error: ‘res_ninit’ was not declared in this scope; did you mean ‘res_init’?

I am trying to install an application from its source code in the alpine it says there is no res_ninit, res_nsearch and res_nclose but we can see here that do exists in the Linux headers and I have already installed apk add linux-headers, how can I resolve this issue?

make install
Consolidate compiler generated dependencies of target save_linker_opts
[  2%] Built target save_linker_opts
[  2%] Built target build_protobuf
Consolidate compiler generated dependencies of target cdk_foundation
[  3%] Building CXX object cdk/foundation/CMakeFiles/cdk_foundation.dir/socket_detail.cc.o
/dep/mysql-connector-cpp/cdk/foundation/socket_detail.cc: In function 'std::forward_list<cdk::foundation::connection::detail::Srv_host_detail> cdk::foundation::connection::detail::srv_list(const string&)':
/dep/mysql-connector-cpp/cdk/foundation/socket_detail.cc:1097:3: error: 'res_ninit' was not declared in this scope; did you mean 'res_init'?
 1097 |   res_ninit(&state);
      |   ^~~~~~~~~
      |   res_init
/dep/mysql-connector-cpp/cdk/foundation/socket_detail.cc:1107:13: error: 'res_nsearch' was not declared in this scope; did you mean 'res_search'?
 1107 |   int res = res_nsearch(&state, hostname.c_str(), ns_c_in, ns_t_srv, query_buffer, sizeof (query_buffer) );
      |             ^~~~~~~~~~~
      |             res_search
/dep/mysql-connector-cpp/cdk/foundation/socket_detail.cc:1143:3: error: 'res_nclose' was not declared in this scope
 1143 |   res_nclose(&state);
      |   ^~~~~~~~~~
make[2]: *** [cdk/foundation/CMakeFiles/cdk_foundation.dir/build.make:146: cdk/foundation/CMakeFiles/cdk_foundation.dir/socket_detail.cc.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:1061: cdk/foundation/CMakeFiles/cdk_foundation.dir/all] Error 2

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Update: I cat the header file /usr/include/resolv.h and we can see that function does not exists, so the question is how can I set up Linux header like ubuntu that can work in the alpine?

#ifndef _RESOLV_H
#define _RESOLV_H

#include <stdint.h>
#include <arpa/nameser.h>
#include <netinet/in.h>

#ifdef __cplusplus
extern "C" {
#endif

#define MAXNS           3
#define MAXDFLSRCH      3
#define MAXDNSRCH       6
#define LOCALDOMAINPARTS    2

#define RES_TIMEOUT     5
#define MAXRESOLVSORT       10
#define RES_MAXNDOTS        15
#define RES_MAXRETRANS      30
#define RES_MAXRETRY        5
#define RES_DFLRETRY        2
#define RES_MAXTIME     65535

/* unused; purely for broken apps */
typedef struct __res_state {
    int retrans;
    int retry;
    unsigned long options;
    int nscount;
    struct sockaddr_in nsaddr_list[MAXNS];
# define nsaddr nsaddr_list[0]
    unsigned short id;
    char *dnsrch[MAXDNSRCH+1];
    char defdname[256];
    unsigned long pfcode;
    unsigned ndots:4;
    unsigned nsort:4;
    unsigned ipv6_unavail:1;
    unsigned unused:23;
    struct {
        struct in_addr addr;
        uint32_t mask;
    } sort_list[MAXRESOLVSORT];
    void *qhook;
    void *rhook;
    int res_h_errno;
    int _vcsock;
    unsigned _flags;
    union {
        char pad[52];
        struct {
            uint16_t        nscount;
            uint16_t        nsmap[MAXNS];
            int         nssocks[MAXNS];
            uint16_t        nscount6;
            uint16_t        nsinit;
            struct sockaddr_in6 *nsaddrs[MAXNS];
            unsigned int        _initstamp[2];
        } _ext;
    } _u;
} *res_state;

#define __RES   19960801

#ifndef _PATH_RESCONF
#define _PATH_RESCONF        "/etc/resolv.conf"
#endif

struct res_sym {
    int number;
    char *name;
    char *humanname;
};

#define RES_F_VC    0x00000001
#define RES_F_CONN  0x00000002
#define RES_F_EDNS0ERR  0x00000004

#define RES_EXHAUSTIVE  0x00000001

#define RES_INIT    0x00000001
#define RES_DEBUG   0x00000002
#define RES_AAONLY  0x00000004
#define RES_USEVC   0x00000008
#define RES_PRIMARY 0x00000010
#define RES_IGNTC   0x00000020
#define RES_RECURSE 0x00000040
#define RES_DEFNAMES    0x00000080
#define RES_STAYOPEN    0x00000100
#define RES_DNSRCH  0x00000200
#define RES_INSECURE1   0x00000400
#define RES_INSECURE2   0x00000800
#define RES_NOALIASES   0x00001000
#define RES_USE_INET6   0x00002000
#define RES_ROTATE  0x00004000
#define RES_NOCHECKNAME 0x00008000
#define RES_KEEPTSIG    0x00010000
#define RES_BLAST   0x00020000
#define RES_USEBSTRING  0x00040000
#define RES_NOIP6DOTINT 0x00080000
#define RES_USE_EDNS0   0x00100000
#define RES_SNGLKUP 0x00200000
#define RES_SNGLKUPREOP 0x00400000
#define RES_USE_DNSSEC  0x00800000

#define RES_DEFAULT (RES_RECURSE|RES_DEFNAMES|RES_DNSRCH|RES_NOIP6DOTINT)

#define RES_PRF_STATS   0x00000001
#define RES_PRF_UPDATE  0x00000002
#define RES_PRF_CLASS   0x00000004
#define RES_PRF_CMD 0x00000008
#define RES_PRF_QUES    0x00000010
#define RES_PRF_ANS 0x00000020
#define RES_PRF_AUTH    0x00000040
#define RES_PRF_ADD 0x00000080
#define RES_PRF_HEAD1   0x00000100
#define RES_PRF_HEAD2   0x00000200
#define RES_PRF_TTLID   0x00000400
#define RES_PRF_HEADX   0x00000800
#define RES_PRF_QUERY   0x00001000
#define RES_PRF_REPLY   0x00002000
#define RES_PRF_INIT    0x00004000

struct __res_state *__res_state(void);
#define _res (*__res_state())

int res_init(void);
int res_query(const char *, int, int, unsigned char *, int);
int res_querydomain(const char *, const char *, int, int, unsigned char *, int);
int res_search(const char *, int, int, unsigned char *, int);
int res_mkquery(int, const char *, int, int, const unsigned char *, int, const unsigned char*, unsigned char *, int);
int res_send(const unsigned char *, int, unsigned char *, int);
int dn_comp(const char *, unsigned char *, int, unsigned char **, unsigned char **);
int dn_expand(const unsigned char *, const unsigned char *, const unsigned char *, char *, int);
int dn_skipname(const unsigned char *, const unsigned char *);

#ifdef __cplusplus
}
#endif

#endif

Answer

in the Linux headers

Linux is generally/colloquially the name of all unix-ish operating systems with a Linux kernel, but specifically, Linux refers to the Linux kernel tiself. The resolve headers are not part of Linux kernel. linux-headers install headers needed to compile Linux kernel modules. It’s unrelated.

The mentioned resolver headers are implemented inside glibc GNU C library. Alpine distribution uses musl implementation of C standard library, not glibc.

how can I resolve this issue?

One of:

• you can implement res_ninit and relevant function that depend on musl and use that implementation when compiling the application
• patch mysql-connector yourself to be compilable with musl
• compile/install glibc to your system and compile mysql-connector against it
• do not use alpine for programs that require glibc and use only glibc-compatibile Linux distribution
• notify mysql-connector developers about the issue and financially support them so they will fix the issue