMDB_entry_s *const start,
               MMDB_entry_data_s *const entry_data,
               ...);
           int MMDB_vget_value(
               MMDB_entry_s *const start,
               MMDB_entry_data_s *const entry_data,
               va_list va_path);
           int MMDB_aget_value(
               MMDB_entry_s *const start,
               MMDB_entry_data_s *const entry_data,
               const char *const *const path);

           int MMDB_get_entry_data_list(
               MMDB_entry_s *start,
               MMDB_entry_data_list_s **const entry_data_list);
           void MMDB_free_entry_data_list(
               MMDB_entry_data_list_s *const entry_data_list);
           int MMDB_get_metadata_as_entry_data_list(
               MMDB_s *const mmdb,
               MMDB_entry_data_list_s **const entry_data_list);
           int MMDB_dump_entry_data_list(
               FILE *const stream,
               MMDB_entry_data_list_s *const entry_data_list,
               int indent);

           int MMDB_read_node(
               MMDB_s *const mmdb,
               uint32_t node_number,
               MMDB_search_node_s *const node);

           const char *MMDB_lib_version(void);
           const char *MMDB_strerror(int error_code);

           typedef struct MMDB_lookup_result_s {
               bool found_entry;
               MMDB_entry_s entry;
               uint16_t netmask;
           } MMDB_lookup_result_s;

           typedef struct MMDB_entry_data_s {
               bool has_data;
               union {
                   uint32_t pointer;
                   const char *utf8_string;
                   double double_value;
                   const uint8_t *bytes;
                   uint16_t uint16;
                   uint32_t uint32;
                   int32_t int32;
                   uint64_t uint64;
                   {mmdb_uint128_t or uint8_t[16]} uint128;
                   bool boolean;
                   float float_value;
               };
               ...
               uint32_t data_size;
               uint32_t type;
           } MMDB_entry_data_s;

           typedef struct MMDB_entry_data_list_s {
               MMDB_entry_data_s entry_data;
               struct MMDB_entry_data_list_s *next;
           } MMDB_entry_data_list_s;

DESCRIPTION
       The  libmaxminddb  library  provides  functions  for working MaxMind DB
       files.  See http://maxmind.github.io/MaxMind-DB/  for  the  MaxMind  DB
       format  specification.  The database and results are all represented by
       different  data  structures.    Databases   are   opened   by   calling
       MMDB_open().    You   can  look  up  IP  addresses  as  a  string  with
       MMDB_lookup_string() or as a  pointer  to  a  sockaddr  structure  with
       MMDB_lookup_sockaddr().

       If  the  lookup  finds  the  IP  address  in the database, it returns a
       MMDB_lookup_result_s structure.  If that structure indicates  that  the
       database  has data for the IP, there are a number of functions that can
       be used  to  fetch  that  data.   These  include  MMDB_get_value()  and
       MMDB_get_entry_data_list().   See  the function documentation below for
       more details.

       When  you  are  done  with  the  database  handle   you   should   call
       MMDB_close().

       All  publicly  visible  functions,  structures,  and  macros begin with
       "MMDB_".

DATA STRUCTURES
       All data structures exported by this library's maxminddb.h  header  are
       typedef'd in the form typedef struct foo_s { ... } foo_s so you can re-
       fer to them without the struct prefix.

       This library provides the following data structures:

   MMDB_s
       This is the handle for a MaxMind DB file.  We  only  document  some  of
       this  structure's fields intended for public use.  All other fields are
       subject to change and are intended only for internal use.

           typedef struct MMDB_s {
               uint32_t flags;
               const char *filename;
               ...
               MMDB_metadata_s metadata;
           } MMDB_s;

       o uint32_t flags - the flags this database was opened  with.   See  the
         MMDB_open() documentation for more details.

       o const char *filename  -  the  name  of  the file which was opened, as
         passed to MMDB_open().

       o MMDB_metadata_s metadata - the metadata for the database.

   MMDB_metadata_s and MMDB_description_s
       This structure can be retrieved from the MMDB_s structure.  It contains
       the  metadata  read  from the database file.  Note that you may find it
       more convenient to access this  metadata  by  calling  MMDB_get_metada-
       ta_as_entry_data_list() instead.

           typedef struct MMDB_metadata_s {
               uint32_t node_count;
               uint16_t record_size;
               uint16_t ip_version;
               const char *database_type;
               struct {
                   size_t count;
                   const char **names;
               } languages;
               uint16_t binary_format_major_version;
               uint16_t binary_format_minor_version;
               uint64_t build_epoch;
               struct {
                   size_t count;
                   MMDB_description_s **descriptions;
               } description;
           } MMDB_metadata_s;

           typedef struct MMDB_description_s {
               const char *language;
               const char *description;
           } MMDB_description_s;

       These structures should be mostly self-explanatory.

       The  ip_version  member should always be 4 or 6.  The binary_format_ma-
       jor_version should always be 2.

       There is no requirement that the database metadata include languages or
       descriptions, so the count for these parts of the metadata can be zero.
       All of the other MMDB_metadata_s fields should be populated.

   MMDB_lookup_result_s
       This structure is returned as the result of looking up an IP address.

           typedef struct MMDB_lookup_result_s {
               bool found_entry;
               MMDB_entry_s entry;
               uint16_t netmask;
           } MMDB_lookup_result_s;

       If the found_entry member is false  then  the  other  members  of  this
       structure   do  not  contain  meaningful  values.   Always  check  that
       found_entry is true first.

       The entry member is used to look up the data associated with the IP ad-
       dress.

       The  netmask  member tells you what subnet the IP address belongs to in
       this database.  For example, if you look up the address 1.1.1.1  in  an
       IPv4  database and the returned netmask is 16, then the address is part
       of the 1.1.0.0/16 subnet.

       If the database is an IPv6 database, the returned netmask is always  an
       IPv6  prefix  length  (from 0-128), even if that database also contains
       IPv4 networks.  If you look up an IPv4 address and would like  to  turn
       the netmask into an IPv4 netmask value, you can simply subtract 96 from
       the value.

   MMDB_result_s
       You don't really need to dig around in this structure.  You'll get this
       from a MMDB_lookup_result_s structure and pass it to various functions.

   MMDB_entry_data_s
       This structure is used to return a single data section entry for an IP.
       These entries can in turn point to other entries, as is  the  case  for
       things  like  maps  and arrays.  Some members of this structure are not
       documented as they are only for internal use.

           typedef struct MMDB_entry_data_s {
               bool has_data;
               union {
                   uint32_t pointer;
                   const char *utf8_string;
                   double double_value;
                   const uint8_t *bytes;
                   uint16_t uint16;
                   uint32_t uint32;
                   int32_t int32;
                   uint64_t uint64;
                   {mmdb_uint128_t or uint8_t[16]} uint128;
                   bool boolean;
                   float float_value;
               };
               ...
               uint32_t data_size;
               uint32_t type;
           } MMDB_entry_data_s;

       The has_data member is true if data was found for a given lookup.   See
       MMDB_get_value()  for  more details.  If this member is false then none
       of the other values in the structure are meaningful.

       The union at the beginning of the structure defines  the  actual  data.
       To  determine  which  union  member is populated you should look at the
       type member.  The pointer member of the union should never be populated
       in  any  data  returned by the API.  Pointers should always be resolved
       internally.

       The data_size member is only relevant for utf8_string and  bytes  data.
       utf8_string is not null terminated and data_size must be used to deter-
       mine its length.

       The type member can be compared to one of the MMDB_DTYPE_* macros.

   128-bit Integers
       The handling of uint128 data depends  on  how  your  platform  supports
       128-bit  integers,  if  it does so at all.  With GCC 4.4 and 4.5 we can
       write unsigned int __attribute__ ((__mode__ (TI))).   With  newer  ver-
       sions  of  GCC  (4.6+)  and  clang (3.2+) we can simply write "unsigned
       __int128".

       In order to work around these  differences,  this  library  defines  an
       mmdb_uint128_t type.  This type is defined in the maxminddb.h header so
       you can use it in your own code.

       With older compilers, we can't use an integer so we instead  use  a  16
       byte array of uint8_t values.  This is the raw data from the database.

       This  library provides a public macro MMDB_UINT128_IS_BYTE_ARRAY macro.
       If this is true (1), then uint128 values are returned as a byte  array,
       if it is false then they are returned as a mmdb_uint128_t integer.

   Data Type Macros
       This  library  provides a macro for every data type defined by the Max-
       Mind DB spec.

       o MMDB_DATA_TYPE_UTF8_STRING

       o MMDB_DATA_TYPE_DOUBLE

       o MMDB_DATA_TYPE_BYTES

       o MMDB_DATA_TYPE_UINT16

       o MMDB_DATA_TYPE_UINT32

       o MMDB_DATA_TYPE_MAP

       o MMDB_DATA_TYPE_INT32

       o MMDB_DATA_TYPE_UINT64

       o MMDB_DATA_TYPE_UINT128

       o MMDB_DATA_TYPE_ARRAY

       o MMDB_DATA_TYPE_BOOLEAN

       o MMDB_DATA_TYPE_FLOAT

       There are also a few types that are for internal use only:

       o MMDB_DATA_TYPE_EXTENDED

       o MMDB_DATA_TYPE_POINTER

       o MMDB_DATA_TYPE_CONTAINER

       o MMDB_DATA_TYPE_END_MARKER

       If you see one of these in returned data then something has  gone  very
       wrong.   The  database is damaged or was generated incorrectly or there
       is a bug in the libmaxminddb code.

   Pointer Values and MMDB_close()
       The utf8_string, bytes, and (maybe) the uint128 members of this  struc-
       ture  are all pointers directly into the database's data section.  This
       can either be a malloc'd or mmap'd block of memory.   In  either  case,
       these pointers will become invalid after MMDB_close() is called.

       If  you  need to refer to this data after that time you should copy the
       data with an appropriate function (strdup, memcpy, etc.).

   MMDB_entry_data_list_s
       This structure encapsulates a linked list of  MMDB_entry_data_s  struc-
       tures.

           typedef struct MMDB_entry_data_list_s {
               MMDB_entry_data_s entry_data;
               struct MMDB_entry_data_list_s *next;
           } MMDB_entry_data_list_s;

       This structure lets you look at entire map or array data entry by iter-
       ating over the linked list.

   MMDB_search_node_s
       This structure encapsulates the two records in a search node.  This  is
       really only useful if you want to write code that iterates over the en-
       tire search tree as opposed to looking up a specific IP address.

           typedef struct MMDB_search_node_s {
               uint64_t left_record;
               uint64_t right_record;
               uint8_t left_record_type;
               uint8_t right_record_type;
               MMDB_entry_s left_record_entry;
               MMDB_entry_s right_record_entry;
           } MMDB_search_node_s;

       The two record types will take one of the following values:

       o MMDB_RECORD_TYPE_SEARCH_NODE - The record points to the  next  search
         node.

       o MMDB_RECORD_TYPE_EMPTY  -  The record is a placeholder that indicates
         there is no data for the IP address.  The search should end here.

       o MMDB_RECORD_TYPE_DATA - The record is for data in the data section of
         the  database.  Use the entry for the record when looking up the data
         for the record.

       o MMDB_RECORD_TYPE_INVALID - The record is invalid.  Either an  invalid
         node was looked up or the database is corrupt.

       The  MMDB_entry_s  for  the  record  is  only  valid  if  the  type  is
       MMDB_RECORD_TYPE_DATA.  Attempts to use an entry for other record types
       will result in an error or invalid data.

STATUS CODES
       This  library  returns  (or populates) status codes for many functions.
       These status codes are:

       o MMDB_SUCCESS - everything worked

       o MMDB_FILE_OPEN_ERROR - there was an error trying to open the  MaxMind
         DB file.

       o MMDB_IO_ERROR  -  an  IO  operation failed.  Check errno for more de-
         tails.

       o MMDB_CORRUPT_SEARCH_TREE_ERROR - looking up  an  IP  address  in  the
         search tree gave us an impossible result.  The database is damaged or
         was generated incorrectly or there is a bug in the libmaxminddb code.

       o MMDB_INVALID_METADATA_ERROR - something in  the  database  is  wrong.
         This  includes  missing  metadata  keys  as well as impossible values
         (like an ip_version of 7).

       o MMDB_UNKNOWN_DATABASE_FORMAT_ERROR - The database metadata  indicates
         that it's major version is not 2.  This library can only handle major
         version 2.

       o MMDB_OUT_OF_MEMORY_ERROR - a memory allocation  call  (malloc,  etc.)
         failed.

       o MMDB_INVALID_DATA_ERROR  -  an entry in the data section contains in-
         valid data.  For example, a uint16 field is claiming to be more  than
         2  bytes long.  The database is probably damaged or was generated in-
         correctly.

       o MMDB_INVALID_LOOKUP_PATH_ERROR  -   The   lookup   path   passed   to
         MMDB_get_value, MMDB_vget_value, or MMDB_aget_value contains an array
         offset that is negative integer or an integer larger than LONG_MAX.

       o MMDB_LOOKUP_PATH_DOES_NOT_MATCH_DATA_ERROR - The lookup  path  passed
         to  MMDB_get_value,MMDB_vget_value, or MMDB_aget_value does not match
         the data structure for the entry.  There are number of  reasons  this
         can  happen.   The lookup path could include a key not in a map.  The
         lookup path could include an array index larger than  an  array.   It
         can  also  happen  when the path expects to find a map or array where
         none exist.

       All status codes should be treated as int values.

   MMDB_strerror()

           const char *MMDB_strerror(int error_code)

       This function takes a status code and returns  an  English  string  ex-
       plaining the status.

FUNCTIONS
       This library provides the following exported functions:

   MMDB_open()

           int MMDB_open(
               const char *const filename,
               uint32_t flags,
               MMDB_s *const mmdb);

       This function opens a handle to a MaxMind DB file.  Its return value is
       a status code as defined above.  Always check this call's return value.

           MMDB_s mmdb;
           int status =
               MMDB_open("/path/to/file.mmdb", MMDB_MODE_MMAP, &mmdb);
           if (MMDB_SUCCESS != status) { ... }
           ...
           MMDB_close(&mmdb);

       The MMDB_s structure you pass in can be on the stack or allocated  from
       the  heap.  However, if the open is successful it will contain heap-al-
       located data, so you need to close it with MMDB_close().  If the status
       returned  is not MMDB_SUCCESS then this library makes sure that all al-
       located memory is freed before returning.

       The flags currently provided are:

       o MMDB_MODE_MMAP - open the database with mmap().

       Passing in other values for flags may yield unpredictable results.   In
       the future we may add additional flags that you can bitwise-or together
       with the mode, as well as additional modes.

       You can also pass 0 as the flags value in which case the database  will
       be  opened  with the default flags.  However, these defaults may change
       in future releases.  The current default is MMDB_MODE_MMAP.

   MMDB_close()

           void MMDB_close(MMDB_s *const mmdb);

       This frees any allocated or mmap'd memory that is held from the  MMDB_s
       structure.  It does not free the memory allocated for the structure it-
       self!  If you allocated the structure from the heap then  you  are  re-
       sponsible for freeing it.

   MMDB_lookup_string()

           MMDB_lookup_result_s MMDB_lookup_string(
               MMDB_s *const mmdb,
               const char *const ipstr,
               int *const gai_error,
               int *const mmdb_error);

       This function looks up an IP address that is passed in as a null-termi-
       nated string.  Internally it calls getaddrinfo() to resolve the address
       into  a  binary form.  It then calls MMDB_lookup_sockaddr() to look the
       address up in the database.  If you have already  resolved  an  address
       you can call MMDB_lookup_sockaddr() directly, rather than resolving the
       address twice.

           int gai_error, mmdb_error;
           MMDB_lookup_result_s result =
               MMDB_lookup_string(&mmdb, "1.2.3.4", &gai_error, &mmdb_error);
           if (0 != gai_error) { ... }
           if (MMDB_SUCCESS != mmdb_error) { ... }

           if (result.found_entry) { ... }

       This function always returns an MMDB_lookup_result_s structure, but you
       should  also  check the gai_error and mmdb_error parameters.  If either
       of these indicates an error then the returned structure is meaningless.

       If no error occurred you still need to make sure that  the  found_entry
       member  in  the  returned result is true.  If it's not, this means that
       the IP address does not have an entry in the database.

       This function will work with IPv4 addresses even when the database con-
       tains  data for both IPv4 and IPv6 addresses.  The IPv4 address will be
       looked up as `::xxx.xxx.xxx.xxx' rather  than  being  remapped  to  the
       ::ffff:xxx.xxx.xxx.xxx block allocated for IPv4-mapped IPv6 addresses.

       If  you pass an IPv6 address to a database with only IPv4 data then the
       found_entry member will be false, but the mmdb_error status will  still
       be MMDB_SUCCESS.

   MMDB_lookup_sockaddr()

           MMDB_lookup_result_s MMDB_lookup_sockaddr(
               MMDB_s *const mmdb,
               const struct sockaddr *const sockaddr,
               int *const mmdb_error);

       This  function looks up an IP address that has already been resolved by
       getaddrinfo().

       Other than not calling getaddrinfo() itself, this function is identical
       to the MMDB_lookup_string() function.

           int mmdb_error;
           MMDB_lookup_result_s result =
               MMDB_lookup_sockaddr(&mmdb, address->ai_addr, &mmdb_error);
           if (MMDB_SUCCESS != mmdb_error) { ... }

           if (result.found_entry) { ... }

   Data Lookup Functions
       There are three functions for looking up data associated with an IP ad-
       dress.

           int MMDB_get_value(
               MMDB_entry_s *const start,
               MMDB_entry_data_s *const entry_data,
               ...);
           int MMDB_vget_value(
               MMDB_entry_s *const start,
               MMDB_entry_data_s *const entry_data,
               va_list va_path);
           int MMDB_aget_value(
               MMDB_entry_s *const start,
               MMDB_entry_data_s *const entry_data,
               const char *const *const path);

       The three functions allow three slightly different calling styles,  but
       they all do the same thing.

       The  first parameter is an MMDB_entry_s value.  In most cases this will
       come    from    the    MMDB_lookup_result_s    value    returned     by
       MMDB_lookup_string() or MMDB_lookup_sockaddr().

       The  second parameter is a reference to an MMDB_entry_data_s structure.
       This will be populated with the data that is being looked up, if any is
       found.  If nothing is found, then the has_data member of this structure
       will be false.  If has_data is true then you can look at the  data_type
       member.

       The  final  parameter  is a lookup path.  The path consists of a set of
       strings representing either map keys (e.g,  "city")  or  array  indexes
       (e.g.,  "0",  "1")  to use in the lookup.  This allow you to navigate a
       complex data structure.  For example, given this example:

           {
               "names": {
                   "en": "Germany",
                   "de": "Deutschland"
               },
               "cities": [ "Berlin", "Frankfurt" ]
           }

       We could look up the English name with this code:

           MMDB_lookup_result_s result =
               MMDB_lookup_sockaddr(&mmdb, address->ai_addr, &mmdb_error);
           MMDB_entry_data_s entry_data;
           int status =
               MMDB_get_value(&result.entry, &entry_data,
                              "names", "en", NULL);
           if (MMDB_SUCCESS != status) { ... }
           if (entry_data.has_data) { ... }

       If we  wanted  to  find  the  first  city  the  lookup  path  would  be
       "cities", "0".   If  you don't provide a lookup path at all, you'll get
       the entry which corresponds to the top level map.  The lookup path must
       always end with NULL, regardless of which function you call.

       The  MMDB_get_value function takes a variable number of arguments.  All
       of the arguments after the MMDB_entry_data_s *  structure  pointer  are
       the lookup path.  The last argument must be NULL.

       The MMDB_vget_value function accepts a va_list as the lookup path.  The
       last element retrieved by va_arg() must be NULL.

       Finally, the MMDB_aget_value accepts an array of strings as the  lookup
       path.  The last member of this array must be NULL.

       If  you  want  to  get  all  of  the  entry  data  at once you can call
       MMDB_get_entry_data_list() instead.

       For each of the three functions, the return value is a status  code  as
       defined above.

   MMDB_get_entry_data_list()

           int MMDB_get_entry_data_list(
               MMDB_entry_s *start,
               MMDB_entry_data_list_s **const entry_data_list);

       This  function  allows  you  to  get all of the data for a complex data
       structure at once, rather than looking up  each  piece  using  repeated
       calls to MMDB_get_value().

           MMDB_lookup_result_s result =
               MMDB_lookup_sockaddr(&mmdb, address->ai_addr, &mmdb_error);
           MMDB_entry_data_list_s *entry_data_list, *first;
           int status =
               MMDB_get_entry_data_list(&result.entry, &entry_data_list);
           if (MMDB_SUCCESS != status) { ... }
           // save this so we can free this data later
           first = entry_data_list;

           while (1) {
               MMDB_entry_data_list_s *next = entry_data_list = entry_data_list->next;
               if (NULL == next) {
                   break;
               }

               switch (next->entry_data.type) {
                   case MMDB_DATA_TYPE_MAP: { ... }
                   case MMDB_DATA_TYPE_UTF8_STRING: { ... }
                   ...
               }

           }

           MMDB_free_entry_data_list(first);

       It's  up  to  you to interpret the entry_data_list data structure.  The
       list is linked in a depth-first traversal.  Let's use this structure as
       an example:

           {
               "names": {
                   "en": "Germany",
                   "de": "Deutschland"
               },
               "cities": [ "Berlin", "Frankfurt" ]
           }

       The list will consist of the following items:

        1. MAP - top level map

        2. UTF8_STRING - "names" key

        3. MAP - map for "names" key

        4. UTF8_STRING - "en" key

        5. UTF8_STRING - value for "en" key

        6. UTF8_STRING - "de" key

        7. UTF8_STRING - value for "de" key

        8. UTF8_STRING - "cities" key

        9. ARRAY - value for "cities" key

       10. UTF8_STRING - array[0]

       11. UTF8_STRING - array[1]

       The return value of the function is a status code as defined above.

   MMDB_free_entry_data_list()

           void MMDB_free_entry_data_list(
               MMDB_entry_data_list_s *const entry_data_list);

       The   MMDB_get_entry_data_list()   and   MMDB_get_metadata_as_entry_da-
       ta_list() functions will allocate the linked list  structure  from  the
       heap.  Call this function to free the MMDB_entry_data_list_s structure.

   MMDB_get_metadata_as_entry_data_list()

           int MMDB_get_metadata_as_entry_data_list(
               MMDB_s *const mmdb,
               MMDB_entry_data_list_s **const entry_data_list);

       This  function allows you to retrieve the database metadata as a linked
       list of MMDB_entry_data_list_s structures.  This can be a  more  conve-
       nient  way  to deal with the metadata than using the metadata structure
       directly.

               MMDB_entry_data_list_s *entry_data_list, *first;
               int status =
                   MMDB_get_metadata_as_entry_data_list(&mmdb, &entry_data_list);
               if (MMDB_SUCCESS != status) { ... }
               first = entry_data_list;
               ... // do something with the data
               MMDB_free_entry_data_list(first);

       The return value of the function is a status code as defined above.

   MMDB_dump_entry_data_list()

           int MMDB_dump_entry_data_list(
               FILE *const stream,
               MMDB_entry_data_list_s *const entry_data_list,
               int indent);

       This function takes a linked list of MMDB_entry_data_list_s  structures
       and  stringifies  it  to the given stream.  The indent parameter is the
       starting indent level for the generated output.  It is incremented  for
       nested data structures (maps, array, etc.).

       The  stream must be a file handle (stdout, etc).  If your platform pro-
       vides something like the GNU open_memstream() you can use that to  cap-
       ture the output as a string.

       The  output  is  formatted in a JSON-ish fashion, but values are marked
       with their data type (except for maps and arrays which are  shown  with
       "{}" and "[]" respectively).

       The specific output format may change in future releases, so you should
       not rely on the specific formatting produced by this function.   It  is
       intended to be used to show data to users in a readable way and for de-
       bugging purposes.

       The return value of the function is a status code as defined above.

   MMDB_read_node()

           int MMDB_read_node(
               MMDB_s *const mmdb,
               uint32_t node_number,
               MMDB_search_node_s *const node);

       This reads a specific node in the search tree.  The third argument is a
       reference  to an MMDB_search_node_s structure that will be populated by
       this function.

       The return value is a status code.  If you pass a node_number  that  is
       greater  than  the  number of nodes in the database, this function will
       return  MMDB_INVALID_NODE_NUMBER_ERROR,  otherwise   it   will   return
       MMDB_SUCCESS.

       The  first  node in the search tree is always node 0.  If you wanted to
       iterate over the whole search tree, you would start by reading  node  0
       and then following the the records that make up this node, based on the
       type of each record.  If the type is MMDB_RECORD_TYPE_SEARCH_NODE  then
       the record contains an integer for the next node to look up.

   MMDB_lib_version()

           const char *MMDB_lib_version(void)

       This  function  returns the library version as a string, something like
       "2.0.0".

EXAMPLE

           #include <errno.h>
           #include <maxminddb.h>
           #include <stdlib.h>
           #include <string.h>

           int main(int argc, char **argv)
           {
               char *filename = argv[1];
               char *ip_address = argv[2];

               MMDB_s mmdb;
               int status = MMDB_open(filename, MMDB_MODE_MMAP, &mmdb);

               if (MMDB_SUCCESS != status) {
                   fprintf(stderr, "\n  Can't open %s - %s\n",
                           filename, MMDB_strerror(status));

                   if (MMDB_IO_ERROR == status) {
                       fprintf(stderr, "    IO error: %s\n", strerror(errno));
                   }
                   exit(1);
               }

               int gai_error, mmdb_error;
               MMDB_lookup_result_s result =
                   MMDB_lookup_string(&mmdb, ip_address, &gai_error, &mmdb_error);

               if (0 != gai_error) {
                   fprintf(stderr,
                           "\n  Error from getaddrinfo for %s - %s\n\n",
                           ip_address, gai_strerror(gai_error));
                   exit(2);
               }

               if (MMDB_SUCCESS != mmdb_error) {
                   fprintf(stderr,
                           "\n  Got an error from libmaxminddb: %s\n\n",
                           MMDB_strerror(mmdb_error));
                   exit(3);
               }

               MMDB_entry_data_list_s *entry_data_list = NULL;

               int exit_code = 0;
               if (result.found_entry) {
                   int status = MMDB_get_entry_data_list(&result.entry,
                                                         &entry_data_list);

                   if (MMDB_SUCCESS != status) {
                       fprintf(
                           stderr,
                           "Got an error looking up the entry data - %s\n",
                           MMDB_strerror(status));
                       exit_code = 4;
                       goto end;
                   }

                   if (NULL != entry_data_list) {
                       MMDB_dump_entry_data_list(stdout, entry_data_list, 2);
                   }
               } else {
                   fprintf(
                       stderr,
                       "\n  No entry for this IP address (%s) was found\n\n",
                       ip_address);
                   exit_code = 5;
               }

               end:
                   MMDB_free_entry_data_list(entry_data_list);
                   MMDB_close(&mmdb);
                   exit(exit_code);
           }

THREAD SAFETY
       This library is thread safe when compiled and linked with a thread-safe
       malloc and free implementation.

INSTALLATION AND SOURCE
       You  can  download  the  latest  release  of  libmaxminddb  from GitHub
       (https://github.com/maxmind/libmaxminddb/releases).

       Our GitHub repo (https://github.com/maxmind/libmaxminddb)  is  publicly
       available.  Please fork it!

BUG REPORTS AND PULL REQUESTS
       Please    report    all    issues   to   our   GitHub   issue   tracker
       (https://github.com/maxmind/libmaxminddb/issues).  We welcome  bug  re-
       ports  and  pull  requests.  Please note that pull requests are greatly
       preferred over patches.

AUTHORS
       This library was written by Boris  Zentner  (bzentner@maxmind.com)  and
       Dave Rolsky (drolsky@maxmind.com).

COPYRIGHT AND LICENSE
       Copyright 2013-2014 MaxMind, Inc.

       Licensed under the Apache License, Version 2.0 (the "License"); you may
       not use this file except in compliance with the License.  You  may  ob-
       tain a copy of the License at

           http://www.apache.org/licenses/LICENSE-2.0

       Unless  required  by  applicable  law or agreed to in writing, software
       distributed under the License is distributed on an "AS IS" BASIS, WITH-
       OUT  WARRANTIES  OR  CONDITIONS OF ANY KIND, either express or implied.
       See the License for the specific  language  governing  permissions  and
       limitations under the License.

SEE ALSO
       mmdblookup(1)

                                                               libmaxminddb(3)

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