getent_passwd_reader1.c - simply demo howto read cygwin passwd/group entries from (Cygwin) getent
Posted by Anonymous on Sat 16th Sep 2023 10:53
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/*
 * getent_passwd_reader1.c - simply demo howto read cygwin passwd/group entries from (Cygwin) getent
 *
 * Written by Roland Mainz <roland.mainz@nrubsig.org>
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

#if 1
typedef unsigned long uid_t;
typedef unsigned long gid_t;

#define VAL_LEN 64
#endif

int cygwin_getent_passwd(const char *name, char *res_loginname, uid_t *res_uid, gid_t *res_gid)
{
    char cmdbuff[1024];
    char passwd_line[1024];
    FILE* getent_pipe;
    int res = 1;

    /* fixme: better quoting for |name| needed */
    (void)snprintf(cmdbuff, sizeof(cmdbuff), "%s passwd \"%s\"",
        "C:\\cygwin64\\bin\\getent.exe",
        name);
    if ((getent_pipe = _popen(cmdbuff, "rt")) == NULL)
    {
        (void)perror("getent failed");
        return 1;
    }

    if (fgets(passwd_line, sizeof(passwd_line), getent_pipe))
    {
        struct _cypwent
        {
            char* loginname;
            char* passwd;
            char* uidstr;
            char* gidstr;
            char* comment;
            char* homedir;
            char* shell;
        } pwent = { 0 };
#define PWENT_ENTRY(var, prevvar) \
            (((var) = strchr((prevvar), ':'))?(*(var)++ = '\0',(var)):(NULL))

        pwent.loginname = passwd_line;
        if (!PWENT_ENTRY(pwent.passwd, pwent.loginname)) goto fail;
        if (!PWENT_ENTRY(pwent.uidstr, pwent.passwd)) goto fail;
        if (!PWENT_ENTRY(pwent.gidstr, pwent.uidstr)) goto fail;
        if (!PWENT_ENTRY(pwent.comment, pwent.gidstr)) goto fail;
        if (!PWENT_ENTRY(pwent.homedir, pwent.comment)) goto fail;
        PWENT_ENTRY(pwent.shell, pwent.homedir);

        unsigned long uid;
        unsigned long gid;

        errno = 0;
        uid = strtol(pwent.uidstr, NULL, 10);
        if (errno != 0)
            goto fail;

        errno = 0;
        gid = strtol(pwent.gidstr, NULL, 10);
        if (errno != 0)
            goto fail;

        (void)printf("loginname\t=%s\n", pwent.loginname);
        (void)printf("passwd\t=%s\n", pwent.passwd);
        (void)printf("uidstr\t=%s (%lu)\n", pwent.uidstr, (unsigned long)uid);
        (void)printf("gidstr\t=%s (%lu)\n", pwent.gidstr, (unsigned long)gid);
        (void)printf("comment\t=%s\n", pwent.comment);
        (void)printf("homedir\t=%s\n", pwent.homedir);
        (void)printf("shell\t=%s\n", pwent.shell);

        if (res_loginname)
            (void)strcpy_s(res_loginname, VAL_LEN, pwent.loginname);
        *res_uid = uid;
        *res_gid = gid;
        res = 0;
    }

fail:
    (void)_pclose(getent_pipe);

    return res;
}

int cygwin_getent_group(const char* name, char* res_group_name, gid_t* res_gid)
{
    char cmdbuff[1024];
    char group_line[1024];
    FILE* getent_pipe;
    int res = 1;

    /* fixme: better quoting for |name| needed */
    (void)snprintf(cmdbuff, sizeof(cmdbuff), "%s group \"%s\"",
        "C:\\cygwin64\\bin\\getent.exe",
        name);
    if ((getent_pipe = _popen(cmdbuff, "rt")) == NULL)
    {
        (void)perror("getent failed");
        return 1;
    }

    if (fgets(group_line, sizeof(group_line), getent_pipe))
    {
        struct _cygrent
        {
            char* group_name;
            char* passwd;
            char* gidstr;
            char* userlist;
        } grent = { 0 };

        grent.group_name = group_line;
        if (!PWENT_ENTRY(grent.passwd, grent.group_name)) goto fail;
        if (!PWENT_ENTRY(grent.gidstr, grent.passwd)) goto fail;
        PWENT_ENTRY(grent.userlist, grent.gidstr);

        unsigned long gid;

        errno = 0;
        gid = strtol(grent.gidstr, NULL, 10);
        if (errno != 0)
            goto fail;

        (void)printf("group_name\t=%s\n", grent.group_name);
        (void)printf("passwd\t=%s\n", grent.passwd);
        (void)printf("gidstr\t=%s (%lu)\n", grent.gidstr, (unsigned long)gid);
        (void)printf("userlist\t=%s\n", grent.userlist);

        if (res_group_name)
            (void)strcpy_s(res_group_name, VAL_LEN, grent.group_name);
        *res_gid = gid;
        res = 0;
    }
    else
    {
        (void)puts("no match for group");
    }

fail:
    (void)_pclose(getent_pipe);

    return res;
}

int main(int ac, char* av)
{
    char name[VAL_LEN];
    uid_t uid;
    gid_t gid;

    if (!cygwin_getent_passwd("roland_mainz", name, &uid, &gid))
        (void)printf("# roland_mainz returned %s, uid=%d, gid=%d\n", name, (int)uid, (int)gid);

    if (!cygwin_getent_group("SYSTEM", name, &gid))
        (void)printf("# SYSTEM returned %s, gid=%d\n", name, (int)gid);

    return EXIT_SUCCESS;
}